QJet Idle question

[Mkos1980]

90 350 Mag. Motor fires right up, revs up good, idles smooth with no hunting. Dead on 700. No hesitation what so ever. One problem that confuses me is on an decel to idle. Rev it up and bring it down it'll idle, then it will idle down 650-550-450 till it dies unless I turn up the idle screw . Once I turn it up it stabilizes then revs up to about 1000. I lower it to the 700ish and start all over again. Idle screws are set at 2.5. Seemed the best there. I rebuilt it last year and it ran flawless. I'd tried timing from 6-12* same thing. Any ideas? I'm going to try to disconnect linkage tomorrow and try it. Maybe need more fuel at idle?

 

[brunolund]

Re: QJet Idle question

does it always happen, or is it only when you bring back the throttle fast or slow?
?

 

[Mkos1980]

Re: QJet Idle question

If I bring it back slow, no problem. Its when I bring it back fast. (not super fast but fast enough) I guess bring it back slow it has time to equal itself out.

 

[brunolund]

Re: QJet Idle question

dont remember the details, but there is a diaphram or valve that closes the plates slowly, the idea is the exact opposite of the accelerator pump.
sorry i cant be any more help than that, but i'm guessing this is your problem.

 

[Maclin]

Re: QJet Idle question

That is called a dashpot, I do not know if that is on the QJ marine carbs or not.

The problem described is typical of a high float level or perhaps a baffle missing inside the float bowl. Just a thought, may not be the problem.

 

[Maclin]

Re: QJet Idle question

I meant high fuel level in the bowl, not necessarily due to a high float level. The needle and seat may not be sealing as good as they used to.