G8 problems

Dpower · 10-05-2015, 07:07 PM

Yamaha G8 engine gets very hot and act like it's running lean sporadic. Carburetor has been replaced, airbox sealed up tight, muffler is clear, valve adjustment spot on, very good compression but still doing it. I'm thinking now it's the spark advance module. Any thoughts? I have checked everything and if one of my G9 modules would work I would have tried that...

Mr. Mike · 10-06-2015, 07:20 AM

Have you checked the plastic cover over the flywheel? That cover sometimes gets gunked up with crap and restricts airflow around the engine.

Also when you say the carburetor was replaced, did you use an aftermarket carb? The jets might be a pinch too small which can cause a lean condition and excessive heat.

Dpower · 10-06-2015, 08:32 AM

Blower screen is clear and tried three different new carbs, 2 were oem mikuni one was Chinese mikuni or whatever they call it. It's intermittent but getting worse. Not fuel has new pump new filter and all lines are good

smallblock450sl · 10-06-2015, 08:48 AM

What spark plug you running?

Mr. Mike · 10-06-2015, 08:53 AM

Ok. When you say the engine gets hot how hot do you mean? Glowing red hot? Have you replaced the carb spacer? That spacer is notorious for cracking. Plus if you've replace the carburetor that many times then there's a good chance that it cracked. Over tighten the carb just a little too much and crack!

Also possible crank seals.

Try spraying starting fluid around certain areas while it's running. If there's an air leak the engine will rev up a little when it sucks in the ether.

Spark advance module...not sure what that is? Do you mean the ignitor? Somebody else should chime in soon.

Smallblock to the rescue!

cgtech · 10-06-2015, 11:48 AM

4 strokes are not susceptable to "burning up" due to bad crank seals like 2 stroke are (because of running lean). On a 4 stroke, its just an oil leak.

Mr. Mike · 10-06-2015, 12:12 PM

Yeah but running lean can cause excessive heat regardless if it's 2 stroke or 4 stroke. So if it's getting excess air anywhere it can cause a lean condition.

Dpower · 10-06-2015, 04:00 PM

It's a 4 stroke and yes new carb spacer. I keep those on hand

hot as in muffler is discolored and you can feel the heat coming out of engine bay. I own 2 g9s so I am very familiar with how this engine should run heat wise and performance wise but it has a different ignition than my g9s

cgtech · 10-07-2015, 01:40 AM

Bad ignitor will cause low power & "super hot" exhaust sometimes. (seems like late timing to me)

Dpower · 10-07-2015, 07:24 PM

That's what I was thinking but know there is a lot of years of experience on this site and was looking for input before I bought one

10-05-2015, 07:07 PM	#1
Dpower Getting Wild Join Date: Jun 2012 Location: Florida Posts: 90	G8 problems Yamaha G8 engine gets very hot and act like it's running lean sporadic. Carburetor has been replaced, airbox sealed up tight, muffler is clear, valve adjustment spot on, very good compression but still doing it. I'm thinking now it's the spark advance module. Any thoughts? I have checked everything and if one of my G9 modules would work I would have tried that...

10-06-2015, 07:20 AM	#2
Mr. Mike It's Beer Time! Join Date: Sep 2010 Location: Vineland, NJ Posts: 1,462	Re: G8 problems Have you checked the plastic cover over the flywheel? That cover sometimes gets gunked up with crap and restricts airflow around the engine. Also when you say the carburetor was replaced, did you use an aftermarket carb? The jets might be a pinch too small which can cause a lean condition and excessive heat.

10-06-2015, 08:32 AM	#3
Dpower Getting Wild Join Date: Jun 2012 Location: Florida Posts: 90	Re: G8 problems Blower screen is clear and tried three different new carbs, 2 were oem mikuni one was Chinese mikuni or whatever they call it. It's intermittent but getting worse. Not fuel has new pump new filter and all lines are good

10-06-2015, 08:48 AM	#4
smallblock450sl Sometime's............ Join Date: Oct 2007 Location: Tacoma Washington Posts: 11,875	Re: G8 problems What spark plug you running?

10-06-2015, 08:53 AM	#5
Mr. Mike It's Beer Time! Join Date: Sep 2010 Location: Vineland, NJ Posts: 1,462	Re: G8 problems Ok. When you say the engine gets hot how hot do you mean? Glowing red hot? Have you replaced the carb spacer? That spacer is notorious for cracking. Plus if you've replace the carburetor that many times then there's a good chance that it cracked. Over tighten the carb just a little too much and crack! Also possible crank seals. Try spraying starting fluid around certain areas while it's running. If there's an air leak the engine will rev up a little when it sucks in the ether. Spark advance module...not sure what that is? Do you mean the ignitor? Somebody else should chime in soon. Smallblock to the rescue!

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10-06-2015, 11:48 AM	#6
cgtech Over This Interview Is... Join Date: Jun 2012 Location: AZ Posts: 17,449	Re: G8 problems 4 strokes are not susceptable to "burning up" due to bad crank seals like 2 stroke are (because of running lean). On a 4 stroke, its just an oil leak.

10-06-2015, 12:12 PM	#7
Mr. Mike It's Beer Time! Join Date: Sep 2010 Location: Vineland, NJ Posts: 1,462	Re: G8 problems Yeah but running lean can cause excessive heat regardless if it's 2 stroke or 4 stroke. So if it's getting excess air anywhere it can cause a lean condition.

10-06-2015, 04:00 PM	#8
Dpower Getting Wild Join Date: Jun 2012 Location: Florida Posts: 90	Re: G8 problems It's a 4 stroke and yes new carb spacer. I keep those on hand hot as in muffler is discolored and you can feel the heat coming out of engine bay. I own 2 g9s so I am very familiar with how this engine should run heat wise and performance wise but it has a different ignition than my g9s

10-07-2015, 01:40 AM	#9
cgtech Over This Interview Is... Join Date: Jun 2012 Location: AZ Posts: 17,449	Re: G8 problems Bad ignitor will cause low power & "super hot" exhaust sometimes. (seems like late timing to me)

10-07-2015, 07:24 PM	#10
Dpower Getting Wild Join Date: Jun 2012 Location: Florida Posts: 90	Re: G8 problems That's what I was thinking but know there is a lot of years of experience on this site and was looking for input before I bought one

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