Topic: CB750 Racing

[Retro Rocket]

Got my new triples installed and my damper fitted up. With the 1" shock extensions that brings my rake down to 24.9 degrees and my trail up to 3.68". I can drop up to another 1 degree of rake and only go down to 3.41" trail. I think I'm in business to play with some settings now, after some track time of course.  Also had to make new steering stops. Was going to drill and tap into the stops on the lower triple, but John gave me a better suggestion. The damper attaches to the frame with a clamp and then I made a bronze bushing that goes through one of the larger holes in the triple.

Alan

Removed my comment because i didn't read your post correctly..    Good luck with the new set up, I think you still have to little trail, and wouldn't want to go any less....

[JohnN]

Alan:
 I see you installed the steering damper as well. The steering stops are Paul's idea so I can't take credit for that! He installed them on mine as well when he added frame bracing and they have worked well for me. Your new geometry is a setup which I have also tried but as you know I eventually switched to shorter triples to increase trail. Since you can remove your shock extensions in a few minutes you can easily revert back to longer trail if this does not feel right during first practice next round. At least you will be able to sample the difference in turning so that would be a useful experiment. Keep up the good work!
John

[Haybus]

Mick, I didn't see your original post. I actually have more trail now than I did, with just the 18" wheel change from stock. I appreciate you wanting to keep me away from a dangerous setup, but I think the changes I've made so far are for the good. As John points out, I can easily go back to previous settings. In fact, I can now correct the anemic trail number the bike started with from the factory just by removing the extension.

John, I'll be sure to show Paul my steering stop setup at the next race so he can take the credit  .

Alan

[bwaller]

Yes good job with the steering stops, It's a good approach, I did the same thing myself. You've got good skills. I think a change of rake can be felt easily especially when the rider is familiar with and pushing the bike at speed. Trail is different. I might only suspect a lack of trail if the front is skittish in a straight line. These are street based bikes, there will be some weave under throttle off the corners, chatter sometimes if entering one too hot. My bike was destroyed because of a violent tank slapper that I couldn't get under control, the rear broke loose, rehooked and it was over in two seconds. Besides the fact I felt it needed less rake to help it turn, the thing never gave me any indication that there was too little trail. It was very civilized, trail was less then 90mm.

I don't believe you'll feel anything but a better turning motorcycle. At 3.68" you might be ok, less than that might not be!!

Good luck I hope it's much improved.

[bwaller]

I know there are guys here that roadrace all three versions of the SOHC4, and I think we all do ok, but it would be great to have someone who knows about chassis geometry and these bikes. Steve McLaughlin raced a CB/CR with Yosh I think and maybe Rob (Voxonda) knows him some. I'll check with Rob.

In stock form understeer costs us time, on fast corners I had to roll off the throttle to get it to turn in, now it's better, but it's no TZ.

It would be great to have an experienced resource.

[Retro Rocket]

I know there are guys here that roadrace all three versions of the SOHC4, and I think we all do ok, but it would be great to have someone who knows about chassis geometry and these bikes. Steve McLaughlin raced a CB/CR with Yosh I think and maybe Rob (Voxonda) knows him some. I'll check with Rob.

In stock form understeer costs us time, on fast corners I had to roll off the throttle to get it to turn in, now it's better, but it's no TZ.

It would be great to have an experienced resource.

Aussie Honda race guru Rex Wolfenden would be the guy to ask, he builds the fastest CB750 race bikes on the planet, I've seen a few of his bikes up close but have no idea what he's done to them...   Brent, Maybe Jerry could get the inside mail on them...?

[bwaller]

Yeah Mick,

I've followed Rex's K&W CB exploits through the years, you're right he might be the best guy to ask because he developed the bike to continue to go faster, not just build correct CR replicas with stock frames. Pretty sure he's not involved anymore though, right? Jerry himself could come up with a blueprint for what works but modifying these stockers he wouldn't be interested. He will surely know Rex well. I'll try to pry a door open and see what gives.

If anything comes of this, I'll post in John's frame thread.

Sorry for the hijack Alan.

[Retro Rocket]

Yeah Mick,

I've followed Rex's K&W CB exploits through the years, you're right he might be the best guy to ask because he developed the bike to continue to go faster, not just build correct CR replicas with stock frames. Pretty sure he's not involved anymore though, right? Jerry himself could come up with a blueprint for what works but modifying these stockers he wouldn't be interested. He will surely know Rex well. I'll try to pry a door open and see what gives.

If anything comes of this, I'll post in John's frame thread.

Sorry for the hijack Alan.

Rex is still involved as far as I know, he has a shop in Melbourne somewhere, I still see his name plastered all over CB750 Race bikes...   I'll be interested to see what comes of this...

