380 hp Magnum crate dieseling problem
Well pulled the car out haven’t touched it in 6 months. Still diesels on shut dow. Holley hp 750 dbl pumper. Yes it will run with mixture screws turned in. I have set the initial timing at 10*,14*,20*. Idles 750 rpm. I had issue with pvc so temp removed. Rear throttle blade shut. It pulls about 9 on vac at idle.
I've never seen a case of deiseling that wasn't related to a combination of open throttles/ too much air, and something hot in the chambers. But this does not mean colder plugs are the answer. Heat range is chosen by the power run, and perhaps tempered by the primary useage.Changing the idle-timing should very dramatically change the idle speed.
The principal thing is to choke the air off at shutdown. I have run up to the 292/292/108 DC cam with no dieseling issues.
You'll get this figured out real soon, cuz 9" vacuum is IMO borderline too low for 750 rpm, for this cam.
I suggest a LeakDown test to prove the valves are closing, and a compression test to prove the pressure is at least even.
I know that engine should be able to idle down to at least 650rpm, with a proper Transferport sync; my 292 cammed 367 went there @5* idle-timing. This was 9 degrees retarded from the 14* is usually ran, and the engine still made enough power to drive around the parking lot, by itself, with no slipping the clutch, but just barely,lol. It took that much retard for the power pulses to calm down enough to where the bucking quit, and the car became driveable down there.
I used a dash-mounted, dial-back, timing delay box; with a range of 15 degrees; which I split to 9retard/ 6 advance, or whatever I wanted on a particular time.
Oh yeah, sometimes, the throttle-opening has to be fudged because the fuel pull-over is too hard, aka too low a fuel level. On some carbs you can prove this by gently blowing into the float bowl and seeing the idle rpm rise.
If you just can't get it, then I suggest checking the cam install.
