Building a Suzuki GS425/GS400 for vintage racing - classes, allowable mods etc.

Discussion in 'WERA Vintage' started by Chuck78, Oct 8, 2019.

  1. Chuck78

    Chuck78 Active Member

    I've been lurking around here for a year or two, hanging out trying to gather some familiarity with WERA Vintage with some dreams of finally getting a track bike together.
    My interest waned after a nasty shattered kneecap surgery this year last March at age 41, and 6 month recovery time to get back to 65-70% with aches and pains, but some of my younger 30-something riding friends' enthusiasm and interest in possibly racing vintage has also renewed my enthusiasm now that I'm recovering closer to normal on the knee surgery.

    I have been fixated for a decade now on building a lightweight track day canyon carver out of a banged up stock '79 GS425 that I have (or identical 77-78 GS400) with the earlier roller bearing bottom end engine as opposed to the more popular GS450 and later GS500 models with plain bearing engines. Displacement is much more limited on the early engines due to inner cylinder stud spacing, but 449cc is no problem at all (GS850 or Wiseco K844 GS750 slugs), and I have 3 used 920cc 750/850 MTC pistons to put it just shy of the stud spacing max (502cc reasonably) at 489cc. Lightweight, narrow, and nimble is the goal, but building a potent but tractable power band overbored engine with 10.5:1 compression + ported head and mild performance cams was the ultimate plan. the widest class-permitted rims I can run in 18", best brakes I can get (single disc front I think will be plenty????), period aftermarket Fox Shox, and a 37mm Suzuki GS500 fork.

    Looking at the WERA rules, it appears that I really only would be building a machine that would qualify AND be competitive in Formula 500, which would be ONLY at AMA Vintage Motorcycle Days (mandatory event for me, an hour from home and 20 minutes from where I grew up!), since it appears that the Formula 500 class runs only at this event, and runs at no other races for the entire rest of the season.
    The other vintage sanctioning body's Formula 500 class may exclude this bike due to being later than 1972 or 1974 but who knows. I would be able to run every event there in Vintage Lightweight Superbike however, with slightly less restrictions on rim width, rotors, overbores, etc. I am trying to build something up to (first run track days, and to eventually...) run both organizations' races within 6 or 8 hours of our home base in Columbus, Ohio.
    It looks like perhaps I would be better off building up a Suzuki GS550/GS650 if my goal was to run lots of WERA events, but I am hanging on to this dream of the 449cc or 489cc GS400/425 twin stripped down all business F500/Vintage Superbike...

    What other WERA classes might I run such a machine in and have any prayer of finishing NOT dead last?!? Or perhaps I could just run in V4 or V5 for fun track time, and not expecting to beat anyone...

    Would this at all be allowed in Vintage 3? That's up to '74 up to 500cc 2-strokes and up to 750cc OHC 4 strokes... Pretty darn fast compared to most mild performance build 400-450-500cc 4 stroke twins! I would probably get TOTALLY spanked in Vintage 4 or Vintage 5...Not even sure they'd allow a bike this small on the grid with those bikes. Not close to fast enough unless I went all out on radical cams and high compression and my 489cc used MTC slugs or 502cc custom JE or Carillo Pistons... That's not really the engine I desired to build, all-out radical, that is. Tractable and fun, fairly reliable, but semi-competitive if needed is what I'm after. Not going after points or any trophies, but a few trophies eventually would be very cool, really just want some fun on the track while being surrounded by lots of other vintage bikes and vintage bike fanatics/junkies, a more welcoming scene than a fun track day surrounded by modern bikes. Riding fast on the track is far safer than blazing 400 miles a day of wildly twisty roads, which is what I generally do as much as possible every season...on vintage performance bikes ('77 GS750 in various incarnations, GS550's, GS1000).

    Is Rich Graver still racing occasionally? You out there, Rich? He seemed to be racing many events up until 3 or so years ago. Lizard seems to be very fluent with the GS450's as well. Looking forward to your feedback, THANKS!

