Carburetor fuel mixture adjustment screw

[Roger K Sterling]

Bought a new carb for mercruiser 305. Fuel was burning rich. I went to adjust and had to turn screw at least 4 times to seat it them backed it out 1.25 turns as per manual. Was running great. Then it start to burn too rich again. Checked adjustment screw and had to turn 4 times again to seat it. Its apparently coming loose and maybe the vibration of the engine. Any suggestions on how keep it at 1.25 turns

 

[Wanderer 290]

There should be a tension spring on the the idle mixture screw(s) that keeps it in place.

 

[Roger K Sterling]

Yes it has a spring

 

[Wanderer 290]

Yes it has a spring

Stretch is just a little to give it more tension?

 

[Roger K Sterling]

I'll have to back the screw completely out. Is that OK?

 

[Wanderer 290]

I'll have to back the screw completely out. Is that OK?

Yes that is fine. It is necessary when rebuilding or cleaning carb.
Very simple also.

 

[Roger K Sterling]

Thanks!

 

[Yendor]

Nothing wrong with stretching that spring (don't go overboard). The advice you've been given is all good.

If however, that doesn't address your problem, and there is a small recess were that spring sits at the bottom, the alternative is to get an o-ring at the hardware store that has an ID to match the diameter of the jet and an OD to match the recess. I doesn't have to seal anything, so the fit need not be perfect. It is just there to put enough drag on the jet so it doesn't move by itself. This was a standard work around for old OMC outboards where they used a 'packing' that was no longer available. The later o-rings were far cheaper, sealed better, and lasted longer.

 

[Roger K Sterling]

I took the spring from the old carburetor and switch it in for the new spring. The new spring felt flimsy and not as stiff as the old one. So far it appears to be working.