Hesitation just off idle

[sailorman1617]

'82 GS1100EZ, stock airbox/air cleaner, Supertrapp 4 into 1 exhaust


In the spring I removed and cleaned the carbs, but hadn't found this site, so didn't dip or replace the 0-rings. The bike ran OK except for a stumble just off idle.

Recently, removed carbs, stripped and dipped, new O rings, installed a Dynojet Stage 1 kit and a larger, 47.5 pilot jet and bench sync. Bike starts better, runs VERY strong, but has a big hesitation just off idle (replacing the stumble). I've opened the pilot fuel mixture screws 1/2 turn at a time from the starting point of 2 1/2 to the current setting of 3 3/4 out. Better, but the hesitation is still there. Will open to 4 out, but feel like the pilot circuit will still be lean.

I have reviewed the CV carb cleaning and process for setting CV carb pilot fuel mixture. Based on those documents, the following observations:
1 - the bike will NOT start without the choke
2 - the bike will NOT run without at least some choke for approx a half hour, and is not fully warmed up for 45 minutes or so, oil temp at 210 F or so.
3 - while it will idle with the choke off after maybe 10 minutes, it won't run safely and the idle speed after full warmup is about 500rpm higher
4 - the hesitation occurs going from a very small throttle opening, < 1/8th to any larger opening, say 1/4 or above, whether rolling or snapping the throttle open. This improves greatly as the engine warms up and is almost gone after an hour riding. Same throttle opening at a higher rpm (say 3000 vs idle) does not produce the hestitation.
5 - air box is sealed, all rubber boots look fine. O rings new, float levels set, valves adjusted, new plugs, etc.

The bike was ALWAYS very cold blooded from new. So is my buddy's bike purchased at the same time in '82. Before changing to the 47.5 pilot (from 45 stock) it required almost full choke to start, immediately ran 4-5000 rpm and required choke for 1/2 hour or so. With the larger pilot, the amount of choke needed is reduced, but still needed until well warmed up.

I am planning to go to a 50 pilot hoping to a) get the bike to run without choke in a reasonable amount of time and b) completely get rid of the heavy hesitation transitioning from the pilot to the needle jet. Note that I drilled the slide as directed by the Dynojet stage 1 install, along with the new needle (middle clip) and larger main jet. So I'd assume the slide is opening sooner/more quickly than stock.

Any advice appreciated. The bike runs great except for the hesitation and extended need for choke.

 

[Rob S.]

'82 GS1100EZ, stock airbox/air cleaner, Supertrapp 4 into 1 exhaust

1 - the bike will NOT start without the choke.

That much seems normal. Is your air box cover removed (I think it's supposed to be for the exhaust)?
I've also read that the mixture screws should not be touched, but that may not apply.

I had mine professionally jetted on a dynamometer after I installed the pods, and it runs perfect from idle to red line. Unfortunately, the tuner did not share the settings he used, other than to say, "Every bike is different."

Wish I could be of more help. Good luck.

 

[chuck hahn]

Recheck float hts..and see the STICKY at the top regarding CV CARB TUNING for more clues. Go maybe 1 MM higher than what the manual call for as theres usually a +/- of 1 anyway.

 

[sailorman1617]

Sorry for the delayed reply, have been under the weather for a week :-(

Rob - I noted that the bike won't start without choke as all the tuning docs I've read state that starting without the choke would indicate a too rich pilot jet.
Also, the airbox cover is in place and well sealed.

Chuck - wouldn't raising the floats increase richness across the board? The bike runs great except for the hesitation transitioning from pilot to needle, so I don't want to do anything to richen the other circuits.

Read the tuning doc in the link. It's interesting the different techniques stated in various documents. That one says you need to tune the main and needle as they affect the pilot; the CV tuning document on bikecliff's site says they don't, and dynojet's doc says the same and that the bike will idle just fine without the mainjet and needle installed. All seem to indicate that the pilot jet and the bypass holes are the primary components for idle, cruise and the transition into the needle circuit. So I think I'll go up one more on the pilot (47.5 to a 50) and hope that addresses the problem, before raising the floats.

Also; the Dynojet troubleshooting sheet states to make sure the carb vent hoses are removed. While I didn't see this in the installation instructions, I've read that a lot of folks do that. I'd assume the T's should be rotated to point downward to avoid getting water into them? Hopefully spiders won't take up residence?

 

[chuck hahn]

No it wont richen it on all circuits. The idle circuit is controlled by the pilot jet and only so much will flow that at a time..period. I just had a guys bie here with CV carbs and it was doing the same thing. Rechecking the floats they were first way out of speck, and secondly I set them at the TOP end of the manuals settings and it runs like a scalded dog without any hint of bogging anywhere now.

being sure the advance governor is free and snaps back when you let go of its a good idea too...along with double checking the timing with a strobe light. And one last note. If you remove the needle jet youll see a hole passing from the pilot jet hole into the main needle hole..be sure its open.

 

[sailorman1617]

Thanks much Chuck. My floats were within stock range, only adjusted one when reassembling after the dip. But looks like it's worth re-setting them at the high end just to be sure. I'll check the advance mechanism and timing (have to find my timing light). Not sure I probed that passage fromt he pilot to the main jet area, nor the bypass holes above the throttle plate, so I'll check those as well.

So.... I hate to change 2 things at once, since you don't know what corrected the problem. But I hate R&R-ing the carbs. So I'd lean toward both going to a larger pilot jet and raising the floats to the top of the stock settings. Do you think this is a bad idea? While I'd like to raise the floats first, I have a limited amount of time to work on the bike, so if I can avoid R&R of the carbs twice, I'd like to go that route if possible.

Thanks again for the reply and advice.