    Chuck in Columbus, OH
    Last edited: Oct 8, 2019
  2. Chuck78

    Chuck78 Active Member

    As far as the build/mods go, from my research a year or 2 ago, it looked like:
    *WERA Formula 500 limits my rim width to 3", and must be 18" or larger diameter. 18" is no problem, I love retaining the vintage period look. I have 3 or more sets of DID rims in GS hubs that are 3.50 rear 2.50 front. I did pick up a set of 2.15 and 3.00" rims in the event that I did need to lace up a 3.00" max width set to qualify within rules.
    *It has BS34 carbs stock. I was hoping to build a twin custom spaced RS34 flatslide pumper set out of a 4 rack with a broken slide (spare slide is NOT AVAILABLE FROM MIKUNI!!!!). It seems that round slide (unless vintage Lectron flatslide) is required, but perhaps I may be able to run the RS34's at first unless I am beating everyone (doubtful!!!), but can be protested if I do start finishing ahead of others who race more seriously for points. GS500 CR33's are a fortune... but may be necessary if I race a lot, and absolutely necessary if I race in the other sanctioning body's events. Perhaps I am best to stick with the stock BS34's for now. I really don't care for CV roundslides, darnit!
    *Formula 500 = solid rotors only, 12" (304mm or 305mm?) max diameter, no floating or semi-floating???? I was planning to run forks with a single 310mm caliper mount, and run 310mm floating rotors (before I read all the rules, and for limited rural backroads street use as well). Will this get overlooked, both being 2.5mm larger radius on the rotor (5mm overall diameter but 2.5mm effective radius advantage over a 12" single disc)
    *Must I run only single or twin opposed-piston calipers? 2 piston max, does not say opposed only. I run the 1989+ Tokico sliding 2-piston calipers from the 1989 GS500, EX500's, Concours, Ninjas, GSX1100G, etc bikes on everything that I can. Will these be allowed????? For the long term, not just allowed when I am just starting, and not yet riding competitively????
    *I did read something of a .060" overbore max, but then F500 says GS450 up to 550cc. I would think I am certainly good on a 449cc GS425 (2mm over), and I think I am good on a 72mm overbore for 489cc vs stock 67mm 423cc. Comments???? Also any comments on how this and the above parts/mods questions may fit into V3 or other classes would be helpful.
  3. Chuck78

    Chuck78 Active Member

    From the rulebook:

    Formula 500 - AMA Vintage Motorcycle Days Only
    Pre 1973 2-stroke factory road racers up to 360cc.
    Pre 1974 2-stroke production machines up to 500cc.
    Pre 1974 4-stroke, 4 cylinder up to 500cc.
    Among the eligible Formula 500 machines are the following: Bridgestone 350; Cagiva-Ducati 500cc Panta twins; Honda CB350F, 400F, 500F, CB450 and 500 twins, CB550 and 1977 MT125; Kasawaki H1, H1R, and S3 400cc; Moto-Guzzi 500 twin; Suzuki 500 Titan, GT 380, GT550, and GS450 any year up to 550cc; Yamaha RD350, RD400 (regardless of year), R5, SR500s (up to 540cc), TR2, TR3, TZ 250 and 350 (twin shock, no “G” model cylinders). TZ 750 cylinder and head (model 409 only) may also be used. The use of cast wheels is allowed in this class.

    The following classes will run at all WERA Sportsman events along with modern classes - Sportsman Double Headers will also be Vintage Double Headers.
    Vintage 3
    Pre 1974 2-stroke up to 500cc.
    Pre 1974 4-stroke push-rod up to 750cc (3 cylinders max).
    Pre 1974 OHC up to 750cc.
    Iron barreled H-D Sportsters up to 883cc (+.060” overbore).
    Among the eligible V3 machines are the following: BMW R75/6; BSA/Triumph 650 and 750cc models; Ducati 750, 750SS; Honda 550F, 750F; Moto-Guzzi 750; Norton 650 and 750cc models; Yamaha XS650 regardless of year.

