[Healeys] Austin Healey 100 Misfire Diagnosis.

gradea1 at charter.net gradea1 at charter.net
Wed Sep 28 20:50:32 MDT 2022

Michael- My guess is dirty fuel. Ethanol? Dirt specs in float bowls?
If ethanol is used with "pink" Stabil it will create small black
particles in the float bowls and cause backfiring. If used with clear
gas its not an issue. If you use ethanol fuel exclusively purchase the
"blue" Stabil...and yes I would use Stabil and possibly a fuel cleaner
to get rid of any water. Two cents from Hank

	-----------------------------------------From: "Michael Salter" 
To: "healeys at autox.team.net"
Sent: Wednesday September 28 2022 3:43:57PM
Subject: [Healeys] Austin Healey 100 Misfire Diagnosis.

	 This problem has plagued me for over 1000 miles. 

	 Today I had to drive some 200 miles and this is how it went: 

	 Starting from cold I experienced a persistent and irregular misfire.

	 Pulling the choke out made no perceivable difference. 

	 Power was not much affected and the car cruised along well in top
overdrive with just regular periods of misfiring. 

	 Climbing slopes really made no difference, even when full throttle
was applied for 10 - 15 seconds. 

	 Misfire continued for some 90 miles with no change when the engine
was fully heated up. 

	 I could really do nothing to influence the rate of the misfire
although it did seem to be slightly less evident at low throttle

	 After 90 miles I stopped briefly to get fuel and upon starting off
it was quite evident that the misfire had disappeared almost
completely and remained that way for at least 80 miles after which it
started to misfire just a little as I came to the end of the trip. 


	 1.  Plugs … not like a bad plug. The misfire seems to be more than
1 cylinder and never came close to being the regular beat that 1 plug
misfiring produces. All the plugs have a healthy brown/ grey

	 2.  Coil …  In my experience coils are very reliable but when they
do fail they tend to fail as they warm up and the problem gets worse
as the coil warms up 

	 3.  Points … a possibility but the dwell is set at exactly 60
degrees and does not waver at all when the engine is running in the

	 4.  Fuel pump … if the engine was starving for fuel because of a
fuel supply issue caused by a blockage or failing pump the problem
would get worse when the demand for fuel increased, as in climbing a
hill of full throttle. This was absolutely not the case. 

	 Any ideas folks?

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