ok folks i need help

[simon_C]

ive got a 77gs400 with a 2-1 MAC pipe and no airbox.

now my problem is, when the bike is cold it idles where it should, but after the bike warms up, say 10-20 mins of riding, the idle slowly creeps up to 3000rpm exactly. ive gone through and cleaned the crap out of the carbs (tore them completely apart) and checked the carb boots (literally brand new). no air leaks anywhere. i messed with the tuning with no result, so i set that back to what it was. now bear in mind this: I HAD THIS PROBLEM WHEN THE BIKE WAS STOCK. the pipe and lack of airbox had no effect on it.

other than that, the bike runs awesome, it doesnt overheat, it has plenty of power, and it runs smooth.

any ideas?

[Steve]

You say the boots are in good shape, what about the o-rings between the boots and the manifold?

Idle speed that climbs as the bike warms up is a classic sign of an intake leak. Manifold o-rings are a typical cause.


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[txironhead]

With no airbox you are running pods, right?

[simon_C]

You say the boots are in good shape, what about the o-rings between the boots and the manifold?

Idle speed that climbs as the bike warms up is a classic sign of an intake leak. Manifold o-rings are a typical cause.


.

i didnt see any o-rings? it didnt even look like there was a place for them to go. looks like one of the POs forgot to put something back.... ill make a run to the hardware store and find something.

[Nessism]

looks like one of the POs forgot to put something back.... ill make a run to the hardware store and find something.

You can't just use anything in there, you need a proper o-ring or it will leak again.

[chef1366]

No o-ring here

[simon_C]

No o-ring here

s'what i thought

[Jagir]

ive got a 77gs400 with a 2-1 MAC pipe and no airbox.

now my problem is, when the bike is cold it idles where it should, but after the bike warms up, say 10-20 mins of riding, the idle slowly creeps up to 3000rpm exactly. ive gone through and cleaned the crap out of the carbs (tore them completely apart) and checked the carb boots (literally brand new). no air leaks anywhere. i messed with the tuning with no result, so i set that back to what it was. now bear in mind this: I HAD THIS PROBLEM WHEN THE BIKE WAS STOCK. the pipe and lack of airbox had no effect on it.

other than that, the bike runs awesome, it doesnt overheat, it has plenty of power, and it runs smooth.

any ideas?

This sounds alot like the airleak situation I just nabbed.


Have you replaced the fuel lines with new clear ones? It's cheap and allows you to see that fuel is moving properly.

[simon_C]

This sounds alot like the airleak situation I just nabbed.


Have you replaced the fuel lines with new clear ones? It's cheap and allows you to see that fuel is moving properly.

hmm the fuel line is a bit ragged. ive got a roll of clear line, ill try it.

[Nessism]

Yup, as the others have said it sounds like an air leak. Regardless of whether or not there is an o-ring, you have a leak. I'd take the carbs back off and make sure everything is sealing fully.

[Steve]

OK, so that model doesn't have manifold o-rings.

Still need to make sure that the gaskets #20 are not leaking. Same principle. 8-[


.

[simon_C]

i think i found the problem...

i put a clear fuel line on there and primed it and started the bike. within 15-20 seconds the fuel line was nearly empty of gas and full of air. there was only a small trickle of fuel going through until i pulled the line off, then it flowed out smoothly. (all over me and my engine i might add.)
im guessing ithe air is coming in through the petcock? how do i fix this?

[txironhead]

Are you running an inline filter? If so, toss it.

Under the "Tips and Tricks" section, there is a post on testing vacuum petcocks.

Sounds to me like you might need a new petcock.

[simon_C]

Are you running an inline filter? If so, toss it.

Under the "Tips and Tricks" section, there is a post on testing vacuum petcocks.

Sounds to me like you might need a new petcock.

no filter inline.

[rustybronco]

Some ideas also...
Inlet screens to carbs plugged.
gas tank not venting (open cap and try).
fuel bowls not vented properly (kinked plugged).
fuel line not routed properly (must go down hill all the way).