GS1100GL stumbles during cruising

[GS1100GLMLA]

I cleaned my carbs earlier and thought every thing was running right. I took my 1982 GS1100GL out for a spin and noticed at cruising speeds 55+ the bike starts to stumble and run rough until I slow it down. It runs real well when I start and at slow speeds, even when doing full throtle runs. But when cruising at 55+ it acts up. Any thoughts on what would cause that?

 

[tom203]

More clues needed ! stock airbox setup? stock exhaust? carb cleaning method?

 

[GS1100GLMLA]

It has the stock airbox with k&n air filter and 4-1 exhuast. It was starting hard last fall so I bought the o-ring kit and did the carb tear apart, dip and spray clean replacing all the o-rings. I also put a new battery in. Oil is changed and full. New o-rings for intake boots. I set the idle and it starts and idles great. Riding around town, it runs great. When I start going down the highway at about 55-70, it will start stumbline and running rough after it gets warm. If I slow down to about 25 then keep going less than 55 it runs fine.

 

[tom203]

Sounds like you've done good; so this problem developed after carb cleaning fun? Did you note main jet size during teardown? It seems lean in this partial load range.

 

[GS1100GLMLA]

Yes, this developed after the carb rebuild. It ran fine before other than hard starting. I took down some info, but not all. #3 carb mainjet is 120 and #3 carb pilot jet is 170. When it starts to stumble, it does it even if I start accelerating more.

 

[Steve]

When it starts stumbling, add some "choke" to see if it clears up.

Your main jet is only two sizes larger than stock, you might need more than that for your header and K&N insert.

Another possibility is that the float levels are a bit low, making the bike run lean.

.

 

[GS1100GLMLA]

Thanks. Floats are all set at 7/8" and I didn't think to try the choke when it was stumbling. I'm going to run out and try that now.

 

[Steve]

Thanks. Floats are all set at 7/8" and I didn't think to try the choke when it was stumbling. I'm going to run out and try that now.

Did you measure to the bottom of the step?

.

 

[GS1100GLMLA]

I just did a ride and the choke does help it to stop or quiet down the stumble. I actually didn't change the floats because they measured according to the instructions.

 

[GS1100GLMLA]

Since the choke helps quiet down the stumbling, does that imply dirty carburetor, or floats?

 

[qcktvr]

Hi,
Thought I would share an issue that I had with my "new to me" 1150 last year, it would surge when cruising, and not idle too well, I was pointed to the petcock, a holed diaphragm was letting fuel leak into the intake of #2 cyl, a rebuild kit fixed it. Think you could check easily for $0 by pulling the vac hose from the petcock, plug it and run her on prime.
Good luck

 

[Guest]

Since the choke helps quiet down the stumbling, does that imply dirty carburetor, or floats?

So you're running a bit lean it sounds... if stock needles, I'd raise them a notch (.040") to help smooth the mid -range transition.

What do your plugs look like?

 

[Paul]

+1 on floats heights....sounds like fuel starvation due to the floats.... and makes more sense if you did any adjustents while cleaning them + you say shes now running lean

 

[Thumper88]

Does your petcock have a "prime" position? Try running it in that position.

EDIT: I was looking at another topic, make sure your tank is properly vented.

 

[GS1100GLMLA]

So you're running a bit lean it sounds... if stock needles, I'd raise them a notch (.040") to help smooth the mid -range transition.

What do your plugs look like?

My plugs are carbon black on the shell face and dark tan on core nose. I'm running Champion N3C's.

 

[GS1100GLMLA]

One other note, I noted that I was overfilled on the oil by about 1/8 of a quart. I drained it down to just below the full mark on the site glass last night.

 

[GS1100GLMLA]

+1 on floats heights....sounds like fuel starvation due to the floats.... and makes more sense if you did any adjustents while cleaning them + you say shes now running lean

I actually didn't adjust the float heights when I cleaned the carbs since it ran fine before the cleaning. Just started hard. They all checked out at 7/8".

 

[Guest]

My plugs are carbon black on the shell face and dark tan on core nose. I'm running Champion N3C's.

Not familiar with those plugs, but a quick web search showed they are cross-referenced to both NGK B8ES and NGK B7ES plugs.

Not sure how one plug can cover two different heat ranges, but I would at least use the OEM specified ones, NGK B8ES I believe...

Overfilling the oil will definitely show black on the plugs. Make sure you're checking it while on level ground, on the center stand. Change out the plugs to OEM ones, and check the color after riding a bit.

As mentioned before, I would also raise the needles to reduce (eliminate) the mid-range stumble, especially with the K&N drop in filter and 4:1 pipe. If your needles aren?t adjustable, you can shim them with tiny washers. RadioShack sells a bag of assorted washers that have the size you need ? I haven?t been able to source them individually anywhere. Each washer is approx. .020? thick or ? notch.

 

[GS1100GLMLA]

Well, after draining the oil to just under the full mark, I took it for another spin last night and it ran fine while cruising. Can too much oil cause this?

 

[Guest]

Well, after draining the oil to just under the full mark, I took it for another spin last night and it ran fine while cruising. Can too much oil cause this?

Yes, in my experience...

Not exactly sure why, but I think too much oil in the crankcase doesn't let the head vent properly, and that extra oil finds its way into the cylinders (fouling plugs) & ends up being spit out the valve cover breather.

If your breather hose is properly connected to the airbox, I would check to see if there's any oil dripping from the bottom airbox vent.