The Stovebolt Site Forums The Shop Area Engine Shop Sputtering,and coughing at 1300 RPM's,

Hi All,

My 53' 3600 with a 235 became roadworthy this week after lots of work. ( woo hoo! How fun is that?)

When driving it performs well except at around 1200 to say maybe 1400 rpm where it acts like its suddenly running on about 4 cylinders.

I put an electronic ignition in it, so no points or condenser to worry about. The distributer does move when I rev it ( It didn't just last week) Fuel filter ls new and clean.

So when driving all is peachy until I get to about 1300 rmps. Under 1200 or so it purrs / after about 1400 it really has some pep. ( surprisingly so)

I'm wondering if I should start with the vacuum advance? As always..thanks in advance for the help!

Troubleshoot it by reinstalling the points, then act accordingly.
Jerry

Thanks for taking the time to respond. Re-installing the old ignition is doable. However The issue was the same ( a little worse in fact) before I installed the electronic ignition. Not being the sharpest tool in the shed I put in the new ignition system in hopes of remedying the issue.

I do <3 fuel injection.

Logically then, the problem isn't the distributor or anything related to the distributor (like the vacuum advance.) There must be another cause. I would look at the fuel/air system. With the engine idling, spray carb cleaner on every vacuum hose. If the engine races, replace that hose.

If you don't find a vacuum leak, look at the carb. Carbs have four circuits; idle, main, accelerator and power enrichment. From your description, the idle and power circuits seem to be fine, but there's a possibility that the main metering jets or the acceleration system might be the problem.

Did you get into the centrifugal timing advance system in the distributor below the breaker plate? Quite often, there's a spring missing or broken, and/or the whole setup is rusted solid so there's incorrect or nonexistent advance at certain engine speeds. "Out of sight- - -out of mind" happens pretty often, and centrifugal advance problems get ignored. The correct advance curve is essential to good performance, especially during part throttle operation.
Jerry

Like Jerry, my first suggestion would have been the electronic ignition.

Since the same symptom occured with points:

From what you have posted, by GUESS would still be distributor. Possibly a "catch" in the rotation of the plates at a certain spot, and then when it rotates past that spot, it functions. Or, as Jerry stated, possibly a missing or broken spring.

I would not guess the carburetor, for the following reasons:

"Under 1200 it purrs"
"above 1400 it really has some pep"

The idle circuit should take you to maybe 800, the idle transfer to a little more than a 1000, and then you are on the main circuit. Cannot think of any way the main circuit would be good from 1000 ~ 1200, bad from 1200 ~ 1400, and then good again from 1400 up.

Carburetors have no personalities (well, maybe Holleys ). But ignition systems do have personalities.

I would suggest a really good look at the distributor.

Jon.

Surely you haven't forgotten the rotten personality traits of a Rochester B, have you? Fortunately, an attitude adjustment with a 3-lb. hammer is usually all it takes to solve the problem!

Jerry

Jerry - the Rochester B has no personality, it just doesn't work 100 percent of the time

By personality, I mean works well sometimes, other times gives problems.

Generally speaking, carburetors will do the same thing under the same conditions, thus no personality.

Jon.

Try running it with the vacuum advance disconnected. Sometimes too much advance at part throttle will cause a rough running condition. If that is the cause you will need to tailor the advance mechanisms to limit the amount of advance.

Thanks everyone! I'll tackle the project this weekend armed with these great suggestions. You guys and this forum are one hell of a fine resource!

Please be sure to get back to us on what cures your problem.