1982 GS750T Idles high on choke and then dies

[jstedmanb]

I have a 1982 GS750T that I've ridden on and off for about 5 years. It's always run great once it got going but would be very difficult to start if it sat for more than a few weeks despite using ethanol free gas. It would also rev up very high on choke and I would have to slowly back off the choke to keep it from revving up to 5k.

I recently took the carbs off and cleaned them thoroughly, I replaced two of the pilot jets that got pretty mangled in the process of removing them, replaced the bowl seals and o-rings on the needle valves, and cleared out all the passages.

Now the bike will start with the choke on, rev up to about 5k, and then slowly die. It will also sometimes start without the choke but runs rough and will still eventually die. The bike ran well before this and I did not alter the mixture screw at all. Nothing should have really changed that drastically. I have the stock airbox, checked the valves a few years ago, and the intake boots seem to be in good shape.

If anyone has any advice on where to start it would be very appreciated.

 

[rphillips]

First paragraph says very hard to start after sitting a few weeks. Wondering if you used the PRI on pet cock. My CB1100F has your problem but they have no PRI nor any other way to prime the carbs... Also the high revving on choke and backing off choke to keep it from revving too high is normal. Sorry, no help with 2nd. paragraph.

 

[Nessism]

Reving up on choke is common with GS CV carbs. Beyond saying that, I have no advice other than to ask if you removed the pilot screws and dipped the carbs when you cleaned them?

Rebuild tutorial in my signature...

 

[Rob S.]

...very difficult to start if it sat for more than a few weeks despite using ethanol free gas. It would also rev up very high on choke and I would have to slowly back off the choke to keep it from revving up to 5k.

Completely normal.

 

[rphillips]

Kind'f seems all fine till it was worked on. Possibly another case of "If it ain't broke"

 

[Rich82GS750TZ]

If the carbs are indeed clean as per Nessism’s thorough rebuild tutorial, then what you describe is normal behavior. After starting on choke, the rpm’s should rise. Continue to back off the choke, decreasing the rpm’s until the bike is more or less up to temp. I think you need to play with the idle screw at the bottom between carb 2 & 3. Turning it one way will raise the idle rpm, turning it the other will decrease rpms. You can use a long flat screwdriver to do this while standing on either side of the bike. While it’s warming up, give the knob a little bump, figure out which way raises the rpm’s. You want the rpm’s to settle around 1100-1200 when warm and choke completely off.

 

[Rob S.]

Kind'f seems all fine till it was worked on. Possibly another case of "If it ain't broke"

If it ain't broke, don't break it.

 

[jstedmanb]

Well it's good to know it was normal before lol. But I'm still confused what the issue is now. This is probably the third time I've cleaned the carbs and I didn't do anything out of the ordinary besides replace the pilot jets that were damaged.

I'm gonna check real good for air leaks and I'll post back if I get it fixed. The weather is too pretty out to not be riding.

 

[rphillips]

You say it will start then eventually die. Possibly starving for fuel? Pull fuel line from carbs, set pet cock to PRI just to be sure plenty of gas getting to carbs. That'd assure screen in tank, pet cock, and fuel line are "NOT" the problem.

 

[jstedmanb]

FIXED. I was dumb and had the carb vent hose on the petcock instead of the vacuum. Lol runs great now.

 

[Rich82GS750TZ]

You will not be the first nor the last to have done that. Glad you got it sorted. Thanks for following up. That is appreciated.