Hey!

I have a 1989 Yamaha Moto4 350, and its starts up great and it runs, but once it gets to higher rpms in every gear it seems to bog out, doesnt die or anything, just runs crappy. Is this a carb issue you think?

 

sounds like valves mine was doing somthing the same have you ever edjusted the valves on it

 

or it could be you main jet iv heard of them doing that to id look there see if its got crap in it before you take the valve cover off

 

ill take a look at the carb this weekend, and how do you go about adjusting the valves? thanks

 

you get the specks there suppose to be set at and there gage you can get to see were they are with yours being older you might have to shim it i dont think they have it so you can edjust them with a wrench and scew driver

 

Having this same problem with mine. 89 Moto 4 250. OP can you shed some light on the outcome?

 

Here is a good 2 part video on doing the Yamaha 348 motor (Its in many Yamaha models). the first video is part 2 the last is part 3 that has the most part of the job.



Part 3

 

Get you a makuni carb kit and replace gaskets and all the jets and seats. Clean in out good with a petroleum based cleaner and blow out all the air holes with and air gun. Adjust the jets to specks and you should be good to go. Youo would do well to aquire the service manual to air you with setting disassembly and reassembly

 

Check the main jet. If it's bogging out at full throttle, it could be that it's getting too much fuel. My 96 warrior did this exact thing and it turns out someone had put a larger main jet in it without having put on a pipe(or perhaps they removed the pipe and were too lazy to pull the larger jet). IIRC, the stock main for the 350 is a 145.

It could also be that your air cleaner is dirty/clogged as that would create a similar issue(rich), but from the other side(air restriction).

 

Alright, I'll check that, thanks.