There are two reasons the carb can be running rich. The first is much more
1) The fuel level is too high due to: A)a needle valve not sealing (I had
this several times) or B) float sunk/not set to the correct height.
2) The Jet and needle are worn out and have WAY too much clearance. (I
never had this)
So, the first thing is to remove the air cleaners and look into the throats
with the engine idling as best it can. What looks different between
the two carbs? Is there fuel dripping out of the overflow/breather hole?
If you have an overflow tube connected to a charcoal canister then
remove the tube from the nipple of the top of the float bowl. If it is
leaking you know that you have a float issue.
Then remove the suction domes and pistons (after shutting off the engine)
and look down at the jets. You should see the
fuel level about 1/8" below the top of the jet (or where the jet is
supposed to be if adjusted correctly). IF the float level is set wrong the
level will be too high on the rich carb.
You ought to be able to diagnose the problem this way.
Message text written by INTERNET:email@example.com
>Date: Sun, 23 Mar 2003 15:26:12 +1200
Subject: Spitfire - one carb too rich
I've been trying to get my Mk IV Spitfire runnung a bit smoother. I've
found the peoblem appears to be the rear carb (HS2 SU I think). It's
running too rich - if I lift the piston with the little rod, the enging
speeds up & smooths out noticably. However the mixture nut is already
wound as far up as it will go. I took the piston out to have a look and
the jet is way higher than the front one. The front one is about level
with the bridge. I tried setting it the nut to two complete turns from
tight (this is the starting position in the manual). It was hard to start,
ran really rough with plenty of black smoke and wouldn't idle. I've put it
back to being screwed all the way up but it's still not great.
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