G2 yamaha won't start

superdave519 · 01-28-2011, 01:37 AM

I rebuilt this engine and had it running last week for a short time twice, but now it won't start. It has 175 compression, has blue spark, turns over great and seems to be getting gas. Even if I add gas in the spark plug hole, it still won't fire. The new spark plug I have is a NGK b5es. I am going to buy a new one and a bpr2es when I get a chance. When I had it running it seemed to run O.K., but wouldn't turn over once it was warm. I did not have the air box on it, so thought that might have something to do with it. Now with or without the airbox, the result is the same, it won't fire. I try with choke, without choke and all different gas pedal positions. Any ideas? Thanks

spriddle · 01-28-2011, 08:38 AM

Sounds like the piston/rings are swelling when it gets hot and sticking. 175 compression sounds a bit high to me. I could be wrong. I rebuilt an old 327 years ago and it was a tight fit after boring 30 over. When the engine got hot it wouldn't turn over at all and it was due to the pistons swelling and sticking against the cylinder walls. Just a thought at this point if your engine will not turn over at all. It could be starter/generator or something else. And this is if it will not turn over.

If it is turning over but just not firing, then I would continue with the tune up items for now: mainly spark plug...... Make sure the spacer between the carb and intake is not cracked or leaking air. Also check the little hose going toward the back of the engine, it creates a vacuum and works with the fuel pump to pull fuel.

Mike Mac · 01-28-2011, 10:15 PM

Any chance the flywheel stripped the key and its out of time?

superdave519 · 01-29-2011, 12:38 AM

Just got the flywheel off and the key WAS stripped!!! It crossed my mind, but I thought no way. I'll need a new key before I try again. Thank you so much. One more question, when I post a thread, what's a tag do?

Flintrock · 01-29-2011, 07:14 AM

Tags are just another name for keywords. It is like marking a collection of selected threads using an unique stamp.

rokcrlr · 01-30-2011, 10:17 AM

Superdave, Lap your flywheel on with valve lapping compound real good, then clean it with brake cleaner before you install the flywheel. Then torque to proper spec. It will hold a whole lot better than just slapping it on .

01-28-2011, 01:37 AM	#1
superdave519 Not Yet Wild Join Date: Nov 2010 Posts: 5	G2 yamaha won't start I rebuilt this engine and had it running last week for a short time twice, but now it won't start. It has 175 compression, has blue spark, turns over great and seems to be getting gas. Even if I add gas in the spark plug hole, it still won't fire. The new spark plug I have is a NGK b5es. I am going to buy a new one and a bpr2es when I get a chance. When I had it running it seemed to run O.K., but wouldn't turn over once it was warm. I did not have the air box on it, so thought that might have something to do with it. Now with or without the airbox, the result is the same, it won't fire. I try with choke, without choke and all different gas pedal positions. Any ideas? Thanks
superdave519 Not Yet Wild Join Date: Nov 2010 Posts: 5

01-28-2011, 08:38 AM	#2
spriddle Admin Join Date: Dec 2006 Location: TN Posts: 101,858	Re: G2 yamaha won't start Sounds like the piston/rings are swelling when it gets hot and sticking. 175 compression sounds a bit high to me. I could be wrong. I rebuilt an old 327 years ago and it was a tight fit after boring 30 over. When the engine got hot it wouldn't turn over at all and it was due to the pistons swelling and sticking against the cylinder walls. Just a thought at this point if your engine will not turn over at all. It could be starter/generator or something else. And this is if it will not turn over. If it is turning over but just not firing, then I would continue with the tune up items for now: mainly spark plug...... Make sure the spacer between the carb and intake is not cracked or leaking air. Also check the little hose going toward the back of the engine, it creates a vacuum and works with the fuel pump to pull fuel.

01-28-2011, 10:15 PM	#3
Mike Mac G8 Specialist Join Date: Jun 2009 Location: Phoenix Posts: 7,799	Re: G2 yamaha won't start Any chance the flywheel stripped the key and its out of time?

01-29-2011, 12:38 AM	#4
superdave519 Not Yet Wild Join Date: Nov 2010 Posts: 5	Re: G2 yamaha won't start Just got the flywheel off and the key WAS stripped!!! It crossed my mind, but I thought no way. I'll need a new key before I try again. Thank you so much. One more question, when I post a thread, what's a tag do?
superdave519 Not Yet Wild Join Date: Nov 2010 Posts: 5

01-29-2011, 07:14 AM	#5
Flintrock Raised by coyotes Join Date: Nov 2008 Location: Central Texas Posts: 5,658	Re: G2 yamaha won't start Tags are just another name for keywords. It is like marking a collection of selected threads using an unique stamp.

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01-30-2011, 10:17 AM	#6
rokcrlr Gone Wild Join Date: Sep 2010 Location: Decatur,IL Posts: 553	Re: G2 yamaha won't start Superdave, Lap your flywheel on with valve lapping compound real good, then clean it with brake cleaner before you install the flywheel. Then torque to proper spec. It will hold a whole lot better than just slapping it on .

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