Not your normal carb fail on my H2 race bike, P2H on Sunday

[mobilespider]

Was good to meet GIVER at the Mosport races and a couple of others from this board.

I race in VRRA as #66 on 750 H2 and when i went to grid for my P2H Final (and last race of the day) i found it rev-ing at 7K!
Throttle and choke cables were fine, switched it off twice and restarted and each time it was solid on 7K. So had to watch the race from the start/finish line.

Worked on it last night and found that the left VM30 carb throttle slide was up, the throttle slide guide pin that is pressed into the side of the carb had loosened, backed out and the slide was no longer being held in alignment so it was free to turn! The pin is located on the (from intake side) right side of the carb and i could move it back and forth but was not loose enough to fall out yet.
Gets better, the center carb was also loose and close to same failure level and the right carb is starting to go loose! I have now applied JB Weld to all 3 pins as a fix till i get my VM 34 replacements.

So, if you are using 1970's Mikuni's on your triple i would advise you to check this. Its easy to check BTW, carbs do not have to come off or come apart, locate the guide pin on the outside of the throttle slide bore and push on it, if it moves in you have the problem, if it doesn't your OK.......for now.

Tried to add picture as an attachment but it says the forum has exceeded its disk space???

[Walms]

Lucky it didn't happen on the back straight! Still a bummer to have it happen just before the last race though.

[Jim]

Do those carbs have brass slides, or the later aluminum ones? I've heard that the early brass ones do have a tendency to stick open the way yours did.

[mobilespider]

It has the teflon coated type, they are gold colored but not brass.

The slide did not stick open, as it was no longer held by the pin in the slot on the slide it was able to turn, which it did, and could not drop into the slide slot in the carb body to close as normal.

I tried it again with slide in correct position and watched it, only took one open close of the throttle to put it to fail mode again.

Yes, it was good it failed at the start and not in the race. Made for a lot shorter trip on the "trailer of shame" as i like to call it.

[ballvo]

Amazing! I just had the same thing happen on my H2 road bike while out riding. Without the guide pin the slide is free to rotate in the bore once off idle. Once it rotates it can't come back to idle position, except by fluke, since the idle screw also fits in a slot in the slide.

I was able to nurse mine home just off idle once I realigned the slide and then I discovered the guide pin flush with the inside bore. Never driven so slow or quiet in my life...

I just did the JB weld repair last night.

Hope it's not an epidemic - worth having a look at your Mikuni carbs boys and catch it before you find yourself revving to the moon.

[givr]

Same thing happened to me at Cayuga track day 2 years ago on 2 of the 3 carbs. We didn't have any jb weld or such on hand so we staked the pins in place with a nail and hammer right there in the pits. Still holding up.

[autofobe]

Thanks for the heads up on the carb issue.Funny how it seems to be happening to a few all at once.

Hey Dave,I am in need of some H2 head bolts.If you have any spares I would be gratefull.

Thanks Brad

[mobilespider]

Hi Brad,
Sorry no head bolt spares so can't help you with that.

I kind of figured there would be more with this carb problem especially as i had all 3 affected.
Easy to check as i describe above if its going on you.