<VV> Re: Dieseling !

[Jim Burkhard]

Nah!  I disagree completely. Sure, an overly high idle speed will 
exasperate the problem, but Corvair carbs will continue to "feed it 
fuel" even at minimum air -- that's what an idle circuit does!  The 
fact of the matter is that the engine won't continue to run without 
*some sort* of ignition source. After you've switched off the key, any 
remaining ignition sources are by definition ABNORMAL. Getting rid of 
those are what you need to do and anything else like purposely 
stalling the engine by popping the clutch or dropping into D are 
pretty crude stopgap measures that make you look pretty silly in every 
parking lot.

The first step is to use the recommended octane fuel. Unless you have 
an 80,84, or 95 hp engine, this means Premium.  If you are at 
sealevel, this generally means 93+, not a midgrade 89 or 91.  If you 
are putting the best "normal" premium (i.e. not racing gas) in the 
engine and it is still dieseling, you could try some of the things Bob 
Helt suggests.  Note, making sure the idle speed is properly set is 
one of these. A high idle speed will definitely make the problem worse.

Jim Burkhard
CORSA


Brent Covey wrote:
> Dieseling is *always* the carbs too far open-
> 
> Get the idle speed down (550 or less) and it should cease. Carbon is not
> able to cause the problem if you arent feeding it fuel-
> 
> Something that you might look at is why the carbs need to be so far open,
> for example insufficent initial timing advance (sounds Ok in your case) or
> weak idle mixtures, or other issues that weaken idle.
> 
> Shutting off Powerglides in Drive Range or stalling the engine with the
> clutch a little as you turn it off in manual trans cars usually works, GM
> has issues around 1972 with dieseling with some horrorshow emissions
> calibrations and used to have either an idle stop solenoid snap the throttle
> right tightly closed when you turned the key off, or engaged the a/c
> compressor brieifly during shutdown to stall the engine.
> 
> Hope thats some help, keep working at it-
> Brent Covey
> Vancouver BC
> 
> 
> ----- Original Message -----
> From: "Secular" <rusecular at yahoo.com>
> To: <virtualvairs at corvair.org>
> Sent: Saturday, September 09, 2006 6:26 PM
> Subject: <VV> Dieseling !
> 
> 
> 
>   What causes dieseling or post ignition and how can it be tamed? - cooler
> plugs, advancing/retarding the timing, or .... ?
> 
>   My 65 - 140 HP has two brand-new Holley 5200 carburetors. The car's idles
> smoothly & is NOT set too high (it idles @ 700 rpm), yet I am experiencing
> dieseling almost all the time when I turn off the engine.
> 
>   The timing is set at 16 BTDC.
> 
>   Could it be carbon deposits? a friend suggested Chevron TECHRON!
> 
>   Regards,
> 
> 
>   Tony