July 26, I wrote;
Listers,
I bought my 1980 spit about a year ago and until recently the engine
performance had been pretty good for a spit. I would experience a nice rev
acceleration to 5500 before shifting when I wanted to get on it a little. The
car climbed hills in forth with two adults and didn't seem to complain too
much. Now the story is very different, the car struggles to rev to 4000 and
the hills require at least one down shift. These symptoms appeared after one
week vacation, the car was garaged and the weather was very hot and humid. The
PO had removed the emission system almost completely - air pump gone,
catalytic converter, exhaust manifold ( replaced with header) and EGR valve.
The anti-run valve is still in place but I don't know if it works, the car
never diesels with the key off so maybe it still functions. I have checked all
valve clearances, plug gaps (plugs new last august - 2500 miles), and ignition
timing is 10 degrees BTDC.The original electronic ignition has been replaced
with a Crane system but appears OK. The carb is a single Zenith Stromberg CD4T
with some problems, I think. However, while trying to follow the Haynes manual
regarding the carb tune up I discovered that there was no vacuum at the front
vapor trap port at the carb, ie no vacuum at the vacuum unit ( retard only?).
I fixed that by tapping into the manifold vacuum line upstream of the anti-run
valve and all was well for about fifty miles this Saturday. Sunday late
afternoon my first drive and all the old symptoms are back. Any thoughts as to
where to begin? I'm still thinking the vacuum retard is not working. Can this
unit be checked? replaced? Also I suspect the carb of several faults that I
left alone because all was apparently well. These are ;
The car runs a little rich or so my nose thought
The By-Pass valve adjustment dose not do a thing
Plugged vacuum port to distributor
Autochoke working?
Well that is about it, your thoughts are appreciated my trial and error
methods
might work just it time to see the leafs change.
Pete VanDuyne
Holden, Ma.
DISCUSSION TO DATE:
1.) July 27
I'd say a good carb rebuild is in order.
A rebuild won't hurt as long as you don't screw up.
Check for clogs in your fuel lines and filter.
Check your fuel pump. Are you still using a mechanical one?
Good luck.
2.) July 27
Hi Pete,
I'd check your anti-run on valve first. This thing works by
dumping air into the intake manifold when you turn the key off.
It sounds too me like you may have a vacuum leak (too lean)
which could point to a leaky anti-run-on-valve or hose. If
this were the case, then the car would not diesel.
I wouldn't be concerned whether the vacuum retard works or
not. It's an emissions device. If it is not working at all
(no retard) there would be no loss in performance. You might
check for spark "scatter" (due to excessive play in the advance/
retard mechanisms) next time you have the timing light out.
10 deg. BTDC is a good setting.
If the autochoke were sticking the car would start up fine when
the engine is cold. After it warms up, it would begin to run
poorly with black smoke from the exhaust and smell rich. If your
symptoms don't match these then, I'd leave it alone. If you
really think it's to blame, you might consider a manual choke
conversion.
I'm sure you'll get some other (probably better) input from
the list.
Hope this helps,
Bob
PVanDuyne@aol.com wrote on July27:
>
> Bob,
>
> Thanks for your input. I just got home from the storage garage where I was
> hunting for the vacuum leak. Checked torque of intake manifold and carb very
> slightly loose all around but now on spec. ( at least not seized ). Test run
> still had poor performance. Based on your input the choke would be OK, runs
> fine warm and cold no black smoke. I will check the anti-run valve tomorrow.
> Can I just remove it? at least temporarily? Can you explain what you mean by
> spark scatter? The timing flashes where very sharp and distinct. This is the
> advice to date except a carb rebuild which I hoped could wait until Fall.
>
> Thanks again Bob,
> Pete VanDuyne
> Holden, Ma.
3.) July 28
Pete,
You can remove the anti-run-on valve with no ill-effects.
(well it may diesel of course, but should "run" ok) Just
be sure to plug the fitting in the manifold so no air leaks in.
Spark "scatter" would be the timing light indication varying
from one position. Instead of a sharp nice 10 deg. reading,
it would vary between, say, 12 and 8 deg. This would indicate
some play or "slop" in the distributor innards. It doesn't
sound like this is your problem. I would only attack the
carb as a last resort, or unless there is some other compelling
reason to do so. It sounds like your problem came on rather
suddenly, which carb wear would not. Typically the throttle
shaft and it's holes in the carb body will wear over time, but
that's a gradual process. Also the needles can wear (gradually).
I think people head for the carb at the first sign of tuning
problems and this can be a mistake. You CAN check the rubber
diaphram does not have a tear in it though. This can cause
problems similar to yours.
Best Regards,
Bob
PVanDuyne@aol.com wrote on July29:
Bob,
Thanks again for your response. Anti-run was disconnected and manifold line
pluged
without any performance improvement. I'm begining to wonder if the exhaust
(Monza system) is plugged up some how, as the engine sounds somewhat muffled
or so my wife thinks. I have the BL manual which gives the inlet manifold
design vacuum as a function of speed, so I hope to find a vacuum gauge to
verify a leak somewhere or not. The manual also gives details on degrees
advance as a function of speed so I should be able to verify the function of
the mechanical advance and look for spark "Scatter" (which was not evident at
idle). I'll do the carb as a last resort
that suits me just fine and was my plan all along.
Pete VanDuyne
ANY OTHER IDEAS? SORRY IF THIS IS TOO LONG!
Pete
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