86 quad racer carb problems need help please!!!!!!!

[Gank78]

This just started. Motor races without help. It is way dangerous. Try the cuttoff and it won't die. Pull spark plug wire and it does not stop. It is scary. It has got to be the carb????? it is a mikuni flat slide carb. We have planned a ride on the 22nd Help please!!!!!!!

[ccdhowell]

Sounds like it is running lean, very lean. Could be several things, but basically it is either too much air getting into the engine or not enough fuel.

Start by taking the carb off and take the fuel bowl off and look for trash. Take the pilot and main jets out and clean them and where they came from. Give the rest of the carb a good cleaning, put it back together and on and crank it, hopefully that will fix it.

If not, start looking for an air leak. I'd check the cylinder base gasket first. Crank it and hold engine speed just above idle if you can. Spray WD40 or carb cleaner around the base of the cylinder and listen for the engine to change rpms or stumble a bit or something different. If the engine reacts to the WD40 in some way, spray it around and listen, find out where you are spraying that makes the engine change. I'd bet you sucked in the base gasket at that location. If so, order a topend gasket set and replace the base gasket.

Hope this helps and good luck.

Chris

[Gank78]

Thanks. I cleaned carb. It did it again. Put fresh gas in and it quit. Must have been some trash? What ratio of fuel to oil would you recommend?

[ccdhowell]

Clean the carb again. Take the front fenders off and the gas tank. Dump all the gas out and take the percock out of the tank and clean the screens on them with carb cleaner. There may be, probably is, some junk in the bottom of the tank. While you're at it, replace the fuel line and put a filter inline between the tank and carb.


If you run it pretty hard, I'd use a synthetic premix oil like Maxima K2 or Bel-Ray H1R at 32:1. If you are more of a recreation rider, the same oil at 40:1 or even 50:1. Lot's of people are running quite lean premix ratios. Guys here on this forum are running 100:1; in my mind that's crazy. I use Bel-Ray H1R at 32:1 with good results and am thinking of going to 28:1. Choose a premix ratio then rejet your carb to match the ratio you've chosen. With almost any ratio with modern synthitics smoke will be minimal and splooge will be nonexistent, if the carb is jetted correctly.

Chris