[gschuld]

Besides those already mentioned, I'd also be VERY interested to hear from Ken regarding what his team learned racing the very successful Cycle X road race bike as well.  I have been toying the idea with doing up a cb750 for the IHMRA sportsman 750 class but primarily for the USCRA period II super vintage class(I'm in the northeast).  Ken's out of the road racing game so he might be more willing to share details.

George

[Haybus]

Brent, no worries about hijacking. Would love to hear about any geometry that worked well for someone that road raced these old bikes. Surprised there isn't more information in this internet centric day and age. Maybe it's just long forgotten information nobody but club racers cares about anymore.

Alan

[seanbarney41]

although there are plenty of exceptions, seems like CB750's really have not been road raced that much. 
Back in the day, if you really wanted big and heavy, Kaws and Suzi's made 20 some more hp to start with.  In more recent vintage racing classes, it seems the class structure of most organizations makes it pretty hard (and expensive!) to have a competitive CB750.
     I feel like they were most successful in endurance racing, but I have no specific examples.  Hell even the 1970 Daytona win of the CR750 basically came down to an endurance race, with only one of several finishing the race.  Have you guys seen the old "Special Frames" thread that has lots of info on the Japauto 750's etc.?

[Retro Rocket]

Brent, no worries about hijacking. Would love to hear about any geometry that worked well for someone that road raced these old bikes. Surprised there isn't more information in this internet centric day and age. Maybe it's just long forgotten information nobody but club racers cares about anymore.

Alan

although there are plenty of exceptions, seems like CB750's really have not been road raced that much. 
Back in the day, if you really wanted big and heavy, Kaws and Suzi's made 20 some more hp to start with.  In more recent vintage racing classes, it seems the class structure of most organizations makes it pretty hard (and expensive!) to have a competitive CB750.
     I feel like they were most successful in endurance racing, but I have no specific examples.  Hell even the 1970 Daytona win of the CR750 basically came down to an endurance race, with only one of several finishing the race.  Have you guys seen the old "Special Frames" thread that has lots of info on the Japauto 750's etc.?

Quite the contrary fella's, Rex's bikes are current Australian champions in their class, fire breathing , methanol drinking 130+hp giants, and all in the last decade mainly, this guy has put more development into the 750's than anyone else around and they handle well, they have to, they are bloody fast ....We'll wait and see what Brent comes up with, Jerry, the guy he's asking, is also a big name in racing in Australia with many championship winning bikes... Not 750's but still Honda's..

[bwaller]

seanbarney41 that's just not the case. Just as there were gads of CB750 roaming the street there were also gads on race tracks everywhere. Production classes and unlimited racing. I cut my teeth learning the trade in a roadrace shop and there were six sponsored 750's racing out of that one shop. Certainly not many searched for better frames, but there were some. This WAS 40 yrs ago.

[seanbarney41]

I was generalizing above...probably I am just wrong as I am too young to have raced back then and didn't grow up around the track...statement was made based on what info I have been able to find and read, and that's not much...Honda was out of GP all through the '70's, have not heard of any successful Honda's in AMA Superbike until the DOHC's came out, and the only older guys I have talked to that raced a 750 are here on this site, and that's kind of a skewed view imo.  I have been going to AHRMA races that are geographically accessable to me for several years now and there are few guys racing CB750's and have perused the rule book, so maybe it's just AHRMA that does not have an obvious class that is advantagious
     But anyway, it's interesting that you currently race a 550, not a 750, BWaller.  That's certainly the 70's Honda I would choose.

[seanbarney41]

Thread I was referring to was this
http://forums.sohc4.net/index.php/topic,65431.0.html

[bwaller]

Again Alan I'm not sure what we should do to continue this discussion and not use your thread. But one more thought. sb41 I find AHMRA isn't SOHC4 friendly and it's the big gun in North America. Certainly there are guys that race with them so not fair for me to judge. I wonder though if that's why there aren't more 750's racing. Alan & John can comment further.

If you want to make wholesale changes to a CB750 you're thrown to the wolves with what you race against, not very practical. Ken at CycleX hired a top gun rider but that didn't last.

My only streetbike since 1973 has been a CB750. I love these bikes, I raced it in a production class way back and to be honest what I remember is it was a bloody handful.  I do remember the 500's handled better, but has anyone ever raced a bone stock CB500/550? Not for me. The two race assn.'s I race in allow some modifications even in a production type class. Now the little bike does better than 140mph, more interesting, fun factor increased.

This is why Alan & John are discussing and performing mods to make the 750 better & more comfortable at speed. More interesting, fun factor increased. Engine work is easy compared to this!

