g9 Ran Great now turns over but won't run

[HPMI]

I have a G9 Yamaha that gets used daily. One day it wouldn't start. If it did start it would die in about 5 seconds. I have good spark and have tries a few plugs. I swapped out the carb all giving the same results. And I did put a new tank filter in it. The compression is 150psi. I have tries two fuel pumps also. What seems strange is my airbox gets gas/oil in it and a get a light air push out on the air box top vacuum hose. It does not draw. Now with the airbox off I am getting it so run it seems almost normal. This makes no sense to me. I am wondering if there are vacuum check balls or something else that could be gummed up. Any help would be great I feel it is something easy but I am not seeing it.

Thank you Bruce

[eph78]

Originally Posted by HPMI

I have a G9 Yamaha that gets used daily. One day it wouldn't start. If it did start it would die in about 5 seconds. I have good spark and have tries a few plugs. I swapped out the carb all giving the same results. And I did put a new tank filter in it. The compression is 150psi. I have tries two fuel pumps also. What seems strange is my airbox gets gas/oil in it and a get a light air push out on the air box top vacuum hose. It does not draw. Now with the airbox off I am getting it so run it seems almost normal. This makes no sense to me. I am wondering if there are vacuum check balls or something else that could be gummed up. Any help would be great I feel it is something easy but I am not seeing it.

Thank you Bruce

Sometimes the plastic carb spacer can crack causing odd behavior.

[CP241]

If you can take off the airbox lid and it runs almost normal like you say, then it’s very very rich with the airbox installed.

First check your carb. If it doesn’t say Mikuni on the side of it, that’s likely a problem. The aftermarket “Mokini” carbs suck. I’ve never had one work right without completely rejetting it and spending hours tuning it. I would only recommend this if there’s absolutely no other option.

If you still have the OEM Mikuni carb give it a good cleaning.

What spark plug are you running?
Have you adjusted the valves?

[HPMI]

It has run tank after tank of gas thru it with this carb on it. I have ordered replacement fuel filters, air filters and spark plugs. replacing all of them and getting no changes. I have another golf cart just like this one that acted the same way.
i toke that motor out and am slowly rebuilding it. My dad always taught me that if the crank seals leak it could act this way. I don't have my dad to lean on for questions anymore. I am stunned that I can have two carts so the same thing and that it is isolated to just my carts. It just seems like I am over looking the simple things.

[CP241]

Crank seals leaking will cause running issues in 2 stroke engines. If you have a G9 then it’s a 4 cycle engine and crank seals just hold in oil. If they leak they leak oil but it won’t make it run funny.

Again did you adjust the valves? What brand and model spark plug are you using? What color is the spark and is it consistent?

[HPMI]

You are correct on crank seals on a 4 stroke engine, I totally over looked that. I ordered a new plastic carb block. When I get it I will replace the spark plug and adjust valve lash. It it will be a few days before I get the parts.