Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
marine quadrajet idles not smooth
beaug:
i have an stock 305 mercruiser i/o. timing 8 btdc fuel pressure at 5.5psi. carb# 17080565. I used cliff rebuilt kit. my idles tubes are .035". I used recipe in his book for stock engine idle down channel .046", upper idle air bleeds .050" in air horn, lower air bleeds .070", idle bypass none, mixture screw holes .090. i have some change in my mixture screw have them at 3 turns. the problem i'm having is that then engine is not idles smooth but if i pull the hose out the secondary vacuum break creating a vacuum leak the engine smooths out any help would be appreciated thanks
Cliff Ruggles:
Sounds too rich at idle speed. Can you lean it out with the mixture screws?
beaug:
I tried screwing in the mixture screw it wont lean out
Cliff Ruggles:
I'm curious why you would have changed anything in the idle system for a stock 305 Marine engine with the stock carb on it?
Marine carburetors are not emission calibrated, and very generous for idle fuel delivery with the stock settings.
They are special units, not like their automotive counterparts, and delivery a lot of fuel everyplace in stock form.
First thing I would do would be to make sure the idle mixture screws are actually seating and not coil binding on the springs instead. Pretty common to find this happening with the later metric pitch fine threads especially if you open up the holes under the mixture screws.
We've also ran into a number of baseplates where the metric threads weren't deep enough to allow the mixture screws to seat, or the threads galled from corrosion not allowing the screws to reach the bottom of the threads......Cliff
beaug:
the reason I changed the idle system because I couldn't get to idle with out the throttle blade being opened too much and little change with idle mixture screws. I spoke with you on the phone about a week ago and told me to open up the upper air bleed to .050"
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