In a message dated 96-06-17 13:16:49 EDT, you write:
>I've finally got the dual SU HS2's into my 78 Spitfire after the
>last of the back ordered parts (throttle shafts) arrived last Friday.
>Everyone when well thanks to the advise of Charlie Brown
>(CBrown1500@aol.com).
>
>I've check and verified that the butterfly valve were in correctly.
>After setting the float levels(1/8"), metering needles and jets I proceed
>to tune the carbs following the instructions in the Haynes manual.
>My problem is I cannot set the idle speed or mixture. The engine runs
>at around 2500rpm even with the throttle speed screw turned all the way
>up. Another problem is the mixture setting, the ColourTune shows rich
>mixture for both carbs. even when I set both jets flush with the
>carb's bridges.
>
>One thing I did notice is the front carb's fuel level was higher
>than the rear. Infact there was gas dripping out of the front carb's
>ventura. Can this be the cause of all my problems?
>
>I'm going to increase the front and lower the rear float level and see
>if this will help. Any useful suggestions, helpful ideas, hints or
>even a prey would be welcome. Please help me!!
Dave,
Have you checked for free piston movement? If the pistons were mixed up
during rebuild, that could cause binding. Those piston/vacuum chamber pairs
are carefully matched. Did you centralize the jets on the needles? If the
needle binds in the jet, the piston will not come down fully.
Are the shoulder of the needles flush with the bottom of the piston. If there
too far up that will give you an overy rich condition.
With the carb off the manifold, and the vacuum chamber/piston removed, sight
through the intake of the carb (filter side). With the idle speed screw fully
off, you should see NO light around the throttle plate. It that plate doesn't
fit exactly in the throat of the carb, you'll never get it to idle properly.
You may be encountering the same problem we went around and around with a few
weeks ago - different fuel levels between front and rear carbs. If the fuel
is too high in the jet - at the very top or flowing over - add a thin washer
or doughnut shim above the needle seat. Remember, a very small adjustment
here will make a big difference in the float level. Also make sure a small
piece of dirt isn't stuck between the needle and seat, keeping them from
sealing.
Look down into the rear jet. The fuel level should be about 3/16" below the
top. If you can't see the level, join the club. Tha'ts why I ended up
swapping out float bowls - from the stock AUD 2140 to an AUC 1310 - to raise
the rear level.
Anyway make sure the throttle plates can close completely, the pistons can
rise and fall freely, and that both fuel level are just slightly below the
top of the jet. One more thing. You may want to make sure your fuel pressure
is around 2-3 psi. You're not running an electric fuel pump are you? If so
you may want to look into a pressure regulator.
Check these things out and get back to us.
Charlie B.
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