Flat Spot in Re-Built Marine Q-Jet

[sprink58]

I have a '79 Formula 255 Liberator with twin 260 MerCruisers...Q-Jet Carbs. I recently re-built the starboard carb with a MerCruiser kit. I was surprised to see that the kit did not have a new float.

Anyway...I put it all back together and took it out for a run. If I push both throttles open gradually, the starboard engine falls flat at about 3000 RPM...and kills the engine. I have found that if I nurse the throttle open VERY slowly that the starboard engine will accelerate as it should, the secondaries open and here we go.

I have not changed the secondary air valve setting. Based on how this thing is behaving I'm thinking that I have a transition problem between the idle circuit and the main/secondary circuit.

If I can supply the mod. number of the card...can you guys suggest a REAL re-build kit for this rig that will solve my problem?

All comments and suggestions are welcome.

[Cliff Ruggles]

Yes, first order of business is to get one of our Marine kits.  It will contain the correct high flow Viton needle/seat assembly, a new float, complete HP accl pump assembly, secondary cam/spring, idle tubes, mixture screws, power piston spring(s), gaskets, and small parts.

Could be a multitude of problems, most likely associated with the substandard parts in the kit that was installed.....Cliff

[sprink58]

Cliff,

I got the Marine kit and installed what I could. First of all...my carb # is 7043208  OC followed with 3332 stamped just below the first row of numbers.

The float supplied in the kit is too large and did not fit...I re-used the old one. I did not change the secondary air valve cam yet...part of my problem is that the secondary metering rods get hung in the up position and will not let the air valve close completely. I know that this has got to be throwing the entire secondary system out of whack. There seems to be a lot of slop in the merering rod hanger and it moves side to side too much for my liking...mabe worn out? What do you suggest.?

Thanks,

John in west Palm Beach

[sprink58]

Cliff,

As a PS to the above...I have been fooling around with the secodary metering rod hanger and I have to say...I think the geometry of the whole assembly is off. I can't get the metering rods to work back and forth by opening and closing the throtle with ot them getting hung in the up position. Sounds like I need a new hangert and rods...what say you?

Thanks,

John in West Palm Beach

[Cliff Ruggles]

7043208 is not a Marine carburetor, it is an emission calibrated Chevy carburetor for automotive/truck applications.  It would not be set up correctly for a Marine engine, not enough idle fuel, off idle fuel, full throttle fuel, etc.

That's why the float didn't fit.  That particular carb would need significant modifications to work correctly on a Marine application.....Cliff

[sprink58]

7043208 is not a Marine carburetor, it is an emission calibrated Chevy carburetor for automotive/truck applications.  It would not be set up correctly for a Marine engine, not enough idle fuel, off idle fuel, full throttle fuel, etc.

That's why the float didn't fit.  That particular carb would need significant modifications to work correctly on a Marine application.....Cliff

Yeah...you know you think when you buy a boat there might be  marine carburetors on the engines

OK..I'm not going to waste any more time or $$ on that one. I ordered a re-built marine Q-Jet online that is on it's way to me as I write this. I checked the serial numbers of both engines when I bought this boat...and they are 5.7 Mercruiser re-built long blocks...I didn't think to check the carburetors. I will be checking the other carb just to insure that I don't have another "smog motor" Q-Jet.

When I saw that "08" on the last 2 numbers I thought I was ok...bad read on my part.

Live and learn...thank for the heads up.