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General Category >> The Cafe >> Suzuki gs400 1978 - when at idle spits vac hose
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Message started by GuiltyInnocence on 03/31/24 at 01:22:09

Title: Suzuki gs400 1978 - when at idle spits vac hose
Post by GuiltyInnocence on 03/31/24 at 01:22:09

After choke starts to come off and the idle gets normal then after a few seconds of sounding not very smooth it spits out the vacuum hose from the petcock to the carburetor. Does run a bit smoother when it does this

Title: Re: Suzuki gs400 1978 - when at idle spits vac hos
Post by Ruttly on 03/31/24 at 07:17:28

I know zip about a GS but you have pressure where you should have vacuum.
Burnt valve
Bad valve adjustment
Cam timing has moved

Two cent

Title: Re: Suzuki gs400 1978 - when at idle spits vac hos
Post by Dave on 03/31/24 at 09:04:58

With so little information it is impossible for us to know exactly what is going on.

Is this bike new to you - or has it been running fine for a long while?
Has the bike been ridden and maintained regularly?
When was the last time the carbs were cleaned?
Do these bikes have a history of diaphragm failures in the petcock?

Can you remove and plug the vacuum line to the petcock and then turn the petcock to PRIME to allow fuel to flow?