In the last episode, our hero had just finished killing JR, and after setting
up the timing on his MG, was about to delve into the carburetors (unable to
believe that his problem could still be timing after all of the time he
spent taking the distributor apart, rebuilding it, and retiming it three
times). Ignition or carburetion, which would be the murder weapon?
Seriously though folks, thanks so much again for all of the tips - and I do
have some progress to report (have you guessed that I work on this on
weekends and lose sleep thinking it over it all week reading your
responses....)?
I removed and disassembled my SU HS4s - they do seem quite simple compared to
other carbs I have worked on. Guess what? The jet seal on the bottom of the
rear carb's float bowl had disintegrated and pieces were completely blocking
any gas from flowing into the rear jet! I cleaned all of the carb parts with
Gumout, found a couple of O-rings that worked as seals, and put the carbs back
together. The PO had a newer intake manifold on my car, so since I had the
carbs off anyways I got an old-style manifold that has all of the ports
plugged with bolts and changed that over too to avoid any vacuum leaks.
I Re-installed the carbs, (no changes to the ignition side since last week),
and tried it.......
It started instantly, no choke required (warm day, in the 50's) - in fact, it
now dies if I put the choke on. The engine ran MUCH smoother than before,
seeming to stay around 2500 rpm for about 5 minutes, then it died and would
not restart. There was no backfiring like before, slight blue smoke out of
the tailpipe - not sure if that's from oil (rings) or becuase I'm way too
rich on the mixture. By the way, all testing has been and is being done
without the air filters on, so my problem isn't plugged filters.
So, I checked out the plug condition. #1, 2, and 4 were BLACK, #3 wet with
gas. Using the "Goldilocks" spark plugs example (great example Jay):
Spark plugs #1,2,4: "This mixture is way too rich"
Spark plug #3: "Duh"
Ok, so maybe I need to check to see if I am getting a good spark at #3 - but
how? Alright, maybe I need to invest in one of those ColorTune gadgets, but
is there another simple way to reliably check?
I set up the mixture as Al suggested: I turned the mixture nuts so the jet
was flush with the top, then backed it down 12 "flats". Since this seemed too
rich, I turned both jets up four "flats", cleaned the plugs, and tried again.
Same result. Ran for about 5 minutes, died, same plug conditions.
I haven't replaced any parts on these carbs yet - I found a great local place
to get parts though - British Legends in Westfield, MA is a Moss distributor -
they stock the common parts and will get anything else overnight with no
shipping charges (they sell at the catalog price). Very friendly, helpful
staff too!
So, what's the deal now? Should I replace the jets? Do I have the mixture
set right? I watched the tops of the jets while the engine was running and I
blipped the throttle a couple of times. The pistons do rise, what should the
gas look like as it comes out? Like a mist or like a bubbling mass of gas?
What I saw, I would describe as a bubbling mass. Like I said before, these
are unknown carbs. I was planning on replacing the jets anyways, but wondered
if I am on the right track?
Do I need to replace the needles on the pistons too? They aren't bent and
don't seem to be hitting anything....
Another carb issue, I noticed that my throttle shaft bushings are worn, and was
wondering if anyone has had success with the reamer/oversize shaft set
from Moss?
Yes, I am having fun - especially now that I've made some progress, however
slight. Thanks again, and stay tuned for the next episode!
Jon Swanson
swanson@zonker.ecs.umass.edu
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