472 caddy, hot restart pings issue

Hey guys, I recently did a HEI swap in my 68 Caddy. The car runs great with this setup, but it has this odd recurring issue.

When I first start it and the engine is cold, all is well. But if I shut it down and restart it while still hot, it acts like there's a vacuum leak (I can't find any). When it does this, it's harder to start, and generally puffs a bit of fuel smoke from the exhaust pipe. The idle will hang, and it generally idles higher than where it's set. It will also ping at part throttle.

I've tried adjusting the advance can, and it doesn't have an effect on the issues after a hot start, but I can feel it change the advance rate when I drive it.

The weird thing is when I do start it cold, I can run around all day with no issues, no matter how hot the engine gets. It's only after a hot restart do the symptoms appear. It didn't do this before the HEI swap.
Thanks guys


Any ideas?

Click to expand...

as with most problems stepping back mentally and asking yourself
"Logically asking.....WHAT changed? what condition, has changed that might cause this ? helps"

never guess, never assume, deal in verified fact!
the first obvious condition is INCREASED engine heat ,
whats the coolant and oil temps?
and that might be effecting fuel/air ratio or fuel delivery .
On a cold start the fuel, and fuel in the carb, will be cooler,and should run cooler, once heated up by the engine having reached operational temps the fuel that would normally be fairly cool as its constantly fresh from the tank, and not have time to absorb heat , in a running car.
BUT, On a restart,it may perform quite differently ,especially if the carb and fuel are allowed to sit and absorb heat and yes that condition should change over a fairly short 10-15 minute time frame , as the fresh fuel replaced the hot fuel , eventually change and get better.(especially with a return style fuel pressure regulator as the fresh fuel circulates and has less time to absorb heat.)

you state that if you take it rather easy you don,t get the pinging issue, And if you remove the ignition advance its not pinging, that indicates the ignition advance is going too far under that operational condition, you might want to change the ignition advance curve but until youve verified true TDC and the timing tabs and documented the existing ignition advance curve your just guessing if you make changes.
FIRST, verifying TDC and the timing tab coincide with fact,
and documenting the ignition advance curve under both conditions would most likely give you facts to deal with and isolate the problems source.
Id also suggest a return line style fuel pressure regulator ,
and a tube of heat reflective material around the carbs fuel feed line
at least in the engine compartment from behind the engine up to the carb inlet port.
I'd carefully inspect the engine compartment for loose or cracked vacuum lines and loose electrical connections.
Id suggest swapping spark plugs to the next colder stage rating.
and verifying your fuel pressures remains absolutely consistent and at near 5 psi,
I'd also install a heat barrier carb spacer under the carb base.
posting clear detailed pictures of all your spark plugs would be helpful.
Id put a heat reflective tube over the carb fuel feed line
ID replace the fuel filter if its over 6 months old.


RELATED INFO
(not reading the links will eventually cost you additional wasted time and cash)
http://garage.grumpysperformance.com/index.php?threads/vapor-lock.12793/#post-66053

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://www.cad500parts.com/catalog/page22.htm

http://www.cad500parts.com/tech/IgnitionTiming.pdf

http://garage.grumpysperformance.com/index.php?threads/finding-top-dead-center.967/

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

http://garage.grumpysperformance.com/index.php?threads/timing-lights.875/