Topic: I race a CB590 Yoshimura kitted bike-interested in contact with similar owners

[JIMLARCH]

I race the above bike in the Vintage Road Racing Association in Ontario Canada.  I'm interested in corresponding with anyone who races a similar bike, in order to exchange knowledge on how to make it more competitive (of course improving my skills would help).

Presently the engine has the following:

590 Yosh kit
Megacycle cam
race valve springs
Barnett clutch
Andrews coils
750 carbs
oil cooler
velocity stacks, no filters

The frame has:

750 swingarm
Koni shocks
stock front end with 20w oil
alloy rims, 18" on front
stock rear sprocket with one tooth down in the front

I've basically only raced the bike the last three seasons at Mosport, which is a fast track.  The main straight is uphill and saps the power on a small engined bike.  It has no prolblem htting 10,000 in the first 3 gears but struggles in 4th and 5th.  I'm considering putting it on the dyno to see if the carburation is off.

I can be reached either here or at www.jimlarch@yahoo.com.

[bwaller]

Welcome aboard Jim, you've come to the right place.

There are guys here racing, past, present and future. I'm in the process of building a 550 to run in the VRRA now.

Were you at Mosport this past August? I think I talked to everyone in middleweight, cool deal.

[turboguzzi]

Welcome indeed Jim

I have gained a good 10% on my first dyno session just playing with main jets, so that's definitely a good investment.

If my 500cc racer puts down a tad over 60 rwhp, I'd say that your should make at least 65+ if it's well tuned.

Changing drive ratios is on of the most important setup steps, by the sound of it you are running way too long at 16:34.

something like 16:36 - 16:37 would be much more realistic, especially if you have trouble pulling even 4th.

Tg

[Rod]

+1 with TG - something really wrong if you're only getting 10k through the gears. The final gearing is definitely way too high - it's even longer than TT gearing, my bike ran 17:37 on the Island. Welcome to the forum, you'll learn all you need to know right here.

[pangloss]

Something definately wrong there.. I have (CB500 ) Yoshi 600 kit with Yosh camshaft (Road and Track..  S&s Springs/ retainers etc with Carillos ) and the power STARTS at 9K and runs through to 12.5 ~13 K  in 1st ~4th..  gears (Standard Gearing..gets to 11.5 +K in top gear about 230Km)  I estimate it's putting about 60HP on the road.

BTW   Clutch is a HUGE hassle..!!  Tried a lot of things to stop slippage..No real successful fix yet

[turboguzzi]

Welcome too pangloss, the 500 racer community is growing fast!

Very impressive numbers, especially the rpm's. My experience, like that of others in this forum is that little sohcs peak early, around 10K for best HP, so kind of wondering if you have a mechanical tacho that is a bit off. Power STARTING at 9K sounds very very peaky, two stroke like....

BTW Pangloss, we LOVE pictures here in this forum, so dont hesitate to post some... 

[Kemp]

pangloss, have you tried using the complete clutch from a CB650. If you use all the metal and friction plates you'll end up with a clutch pack that is exactly the same stack height as the 500 but with an extra friction and steel plate. This clutch should not require heavier springs either (at least not on a street bike, maybe the racer) and solves the clutch slip design problems inherent in the original 500 friction plate.

[pangloss]

Hi There, Thanks for that tip, but when you say complete clutch, do you mean just the friction plates or the complete unit. ?? ie Basket and centre hub.??

[Kemp]

you need to use only the friction plates and the drive plates. It will all fit in your CB550 basket

[pangloss]

Tacho could WELL be out.. It's just the standard item and does dance around a lot.. 

Having said that however, the bike was raced by me from new in 75 in production races in NZ and would show an indicated 11500 in 4th gear. (Standard with no air filter.110 mains)

 After this i did some port work and fitted the 600 kit... Not any more revs but a bit more low down pull.

 What gave me an extra 2000 + RPM was the Road and track cam AND larger carbs off, I think a 1000 honda four ,circa 79~80
see pic.


 

Welcome too pangloss, the 500 racer community is growing fast!

Very impressive numbers, especially the rpm's. My experience, like that of others in this forum is that little sohcs peak early, around 10K for best HP, so kind of wondering if you have a mechanical tacho that is a bit off. Power STARTING at 9K sounds very very peaky, two stroke like....

BTW Pangloss, we LOVE pictures here in this forum, so dont hesitate to post some... 

[pangloss]

Thanks for that. I'll have a look around, see if I can find the parts..  My bike is now in OZ and the 650 wasn't imported here but some overseas suppliers may have 'em

you need to use only the friction plates and the drive plates. It will all fit in your CB550 basket

[turboguzzi]

Tacho could WELL be out.. It's just the standard item and does dance around a lot.. 

