Late model carb with four bolts

[Tryoung]

I disassembled, cleaned, and reassembled my carb tonight for the first time (with a LOT of help from Don's manual and the forum here). I thought my A4 was a late model - based upon the oil fill, thermostat, distributor, and carb.

However, I saw tonight that while the carb looks a lot like the late model pictures (more than the early model), it only has four bolts. Also, it has a plug that looks like it is for draining the fuel from the float chamber. The pics in Don's manual seem to show a plug like this in the early carb, but not in the late model (though it is not exactly clear in the pic). So, what I have seems to be a hybrid. Has anyone else seen a carb like this or have one? Mine is in a 78 Catalina 27.

Thanks,
Tim Young

[Dave Neptune]

3 I think!

Tim, I know of 3 for the A-4. There is th old early cast irn carb and 2 models of the aluminum one, one has 4 screws and the other 5. The 2 aluminum models are basically the same except for the extra screw which does a bit better job of holding the halves together. Note there are a few subtle differances between the two however most of the jetting is interchangeable.

Be careful setting the float level and keeping the float paralell at the same time, this will make sure things are right on the inside as the level of the fuel DOES influence the "mix".

Dave Neptune

[roadnsky]

Here's more to go with Dave's input:

All Zenith carburetors produced since the mid 1980's have a fifth retaining bolt in the front of the upper and lower housings. Prior to this generation of carburetors, there were only four bolts holding the two housings together, and all four bolts were located around the float chamber. This configuration left no fastener to pull the front of the housings together. How this fifth bolt (or the lack of it) relates to a rich running condition can best be understood by a quick review of how the internal pressure within the carburetor is regulated to maintain inlet pressure instead of ambient atmospheric pressure.


You can read more about it in the TECH TIPS section...

http://www.moyermarine.com/pressure_regulation.htm

[Tryoung]

Thanks for the replys!

I had read that particular Tech tip sometime ago. Apparently not closely enough! I thought the 4-screw carb referred to the Early model, rather than a second version of the Late model carb.

At this point I am learning new stuff about this engine everyday, so learning this should not surprise me.

Thanks,
Tim