1982 GS750E will not rev under load

[DucatiDave]

My 1982 GS750E does not want to rev while under load (on the street with rider). It starts, idles and revs to 8K+ RPM on the bench or if I pull in the clutch while in motion. But while riding, it is extremely underpowered and will not rev past 3 - 4K RPM and has no power. See list of what has been done below, educated suggestions are welcomed:

• Stock exhaust, airbox and new air filter
• Stock carb settings, recently cleaned and rebuilt (replaced all jets, etc.)
• Brand new Dyna ignition, coils, plug wires and coil relay mod. Huge blue spark all cylinders.
• Ignition advance works freely
• 12.6V to the coils at 3K+ RPM
• Fuel flow is fine, not a plugged vent on the tank and vacuum line from carb to petcock is fine
• 160+ PSI compression for all cylinders
• Does not surge at idle or backfire on decel
• Plugs appear to be slightly on the lean side, all four look identical.
• New battery and spark plugs
• Timing marks on cams align, timing is set, cam chain nice and snug (tensioner works freely) no noise or rattling from top end.
• Valves are all adjusted properly.

Need to recheck float bowl levels. Could that make it run fine with no load but like crap when there is a load?

[Denh]

Hi Dave that sounds like fuel to me,check float heights maybe some sea foam as well.

[Denh]

Yep check float heights,if they were too low bike would die when under load !

[Big T]

Air leaks can cause that
Did you replace the carb boot or those O rings?

[Nessism]

The '82 750 doesn't use carb boot O-rings so that can't be it.

When you replaced the jets where did you get them? And did you take the carbs fully apart as detailed in the carb rebuild tutorial linked in my signature? I'm wondering if the carbs are the problem, maybe some crap aftermarket jets or some passages are plugged?

[DucatiDave]

Hey All;
Thanks for the responses! Haven't been here for a bit, too hot to work in my garage. I pulled the head as it appeared I had a head gasket leak (confirmed). I noticed the valve oil seals were leaking so I will be replacing them as well as the head gasket, etc. Since I have the carbs off I will check the jet sizes and also float bowl levels. When I cleaned the carbs I did take them apart and fully clean as per the rebuild tutorial. All passages appeared to be clear.
The carb kits I used were K&L bought on eBay. Here is their description:
This listing is for 4 new K&L Pro brand carburetor repair kits for the models listed below (1 kit per carb). These quality Made in Japan parts are fresh stock and ready to install. This 15 piece kit includes all of the standard parts needed to rebuild one carburetor. Please note that this kit includes jet sizes 42.5, 112.5 and 170.

[salty_monk]

The KL stuff is not the best. It's better to just change the gaskets & O rings, usually the rest of it doesn't need changing but occasionally you get an bowl valve or something that needs to be replaced... those can be bought OEM.

cycleorings (Robert Barr) is the place for O rings

[Northern Mike]

I pulled the head as it appeared I had a head gasket leak (confirmed).

I was just about to suggest this as a long shot. My 79 gs750e was acting similar. low gears in town, was ok, but would fall on its face under heavy acceleration or under load in higher gears.

[DucatiDave]

Thanks Mike! I am hoping to get the head work done over the next month or so, will let you know if it helps. Good to hear that this fix helped your situation.

[DucatiDave]

Just updating to close this out... after replacing the head and base gaskets, rechecking valve clearances, replacing/adjusting the air mixture screw, readjusting timing and adjusting float levels, the bike runs great. I think it was a combination of small problems all contributing to the issue. I still need to sync the carbs to smooth out the idle a bit (not bad now) and then I think I can just ride and enjoy.
Thank you all who contributed suggestions!

[steve murdoch]

Glad to hear you got it sorted.