Hi group,
I got the following e-mail from another mailing list that I am on (one for
professional mechanics)
I responded to him with a few sugestions and I told him that I would repost
to the list for it's collected wisdom. So what do you think?
Respond to jkasc80180@aol.com direct.
PS It's a DCOE Weber.
Rick Ewald
73 MGB rough idle
Trans: Standard
Mileage: 10 miles
VIN: GHN5UD298775
Fuel: Weber conversion
Ignition: Mallory dual-point
Emissions: U.S. Fed A.I.R.
Misc Data: conv restored
Symptoms: Poor Idle Quality, Misfire
Occurs: Always, Cold, Hot, Idle
Hi Guys, Please read related repair history first as it
relates quite a bit of info before I got to work on this
vehicle.
Vehicle came to me it would run but would not idle. It also
backfired thru both carbs and the exhaust. I set both sets
of points, set timing, adjusted valves, adjusted carbs,
removed the plugs form the crankcase breather pipe and the
pcv port in the valve cover. I took a compression test on
all 4 cyl and came up with approx 110 psi. A cyl balance
test showed cyl 1 and 4 not pulling their share of the load
(very little rpm drop when shorted). A running compression
test showed cyl 2 and 3 building to 110 - 120 psi but 1 and
4 barely reaching 60 psi (keep in mind cranking compression
was ok). I removed the exhaust header pipe from the
manifold and rechecked. No difference. The next step was
the cyl head. The machine shop I deal with checked the cyl
head for combustion chamber leakage OK The valves were
removed. Springs tested ok but one valve in cyl 1 was over
.003 out of concentricity as was 1 valve in cyl 4. Aregrind
was done, the head was checked for cracks and surface
warpage. I also removed the pistons to check the rings
since the engine was down this far (the tops of cyl 2 and 3
were black and 1 and 4 were clean). I reringed the engine
and replaced all the rod bolts. I reassembled the engine
and set all specs. The engine now starts fine and after its
warmed up there is no backfiring BUT it still has a
somewhat shaky idle and a cyl balance test still shows
negligible rpm drop on cyl 1 and 4. WHY??? My only thoughts
are somehow the mallory dist or the Weber carb is causing
the problem but I cant understand how. There is no problem
with spark, plugs wires and cap all check ok and one cyl
supplied by each manifold/carb is faulty. Does anyone have
any thoughts on this or has anyone run into a similar
situation??? Also does anyone know if Mallory or Weber have
tech assistance hotlines and if so, can you supply me with
phone numbers.
I hope this post didnt bore you or that it isnt too long
but I wanted to give all the info I could so that we may be
able to solve this problem. Thanks very much for taking the
time to read this and for any help you may be able to
supply.
Joe Kaschak CMAT L1
Joseph Kaschak
jkasc80180@aol.com
Owner/Technician
Foreign & American Auto Clinic
Wilkes-Barre, Pennsylvania, USA
jkasc80180@aol.com
RELATED REPAIR HISTORY
10 yr restoration project by owner. all body panels
flooring trans and engine replaced or overhauled. Ign
distributor replaced with Mallory dual-point. Carb and
manifold replaced with Weber conversion (Twin intake
manifold connected with common boss with one manifold
supplying cyl 1 and 2 and other supplying 3 and 4) Dual
carbs attached to common float bowl with one carb supplying
cyl 1 and 2 and other supplying 3 and 4. engine bored .030
over All work done by owner or contracted out by him.
Engine would not stay running and ran very poor.
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