GS850G Carb or spark issue ?

[ray illuminati]

Need some help debugging this. Got an 1981 gs850g which starts and runs for a minute or more on high idle. It use to let me pump the throttle while it was on high idle but not anymore. Did a major cleaning of the carbs and checked the float levels. Same thing happen, it chokes off when I touch the throttle or after a minute or two.
-Coils were getting spark when hot or cold but I purchased two coils from a running gs850 anyway and swapped them in. Same thing happens.
-Checked the compression on all cylinders and that is fine.
-Checked the spark on the coils I swapped in and they are fine.
-Everything is tight on the carb and airbox and no vacuum leaks that I can tell of.
-I am running the bike from a bottle of gas and not the tank.
Any ideas would be appreciated. Thanks.

[Steve]

First of all, "pumping the throttle" while on high idle will defeat the enrichment circuit that most people call "choke". Don't do it.

Let's make sure everything else is correct:
Valves adjusted?
Float levels in the carbs?
Idle mixture screw setting?

.

[BassCliff]

Hi,

When using an auxiliary tank you must plug the vacuum port on the #2 carb. That is a big vacuum leak otherwise.

I concur with Mr. Steve and ask, "Have you done ALL of the necessary maintenance?" You'll find the maintenance lists HERE. Skipping any steps or taking shortcuts will cause much frustration and catastrophic failure. My first suspect would be the intake boot O-rings.


Thank you for your indulgence,

BassCliff

[ray illuminati]

Thanks Steve.....
-I haven't touched the valves for adjustment. I don't know anything about engine internals to do that....... yet......
-I have checked the float levels and they fall in the specification range.
-I have adjusted idle mixture screw setting. I have been told that it is 3 half turns. Is that correct?

[ray illuminati]

Thanks BassCliff. I do have that vacuum port on carb #2 plugged. Thks for the reminder and for the To Do list. I will go over that.
When you say the intake boot o-rings..... you are speaking about the boots that each of the carbs bolts to on the intake correct? What could be the problem with them? Too loose? Too tight? Is that what you are referring to? Thks again.
Ray

[Steve]

Thanks Steve.....
-I haven't touched the valves for adjustment. I don't know anything about engine internals to do that....... yet......
-I have checked the float levels and they fall in the specification range.
-I have adjusted idle mixture screw setting. I have been told that it is 3 half turns. Is that correct?

- If the valves (especially the intakes) are too tight (a rather common occurrence), it will be hard to start.
- Did you measure from the proper point on the float? Not the top, next to the hinge pin, should be from the bottom of the "step", or top of the round part.
- No, you should start with 3 FULL turns. You might end up tweaking the screws down to the vicinity of 2 turns or so, but start with 3.

Just a note: I was having some difficulty getting my son's bike to run on all four cylinders just a couple of days ago. TheCafeKid came over to help me and played with the mixture screws. He tried turning out the screw for #3, which is the one that was giving us problems. I think he ended up at about 4 to 4.5 turns before that cylinder finally kicked in. All the others are between 2.5 and 3. This just shows that the 3 turns that is suggested is just a starting point, not an absolute "must have it HERE" point.

.

[ray illuminati]

BassCliff.... got what you mean for the o-ring stuff after reviewing the documentation you forwarded me to. Thanks again.

[tkent02]

Pumping the throttle does nothing, there's no pump.

[Steve]

Pumping the throttle does nothing, there's no pump.

Only GS I have seen with a pump is the 450GA.

.

[oldgsfan]

- If the valves (especially the intakes) are too tight (a rather common occurrence), it will be hard to start.
- Did you measure from the proper point on the float? Not the top, next to the hinge pin, should be from the bottom of the "step", or top of the round part.
- No, you should start with 3 FULL turns. You might end up tweaking the screws down to the vicinity of 2 turns or so, but start with 3.

Just a note: I was having some difficulty getting my son's bike to run on all four cylinders just a couple of days ago. TheCafeKid came over to help me and played with the mixture screws. He tried turning out the screw for #3, which is the one that was giving us problems. I think he ended up at about 4 to 4.5 turns before that cylinder finally kicked in. All the others are between 2.5 and 3. This just shows that the 3 turns that is suggested is just a starting point, not an absolute "must have it HERE" point.

.

Not to hijack the thread but im curious how your sons bike performed before you got the air mix screws right.