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Carb Issue.....

  • Thread starter Thread starter hvfracingwilly
  • Start date Start date
H

hvfracingwilly

Guest
Here is the info.

Bike: 1981 GS750L
Mods: Emgo Pods, V&H Pipe, Coil Relay, New Plugs

Carbs have been cleaned and synced, the issue I am having is between 3100 RPM and 3500 RPM the bike "hesitates, and sputters" before that it runs fine and after that it runs fine. I checked the plugs and all of them are black around the edges with a clean insulator.

Jetting Info:

42.5 pilots
needles in 3rd notch from top
mains=130 DJ
Air jets were at 155 and just changed to 170(this seemed to help slightly)
Mixture screws are at 2 on the outer two cylinders and 2.5 on the inner two.

I continue to here a popping on deceleration which would indicate a lean condition so I moved the needles from Position 2.5 to 3 and the hesitation got worse.

I have tried to lay as much info out on the table as possible and if anymore is needed please ask!
 
Put the 155s back in. This is where the popping is comming from. Too lean on the pilot circuit. I bet setting the mixture screws was fun if possible.
Try the needle on the second notch from the bottom.
Did you install the Dyno main air jet?

Try the second notch from the bottom. Dynojet suggested settings tend to be on the lean side.
 
Do you have pods on it? I am experiencing similar problems with my 82 GS1100E, feels like its starving for air? let me know what you find out.
 
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jwhelan65 said:
Do you have pods on it? I am experiencing similar problems with my 82 GS1100E, feels like its starving for air? let me know what you find out.
Click to expand...
How are your carbs jetted and are you running pods?
 
As of today carb # 2 leaks following a ride. Just had them cleaned and rebuilt so I am not totally sure. I am going to upgrade to Mikuni flatslides, I have spent way to much time and money on these things only to have it still sitting in the garage.
yes I have pods on it, the last guy who did my carbs installed them.
 
jwhelan65 said:
As of today carb # 2 leaks following a ride. Just had them cleaned and rebuilt so I am not totally sure. I am going to upgrade to Mikuni flatslides, I have spent way to much time and money on these things only to have it still sitting in the garage.
yes I have pods on it, the last guy who did my carbs installed them.
Click to expand...
Whoa! Slow down. The leaking carb is due to a bad petcock. It is probably leaking gas through the vacuum line into #2 cylinder.
 
chef1366 said:
Put the 155s back in. This is where the popping is comming from. Too lean on the pilot circuit. I bet setting the mixture screws was fun if possible.
Try the needle on the second notch from the bottom.
Did you install the Dyno main air jet?

Try the second notch from the bottom. Dynojet suggested settings tend to be on the lean side.
Click to expand...

I did install the "air corrector" the issue seemed to get better with the 170s in it though??? low end throttle response was improved and the hesitation ranged dropped a few RPM. when I went from position 2.5 to position 3 on the needles the problem got worse??
 
I had exactly the same hesitation with my 1100 after installing the DynaJet stage 3, (pods and 4-1)...

I did just like the instructions said and moved the needle up one notch...(moved the clip down one, to the fourth from the top)...
Runs much, much better...
I'm going to try going one more notch this weekend just to be sure, but it works pretty good right there.

Oh and BTW...your mixture jets should be the same for all four carbs.

HTH,
 
Baatfam said:
I had exactly the same hesitation with my 1100 after installing the DynaJet stage 3, (pods and 4-1)...

I did just like the instructions said and moved the needle up one notch...(moved the clip down one, to the fourth from the top)...
Runs much, much better...
I'm going to try going one more notch this weekend just to be sure, but it works pretty good right there.

Oh and BTW...your mixture jets should be the same for all four carbs.

HTH,
Click to expand...

When I moved the needles from position 2.5 to 3 the problem got worse. I am scared to try position 4. This "hesitation" only occurs at steady throttle input between 3100-3500 RPM.
 
Here is where I am at after a night of work.

Mains= 130 DJ
Needles@1.5 from the top
Pilots=42.5 mikuni
Mixture Screws@ 2.5 turns
Air jets@ 170


There was no "hesitation" with the mixture screws at 2 turns out, but the idle would hang slightly and there was heavy "popping" upon deceleration. That is when I moved the Mixture screws to 2.5 turns. This helped the popping on decel but Brought back my steady throttle "hesitation" Plugs are still black on the outer edge and the insulators are tan.

Now what............
 
I would set it up per the DJ instructions, screws to 3 turns out and needle in fourth position, then tune from there.
 
I was concerned about the jump from a 155 pilot air jet to a 170. I checked and the 170 is stock so this is ok.
Are there any air leaks from the intake pipes?
Are the valves adjusted?
What's your compression like?
Is the petcock flowing good?
If all this is good go up to a 45 pilot jet.
 
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So here is where I am at after today.

Mains=130 DJ
Pilots 42.5 mikuni
Mixture screws @ 2.25 turns
Needles in the first position(leanest)


Amazingly enough the bike is running great idle is rock steady at 900 RPM and the stumble is almost gone...... yes almost.
 
Seems like your leaning the needle to compensate for a rich main jet.
 
Strange how these bikes act the same but can have such different causes. I had a bad stumble around 3k RPM after rebuilding my carbs and putting in a Stage III kit (130 mains/clip at 4th position). My engine was too rich with some very black plugs. Kept screwing in the pilot screws (currently around 2.25) and it is almost there.

Doing plug chops was the best method for me to get each carb dialed in using the pilot screw.
 
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