Hopefully someone has experienced this problem and may be able to help
me. I am in the process of getting my 1976 spitfire ready for our local
dyno smog check. I wrote last week that I was unable to get the emissions
down at idle. I found after replacing the fuel pump the emissions went down
some but not much. I continued to test and found that if I allowed a vacuum
leak at idle the emissions cleaned up. Even though the needle was all the
way down lean. What I found was that someone had drilled a hole in the
bottom of the Mixture Piston assembly and inserted a screw to hold the
needle up off of the bottom of the carb. This is what was causing the rich
mixture at idle. I removed and plugged the hole where the screw was. This
allowed the piston to go down and for me to adjust the mixture at idle.
The problem I have now is that the idle does not seem to hold. When I
accelerate the engine and hold the RPMs at 2500 then back off the engine
will decrease to about 1300 rpms and slowly return to idle within a minute.
I initially thought something was wrong with the decel valve. I closed the
decel valve completely and the engine is still performing the same way.
The problem is they need to run the engine on the dyno and then check
the idle ignition timing(2deg After TDC). When they run the engine on the
dyno and it does not go back down to idle they will be unable to check the
base timing. Has anyone else seen this problem?
The second problem is that at times the idle will be perfect for about
2 to 3 minutes then it starts running very slowly. If you give it some gas
then back off it will do the same thing. Not sure why it is doing that.
Lastly when I disconnect the air injection tube to set the fuel mixture
in the carb the idle rpms drop. Has anyone else disconnected and plugged
the air injection system and seen a rpm drop?
I have done alot of repairs on the engine already. I am starting to get
to the point where everything looks correct, it is just not working
properly. I have replaced the EGR valve, Installed a new exhaust manifold,
rebuilt the carburetor(with new throttle shaft bushings), installed a new
intake and exhuast gaskets. Replaced the air diverter valve. Performed a
tune up as best I can(plugs cap rotor and wires)
Any assistance would be greatly appreciated. Thanks Bobby.
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