[JohnN]

AHRMA includes the CR750 in their rulebook list of eligible Formula 750 machines but also singles them out by stipulating use of a stock frame and unmodified swingarm. Other makes are free to use works/Trackmaster etc. so that does put the Honda at a disadvantage. That's why we do crazy things with long shocks and swingarm angles that don't make sense! Fortunately it's all in good fun! I raced one AHRMA race last year and Yamaha represented 3 of 10 entries with XS650 based machines on custom frames that had the proper setup for a real race bike. The Yamaha's took 3 of the top 6 positions (including 1st & 2nd), along with two Honda's and one Norton.

Anyway, back to Alan's thread it's clear he, like many of us, builds a Honda 750 racer because he wants to! It's good to see the progress and results of such a project and I'm glad to see activity continue in the thread.

P.S.- WMRRA Round one last month actually had (4) Honda 750's preregistered to race, but unfortunately (2) were unable to attend at the last minute. I'm keeping my fingers crossed that it will eventually happen!

[Haybus]

Brent, I'm ok clouding up my thread with tips and tricks on handling improvements. Makes it easy for me to find  . However, having trolled many threads looking for the nugget of information I was searching for, it's helpful reading the title and knowing you're probably not wasting your time reading a bunch of drivel. That goes for searching within the forum or from Google. Like John's frame thread, you know what you're in for before diving in. Maybe better if John wants to start a thread explaining his journey to find better handling road racing his 750 over 4 (5?) seasons. Not that I would necessarily do anything different, but it would have been nice to have read his account during my planning stages to be prepared for possible changes. Obviously John's just at a point where he's happy with his handling, so the timing is right.

John, there were 2 750's on the track, but only 1 was really racing     

Alan

[JohnN]

You were racing, just a little slower with one cylinder out of commission! I should have posted my journey, but I was focused on pulling information from this site at the time. Timing was at a point where I was following Brent's thread at the time and even though it was a 500 chassis the same path worked for me. I think your thread can document the 750 process now, and George has a thread going as well.

[bwaller]

Yes it's helpful information in one place. We talk about how many of these bike raced in the early 70's especially, but it was rare that anyone made these type changes. There was no information. Forty years on and loads of aftermarket stuff still available is awesome.

[Just4fun]

Alan,

It has been fun reading about your mission to get on track.

I am thinking about driving down for a day next weekend to watch a day of WMRRA to get a bike fix.  I have quite a bit of track time at SIR/Pacific Raceways, but have never seen the Ridge. 

I downloaded the event schedule, but was curious whether you thought Saturday or Sunday would be the best day to see the vintage classes?

The run group descriptions are a little confusing. Which group are you running in?

Pat


Sent from my iPad using Tapatalk HD

[Haybus]

Pat,

Vintage only practices on Saturday, so if you wanted to see the races Sunday would be the better choice. Spectating at the Ridge isn't the greatest. Last year they wouldn't let the spectators cross into the middle of the track like they do at Pacific. You get to watch a couple slow turns and the straight. I don't imagine it will be any different this year, but maybe. But you could see the track first hand for $20/20 minutes at lunch time with your own bike  .

Alan

[Haybus]

Had a great time this weekend and the bike ran perfectly. Weather mostly cooperated, though it was a bit cool in the mornings with light mist. I've ridden this track during the new rider school, but I've got a lot to learn. My lap times kept improving and I was feeling more comfortable on the second race. I felt like the suspension changes helped with cornering, but I picked up a bit of chatter after lowering my tire pressure to 30 psi. It was kind of bad at first just cruising around the big corners. Like riding a pogo stick. Then it mostly went away as I picked up speed in those corners. Didn't seem too bad in the end, or at least I didn't notice it that much. Started dragging my left frame slider. A bit disconcerting the first time it happened, but that's what it's there for. I can tuck it in a bit more so I don't low side in a hard corner, but I'll probably need to do something to narrow up the left side more permanently in the future.

Thank you again John for your words of encouragement and helpful tips. I got a lot to learn but I sure am enjoying this experience.

Alan

[bwaller]

Good news Alan, glad it went well.

Front chatter...can be just a corner away!  You're probably already doing this so disregard. My perspective, scrub off as much speed just before you tip it in, trail brake a tad to keep the front loaded and keep it on the throttle slightly all the way through until you can get back on it. Get in too hot with no throttle will nearly always cause chatter no matter how good your forks are set up. 35mm forks, gotta luv em.

[Old Scrambler]

GREAT ADVICE

Braking before the turn ..........then DRIVE through the curve or turn..........SHOULD be practiced by all street and open-road riders   That goes for OFF-ROAD as well.

My first driving experience was a FARM TRACTOR. Bikes are so much more fun