bucking C1

[Pat #25912]

My '59 (350 ci, mild cam, Edelbrock carb and Torker intake) has a slight
"surge" or "buck" under light accelleration. Not a once or twice thing, but a steady pulsing till it is given more or less throttle. It's not there under hard acceleration and it doesn't seem to be RPM specific in range or frequency . The car starts quickly and easily and pulls strong.
This past weekend I tried a different carb and I tried a different distributer and coil but the problem persists. It has been there the short time I have owned the car. Probably related is the fact I can't get the hot idle to set where I'd like. When I try to adjust it under 1000 rpm, it drops to about 500 with no in-between. I'm not sure what to check next and certainly welcome suggestions. Thanks.

[Terry D.]

Re: bucking C1

Pat
Check the archives for articles by Hickley, Duke etc. on timing and vacumn advance.
Terry

[Chris H.]

Re: bucking C1

Pat, if you find the thread in the archive please let me know. I could not find it. Tried buck, timing, advance.

Chris

[Mike M.]

Re: bucking C1

Every time I experienced a "Surging" condition I have found it was due to the engine seeing a lean fuel mixture at that particular rpm range. Probably why you do not experience the problem during acceleration; the carb power circuits are in use. Given the problems you have with setting the idle, I have two suggestions.
First, make sure you are not leaking vacuum anywhere. Even a slight leak can cause idle issues and off-idle transition problems. I think it is the off-idle transition area that is "acting" lean in this situation.
Secondly, what Edelbrock carb are you using, the AFB version? Edelbrock makes or sells various model carbs based on the Carter AFB, Carter AVS and Rochester 4MV designs (Q-jet). It is possible to richen the off-idle transition on all of these carbs. And that may have to be done if no vacuum leak is found.

Mike

[Pat #25912]

Re: bucking C1

Thanks guys. Terry, I searched the archives and have come to the conclusion Duke should have his own FAQ page. I have printed out several of his very helpful tips. Chris, in the most current archives try searching timing Duke. Sorry I didn't note any post numbers, if you don't have any luck let me know. Mike, the carb is a 600 cfm Performer 1406 carb which I believe is the AFB square bore version. No vac leaks were found.

A big part of the problem is not knowing what I have for cam, pistons etc and where to set the timing. A compression test last night turned up 3 things. My 350 has domed pistons, the compression ranges from 201 to 205 across the board, and there was a piece of carbon wedged into one of the spark plugs. I set the timing using Duke's method (couldn't find the post so went from memory), at about 2500 rpm advanced the dist till the engine started to stumble then backed it off a bit. A short road test (it was late) showed no more bucking. Possibly the piece of carbon was causing a lean load missfire? I will road test the car again tonight.

Thanks for all the help. Pat