    Vintage 4
    Pre 1982 Twins/Triples up to 1000cc.
    Pre 1979 SOHC up to 840cc.
    Pre 1982 Air cooled, 4-stroke OHC multi cylinders up to 570cc. Twin shock only, twin piston opposed Lockheed style calipers permitted.
    Among the eligible V4 machines are the following: BMW R100 regardless of year; Pre-1974 BSA/Triumph with big bore kits; Pre 1988 Cagiva/Ducati 650cc Desmo types and Ducati 900SS bevel drive; H-D Sportsters up to 1000cc including Evo models; Pre-1974 Honda CB 750 overbored to 840cc and Rickman single cam; Honda Ascot/GB singles up to 600cc regardless of year. Kawasaki GPZ550 and KZ 550 (both up to 3mm over); Moto-Guzzi small block V Twins regardless of year and pre-1974 Moto-Guzzi 1000; Norton 850; Suzuki GS 450 and GS 550; Yamaha SRX 600 regardless of year and Seca 550.

    Vintage 5
    Pre 1983 2-stroke factory road racers up to 500cc.
    Pre 1983 Production based 2-stroke up to 750cc.
    Pre 1983 4-stroke push rod unlimited displacement.
    Pre 1983 OHC Twins to 1200cc.
    Pre 1983 OHC 2 valves per cylinder to 1200cc.
    Pre 1983 OHC 4 valves per cylinder to 1025cc.
    Among the eligible V5 machines are the following: Ducati F1A and F1B, 750cc limit; Honda CB750F, CBX, CB900F, pre-1986 Honda VF500, VF700, and VF750; Kawasaki KZ750, KZ1000, Z1, GPZ 550/750/1100, EX500, and EX250 without restrictions and regardless of year; Suzuki GS1000, Seeley Suzuki 750, pre-1986 Suzuki GS 750 (no hybrids, i.e., Suzuki GS 1000 motor in a 1985 mono-shock frame), GS 500 (no restrictions); Yamaha FZ600, Seca 550, Seca 750, Virago 980, TZ 750. RZ 350 with maximum displacement of 450cc.

    Machines are eligible to “bump-up” to a second class. Certain machines may be eligible to bump-up to a third class if they meet all eligibility requirements for each class entered. Bump-up eligibility is as follows: ...350 and 500 GP machines may be entered in Formula 500, or an appropriate Vintage class; ***Formula 500 to V 3.***

    *Suspension: Forks: All machines must use period type forks. Maximum diameter is: GP, V 1, V 2, Formula 500 and V 3 - 38mm (I'm good with my forks: 37mm 1989 GS500 or 77-82 GS550/650 dual disc 35mm)
    *Brakes: Formula 500, ...and V3 will employ expanding drum brakes or disc brakes up to 12” in diameter, no floating rotors. Calipers may be a maximum of two pistons and may float ***(all components must be period correct)*** (was planning to run single floating 310mm disc, 2.5mm more radius over 12", and not solid... may need to run the dual disc 35mm's and make solid rotor centers for stainless rotors within regulation max diameter)
    *Wheel Types: ...V3 will use wire spoke built-up or cast wheels if they were OEM equipment on the production bike. Formula 500 may use cast wheels. (no prob? stock GS hubs, laced into period aftermarket rims okay?)
    *Wheel Sizes: ...Formula 500 and V 3 rim diameter will be 18” or greater unless original equipment was fitted with smaller rim diameter. (no prob, I prefer the classic 18/18 look)
    *Rim Width: Formula 500 and V 3 may not exceed 3”. Tires will be in accordance with WERA Technical requirements as set forth in Chapter 8. Formula 500 and V 3 cannot use racing slicks or racing rain tires. (can I run my first races on 3.50 rear rim? High performance Pirelli Sport Demon street tires okay? Or race rubber ONLY?)
    *Engine: Make and model of carburetor is unrestricted provided that the design and operating principle was in use prior to the cutoff date (round slide or Lectron?????). Internal engine components may be modified, altered or changed as per Chapter 9. Cylinders may be bored to a maximum of .060” twins, and .040” three and more cylinders from the class limit. Any machine with a dispalcement limit following it in the class rules cannot use these overbores, the listed displacement is absolute. If there is no class limit then stock bore is the limit. (I think I'm good in F500 and V3 with 2mm or 4mm overbore from 398cc or 423cc stock to 449cc or 489cc performance pistons in these classes?)
    * Proof of eligibility: Eligibility documentation must be furnished upon request by the entrant. The following are evidence of proof: ORIGINAL magazine articles from the period, factory racing bulletins, manufacturer’s affidavit, historic journals or publications and other dated material. Replicas must conform to the original historic configuration in major components. (Major components are frame, engine and transmission.) ***Original publications are required, photocopied articles/documents are not acceptable.*** ****If the motorcycle that you would like to race is not listed under “Among the eligible machines…” eligibility must be confirmed with WERA for approval prior to racing the machine.**** (I don't think I will have to prove much here unless my engine turns out to be a beastly monster with the head porting and GR650 cams ground into higher performance profiles, then someone may possibly protest to a teardown to measure the bore and stroke of my machine, but this is highly unlikely to ever happen!)
    Last edited: Oct 8, 2019
  4. Chuck78

