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After carb rebuild my GL1000 Air Cutoff Valve is making noise, problem?

2151 Views 4 Replies 4 Participants Last post by  CaptainMidnight85

I just rebuilt my 1976 GL1000 carb array.

I am now noticing a 'sucking sound' coming from the carb that the air-cutoff valve attaches to.

The sound appears to be related to the air-cut off valve and the sound reduces with RPM.

I rebuilt the valve with the rebuild kit.

Am I supposed to get this sucking sound or did something go amiss with my rebuild?

Please help if you can. Thanks!

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The cut valve is normally open. The vacuum line from the carb up to the valve is manifold vacuum. If the rubber diaphragm is not seated correctly, the small o ring cannot seal the two halves, and you will have a vacuum leak to atmosphere.
I found this out yesterday when I reinstalled my '78's. DOH!
If this is the case, it's easy to diagnose. The #1 carb has the vacuum line. It is clearly visible (on a naked wing). Pinch the line closed with a pair of needle nose pliers and see if the noise goes away. The rpm's changing would be a good indication as well.
Check the hose for leaks? Was the spring & diaphram installed correctly NT. upside down?
Thanks guys!

I checked to see if I put it in upside down, nope.

BUT I found that I had pinched one of the o-rings on the bottom.

However, after replacement, still had the sucking sound.

Further investigation reveled that when I tighten the hose clamp on the manafold rubber only a few turns past seated it starts leaking (sucking sound).

I backed it off to 1 turn past seated and things seem OK.

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Put a smaller diameter hose on there.
Tightening it to the point of leaking is a indication that it is too large.
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