The Stovebolt Site Forums The Shop Area Engine Shop surging at 30-35 mph---HELP!

hello, I have a stock fleetline 216 ci three speed manual sedan. the engine is stock except for 12 volt system and electronic ignition. the problem i'm having is the engine is surging at mid throttle (right where I do most of my driving!) I have rebuilt the carter YF carb and replaced the vacuum advance and checked for a vacuum leak to no avail. the engine runs great otherwise, the timing is set at 5 degrees btdc. it does NOT surge if the engine is under a load like driving up a slight grade. it will also do it in the driveway. I will have it idling wonderfully and when I increase the rpms to a steady rate, it starts surging. HELP!!! thanks, mackj

A couple things come to mind;

The float level is too high

worn/broken centrifical advance

Vacuum or vacuum advance problem

loose distributor

The fact it does it in the driveway is really helpful.

Set the throttle so it is hunting. Go around and look at the distributor. Is the vacuum advance moving in and out as the engine hunts? If the distributor isn't moving, think centrifical advance or float level. If it is, take the vacuum line off the advance and put your thumb over the end of the line and see if it makes a difference. Also try holding the base of the distributor and putting a little pressure towards the advance to eliminate slop in the linkage.

Jim, thanks for the info. what do you mean by a loose distributor. My distributor is not locked down but the vacuum advance is. When my timing advances or retards, the whole distributor turns. mackj

Do you mean the plate on the floor of the inside of the distributor? Or the outside body of the distributor? If that latter, that is most definitely a problem. The body should not move at all?

the dist body does turn when the vacuum advance activates, but the shaft shouldn't be sloppy in the hole and should have a clamp to 'fix' it in place

Bill

Thanks for all the input guys! I still have not figured out the problem but I am trying EVERYTHING you guys say. Yes, my whole distributor turns while advancing or retarding. The dist. is held in place by the "economizer" slot on the vacuum advance and the vacuum advance kinda clips on the clamp around the dist. shaft. The "economizer" has a scale on it and gives you the freedom to set your timing then you lock it by tightening the dist. hold down bolt. I'm going to mess with it some more today. thanks, mackj

You wrote it has "electric ignition". What has been replaced: points?

Just throwing this out there, but you could have a worn distributor gear.

check the firing order make sure it is wired correctly.

I would look at the mid range section of you're carb I'll bet it's somthing in there.

If you have another carb try it and see if the problem changes.

Pete

I meant to say "electronic" ignition. Its does away with the points and condenser altogether and works very well. mackj

(1) Compression test
(2) Ignition test
(3) Fuel delivery
(4) Carburetor

In (2) if the points/condenser were replaced with electronics, was the generator also replaced? Electronics DEMAND a stable voltage! Using electronics with a generator is like playing with a molting rattlesnake!

Probably not (3) as no issues under load

In (4) if you are forced to use fuel with ethanol, the carburetor MAY be lean due to the reduced energy content of the ethanol. When under load, the metering rod is pulled up in the jet to the power (richer) step.

IF YOU ARE ABSOLUTELY POSITIVE 1, 2, and 3 are not an issue; try increasing the diameter of the main metering jet by 0.001.

Jon.

the firing order is correct and I tried another carb already but I think I found something by following what you guys said. I raised the idle adjustment to where it was surging and then dis-connected the vacuum advance and plugged the vac. line and it stopped surging !. The vacuum advance seems to be working though as the distributor turns when it is hooked up ?. I just ordered a new vac. advance from National Chevy [censored]. today. One more thing, where do you guys set your timing? TDC or 5 degrees BTDC? 1951 216 ci. Thanks for all the great info from everyone! this was my first time ever doing anything online. the stovebolt forum is very nice and I WILL use it again. ps I turn 65 yrs old tomorrow! mackj