    Chuck78 Active Member

    So with Bump Up, could I run this proposed machine's build in V 3?
    With some of the eligible competition that I bold highlighted, many of which are easily tuneable to 70 or 80+hp, a 449cc or 489cc GS twin would not be so competitive, against, say a V3 1973 CB750 with a mild big bore kit up to around a true 750cc and high compression + aftermarket cams... let alone a really big big-bore V4 CB750 or GPz550... V4 says GS450 and GS550... I may be able to really tune this thing with Keihin CR33's and an aggressive cam, to beat on a pods/jetted/4-into-1 GS550 4 cylinder, but the V4 competition of many models like larger big-bore CB750's, XS750's, even XS650's, and some other models up to 1000cc would be pretty fierce. I think this bike would be better suited to V 3, and if built to Formula 500 spec, should be eligible for "bump-up" to V3, but would that be allowed as my only class entry, or would bump-up only be allowed if I am running my primary allowed class PLUS a second class at each race? Running in V3 against a 2 stroke 500cc from 1974 would even be some fierce competition! V

    I'm a newb to all of this racing structure, so pardon my extensive questions.


  5. Pneumatico Delle Vittorie

    Pneumatico Delle Vittorie Retired "Tire" Guy

    Rich is still around here from time to time

    Rich to the white courtesy phone please
  6. kenessex

    kenessex unregistered user

    This gets pretty convoluted and should probably have a definitive ruling from Mongo. But, I think that since you are building a legal Formula 500 bike, according to the rulebook the bump class is V3, so you should be able to run that and V4 at all WERA vintage weekends. You would also be eligible for Clubman and D superbike. I think that to run the bump up class you have to maintain the eligible configuration from the original class, i.e. wheel sizes and brakes.
    For instance, I am running V4 and V5 on my Ascot at the GNF because I am running 17" wheels. The Ascot is legal for V2 which bumps to Formula 500 which bumps to V3. But V2 has a minimum rear width of 2.75" rather than the 3" limit for the bump classes and since the Ascot is not legal for either Formula 500 or V3 as an original class, I have to run the V2 legal wheels. So I could run V3 at the GNF, with my 18"wheels and then switch to my 17" wheels for V4 and 5, but I don't feel like swapping wheels at the track.
    So, to sum it up, build your bike however you want it and bring it out. There will always be a class or two to run it in. V4 and V5 have been pretty light in attendance, so I wouldn't worry too much about what somebody may bring out. If somebody shows up with a pre74 500 two stroke it will be cool. H1 Kawasakis are fun to race against.
    Chuck78 likes this.
  7. Pooh

    Pooh Administrator

    Like I have a clue :crackup:
    rd400racer likes this.
  8. Chuck78

    Chuck78 Active Member

    Ken! Thanks for your reply! I recognize your username from other vintage bike (non-racing) forums.
    I saw no mention of WERA Clubman and D-superbike when browsing the rules. Are those not just at the vintage events, but at all WERA events or something? Not sure where the info on those is contained in the rulebook.

    So V4 is not very heavily attended these days? 2 of my 3 buddies are looking at building KZ/GPz550's (twin shock) or GS650 (673cc) to race, and I thought the 550's would run V4. What classes would they also be able to run in aside from V5 bump-up?
    I'm curious as to the Clubman and D-Superbike rules now!

