I have two 650 dp's on different 350's, one with a 292/.480 hyd and the other a 282 solid. They run dead on at the track but foul the hell out of plugs backing out of the shop and driving aroun the block. They will idle all day and run clean. If I have power valves that are opening too late can the pump shot and duration of itbe tuned to override the pv delay to let the car run good at the track but foul plugs at the transition? I have been fighting this for a year, got any ideas other than this?

Could be that your plugs are too cold. What plug are you running?

I had this prob when running FR1LS Delcos in my 383, especially in cold weather. When I went to FR3LS the prob went away. When I went another step hotter, I started getting detonation.

PS. I assume you have set your idle mixture for highest vacuum at idle, and replaced the power valve (in case it was blown), right?

I have ran autolite 24,25 and 26's. 26's seem to be the best going by electrode color. The 282 engine pulls about 11" in gear and the 292 pulls about 9". I had a bucket full of 6.5's and I got both engines running good on them but I got to thinking that too much pump shot makes up for the pv at wot but fouls the plugs at short puts aroud the yard.

what intake? using a carb spacer?

RPM's, no spacer.

marty i used to foul alot of plugs fooling with the car around the house finaly went to electronic distributer and it helped then went to crane hi 6 box and i havent fouled a plug since i even filled cylinders with gas before and pulled plugs let them dry and they fired right off as for as power valves go i thought you took your vacume reading and devided it in half at least thats what i did

The pump shot doesn't really "make up" for the PV. The Power valve just adds fuel enrichment when the engine is loaded (like at WOT or when pulling up a hill in high gear), if the PV is leaking it will add fuel all the time making your mixture too rich. The accelerator pump shot covers the lean situation that occurs during the transition from the idle circuit to the main metering circuit when the throttle is snapped open.

When the car is idling the screws on the sides of the metering blocks control your idle mixture and keep your engine happy. But when you nail the throttle, suddenly a large amount of air is made available to the engine and the idle circuit no longer can supply enough fuel and there isn't enough air velocity past the venturi to start pulling fuel through the main jets (you go lean). Well the accel pump just squirts enough fuel to "cover" this transition --- once the engine RPMs start coming up the main jets start flowing fuel and you're good to go.

If your plugs are fouling when idling you have either a mixture problem or an ignition problem. If your spark is too weak or the plugs don't get hot enough to "self clean" (plug heat range) then they will foul. Timing that is retarded will affect this somewhat too because less ignition advance generally lowers combustion chamber temperatures. 12-14* base timing with 36* total timing is a good place to start with a small block Chevy.

If your idle mixture is screwed up (too rich) then your plugs will load up no matter how hot your spark is. If your engine is idling on the main jets instead of the idle circuit you can load up your plugs pretty quick too; you can tell if this is the case because the idle mix screws won't affect your idle.

Aside from some major mechanical problem is HAS to be one of these two things - mixture or ignition.

I run MSD everything on both cars. The cars will idle fine and never have a problem. When I'm at the track, they will come off the trailer with new plugs boardering on fouling but stay clean the rest of the night. Its just the idle to low speed trnsition that seems to be the problem. I guess I need to spend the day on one and work it out.