Jon Swanson writes:
First of all, many thanks to everyone who responded with helpful
suggestions......
I checked the plugs and found #1 and #2 dry, #3 and #4 wet with gas...
The engine in my MGB is an 18V672Z
I have SU carburetors, I think they are HS4's...
My compression tests out at 110, 115, 115, 120
I checked my valve clearances and they are all fine, the valves are all going
up and down in apparently (as far as I can see) correct order. There is no
sign that the PO messed with the timing chain cover or the valves.
I have the distributor cap wired 1-3-4-2, counterclockwise with #1 on the cap
at about the two o'clock position. I took out all 4 plugs, grounded them,
cranked the engine, and observed spark on all of the plugs.
New parts: Distributor cap, rotor, plugs (gapped at .025), plug wires, points,
condenser. The dwell is set for a .015 point gap, verified at close to 60
degrees while sputtering along on #2 only.
What is the best thing I can do with these carburetors of unknown pedigree?
Should I attempt to clean them? How? Rebuild them myself? Is there someplace
that rebuilds them reasonably? Should I give up and get an aftermarket
Weber...
Jon -
I don't have the info in front of me, but I do believe that the 18V672
engine IS correct for the '73. But it is still possible that you have an
earlier style timing cover - the timing marks should be at the top of the
cover, not the bottom. I say this because the cover was switched on my '71
and I have to set dynamic timing to #4 instead of #1. Before this was
discovered, it was missing like crazy. The wrong cover - correctly
installed and painted black - would LOOK perfectly correct even though it
isn't. WAIT A MINUTE - I just thought - if you have even the right cover
but the wrong pulley, the timing marks would be 180 degrees off, and you
would have the same problem. If in doubt, it won't hurt to try setting
your timing to #4 instead of #1 - at least as an experiment.
About the only other variable I can think of would be the timing chain
tensioner. With the plugs out and the valve cover off, put a 1-5/16"
socket on the front pulley bolt and try turning the crank back and forth
while observing the rockers. Does there appear to be any slack in the
timing chain?
Your '73 should have HIF carbs - not HS4s. HIFs have the float built into
the bottom. No matter - it should run equally well on HS4s (separate float
chambers hanging on the sides) but HS4s would indicate some PO has messed
with it. Rebuilding them is not difficult - just buy the full rebuild kits
and follow the instructions thoughtfully. You only need help if there is
slop in your throttle shafts - then you need a machine shop to rebush them.
Badly worn needles and jets can make SUs about impossible to adjust... A
Weber is not necessary - SUs work great.
BUT if you're getting spark all the way around and #3 & #4 plugs show
evidence of gas - you've got the essential elements of combustion here - I
still wonder if they are getting there at the same time.
Keep us posted!
Allen Bachelder
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Allen H. Bachelder, Associate Professor of Trumpet
=iii=<
Department of Music, Virginia Tech, Blacksburg, VA 24061-0240
E-mail: Allen.Bachelder@vt.edu, Phone: 703-231-6713, Fax 703-231-5034
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