    I'll be sticking to the Formula 500 rules for my GS400/425 buildup, but looks like I may either need 2 engines, or need to just run Wiseco K844 GS750 pistons for 449cc, as the other vintage racing organization has a 470cc displacement limit on Vintage Lightweight Superbike, and all 4 of us friends here (1 in Chicago) are looking to just run as many races not too far from home as we can, and not concerned with total points or race appearances with each organization. So having a bike to run legal in classes in both would be a good thing to get the most races within 6-8 hours drive.

    If I get real serious, I can run a GS550 or if I really want the big big classes, I can run what I run on the street, big bore GS750's or a GS1000/1100 8v big bore. At this point (of no formal racing experience) and with my middle aged and not getting any younger status, lightweight and middleweight "pretty fast bikes" sound better than 844cc-1136cc big bore heavyweight vintage rocketships.... Although I do have GS750's and LOTS of spares, a $300 GS1000 + upgrade parts galore to do a performance build on, and a '76 Rickman CR900 chassis and bodywork, hubs + wider rims, rear brakes rearsets, with GS engine mounts, and a spare GS1000 engine and welded stroker crank.... haha! Frame is repaired/modified so not as valuable, but all the Rickman bodywork and other parts are, so I'm not sure I'd ever SERIOUSLY/COMPETITIVELY race that, but it would be fun once in a while... I'm having trouble justifying owning both the Rickman with GS1000/1100E engine mounts, AND a GS1000C 8v... but hope to hang onto both for a very long time.

    EDIT - I just browsed again with a Ctrl-F for Clubman and D Superbike, found the info, no restrictions based on model years, but varying allowable displacements based on air vs water cooled, # of cylinders, # of valves per cylinder, 2T vs 4 stroke, etc... to even the competition. Got it. D Superbike sounds a lot faster. Clubman could give me a chance to race against by buds on KZ/GPz550's. I suppose V4 would as well!
    Last edited: Oct 8, 2019
  9. Chuck78

    Chuck78 Active Member

    Another newb question, what WERA VINTAGE event locations are within 6 or 9 hours drive of Columbus, OH? Am I looking specifically for events listed as WERA Sportsman/Vintage on the schedule if wanting vintage classes?
    AMA Vintage Motorcycle Days - Mid Ohio SCC @ Lexington Ohio 1hr north of home
    Nelson Ledges - 3hrs
    PIRC - 3.4hrs
    Grattan - 5.5hrs
    Talladega - 9hrs
    Barber - 9hrs
    Roebling - 11hrs
    Road Atlanta - 11hrs

    are the vintage events ran at all these locations?
    What's the difference between:
    Pirelli WERA National Challenge Co-Sanctioned by AMA
    WERA Sportsman Series (various regions' schedules listed seperately)
    and can a member run vintage in multiple regions of the various regions listed seperately for the WERA Sportsman Series? Not considering points, just racing for fun, I'd assume points are only per region and not cumulative for all regions/races for the season??? Atlantic Coastal Region vs Mid-Central Region vs North Central Region vs Southeast Region

    Definitely far better/preferred vintage races for my geographic location vs the other sanctioning body.
    Last edited: Oct 8, 2019
  10. kenessex

    kenessex unregistered user

    Next year's schedule isn't out yet, but I am sure it will be similar to this years. Don't forget that even if vintage isn't running, Clubman and D super will be. You should come down to the GNF in a couple of weeks and check it out. I will be there, come hang out.
    Chuck78 likes this.
  11. rd400racer

    rd400racer Well-Known Member

    Yep, I ran my MZ Skorpion in Clubman and D Super at Nelson last weekend and totally got my ass handed to me, so much so that I almost felt like I was getting in everybodies way. The only person that I was even slightly competitive with was a 14 year old kid on a 125 2 stroke and even he beat me! I've always gravitated towards strange bikes to race, but after last weekend I may be looking at an R3 for next year:D I probably still won't catch those damn kids but at least I may be able to keep up with them.

