Light Throttle Cough

Ok! I advanced the timing to 12* BTDC and it definetly seemed to run better. I still got a couple of coughs, however they happened under different throttle conditions than before. I did this in a rush last night before heading off to another appointment. I'll do some more test driving with the current set up and evaluate. If it still coughs should I try advancing the timing even more?

 

No, I'd say 12* is about as advanced as you would ever want to go unless you're running a big cam. I'd imagine that some here would argue that 12* is too much since the factory setting is much less. I'm of the school that these things run best with as much advance as possible without pinging or heating problems. These engines are old. Most have had rebuilds that included head milling, camshaft replacement and whatnot, that allows for a higher initial advance setting, but not always... It's sure worth a try though. If you've got a good ear your engine will tell you when it's happy at a particular setting. Sounds like the carb is definetely a factor too. Fun huh?

 

bowtie-
I appereciate the assistance you've offered. You know it's interesting you mention, "If you've got a good ear", because last night when I advanced it to 12* the motor just sounded smoother. Anyway, I'm going to drive it some more to get a better feel for what might be causing the cough now. One thing I did check really quickly last night after I changed the timing and re-hooked up the vacuum advance was I increased rpm's until I saw the timing start to advance. It looked like it started moving around 900 definitely before 1000 rpm's. Does this sound correct?

 

If it's coughing back through the carb then it sounds to me like you are running lean. The accel. pump is only going to help just in the instant when the throttle is pressed. If it is coughing through the carb when running at steady throttle and light load then I'd go with bigger main jets. The power valve mainly comes to play when the engine is under heavy load (which causes low vacuum). If the main jets are too small you will get coughing and loss of power whether accelerating or cruising at a steady speed.

 

mine runs the best at 5* advance.

 

One other thing... If you are running lean then advancing the timing is just asking for trouble IMHO. You can't always "hear" detonation.