Yamaha g9 backfire through carb

[Bryans200583]

Well, the backfiring is gone but it still won’t start. It turns over great. I replaced the solenoid with another and it seems to turning over faster for some reason. I’m getting plenty of fire, factory air box sealed up nice and tight and even sprayed gas in the carb and still won’t fire off and run. Got good compression, I guess with the engine turning faster it produces more compression cause I was getting around 140 now it’s 150. Installed new spark plug still just turns over and never starts. Could this be a Cdi box problem?

[slonomo]

Originally Posted by Bryans200583

Well, the backfiring is gone but it still won’t start. It turns over great. I replaced the solenoid with another and it seems to turning over faster for some reason. I’m getting plenty of fire, factory air box sealed up nice and tight and even sprayed gas in the carb and still won’t fire off and run. Got good compression, I guess with the engine turning faster it produces more compression cause I was getting around 140 now it’s 150. Installed new spark plug still just turns over and never starts. Could this be a Cdi box problem?

Well you said you have spark right? If you have spark, the CDI should be ok. Unless the CDI controls the timing and that could be an issue.

As I said before: fuel, spark, compression, air....typically if you have all 4 it should run. Now that assumes an engine is timed properly. You said you checked the timing marks etc. No clue.

[Bryans200583]

Don’t know if I did that right for the picture but I don’t know how to upload picture on here. That’s a picture of the timing marks. I took it this morning to just check again

[slonomo]

That's definitely not right. At TDC your timing marks on the cam and the crank must be lined up. When you assembled this engine, did you use a service manual? Your cam is out of time. That would surely cause it not to start.

Cam is top gear. Crank is middle gear. Bottom is governor or counter balancer I believe?

[cgtech]

The cam is actually timed correctly, the one you pointed to is the balancer. This picture does not represent the normal direction the engine points. Look at the cylinder bore, its pointing down & forward in this pic.

[slonomo]

Originally Posted by cgtech

The cam is actually timed correctly, the one you pointed to is the balancer. This picture does not represent the normal direction the engine points. Look at the cylinder bore, its pointing down & forward in this pic.

Ok, I see that. Good catch CG. The position had me confused. So the cam is timed properly then. Why is he having a problem?

I looked it up in the service manual, it says there should be an ink stamp on the crank gear for the balancer, but it appears to be lined up correctly.

[Bryans200583]

Sorry about the angle of the picture. I had it sitting on my work table on its side and didn’t think about the direction it was sitting. I already put it back in and still nothing. I’m tired of messing with it and I got another cart to work on so I’m just gonna move this one to the side and start something else and come back to it later. I guess that’s a good thing that it’s mine and not someone else’s I can just push it to the side and come back to it later. Thanks for y’alls help. If I ever figure it out I’ll let you know. Thanks again

[slonomo]

Originally Posted by Bryans200583

Sorry about the angle of the picture. I had it sitting on my work table on its side and didn’t think about the direction it was sitting. I already put it back in and still nothing. I’m tired of messing with it and I got another cart to work on so I’m just gonna move this one to the side and start something else and come back to it later. I guess that’s a good thing that it’s mine and not someone else’s I can just push it to the side and come back to it later. Thanks for y’alls help. If I ever figure it out I’ll let you know. Thanks again

Gotta be something simple. I've been in the same situation many times. It's always something I overlooked. You'll find it. I just want to help you figure it out.

[cgtech]

Originally Posted by slonomo

Ok, I see that. Good catch CG. The position had me confused. So the cam is timed properly then. Why is he having a problem?

I looked it up in the service manual, it says there should be an ink stamp on the crank gear for the balancer, but it appears to be lined up correctly.

Probably ignition timing, or maybe weak spark (not "no spark"). I'd also physically verify airflow into the carb & out the end of the tailpipe (probably put your finger over the opening to "physically verify"). Even if the intake & exhaust valves dont open at all, it would still have compression..

[Bryans200583]

So when you say ignition timing, would that come from the cdi or the ignition coil. I have tried two different ignition coils but I don’t know if with were good or not and I took my cdi to my buddies and plugged it in on his cart and it ran just to make sure it was good. I guess I could do the same thing with the ignition coil. I thought about ordering new valves and trying those also. Appreciate the help and I’ll let you know what I come up with. Thanks again