Yamaha G9 running rough

[u122423]

Hi I have a Yamaha G9 that is driving me crazy. The cart ran good but started to smoke, found out i was putting too much oil in it and it was filling the air box, took the box apart cleaned it out and cleaned the almost new air filter, checked valve adjustment and put everything back together, now it runs really rough and is carbon fouling the plug. I have a brand new air box that seals good. I did a cylinder leak down test and it appears to be good, just a little leak by from the valves. checked all the grounds there good. The govener is bypassed and the cable direct to the carb and it is working correctly, took carb apart cleaned it checked float level its good. It has to be something simple because the cart ran good before, maybe the air filter is no clean enough? something wrong with the spark? Any suggestions or ways to check things would be great, sorry for the long post and thanks in advance for any help.

[griffo002]

My experience with 4 strokes are...Carb or timing or valves or fuel,thats put it simply of course...When i say carb,Thats all thats connected to it, just not the air and mixture.

[sho305]

You may have to buy a new filter, if it is the paper one the oil can plug it up. Many people have been there. It is best to change the oil and put one qt in, then check the stick and mark where it is at and that is your full line. Also use the newer plug the ngk bpr2es I think it is, for G16, it will not foul out as much. Usually either the airbox is leaking, the carb is dirty, or the spacer to head is cracked from age or over tightened. But too much fuel could be the filter soaked, see if it runs different with filter out just test run it, of course don't drive it around with no filter.

[CP241]

Also, if it was smoking real bad the top of the piston and the valves are probably coked up pretty good with oil. Gonna take a bit to burn it all out. And if it's in the exhaust you'll have to burn that out too.

[JRL]

Might be carb issues. Verify that the float and float valve are not causing a rich running issue. Also the oil level will increase with fuel contamination. As it warms up, it cooks off the fuel in the oil, which goes into the air box and soots up the plug. Might cause black exhaust smoke.
The valves should be airtight when closed. May want to recheck the clearance. They wear and at some point it gets to be a problem. If it's spitting fuel out the air horn, gotta resolve that.
If you have not changed the oil, consider doing so and see if it runs better.
A failing fuel pump will also dump fuel into the engine.
Enough soot will plug an exhaust system. Loosen up and check for improvement. Won't hurt to run without a muffler for a few minutes...just watch that fuel in the exhaust isn't going to set a fire. You can also operate for a few minutes without an air filter...if it runs better, it's too rich. Try a new filter. It may not run well without an air filter.
If the rings are damaged, it might blow oil from the crankcase even with proper oil and level. Did you say that the gov was defeated? Leakdown into crankcase would suggest. That's where leakdown ratios help sort out the problem (s)..

[G1-G9]

My money would be oil in the muffler. But that all depends on how long you ran it with to much oil. No matter what only 1qt of oil.

[u122423]

Thanks for the replies, I took the carb off replaced needle and seat, cleaned it real well replaced intake spacer and gaskets, and put in a new air filter. Runs good again, I think it was the air filter all along. I cleaned the old one and blew it out but I guess it must not have been enough. Thanks everyone

[sho305]

Its paper, they don't like oil. The K&N like oil, foam can like it, paper don't. It can be ok since the filter is huge, but if enough is oiled up it can be a problem. Glad you are running again, go have some fun!