Having said that however, the bike was raced by me from new in 75 in production races in NZ and would show an indicated 11500 in 4th gear. (Standard with no air filter.110 mains)

 After this i did some port work and fitted the 600 kit... Not any more revs but a bit more low down pull.

 What gave me an extra 2000 + RPM was the Road and track cam AND larger carbs off, I think a 1000 honda four ,circa 79~80
see pic.
 

Welcome too pangloss, the 500 racer community is growing fast!

Very impressive numbers, especially the rpm's. My experience, like that of others in this forum is that little sohcs peak early, around 10K for best HP, so kind of wondering if you have a mechanical tacho that is a bit off. Power STARTING at 9K sounds very very peaky, two stroke like....

BTW Pangloss, we LOVE pictures here in this forum, so dont hesitate to post some... 

those are 28VM's, pretty common tuning mode for small sohc's,

but.... thats a VERY SOLID solution to mounting them though!

the original tacho couldnt keep up with the motor, switched a very long time ago to an electronic one from a GSXR and it works much better

if you dont find stock plates, try barnet kevlar plates, it solved all the slippage problems my 500 had, i am running them with an extra 1.5mm washer for preload.

[paulages]

Hi There, Thanks for that tip, but when you say complete clutch, do you mean just the friction plates or the complete unit. ?? ie Basket and centre hub.??

with a little material removed from the inside of the clutch cover, you can actually use the 650 primary gear and clutch gear ring, effectively reducing the primary ratio to the clutch; you just need to remember and correct the final drive ratio accordingly. my 718cc cb550 makes about 70 RWHP, and i get no slippage at all with the stock 650 clutch basket and springs, using barnett plates.

[JIMLARCH]

Welcome aboard Jim, you've come to the right place.

There are guys here racing, past, present and future. I'm in the process of building a 550 to run in the VRRA now.

Were you at Mosport this past August? I think I talked to everyone in middleweight, cool deal.

Brent,

I was at Mosport for the 'vintage festival'.  I don't remember speaking to you.  I was also in the endurance race riding a CB900f with 100 rear wheel horsepower.  As you probably know there were two major crashes in the first few laps and the race was eventually cancelled.  Pity, that bike was a lot fo fun to ride.  I found my 550 a lot more relaxing to ride.

[JIMLARCH]

Welcome indeed Jim

I have gained a good 10% on my first dyno session just playing with main jets, so that's definitely a good investment.

If my 500cc racer puts down a tad over 60 rwhp, I'd say that your should make at least 65+ if it's well tuned.

Changing drive ratios is on of the most important setup steps, by the sound of it you are running way too long at 16:34.

something like 16:36 - 16:37 would be much more realistic, especially if you have trouble pulling even 4th.

Tg

TG,

You are probably right about the gearing.  I bought the bike off my brother and ran the gearing he recommended.  Firstly I'm going to dyno it, and then play with the gearing.  One thing I keep having to remind myself is that I need two handfuls of throttle to wide open.  My modern sport bike just needs a smidgin.

[JIMLARCH]

Tacho could WELL be out.. It's just the standard item and does dance around a lot.. 

Having said that however, the bike was raced by me from new in 75 in production races in NZ and would show an indicated 11500 in 4th gear. (Standard with no air filter.110 mains)

 After this i did some port work and fitted the 600 kit... Not any more revs but a bit more low down pull.

 What gave me an extra 2000 + RPM was the Road and track cam AND larger carbs off, I think a 1000 honda four ,circa 79~80
see pic.
 

Welcome too pangloss, the 500 racer community is growing fast!

Very impressive numbers, especially the rpm's. My experience, like that of others in this forum is that little sohcs peak early, around 10K for best HP, so kind of wondering if you have a mechanical tacho that is a bit off. Power STARTING at 9K sounds very very peaky, two stroke like....

BTW Pangloss, we LOVE pictures here in this forum, so dont hesitate to post some... 

the original tacho couldnt keep up with the motor, switched a very long time ago to an electronic one from a GSXR and it works much better

What year tach did you use?  What is required to wire it up?

[turboguzzi]

hei jim, good to see you here again

A nice set of sprockets is essential, i have a 15, 16, 17 fronts + 35, 36, 37, 38 rears to play with, hope you are running a lightweight 520 chain, right?


definitely go for a quick throttle, the stock one is way too slow (though works fine with Keihin CR's)

I am running a 90's GSXR ignition box so it was easy to hook the gsxr tacho up, but I think it could work also with dyna ignitions. there are quite few other option for electronic tachos out there. Scitsu for instance (if you have the dosh)

[JIMLARCH]

hei jim, good to see you here again

A nice set of sprockets is essential, i have a 15, 16, 17 fronts + 35, 36, 37, 38 rears to play with, hope you are running a lightweight 520 chain, right?


definitely go for a quick throttle, the stock one is way too slow (though works fine with Keihin CR's)

I am running a 90's GSXR ignition box so it was easy to hook the gsxr tacho up, but I think it could work also with dyna ignitions. there are quite few other option for electronic tachos out there. Scitsu for instance (if you have the dosh)

I obviously have a lot to learn.  Thanks to all you guys for the info.    I'll be picking your brains for some time to come.