    Good luck in your endeavor Chuck, but as someone that has dabbled in V1-V4 the last few years, the reduction in the number of participants makes it almost no fun. I picked up my share of participation trophies.
    Killswitch and Chuck78 like this.
  12. Chuck78

    Chuck78 Active Member


    Thanks for the offer! I just noticed that the GNF is at Barber in a few weekends... I just got back from hanging out in the pits at Barber for the Vintage Festival a few very soggy days ago (rode into the darkness through torrential downpours the entire duration of the state of Kentucky south to north!). I don't think I can swing another weekend trip that far from home for the rest of the year.
    If you were able & willing to extend the same invite this spring somewhere closer to Ohio, that would be amazing... There are 3 of us here in Columbus, Ohio interested in WERA Vintage racing (KZ/GPz550 or GS650, & my little 449cc or 489cc GS425) & 4th in Chicago (CB350 serious racer build).
    I think one of my buddies whom I just spent the last weekend with chatting up racers and drooling over race bikes, would definitely also really enjoy an opportunity like that.
    Where are you based out of, Ken?
  13. kenessex

    kenessex unregistered user

    I am in Western Wisconsin, but now that I am retired, I plan on doing more races next year than I have been able to do recently. I am sure I will be at Grattan and Mid-Ohio next year. I have family in Atlanta, so I will likely try to fit in Talledega and Roebling Road as those are tracks I like. I may also do some AHRMA races again, like Road America.
  14. fastedyamaha

    fastedyamaha Well-Known Member

    Rich is definitely still around. I have a very nice gs500 that he built for me that’s just collecting dust, I’d be willing to let it go for a song. It’s a very fun bike but limited in performance compared to other bikes in the classes it’s eligible for. I enjoyed racing it though, very fun and easy bike to ride.
  15. JBall

    JBall REALLY senior member

    Hi Chuck,

    After your first post I was going to reply RTFRB - but you actually did that so you are actually ahead of most people who just launch in with questions that could be easily answered by reading a couple of pages.

    Bottom line is that WERA is pretty good about making sure that anyone that wants to race will have a place to do it, they just can't guarantee that the bike you pick will be competitive. Vintage runs at every Sportsman weekend (getting put in with modern classes that are not too much faster). You can always run the modern classes as well (like Clubman) but know that there are some fast kids out there on the new small bore sport bikes that are really flying (see RD's post above).

    AHRMA certainly is another choice, but they don't have a lot of events that are close, and in my opinion they have a lot of rules about appearance type stuff that doesn't affect performance (which hurts stuff like my bitsa EX-500). If your vintage race bike has some one off piece that is not quite correct, no one here is going to rain on your parade about it.

    The GNF would certainly be a good place to see a lot of different stuff, but Vintage days at Mid-O gets a lot of bikes out, and is just down the road from us. I live in Westerville, and would be glad to visit about this stuff with you and your buddies.

    BTW, Rich Graver is pretty much retired from riding, but he works most of the regional stuff around here as an official, and I am pretty sure he will has his shop.

    Good luck, and maybe we'll get a chance to talk a bit!
    Chuck78 likes this.
  16. Chuck78

    Chuck78 Active Member

    Great to hear from you & Ken especially, thanks for chiming in...
    What bikes do you race? What other vintage bikes are you into?

    I was wondering if I needed to put a few items on the priority list, like:
    *lacing up a 3-inch maximum width set of wheels to race Formula 500 at AMA Vintage Motorcycle Days (F500 rules say 3" max, but I have 4 sets laced up with 3.50" DID or Sun rims!!!),
    *as well as the Formula 500 rule of no floating rotors, & of 12" max rotor diameter (304.8mm).
    The setup I was going to run was 310mm single disc floating rotor, as I can just enlarge the six 6mm holes to 8mm & bolt 98-99 CBR900RR rotors straight onto my old Suzuki GS hubs & mags... 2.6mm larger effective rotor radius than rules, AND floating rotors (must be solid per rules). But possibly overlookable since I'm only going to be running single disc on that fork?

    I realize that if I was winning, that would be an issue of contention that others may protest. & F500 being on weekend a year only, may be a bit more touchy than me running the same bike in V3 or V4 where I would really have to have a healthy performance cam ground + ported head + excellent tuning in order to keep up with the rest of the field...

