Rochester quadrajet

[oldboat1]

New season, last years carb issue.

I have a 5.0 Mercruiser inboard in a 1980 Trojan F26. The Rochester quadrajet idles down perfectly, no stalling -- no complaints. I have not been able to get the secondaries adjusted, however -- wants to blubber and struggle at about 3000 rpm or so. I was thinking it's running too rich -- thinking I would experiment with bending the hanger for the metering rods downward slightly to (hopefully) force leaner running when throttling up.

I'm wondering if anyone has tried that.

 

[76SeaRay]

This sounds more like a problem with jet sizing and or linkage adjustments. My experience with QJets has always been that you never have to do any bending or adjusting like that. Got any friends that run them on cars that know how to set them up?

 

[oldboat1]

Thanks. Have a marine source who might be able to help. Possibly the wrong metering rods too.

Seems close -- like adjusting an air/fuel needle on an outboard.

 

[Lou C]

Another issue with the QJet is when the secondary air doors open. If they open too soon then you get a stumble. On the QJet the actual secondary throttle plate is mechanical but the air doors above them are vacuum operated. There is a spring adjustment that controls the opening of the secondary air doors. For more information check out Cliffs High Performance Quadrajets, this is probably one of the best sources of information on QJets. It is an excellent carb when properly cleaned and adjusted.
The other thing is that for marine units they use a slightly different accelerator pump with longer travel for marine use, Cliffs sells them to as well as really nice rebuild kits.

 

[oldboat1]

good info. Thanks.

 

[kenny nunez]

Those springs have been known to break. Is there any resistance when the butterfly is pushed on ?

 

[oldboat1]

Yes, spent a considerable amount of time adjusting the tension. It's close, I think -- but might tighten it up just a little more and see if that makes a difference (would do that before bending the hanger). I'll also look into differences in accelerator pumps.

 

[kenny nunez]

Most times by winding the spring until the butterfly just closes then 3/4 more of a turn will put it real close. I always did that with the throttle held wide open.