Richening the mixture can 'cure' ignition problems, try going through plugs,
points and timing as well.
PaulH.
http://freespace.virgin.net/paul.hunt1/
-----Original Message-----
From: Eric Kutzli <ekutzli@netins.net>
To: mgs@autox.team.net <mgs@autox.team.net>
Date: 09 March 1999 03:16
Subject: Lean at cruise
>Hello everyone,
> New to the list but have owned my 1974 B since 1994 and spent three
>years in restoration. Any info appreciated on a problem that shows up at
>cruising speed ( between about 50 and 60) The engine seems to miss on light
>throttle going up hills. Under hard acceleration no problem, but to just
>hold constant speed ascending a grade with gentle increase in throttle the
>engine misses. One day just as a test I pulled the choke out to richen up
>the mixture and the miss dissapeared. OK, so this suggests engine is
running
>lean.
> I checked vacuum advance, timing, and HIF carbs. Smog pump and
>associated technicalities were all removed by previous owner. I looked and
>poppet valves in the butterflies are soldered shut. Idle is a little lumpy,
>and seems hard to get idle mixture from running too rich ( according to
>colortune) Ignition seems to be hot enough ( according to the
oscilloscope).
>
> The final culprit is the carbs. The car has 68,000 mi and engine was
>rebuilt 2,000 mi ago, but carbs were not. I have tried the old spray em
with
>something and see if the idle changes but can't seem to find the problem.
>Idle is too rich and cruise is too lean. So if the problem is the carbs,
>several questions come along A. to replace or rebuild. Is new better? Is
>rebuild or just new needles only delaying the inevitable? B. SU or Weber?
I
>guess I really don't mind tinkering with the stock dual carbs. It's kind of
>a badge of honor to keep them happy C. HIF 4s or HS4s? I have a set of
>used HS4's on the shelf that could be rebuilt. Do HIFs have
>problems/drawbacks in being designed for emissions compliance rather than
>engine performance? Might even buy new HS4s?
> I'm going to need to decide, my wife actually asked me what I wanted
>for my birthday coming up soon, and someday the Iowa snow will melt and I'm
>going to want to drive.
> All two cent suggestions considered at current market value.
>Thanks everyone,
>
>Eric
>ekutzli@netins.net
>1974 MGB "Maggie"
>Now Glacier White - just couldn't talk myself into respraying the original
>Citron...
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