    As far as AHRMA vs WERA, going to Barber Vintage Festival, there is just an absolute awesome awesome turnout of vintage race bikes. But in Ohio, there is only one AHRMA event within 5.5 hrs. With WERA Sportsman, there are 4 or so within 5.5hrs of home, plus I have track day options at Nelson Ledges, Mid-Ohio SCC, & a motard/karting track down by Circleville. These may be plenty enough to appease myself and my buddies...

    My GS400/425-489cc & my buddies' favoring KZ/GPz550 twin shock bikes & maybe a GS650 bought from TZRusty, WERA has classes that would be more favorable for the 550-fours vs AHRMA, geographically it's MUCH closer to do 4 WERA events a year, so that seems the target goal. Perhaps race Gingerman & Barber Vintage Festival to get a heavier dose of our Vintage fix, but WERA is much more do-able with traveltime.... & I believe I was told that you may have to finish at least 3 AHRMA races in order to even qualify to run Barber Vintage Festival????

    Track days are the plan first. After bike building/prepping this winter...
    Then race school and enter a few events.
    We have a 4th buddy, now in N.E. Ohio, who has started doing track days I believe on an EX500. We can start riding tracks with him, & maybe get a 4th racer buddy out of it! Take 2 trucks & share some expenses & gear/tools. Get the vintage race #'s up there. Perhaps I can campaign a little bit on some of the vintage bike forums to solicit a little more interest in vintage light and middleweight bike racing to get the grid numbers up! That would be awesome if others were interested in trying to do the same as I, to get vintage lightweight/middleweight grid attendance back up in this region.
    Sure the 750's & big bore 1000's sound AWESOME to run, but I love the flickability of the light bikes... And the all-out speeds of bigger or more modern bikes as well as handling that extra excess weight, puts the rider into more risky territory...
    Last edited: Oct 12, 2019
  17. Chuck78

    Chuck78 Active Member

    Due to AHRMA rules, my bike would probably have a lot bigger grids to run on in vintage lightweight superbike, but I would be limited to 470cc, which means unless $$$ custom 71mm pistons & re-sleeving, I'd be limited to Wiseco GS750 K844 pistons for 449cc. My goal was to build the fastest GS400/425 that I could with these 72mm 489cc (920cc GS750/850) pistons, ported head, & GR650 cam or perhaps a really hot but still agreeable cam grind...
    The 489cc WERA-compliant (19cc's too big for AHRMA Vintage Lightweight Superbike) engine is going to work out a lot better if I am frequently racing against my good buddies on faster 550-fours... Although big cams & ported head with GS500 Keihin CR33's, a 449cc 10.5:1 might not be too far off from the performance of a 40cc / 9% larger displacement, heavier piston'd bike...
    If I got real competitive in both organizations, a custom run of 470cc 10.75:1 or 11:1 pistons & some GS850 sleeves in 400 cylinders may be on the shopping list...

    At this point, coming off of spectating the pits at Barber Vintage Festival, I'm soooo psyched that I'm on the lookout for another cheap 77-79 GS400/425 to build up as a Wiseco 449cc anyway, to have a spare engine in the event of failure, & to have AHRMA-legal displacement if I could race Gingerman and Barber as well.
  18. Chuck78

    Chuck78 Active Member

    The bike I have is a $400 banged-up '79 GS425E stocker with broken turn signals & headlight bucket, bent shifter & brake pedals, etc but pretty clean.


