Hi guys. Hope you can help. I recently bought a 1987 yamaha moto 4 350 that had been sitting for about 3 years. It belonged to a lady whose husband had passed away and she just wanted it gone. I took it home, cleaned the carburetor, changed the gas and it fired up. The bike idles well and it will rev up with a smooth acceleration, but if I snap the throttle open it just quits. I've played with it and noticed that the problem is from about 1/8th throttle to 1/4 throttle. After 1/4 throttle if I snap it, it opens up fine. I noticed that occasionally it will backfire through the carb also.

So I ordered a carb kit for it, and while I was waiting for the kit to come I left the carb soaking in a carb gunk/premium gas bath for several days and before I installed the new parts I used tip cleaners (that welders use) and compressed air to make sure the carb veins were clear. I bought the repair manual and it says to set the float between 11.4 mm and 13.4 mm so I split the difference and set it at 12mm. It also has an adjustable jet needle and I put the clip on the middle notch, the same as where the old one was.

I have now put it back together and it still does the same thing. Do you guys have any ideas on what else to look at?

 

Sounds like you just need to get your carb tuned correctly.

i realize this is for a different machine and carb, but the principles should be the same: Carb Tuning - Suzuki LT230S Vault

It helped me alot with my little quadsport, and i will use it as a reference when i restore my 350 Moto4 as well

 

Wats the plug look like? i would do a plug chop, sounds like a pilot jet or needle on the wrong clip, adjusting fuel screw may also help it, assuming spark is good, filter is clean and that the compression is sufficient.