GS750T starting and other problems

[willbob]

Here is the list of what I am experiencing. I have read as many of the od FAQ and current posts, but I don't know if I am diagnosing properly. It's a 1983 GS750T with the CV carbs. Bought it 3 years ago and ran it for the summer on a daily 160 mile commute for work. Ran June to mid Aug and then wouldn't hold a charge. Not having seen this web site and the stator papers, I parked it and bought a new battery the next summer. Needless to say, 2 summers later, I've replaced stator, and regulator, and tried to run it. Issue 1) Went 25 miles on first trip to girlfriends house and that's where we sit. Has started, but dumps fuel through airbox. Took apart and cleaned carbs as CV series papers instruct. Did it again. Issue 2) Has a popping noise as engine turns over. Still makes the noise without carbs and airbox. Is there a problem in valve area, or gasket leak in vacuum system. I really want to ride. Been missing the fun way too long. Had a 82 GS850L 13 years ago and stupidly sold it because with kids, no time to ride.

[Dave8338]

How many miles are on the bike? Have you set the valve lash to spec? Did you replace the intake o-rings yet? Did you tear the carbs down, soak them in Berrymans or similar carb cleaner < or > spray them with carb cleaner? When you say poping noise, are we talking internal from the engine or external ie. the starter/clutch area? If the valves are way off, or the cam chain jumped, you could be trying compress when the intake/s are open slightly. :?

[willbob]

16000 miles. The popping is definety internal. I think it's from #1. I just determined that by slowly bumping starter to specifically find the noise. Maybe compression coming out intake instead of exhaust? The intake area looks dryer in that cylinder than in the other 3. I did not replace the intake o rings yet. I dissambled the carbs and cleaned with spray cleaner. Only issue seen was in #1 carb, some debris trapped by screen above the needle valve connected to float. Sorry for my ignorance, but what is the valve lash? I haven't purchased the manual yet, because I figured as well as it worked the last summer I used it, shouldn't be anything mechanically wrong. The only problem had been bad charging system. Fixed it, and now this happens.

[Dave8338]

Valve Lash is the amount of clearance allowed between the valve shim and the cam lobes. You need to measure that distance and re-shim to the factory specs that will be provided for you in the repair manual that you are going to purchase. :-D

[relic-rider]

You have the 16 valve 750 engine in that bike. It doesn't use shims for valve adjustment. Each valve has an individual tappet with adjusting screw and locknut. You measure the clearance between the tappet and valve stem end and adjust accordingly. This engine also does not have intake boot o-rings. The 16 valvers use an intake boot that is clamped on both sides.

[t3rmin]

Whoa there...!

If gas is coming out of the airbox you almost certainly have a float valve issue. Cleaning is nothing without replacing those float valve seat o-rings. Head over to cycleorings.com and get a set from Mr. Barr. Check the condition of the float needles and seats, put in the o-rings and verify zero leaks by hooking up the carbs to gas on the bench (before spending all that time re-installing them).

Also make sure your petcock vacuum spigot isn't leaking gas.

Adjusting valve lash is certainly important, but it's not even remotely related to your immediate problem.

[Dave8338]

You have the 16 valve 750 engine in that bike. It doesn't use shims for valve adjustment. Each valve has an individual tappet with adjusting screw and locknut. You measure the clearance between the tappet and valve stem end and adjust accordingly. This engine also does not have intake boot o-rings. The 16 valvers use an intake boot that is clamped on both sides.

Glad you've got my back, the 16 valve engines ...throw out all prior comments!!

[Dave8338]

Whoa there...!

If gas is coming out of the airbox....

Missed that also...is it the 4th yet?

[willbob]

Thanks

I will do as suggested and thanks in advance. Should have thought of testing on the bench without reinstalling carbs to determine which is bad. Will replace all o rings and go from there. Nothing simple enough that I will be riding within a short time frame, but your help will make the riding longer and better. This one should resurrect and go a long time. Sat on the show room floor 9 years before finally purchased. I am 3rd owner. \\/

[t3rmin]

Last carb cleaning I did on the new 750 I only replaced the float seat o-rings. If you don't separate the carbs and nothing else is leaking, that may be all you need to do. Pretty quick job, actually!

[Dave8338]

Last carb cleaning I did on the new 750 I only replaced the float seat o-rings. If you don't separate the carbs and nothing else is leaking, that may be all you need to do. Pretty quick job, actually!

Great Point...don't OVER repair if you don't have to! :-D

[willbob]

Won't try and overrepair. Gas overflow came from upside needle valve from my carb cleaning. Put it all back together this morning and was able to start. Had to give extra throttle, but idle screw may need adjust from the in and out. Did experience backfire. Possible what began all trouble on first start and ride this year. Had to replace boot between carb and intake on #1. Thought cracks came from time. Could've blown because of backfire. Probably need to adjust valves or whatever is causing backfire problem.