    I have been hoarding parts:
    *GS500 37mm forks + 1/2" billet fork brace
    *GS500 front brakes 2-piston sliding caliper
    *310mm floating rotors
    *clubman, drag, & superbike bars
    *Hayabusa rearsets
    *Fox Factory Shox nitro/emulsion version set up for lightweight Honda twins, several piggyback sets for GS750/1000 Z1 etc to swap bodies
    *custom TIG'd cromoly swingarm, Delta-style? Came with Rickman CR project, just a hair longer than stock GS400 swinger.
    *GS1100E aluminum swingarm - longer, stiffer, lighter.
    *GS550 OEM rear drum and disc swingarms, stiffer & slightly longer than stock.
    *MAC GS400-450 2-into-1
    *Unknown GS400-450 2-into-1 with #2 cylinder pointing toward #1 halfway down, then bending back to right side of bike
    *Kerker System K baffle (may just make a Yoshimura stovepipe setup with stainless tubing anyway)
    *F1R aluminum dual mufflers if I run stock headpipes and dual exhaust
    *GR650 Tempter camshafts, 3 sets, biggest lift of factory cams of any of the vintage GS twin (&cousin, the GR) range...and on hollow cores!
    *Mikuni RS34 carbs with 1 of 4 slides broken, not available new so convert 4cyl to a 2cyl rack... But not so vintage-legal being a newer flatslide pumper, ESPECIALLY illegal for AHRMA...
    *Several GS disc wheelsets laced with 2.50x18 front & 3.50x18 rear D.I.D. rims (3, + 1 Sun rims on my GS750 - primary street bike)
    *2.15x18 & 3.00x18 rims to fit within Formula 500 & Vintage 3 rules
    *TWO sought after GS450S gas tanks (boxy with knee dents, "cafe racer types LOVE THEM for all makes of hipster bike builds)
    *Guiliari GS400 seat
    (May save the nice tanks and seat for the street version of this bike that I may be building as a spare with AHRMA-legal displacement)




    Stock, as it sits, behind a GS750 (4cyl) of same color scheme...

    I have been threatening to send a set of cylinders and GS850 or GS450 sleeves off to Rapid Ray Rains aka Suzuki Ray out in California, to get re-sleeving to bore in these 489cc pistons that I have... As well as send a head out for porting to Ray. He's a pro with GS & KZ/GPZ race engines. And right down the street from both Web Camshafts & L.A. Sleeves.
    That is likely to happen SOON. Unsure if I'll go performance cam grind over the big lift OEM's that I have, but may need to if I'm running against 550-fours of my buddies as well as big middleweight 2 strokes...

    I do LOVE the challenge of taking the smaller bikes and building them as fast as I can reasonably do so. Two of my 4 potential racer buddies flat out told me that the previous incarnation of my '77-79 GS750 was the absolute fastest air cooled 750 they have ever ridden with! They were usually riding 110-120hp ZRX1100's & ZRX1200's, occasionally a killer KZ/GPz750...
    I have parts to build a big mean nasty GS1000 or Rickman CR with GS1000 power at 1136cc with stroker crank, D-port 1100GK head, Yoshimura cams, CR33 carbs... as well as a second engine, D-port head, stock stroke welded crank, more CR33 carbs, another set of Yoshi cams.... But I think I'll just stick to the small bore bikes for now!
    The Rickman would be a great novelty race bike eventually to run at AMA Vintage Motorcycle Days in V5 or whatever classes, but not to race hard (parts are rare & $$$!).
    I do have a FLEET of 77-79 GS750 spares with extra frames, a pallet rack of spare engines, 41mm cartridge forks & GS1100GK 41mm fork options, spare wider 18" rim wire spoke wheels etc...
    Last edited: Oct 12, 2019
  19. Chuck78

    Chuck78 Active Member

    Well the 5th buddy of our friends group interested in racing is planning on racing an EX250 in WERA next season (not a 500 as I thought), so that's one more of us in...
    I'm shopping for another GS400-425, found one in upstate NY for $750 but looking for a bit cheaper and closer...
    Another acquaintance was running a GPz750 this season in AHRMA, not sure if WERA or not...
    Hoping to get numbers up and get out & have some fun!
  20. 2Big4Bike

    2Big4Bike Well-Known Member

    So V4 is not very heavily attended these days? 2 of my 3 buddies are looking at building KZ/GPz550's (twin shock) or GS650 (673cc) to race, and I thought the 550's would run V4. What classes would they also be able to run in aside from V5 bump-up?
    I'm curious as to the Clubman and D-Superbike rules now!

    Hey Chuck,
    Just have one of your buddies buy my KZ650 and run it in V5 and V6 Middleweight.
    I want to focus on dirt riding with my son and am ready to take a big loss on the KZ just to move it.
    PM me for details if interested.


    Attached Files:

Share This Page