<VV> Unusual Cold Jetting Question?
brentcovey at hotmail.com
Sat Jul 15 01:52:06 EDT 2006
Stock jetting seems pretty much OK for cold weather, I used to regularly
operate Corvairs in forty below weather at 3500-4000' (yes, a direct air
stock heater is ample- even will keep the windows clear thoughout the car)
and the cold weather does not seem to materially effect operation on a warm
engine. Whatever worked well summers would run just fine in arctic weather.
They are very prone to flooding and hard to start if not perfectly setup,
vacuum break needs to be spot on in cold weather and choke unloader needs to
be set at least half an inch- when its below zero farenheit, cranking speeds
plummet, a Corvair without an oil pan heater will crank one tooth at a time
over the flywheel if its cold enough, but generally will start anyhow,
problem is you dont get two attempts before it wont turn at all sometimes.
It is important in cold weather it catch and run almost instantly, they wont
crank fast or long.
At -40, you slowly turn the key trying to overcome the thick grease in the
ignition cylinder, then as you pass 'on' the warning lights light, and as
you get to 'start' theres a clunk when the starter engages and the lights
dim in time with the teeth counting off one by one on the starter ringear.
When you've passed a compression stroke, theres a slow whirrrrrr and then
tooth by tooth again or the engine catches and runs.
For good starting in extraordinarily cold weather, initial ignition advance
must be pretty low, say 6-8 degrees BTDC or less. Carb icing is not an issue
below freezing, and warm air is not required to feed the carbs. The standard
phenolic insulator without gaskets is ideal for maintaining the carb at
working temperature. Automatic chokes work fine in very cold weather
provided vacuum break and unloader are adjusted correctly. If the car
floods you will not get it cleared at the cranking speeds possible in very
cold weather, it's dead until the weather improves.
I would not use less than a 50 jet, if it runs slightly rich this shouldnt
be a problem, and a 50 is adequate for lower altitude operation from time to
time. Steve Goodman's advice rejetting for standard passenger car use with a
similar engine at high altitude would probably be just fine. Your customer
will likely want to set the choke vacuum break to suit his usual altitude
(slightly wider probably). Chokes must snap closed TIGHTLY on a cold engine,
not just touch like many set them up.
Hope thats some help
> He will be operating between 5000 and 10000 feet above sea level only in
obviously cold conditions.
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