The Stovebolt Site Forums The Shop Area Engine Shop Miss at higher RPM's

Got the 261 in my '53 3/4 T. with T-5, but still have a miss as RPM's increase. Have replaced fuel pump, coil, points, condenser, rotor, fuel filter--also now a new rebuilt carb. Checked fuel lines--I'm beginning to suspect that new fuel pump may be bad??

I've read past posts concerning same kind of problem--any suggestions?

tk261,

As you troubleshoot, don't forget that the valvetrain figures into this equation too.

Stuart

Make sure the vacuum advance on the distributor is working and that you don't have any vacuum leaks.

I worked on my 261 several hours for the same issue only to discover that the vacuum advance was shot.

Hobert

You didn't mention plug leads of plugs.I put AC spark plugs in my 350 once.At least one misfired at freeway speed.Replaced them with the Autolite that I usually ran.Problem solved

I once had a Pontiac that did that. Turned out to be a small crack in the distributor cap.

Since they're not on your list, vacuum advance and distributor cap. Based on your description, I would lean towards the vacuum advance first, but the distributor cap is easy enough to check/fix, so half a dozen of one six of another.

Just out of curiosity, how do you suppose a faulty vacuum advance unit would cause the engine to miss as it was brought up in RPM's.

If the diaphragm were leaking, the vacuum advance would be "faulty", but it would now be classified as a vacuum leak wouldn't it. Will a vacuum leak make a engine miss at higher speeds?

I don't see the correlation between the vacuum advance and a miss. If one were to pull the vacuum line and block it at the carburetor and the miss disappeared, case closed! I don't think this would happen.

But as many can attest to, I have eaten my fair share of CROW before!

Stuart

You might give the fuel pump a second chance and check your tank and lines for blockage and make sure the parts store gave you the correct fuel pump. Also check and make sure you have the correct dwell setting on the new points and make sure the coil is not wired backward and the fireing order is correct.

This is a very good explaination of vacuum advance and its relation to correct timing in relation to a correct timed engine under load.

HERE- http://www.classicchevytrucks.20m.com/vacuum.htm

In my case the vacuum advance had a busted diaphram ( I took it apart) which I theroized caused the engine to be "out of time" under load.

Hope this helps.Hobert

In addition to all the above how about the distributor shaft bearings and gear? A worn out distr. wreaks havoc on timing. Maybe a good time to upgrade to HEI? Good luck.