If you have never opened up and overhauled or cleaned your carburetor the following photographs should convince you that you need to do so. This carburetor was the original one installed on the Atomic Four engine in a 1975 Pearson 28. It had been there for about 15 years, prior to its removal . After seeing what the interior of this carburetor looks like, you will probably be as amazed as I was that the engine would start or run at all. This engine installation has a Fram Fuel filter installed ahead of the fuel pump. So all of the residue in this carburetor was what accumulated after the fuel passed the filter. I finally decided to tackle the carburetor when the engine started to develope intermittent stalling, hessitating and occasional difficulty starting.
Note in the photo above that this particular carburetor has a fuel bowl drainage bolt on the bottom. Some A4 carbs have this, some don't. This is not the same as the main jet access bolt that is on the bottom left of the fuel bowl. If you have one of these drainage bolts it would be a good idea to check it every year or so to remove any debris and it could reduce the residue accumulation that you will see in the following photo's.
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carburetor with the top off, the floats are visible.
Why you should clean or overhaul your carburetor: This photo shows the residue that has built up inside the carburetor throat and in the float chamber. I assume this is what is refered to as "varnish". The residue in the float chamber has caked up so thick that it has cracked and formed flakes, similar to the mud on the bottom of a pond that has dried up. The round hole in the bottom of the float chamber leads to the main jet. Any loose flakes or chunks that work thier way loose will eventually settle down into this hole, where they could block the main jet or be sucked up into the high speed fuel delivery system.
Some of the chunks show up pretty well in this photo. Some of the chunks are so big they cast shadows.
This shows the pile of varnish and residue that I scrapped out if the carburetor bowl.
Here the residue almost fills up a teaspoon.
This shot shows a little of the residue that has accumulated around the main jet.
How to overhaul a Zenith 68 Series carburetor Pages 10-11 of the Owners Manual.
It is really quite easy to overhaul these carburetors yourself, you shouldn't hesitate to try it even if you have never done anything like this before. It is especially easy to perform this overhaul if you buy a carburetor kit from Don Moyer, as the kits he sells come with great step by step instructions and photographs to guide you through it. It is a good idea to keep a carburetor kit aboard for emergencies, but the parts that are needed to overhaul a carberetor seldom wear out. If done carefully it is possible to disassemble, clean and reassemble the carburetor without damaging any of the parts. However, carburetor kits are not expensive, so I recommend that you get one.