Carb Rebuild Or Clean

[CatMan1]

I bought this '28 3 years ago and it was restored back in 2005. I have some homework to do, but I'm chasing some backfiring out of the exhaust and occasional intermittent rough running. It also acted like it was fuel starved the last time it was out. I've done the research and read the different threads and know I can have an electrical issue. All that said, I am planning to take the carb apart to clean it. When is it time to just clean and adjust the float and when is it time for a full rebuild? How would I know? It's been nearly 20 years and who knows what the last guy did to it.

[jb-ob]

With the carb bottom removed, squirt some carb cleaner down the jets. Next 'eye ball' the float level. Done.

Most carb issues are electrical in nature. Being a simple six volt system, ALL connections need to be 'tight & bright'.

[1928Mik]

I agree with jb-ob. I take my carb off twice a season and spray carb cleaner everywhere. I also use non-ethanol fuel.

[CatMan1]

Originally Posted by 1928Mik

I agree with jb-ob. I take my carb off twice a season and spray carb cleaner everywhere. I also use non-ethanol fuel.

Same here......except the last time I was out, the small town we filled up at only had Ethanol. I started it up (It was warm out) and instantly it wanted to die while idling and trying to accelerate. I assumed that it was maybe vaporlocking at that point, but I was able to get it up to 40 and limp the 15 miles home.

[CatMan1]

Originally Posted by jb-ob

With the carb bottom removed, squirt some carb cleaner down the jets. Next 'eye ball' the float level. Done.

Most carb issues are electrical in nature. Being a simple six volt system, ALL connections need to be 'tight & bright'.

We are planning to check everything electrical we can think of before pulling the carb.

[Kurt in NJ]

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I just take the bottom half off, a bucket to check fuel flow, a large enough jar to check float level, slosh the fuel in the bowl around some and dump the fuel.
If there looks to be accumulated goo on the jets or I want to check the passages a can of 2+2 carb cleaner sprayed through the passages .
It’s quick and easy with the original zenith, just one bolt.

[Big hammer]

Originally Posted by CatMan1

Same here......except the last time I was out, the small town we filled up at only had Ethanol. I started it up (It was warm out) and instantly it wanted to die while idling and trying to accelerate. I assumed that it was maybe vaporlocking at that point, but I was able to get it up to 40 and limp the 15 miles home.

Last year we were out and about, needed fuel and they didn’t have pure gas, 4 miles from the station it started missing, stopped at the next station and bought some gas line drier, it stopped missing, probably had water in the gas

[mcgarrett]

Just to provide some contrast to the various woes stated in the posts above, here are some personal protocols:

*I use regular ethanol gasoline all the time and so far, have not had any issues with vapor lock or other fuel related problems. Guess I've been lucky there!
*I always add Marvel Mystery Oil or Seafoam to the fuel at every fill up to help stabilize the fuel and reduce the chances of rust in the fuel system.
*When putting the car up after a drive, I always shut off the fuel tank valve and run the engine until it dies - I NEVER leave fuel in the float bowl.

[1crosscut]

To me there is not much difference in a good carb cleaning and a "rebuild".
If your jets are good ( and most times they are) then a thorough cleaning and a new set of gaskets is all you need.

With your back fire check your manifold gaskets and also check to see that your points haven't closed up too much.

[mcgarrett]

If the engine is backfiring out the exhaust, most times it's due to fuel starvation. Check to make sure you have good, strong fuel flow to the carb.

[gdmn852]

Hello, I always like to clear out the drilled passages on the cast iron carburetors ,be suprized how much rust in them , have a bad tendency to accumulate rust if sitting empty for awhile.

[Russell Reay]

Several reliable (imho) sources have criticized the quality of new jets. I have two Zenith carbs that I have disassembled, cleaned, and re-assembled with only new gaskets and float valve. Cleaned out (NOT reamed!) the jets with acetylene torch tips, and they seem to work just fine. Of course, as a newbie there may be deficiencies that I don't see.

[Ed in Maine]

I agree with 1crosscut. It only takes 5 minutes to remove the carb from the engine and 1 bolt to disassemble the carb. I have a gallon of carb cleaner to soak the parts in overnight. Hose the parts with water pressure, especially the jets. I flow test every jet before I put them back into a carb. I have had the opportunity to redo a carb after a couple of years in service when the owner was having some problems. I did flow check the jets and found that they had approximately a 10% decrease in flow. Obviously, our lousy gas degrades our carburetors with use and storage.

The carburetor plays such an important role in the operation and enjoyment of the Model A. I would recommend you get the repair books that are available, build the simple jet flow tester and understand how the carburetor works. Become the expert in your club and for yourself in rebuilding a great operating carburetor. Ed

[Ed in Maine]

I had one other comment to make. Actually, the new jets purchased today are very good reproductions of the original except for the fact that they do not flow the correct amount of gas. If you do not flow test the jets to be used in a rebuild, you most likely will have a Model A that is running too rich. The car might run but will get poor gas mileage have other performance issues. Do not use anything metallic to probe the jets. Most of the jets I have worked with have to be soldered up and drilled to meet the correct flow requirement. You cannot simply use the correct micro drill size for the jet to get the correct flow. Depending on how the drill makes the hole and leaves the edges of the exit hole affects the quantity of flow of gas through the jet in one minute. I flow test the jet and use the appropriate drill to hone the hole like you were using a round file to get the correct flow. Ed