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Gs850Gl bogging at speed.

  • Thread starter Thread starter stoy75
  • Start date Start date
spacepirates said:
A good test to do would be to take your tank off (with the fuel lever on "ON") and set it in your garage overnight to see if the petcock leaks.

Then, you can hook up your vacuum line to the petcock (with the tank still off) and apply a vacuum to it (suck on the end of the line) to make sure that fuel flows out of the petcock when a vacuum is applied.

New rubber parts (vacuum hoses, fuel hoses) isn't a bad idea for a 30 year old bike in general, especially when fuel/vacuum hose would only be a few bucks.
Click to expand...

I know this was mentioned awhile ago but, this method would not work. unless the gas had JUST leaked from petcock you would not find fuel on the ground as it evaps to quickly.

on another note I had the same sort of problem after replacing my exhaust. I tried everything, finally going up one size on main and pilot jet and shimming the jet needle fixed problem. And proper setting on mixture screw.
 
I don't know it is was rejetted for the 4-1 exhaust that was put on. It looks like its been on there a while.
 
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.
 
althomas101 said:
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).
Click to expand...
I must say, ... you have the most convoluted method of adjusting mixture that I have EVER seen. :clap: :clap:

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.

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

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.
 
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.
 
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
 
7sixer said:
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
Click to expand...

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.
 
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