[haill]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

[Bill/BentON Racing]

I used a 86 GSXR tach on my CB590 Yosh kitted race bike,wires to coil,easy to install,goes to 13,000,11,000-13,000 outlined in red(where it should live,Yosh recommended 11,500 shift pt.,Bill

[JIMLARCH]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

My bike has alloy 18" wheels.  An 18" front quickens the steering slightly.  I run a 100/90/18 front and 120/90/18 rear.  It's a pretty standard mod on the front.  Judging by the way the fast riders in the club perform on skinny tires, it all comes down to race rubber and talent.

[turboguzzi]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

judging from the looks, its a 90/90-18 AM20 front, 110/80-18 AM22 rear, pretty typical as a tire setup for a light 500 twin. I run the same front with a 130/650-18 rear on my (heavier) 500-4, works like a charm

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

My bike has alloy 18" wheels.  An 18" front quickens the steering slightly.  I run a 100/90/18 front and 120/90/18 rear.  It's a pretty standard mod on the front.  Judging by the way the fast riders in the club perform on skinny tires, it all comes down to race rubber and talent.

try a 90/90 front, it will make steering lighter still.

[JIMLARCH]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

judging from the looks, its a 90/90-18 AM20 front, 110/80-18 AM22 rear, pretty typical as a tire setup for a light 500 twin. I run the same front with a 130/650-18 rear on my (heavier) 500-4, works like a charm

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

My bike has alloy 18" wheels.  An 18" front quickens the steering slightly.  I run a 100/90/18 front and 120/90/18 rear.  It's a pretty standard mod on the front.  Judging by the way the fast riders in the club perform on skinny tires, it all comes down to race rubber and talent.

try a 90/90 front, it will make steering lighter still.

So you are racing with AM's.  What other tires have you raced on, and how do you rate them compared to the Avons?

I have Dunlop GT501's on my bike presently, because the Avons are pretty expensive and I can't justify the cost in my own mind.  How many races do you get out of a set of tires?

[turboguzzi]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

judging from the looks, its a 90/90-18 AM20 front, 110/80-18 AM22 rear, pretty typical as a tire setup for a light 500 twin. I run the same front with a 130/650-18 rear on my (heavier) 500-4, works like a charm

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

My bike has alloy 18" wheels.  An 18" front quickens the steering slightly.  I run a 100/90/18 front and 120/90/18 rear.  It's a pretty standard mod on the front.  Judging by the way the fast riders in the club perform on skinny tires, it all comes down to race rubber and talent.

try a 90/90 front, it will make steering lighter still.

So you are racing with AM's.  What other tires have you raced on, and how do you rate them compared to the Avons?

I have Dunlop GT501's on my bike presently, because the Avons are pretty expensive and I can't justify the cost in my own mind.  How many races do you get out of a set of tires?

I've stuck with the Avon AM20/AM23 combo for my three years of racing, just felt fine with them and my limits still lie with my riding not tires, never run out of traction. the faster guys seem to preffer a mix of AM20 front and KR164 dunlop rear.

In my first season, when I was riding slower, I managed to get 5 races out of the rear, 3-4 from the front. Yes, they are expensive and it sucks, but at my current level would have trouble downgrading to cheaper road based tires. the other race compund possibility you have are the german Hidenau, dont know if they are brought to north america.

seen people racing also with Conitnental TKV, might give those a try. Bridgeston BT45 have double compound but there's no 90/90-18 front.

Big subject but wouldnt worry too much about full on race tires until you get to 2-3 secs a lap seconds from the top runners.   

[JIMLARCH]

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

judging from the looks, its a 90/90-18 AM20 front, 110/80-18 AM22 rear, pretty typical as a tire setup for a light 500 twin. I run the same front with a 130/650-18 rear on my (heavier) 500-4, works like a charm

rims size you mentioned 18's is that a standard switch these days? what tire size goes best with that combination? saw this bike, was a race winner for some years, looks well set up.

I've stuck with the Avon AM20/AM23 combo for my three years of racing, just felt fine with them and my limits still lie with my riding not tires, never run out of traction. the faster guys seem to preffer a mix of AM20 front and KR164 dunlop rear.



Big subject but wouldnt worry too much about full on race tires until you get to 2-3 secs a lap seconds from the top runners.   

Interesting that your fast guys mix an Avon front with a Dunlop rear.  In years gone by before radial tires on bikes road riders were always matching different brands on the front and rear.  Now, with modern bikes and tires it seems the new breed of riders make a big fuss at the thought of mixing tires, and it now appears to be a great no, no.