Racing a 81 CB900F. Good or bad?

Alright, I need some advice and input on whether I should try to race a 81 CB900f. I can get the bike cheap, but would it be worth putting it on the track? Any advice on this matter would be helpful. What mods should be done? Upgrades? and whatever else? Thanks,

 

They are beautiful, that's for sure!

 

Dont over build the motor, not as robust as a Kaw or Suz, cam chain snapping issues with big hp, use a CB1100f chain tentioner (spelleing)

B

 

I don't plan on over building the motor. I plan on suspensions first. Thanks, keep the advice coming. :up:

 

i think the 1100f chains were heat treated also

 

Thanks for the help. Took the bike out for a ride this weekend. I like it. What suspension upgrades? Thanks, :up:

 

doit! i was at loudon in 82 and was pitted next to mike baldwin and steve wise, roberto peitre the hrc crew . and the 900f,s they had were awsome the motor,s loped wildly from idle to around 4 grand before smoothing out . ive been riding and racing since then and have never heard a better sounding inline 4. mike and steve led the race till they took each other out about half way , wayne rainey won his first ama superbike race . on the muzzy kawasaki .

 

watch out for and old fart on a wicked fast gs850 suzki.....

 

Racing a CB900F

Hey - a friend of mine (he has a TZ750 so he likes vintage bikes too) pointed me over here asking if I had any inputs for the guy who wanted to race a 900F...

I've been running a 900F based bike with AHRMA for 3 years and have a couple of suggestions.

Frame: pull the motor and replace all the rubber mounts (4) in the motor with aluminum plugs and the two in the lower frame rails with steel plugs. You can weld the steel frame plugs in and press/slide the motor lugs in. That way the engine will help brace the frame and you'll feel a ton more stable.

Suspension: I have 15 3/4" long rear shocks on my bikes. You'll need the ground clearance if you have decent tires and it'll help it steer a little quicker than the Queen Mary. I also went to an 18" front to help speed the steering up. The forks are junk with light oil and weak springs - you can work out what you'd like to do but I run 12# of air and 20w fork oil and they work okay. I'm also working on a set with Racetech emulators and another set of 41mm '94 CBR600 F2 cartridge forks. Not done yet...

Pipe: DON'T get a V&H 4:1 or Jardine or anything else you can get easily new. The collectors all rob so much ground clearance you'll be on your butt. Look for a Yosh pipe that is centered under the motor, or an OMT, or build your own...

Motor: I run a 985 Wiseco kit with .365 lift Webcam in one motor and the same thing but a .375 lift Megacycle cam in the other with 29mm CRs (AHRMA rule). Trannies on both have 3rd/4th gearsets from a CB1000C or CB1100F as they're undercut and the 900F tranny isn't. In the same bike my two stock 900 trannies each lasted less than half of one season each before they started jumping out of 3rd under power. The right way is to get a 900F tranny undercut, but if you're 'frugal' you can try the 1000C/1100F route. The 900F cam chain tensioner is junk; they'll break - guarranteed. Use a CB1100F / CB1000C tensioner as they last and work good. Don't over-rev the motor. I use 10.5K as the max upper limit and shift at 10K. If the motor is stock shift at 9K.

I raced the 900F in nine AHRMA races this last year and won 4, finished 2nd three times, 3rd once and 6th once when my Dyna2000 ignition failed causing a miss. I'm not sold on the Dyna2000; I have three that don't work now. Overall the bike works good.

In order of what I THINK will make you want to ride the bike more than once:
0) Get good tires (talk to your vintage peers with similar wheel sizes and bike weights)
1) Solid mount the motor
2) Get HH pads
3) Improve the suspension
4) Make the motor reliable - 1100F tensioner & tranny mods (or undercut)
5) Make the motor fast (cubic dollars)

This is all free advice and it's worth every penny!

Actually, I race a '74 Z1 as well and the Honda does everything a little bit better than the Z1 except for being as reliable. With more work the Z1 could be as good as the Honda - but it isn't because I haven't put the effort into it. I like riding the Honda better.

Good luck!

(my Honda w/ local club number - AHRMA #490, green plate)

 

What kind of swingarm & wheels are those?

 

Thanks for the info. Nice looking bike.:up:

 

CHEATER !!!! . side covers claim 750 and you running bigger....

 

The rear was a Dan Gurney 18x3 magnesium wheel from back in the day. The bike has an '80 CB750F Wasco modified frame that was campaigned back in the day by a privateer out of the Seattle area - don't know who. When I got it as a roller it still had an AMA tech sticker on the tank.

You know how you hear that those old mag wheels get brittle and break? I wasn't worried... but my rear broke at Barber's this October. Now I'm a believer! Thankfully it was a big enough break that the broken part stayed seated in the tire on the right side and the tire stayed seated on the left side of the rim so I didn't go down. This happened on the exit of the right-hander going onto the back straight at Barber's. I was able to continue straight off the left side of the track into the grass without falling. I thought I threw my chain the bike jerked so bad.



The front wheel is a Honda aluminum 18x2.5 mag that kinda matched the rear style and is off a Sabre or some similar Honda from early '80s vintage. The swingarm is off an '81 GS1100 Suzuki and about 1/2" longer than stock. Pivot bolt size is the same, but it's narrower and needed spacers on each side. Shock mounts (clevis) lined right up.

Cheater is right! I want to make anyone who gets passed by a 750 feel bad that some guy went by 'em on a "little" bike. I'm 6'3" and ~245 so I do make the bike look small, too. It's all part of the psych war

 

Nice bike. I'd love to try an old I-4 like that for a vintage bike. I can see myself the first time I turn in to a corner: "I'm gonna die, I'm gonna die"

 

Man that is a nice bike,i have a factory frame 900f racebike,i hope to get back out next year

 

what happened with your wheel is proof that AHRMA needed to get off that period correct stuff,i'm glad that little by little they have opened up the superbike rules some

 

sweet ride !!!

 

[Cheater is right! I want to make anyone who gets passed by a 750 feel bad that some guy went by 'em on a "little" bike. I'm 6'3" and ~245 so I do make the bike look small, too. It's all part of the psych war [/QUOTE]

awesome, brother. now i don't feel so bad with my 240 lb. frame strapped on a little 850..

 

Thanks for the compliments on the bike - it's a lot of fun to ride and as long as I don't get around any recently manufactured 600cc sport bikes it even feels like it's fast and has good brakes.

I'd go ride with those WERA guys but I hear they're nuts fast and their bikes are too trick... oh yeah - and my money is already running out of my wallet so fast I'm getting burns on my fingertips and the numbers are worn flat on all my credit cards. Going to more races won't help!

Here's another photo of my bike from (I think) two years ago at Mid-Ohio exiting the chicane after turn one on the way to the keyhole. You can see my size swamps the bike and makes it look like a little 750, right?

 

slide, spin, wobble, repeat !!!!