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351C dieselling
My rebuilt 351C has about 2,000 miles on it. The last 3 days, 3 times after i've shut it off it wanted to diesel on me. It's never done that before. Any ideas? Maybe bad fuel?
base timing too far advanced. Engine getting too hot. try stopping it in gear or with the A/C on.
total timing advancing too far. Did you shave the heads, use higher compression pistons, somehow increase the compression ratio of the engine?
I have had a leaky intake gasket do that on me.


1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]

Too low of octane fuel for the compression you are running
The heads/block were milled .029, partially to true them (just slightly warped), partially to raise the compression to 9.3, which should run fine on hi-test pump gas. I also run flat-top hypereutectic pistons so they could be running a bit hotter than stock. Around here, it's hard to find pure gas, we end up with a lot of 10% ethanol stuff, which I suspect could be a problem as well. It's been warm around here, in the high 80's, so not really hot, and by the temp gauge (running 180 degree thermostat) I'm not running hot.

I don't have AC, by the way. What would be the point of stopping it in gear?

The main question is: why now after 2k miles? No mods or adjustment to the motor since it was installed with timing & carb adjustments made, with the exception that I raised the idle about 75rpm because it was set too low initially. I believe (I'll have to check) it's timed at 10 degrees BTDC, which works for this altitude (around 6,000 feet). It runs fine otherwise, and has been operated in higher temps than this. I'll check the timing tomorrow if I can, and I'll also check the intake bolts (although I'm not showing any of the classic signs of a vacuum leak caused by a leaking intake gasket).
The idle is set with the solenoid. the screw on the carb is set so that it barely idles OUT of gear. Purpose of the solenoid is to get an idle of about 800 RPM in gear, when you cut off the key, it basically shuts off the fuel.
unplug the solenoid to set base idle.
TIMING timing timing
turtle5353;31853 Wrote:I have had a leaky intake gasket do that on me.

Same with me a couple years ago. It was a real PITA to figure out what was going on.
I don't have an idle solenoid on my carb (Holley 80475S).
danoreilly;31884 Wrote:I don't have an idle solenoid on my carb (Holley 80475S).
You may have answered part of your own question.You said you "raised" the idle speed. This may be what is going on besides maybe the timeing being to far advanced. That is why it was recomended that you shut the engine off while the car is in gear,to slow the idle speed. Try lowering your idle speed slightly, and play with the timing.

[Image: 16kuyc0.jpg]
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