Won't run well on choke

[Skinner]

1981 GS650GL, stock

I thought I finally had my bike dialled in. I adjusted the mixture screws with the Colortune and the engine is running very well. When warmed up it idles at 1100 or so and the hanging idle issue I had is now gone thanks to my new boots. But when starting from cold it does not run well on choke. It fires immediately but does not rev progressively higher as in the past. It actually struggles a bit. I used to start it on choke and, after a few seconds, it would rev to about 3000. I would then progressively close the choke (less choke, to be clear) as it warmed up. After 45 seconds or so I'd be good to go. Now it will not rev high at all no matter the choke position. It still runs great after that initial 45 -60 seconds but the choke isn't helping.

Just to be clear, the carbs were completely stripped, dipped and re-built with new o-rings during my restore in May of this year. Other than the choke issue the bike runs like a top and pulls like a train.

Any thoughts?

K

[OldVet66]

Glad to hear the hanging idle issue is gone. Fixing that has obviously brought another issue to light. (http://www.thegsresources.com/_forum...d.php?t=224171) This thread may be relevant to your problem and would be an easy thing to check out without removing your carburetors. I don't agree with his methods, but being an aircraft mechanic his skill set is probably well above most. It's worth a shot, but again be careful. I would recommend doing this by hand with a small chuck of some sort to hold the drill bit after soaking the bowls in dip again.

[mrbill5491]

Some where in the choke circuit you have a blockage. Lots of tiny passages in these carbs. When I rebuilt my carbs, I bought a carb passage cleaning tool and went after every one of them with that and with Berryman's carb cleaner and compressed air.

My bike will run up to 4,000 rpm in a heart beat on a certain setting of the choke. I usually run about 2.600 rpm on the choke for a a few minutes. I read somewhere once you open the throttle any it over rides the choke circuit. So according to this, running with the choke on is pointless.

[Skinner]

My thoughts were a blockage of some sort as well, but why all of a sudden? I was very thorough when I stripped, dipped and cleaned the carbs because I didn't want to do it again. And the choke worked just fine until after I adjusted the mixture screws. I'll check the bowls as per OldVet66's advice, and failing that, will pull the carbs and check the choke passages.

[Steve]

My bike will run up to 4,000 rpm in a heart beat on a certain setting of the choke. I usually run about 2.600 rpm on the choke for a a few minutes. I read somewhere once you open the throttle any it over rides the choke circuit. So according to this, running with the choke on is pointless.

Most bikes will do this. Personally, I prefer to not have my bike start and race to 4,000 before the oil gets a chance to get moving properly. I have found a "happy spot" in the "choke" setting that allows easy starting, but only revs to about 2,000. 20-30 seconds there, it's good to go. I will take off with some "choke" still applied, but by the time I get into third gear, I turn it off. By the time I get to the next traffic light (either 1/2 mile or 1 mile, depending which way I turn out the drive), the bike is plenty warm enough not not need any "choke".

You are correct, mrbill, using any throttle will over ride the "choke" circuits. They rely on the high vacuum of a closed throttle to pull the gas and air through the ENRICHENER passages. Opening the throttle will remove that vacuum.

.

[tkent02]

It's not a high idle, it's an enricher. In hot weather making it too rich doesn't help, just makes it run like crap.
When it's cold out and the engine needs to be richer until it warms up it does. 70ish temperature maybe just use a little choke until it fires up and shut the choke off. Hotter than that you shouldn't need to use it at all, even with a stone cold engine.

It probaby won't idle at first when the engine isn't warm, just hold the throttle open a bit for a few seconds, or just fire it up and ride away gently.
No point in sitting there warming it up in warm weather, just hop on and ride, but don't beat on it until it's up to a more normal operating temperature.

[Skinner]

It's not a high idle, it's an enricher. In hot weather making it too rich doesn't help, just makes it run like crap.
When it's cold out and the engine needs to be richer until it warms up it does. 70ish temperature maybe just use a little choke until it fires up and shut the choke off. Hotter than that you shouldn't need to use it at all, even with a stone cold engine.

It probaby won't idle at first when the engine isn't warm, just hold the throttle open a bit for a few seconds, or just fire it up and ride away gently.
No point in sitting there warming it up in warm weather, just hop on and ride, but don't beat on it until it's up to a more normal operating temperature.

Thanks tkent02, that pretty much sounds like my issue. It's been hot and humid of late and choking made it run like crap, as you stated. That would explain the sudden onset as well. I'll just leave it alone for now.

Cheers!
K

[gspower]

Thanks tkent02, that pretty much sounds like my issue. It's been hot and humid of late and choking made it run like crap, as you stated. That would explain the sudden onset as well. I'll just leave it alone for now.

Cheers!
K

I also dipped my carbs overnight and, if it's of any consolation, I have the same problem as you on my 425. The problem may be that dipping the carbs frees up the paint/finish on the carbs (maybe someone can chime in and tell me what I stripped after leaving them in overnight? Finish looked dull-er than usual afterwards), thus causing clogs. I needled away a few of what I'll call these "finish clogs" before reinstalling. Low and behold, using the choke will kill my engine. I already had the carbs off as I'm polishing up the engine casing a bit so I looked at the choke circuit again. Sure enough, it was totally clogged. After a couple minutes of jamming the carb cleaner straw through the hole and forcing the clog out a load of black gunk came through and I think I may have fixed the problem. Will post again when I reassemble to let you know for sure.