OK, I'm stumped and I'm hoping the collective wisdom of the net will
help me solve this problem.
I have a '73 MGB with a new engine. I rebuilt the carbs before
installing the new engine, and Scott Fisher and I were able to tune
both carbs (using a Colortune) when the engine first went in.
Sometime in the first hundred miles the first carb started to run
rich. That's the problem I can't correct. The engine is fine. I've
done the 100-mile valve adjustment and head retorque and have
proven (?) that the carb is the problem, there's no oil fouling and the
electrical system (points, timing) is ok.
The carbs are type SU HIF-4
Here is a summary of changes to the carb. Before the new engine:
-Misc. gaskets plus a good cleaning
-New needle and seat assembly (jets)
New parts on this carb since this problem started:
-metering needle (but not the spring, out of stock) on both carbs
-float and lever (lever looked pitted)
-jet assembly (plastic looked cruddy)
-dust seals on the throttle shafts
-jet bearing gasket
Yesterday it was suggested I lower the metering needle, which is the
same as raising the jet assembly beyond its limit. This sounded
promising but had little effect also. I also installed a fuel pressure
regulator. I later tried switching the two bi-metal control springs,
thinking one may not be square. But the problem stuck with carb #1.
With the Colortune in cylinder 1 I was able to monitor the effect of these
changes. The best I got was the carb running rich only at idle.
With the throttle linkages disconnected I can rev either carb and cyl. #1
will run lean, this happens quicker if I drop the pressure regulator to
a lower level. To me, this indicates a problem with the float and/or
needle. Since both are new and I know the float is adjusted properly
this theory doesn't help much.
Any ideas before I take the carb in to a pro?
-Dan Dasaro
|