The 86 quadracer came stock with a 34mm carb. The rubber boot that attaches the carb to the motor has a center opening of 34mm. Now I have been running a 35mm pwk and it runs great, but I just bought a 36mm that I wanted to try out. Heres what I realized while I had everything apart, the boot still has a 34mm opening, and the intake side of the motor is 35mm. So for example, with that 35mm opening on the engine, and a 35mm carb, I think it is being restricted by the 34mm opening of the boot. So i took my dremal and opened that boot up to 35mm. This should flow more, correct?
So am I on to somethin here?
I had my motor ported, but I never thought about that boot. It makes sense, that the carb can be any size, but if the air still has to go through a smaller hole somewhere down the line, it is being restricted
This may applie to 87-92 in some respect, but mainly 85/86

 

I have the same idea with a mikuni 38mm flatslide carb that I have around. I can't find a boot to fit the 38 so I think that is what I have to do. Do you think that this carb will make a difference or do you think that I'm wastihg my time.

 

Since you ahve some work done to your motor it will probably help, althouth I have tried a 38 mikuni, and I think the Keihin 35 worked just as well, although the 38 was probably too much for my quad at the time. Since you have a 89, I am not too familiar with how the inside of the boot looks. Heres what you can do. Take the boot off the motor, then put it on the carb. feel around the inside where the carb and boot meets and see if there is a ridge. I believe the smoother the better. IF there is a step-up ridge from the carb to the boot, then the boot is restrictive.

 

i have a 1990 lt with a 38mm pj keihin carb, and to install it to my intake boot i had to remove some rubber with a razor blade. This is a temporary installation because i have a restrictrion in this area, know, what i was thinking is maybe take the old intake and make one bigger from aluminium. Or i will ask if the intake of a rm250 would fit on my lt since it has a 38mm carb.

the thing is, after you've installed the carb with the intake boot you should put your finger inside and feel no edge at all...should be very smooth. You do this and its very good. But i believe that making the opening bigger is not enought, the rest is still to small if you pass from a 34mm to a 38mm.

 

I think its a good thing to do Bobby, I slammed my taperbored VM44 into the stock boot and felt the same restriction. I carefully opened it up to match... Every little bit helps.