Ron 75 L48

Ok here is my problem and I know someone on here has to have an answer for me! :yesnod: I am getting either a spark knock or a warm start problem depending on what my timing is set at. I had my engine (L48) rebuilt over the winter and had the following done: Block was machined and punched .030 over, the heads were ported and matched, the pistons are Hyper-Dome, Stainless intake/exhaust race valves, exhaust seats were cut to 1.60, Comp cam 268 XE, comp cam valve springs, valve spring retainers, and valve spring locks, performer 2106 aluminum intake, and a Edlebrock performer 4106 carburator. The compression is 9:4 to 1. Also, I had a new Proform HEI distributor (replacement to AC Delco) with a mechanical advance put in recently.

If I retard the advance enough for the spark knock to go away the engine does not want to start when it gets warm and the engine has sat for 15 to 20 min. It will crank for awhile and then finally fire up. If I advance the timing for it to start with no problems after it is warm I get the spark knock. The springs on the distributor has been changed to a heavier spring but that doesn't seem to cure it. What are my opitons to cure both the spark knock and the warm start problem?

joeveto

Do you have an adjustable vacuum advance? Where is it knocking? Light throttle, heavy throttle, at what RPM range? Idle?


[Modified by joeveto, 8:54 PM 4/19/2004]

Ron 75 L48

I have a mechanical advance. The vacuum advance has been bypassed. It is knocking at both light throttle and heavy throttle. Of course this depends on where my advance is set. It is set for 35-36 deg @ WOT right now. If I go a little higher the heavy throttle knock goes away but the light throttle knock is still a problem. The RPM is usually around 2500 to 3K. No problem at idle.

Ron

joeveto

How's your jetting? Do you know what your mixture is?

stickboy

:iagree:, Sounds like you could be running lean

Ron 75 L48

I'm not sure about the jetting. It is stock out of the box. I was thinking that I may have to get the jet kit.

Thanks,
Ron

Vetterodder

Mechanical advance increases dependent on rpm, not throttle position. I'm not sure how timing could be set at WOT without blowing the engine up (an in car adjustment while driving?). Total timing should be set at an rpm that is at or above the point the distributor stops adding advance. Depending on how the distributor is curved that could be anywhere from 2,000 rpm to over 5,000 rpm.