Glenn,
You'll need to get the proper 1/8" allen wrench tool to do a big
adjustment. The fine adjuster under the cap has a very limited range. It
sounds like you'll need to do a coarser adjustment of the mixture needle
first.
The 412 ppm figure is really your HC (hydrocarbon) measurement; i.e.
unburnt fuel passing out the exhaust pipe. What was your CO reading? That
should be given in a figure represented as a percentage. If your CO was
high, you're definately running rich.
Try finding the tool either locally (from a sympathetic LBC repair shop)
or mail order. It only cost about $8 and they're handy to have in your
tool box--once you get the hang of it, you can impress your friends, who
have similar cars, with your knowledge. Use the correct tool, which
keeps the diaphragm from twisting, thus tearing. Bummer!
Anyway, to adjust the fuel mixture, turning clockwise richens, turning
counter-clockwise leans.
Good luck,
Charlie B.
Spitifre Pilot
>
> Hello all-
> I was wondering if anybody could tell me what the small screw inside the
> plastic cap on the right side of the carb does. The Haynes manual I have
> refers to this screw as a "fine idle adjustment screw." The reason i'm
> asking is that i'm trying to get the car to pass emissions ('75
> Spitfire).
>
> I took the car through emissions once and my CO level was 412ppm, the
> max allowable for my state is 300ppm. I did realize the exhaust had a
> smell like the car was on the rich side of the mixture. I did as the
> manual suggested, and lifted the slide on the carb slightly (1/16"), and
> the engine did indeed speed-up. The manual said that this was the sign
> of an overly rich mixture. I then proceeded to adjust the previously
> mentioned screw, it was screwed fully clockwise when I started. The
> manual said this screw was for fine adjustment of the mixture in one
> part of the book, and fine idle adjustment in another. Anyway after
> backing out the screw a few turns, I got the motor to run evenly and not
> to rev so much when lifting the the slide. The exhaust seems to be less
> rich, hard to tell without an analizer, and the car runs much better on
> the road. However I cannot get the idle to below 1000rpm, even with the
> stop screw for the butterfly backed all the way out.
>
> I guess my real question is should I switch to adjusting the needle
> itself, and then move back to the external screw? And what is the
> correlation between the needle adjustment, and the "fine idle adjustment
> screw?" Is this screw a mixture adjustment, or an idle adjustment?
>
> Any comments/suggestions?
> Thanks!
> Glenn Bowley
> '75 Spitfire 1500
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