Gs850Gl bogging at speed.

[7981GS]

How would I know if it was rejetted?

Pulling the jets and noting the numbers on the current ones would help.

Eric

[althomas101]

I'll try to help. First off do you have good spark on all 4 wires? It should be able to jump a 6mm gap, and the spark should be bright blue not yellow. You state that you have replaced the intake boots, their o-rings, the airbox boots, and air filter, you also state that you did a complete and thourough carb cleaning according to the document. Additionally I would recommend that you adjust the valves. But assuming they are good as well, then lets start by tuning your carbs. How are you adjusting the mixture on the carbs? How I do it is I install a sync ports into the intake runners (Z-1 sells them). By uncapping a sync port it and allows it to bleed air, so you can get a feel for what the mixture is like. If when you introduce an air bleed and the RPMs go up then you are at least in the ball park. How I do it is: introduce the air leak, then lean the carb till it doesn't have any affect between having the air leak plugged or not. Then I richen it up till RPMs dropp off, set the air screw in the middle of the two settings. I do this for all cylinders (you want roughly the same RPM rise on all cylinders), then I take a infrared thermometor and check the temperature of the pipes fiddle with the air screw to get them the same (center cylinders should be slightly richer). After this do a vacume sync, and then check the pipe temps again, adjust if needed. I have done cars and bikes this way all with good success. The next step would be if it is falling flat when running on the needle. To do that you have to start with getting the right main jet installed, this can be accomplished by simply changing main jets till your butt dyno says you got the right one, or do plug chops at wide open throttle (WOT). Once you have the right main jet that gives the best performance at WOT, then you need to raise or lower the needle to smooth out the transition and give the best mid-range power. I just use the butt dyno for that as well. Remember 0-1/4 throttle is the pilot circuit, 1/4 - almost WOT is the needle clip setting, WOT is the main jet. Use that as a guide to determine what circuit is the culprit. I hope that helps.

[Steve]

How are you adjusting the mixture on the carbs? How I do it is I install a sync ports into the intake runners (Z-1 sells them). By uncapping a sync port it and allows it to bleed air, so you can get a feel for what the mixture is like. If when you introduce an air bleed and the RPMs go up then you are at least in the ball park. How I do it is: introduce the air leak, then lean the carb till it doesn't have any affect between having the air leak plugged or not. Then I richen it up till RPMs dropp off, set the air screw in the middle of the two settings. I do this for all cylinders (you want roughly the same RPM rise on all cylinders), then I take a infrared thermometor and check the temperature of the pipes fiddle with the air screw to get them the same (center cylinders should be slightly richer).

I must say, ... you have the most convoluted method of adjusting mixture that I have EVER seen.

How long does it take to do all of that, including the vacuum sync?

I just did this yesterday for recycled64, on his 650G, the process takes about 15 minutes, including installing the adapters for the sync gauge.

I start with the mixture screws out about 3 turns. This gives it a nice rich mixture to start a cold engine, requires minimal (if any) "choke". Sync the carbs first, you want to be sure the cylinders are all drawing similar amounts of mixture before you try any fine-tuning.

With the sync gauge still attached and the carbs all balanced, slowly turn the mixture screw in until you hear the engine slow down just a bit. If you watch the sync gauge, you will also see the vacuum level start to drop a bit in all cylinders as the engine slows down. When you get to that point, back up about 1/8 turn on the screw, move to the next carb, repeat. If you want to be anal about it, go back to the first one and do them all again, just to make sure they are right on the edge of running too lean. Remove the sync gauge and adapters, put the plug screws back in the intake tubes, you are done.

.

[althomas101]

About the same as you 15 minutes. I may be over zealous about tuning but my stuff does run good.

[stoy75]

Update

So resynched the carbs. Problem greatly reduced. Running smoother. Taking plug cap 4 off kills bike. Plug cap 3 removal no change at all. Engine runs. Ideas.

[stoy75]

FYI thanks Mr Cliff dor the idea to recheck.

[stoy75]

Ok jetted at 120. Carbs stripped and dipped and re o ringed again. Problem may have worsened actually. On highway lost all power and died. Would only restart on choke. Ran off of choke roughly after that. Cylinder three plug cap removal has little if any change on idle and all others will kill bike. Swapped leads and still #3 is the issue.

[7sixer]

I'm having the same issue with #3 not seaming to affect how the engines running. My best guess is a replacement plug cap, I am getting a strong, blue arc from just the bare wire? What was your solution?

1980 GS550

[wymple]

I'm having the same issue with #3 not seaming to affect how the engines running. My best guess is a replacement plug cap, I am getting a strong, blue arc from just the bare wire? What was your solution?

1980 GS550

I just went thru this little problem in August, my 2-3 coil stopped firing properly, only affecting #3. I replaced it with another coil I had laying around off a Honda. A new set is on my list.