The Stovebolt Site Forums The Shop Area Engine Shop Zenith 228 Help

Im having trouble with my 270, it has a zenith 228 on it and I just rebuilt it. First problem is the idle is very high and I can't get it to seem to come down. Second issue is that when I floor it the motors revs up to maybe 50% and just starts stumbling and wont go any faster(almost sounds like modern day cars with launch control or 2-step). I am thinking my idle issue may be the throttle shaft leaking alot. I can't tell if the 50% problem is lean or rich because when it pop and shudders it looks like its getting some black smoke. Any help or advice would be amazing.

The high idle might be a vacuum leak somewhere, not necessarily the carburetor.
It also might be (no offense meant) installing the throttle plate in the carburetor upside down.
Check the throttle positioner screw to make sure it is not making contact, and the fast idle (if present) linkage is correctly adjusted.

Regardless of what some might have you believe, you MUST have some clearance with the throttle shaft to throttle body. Design clearance was 0.004~0.006 inch. An additional wear of 0.003 inch is acceptable. Measure the clearance with a dial indicator. If it does not exceed 0.009 inch, no problem.

Lots of black smoke could be either ignition or carburetion (come to think of it, the high idle might be a faulty pertronix conversion, if you have one).

For the black smoke, you should test for fuel pressure at the carburetor (less than 5 psi). Did you test the float while you had the carburetor apart? You also need a compression test on the engine, and a firing voltage test.

Run some tests, you will figure it out.

Jon.

Your "50% problem" may be caused by points set incorrectly. Check the dwell.

"Its never the carburetor."
This is my mantra. I force myself to say this over and over again. Doing so makes me test every other component which makes an engine run right BEFORE I dig into the carburetor.
Even if it turns out to be the carburetor, if there is a secondary issue which was not tested and fixed, "fixing" the carburetor will not result in an engine which runs right.
The other tests are simpler to perform than diagnosing a carburetor (which is seemingly, never the problem).
Carl

AMEN!

Jon.

I have all new ignition parts so I will change those out and go from there, thanks for the help guys

Better yet, try some testing before changing everything again.

(1) Compression test
(2) Vacuum test at idle
(3) Set the points using a dwell meter
(4) Check the timing

Good luck.

Jon.

The main reason that Jon's suggestion of not jumping the gun and replacing all of the ignition parts is a good idea, is that some new ignition parts have a history of being bad. You risk introducing a new problem into the mix if you don't do the other tests first.
It may sound a bit on the nitpicking side, but tracking down two separate problems simultaneously will cause one to pull ones hair out, and all I have left is ear hair.
Don't be surprised if you discover that you already have two separate problems going on already. You definitely don't want 3 at the same time.
Carl