After 15 years of thinking about it, I finally made the plunge and
bought a 72 MkIII. (133/5535) Darn fun machine. Have had the carb
rebuilt and set for high altitude, (Colorado) and changed out the
distributor pieces and wires.

Between 1500 and 2500 RPMs, I get a very bad miss or stumble. The
strange part is sometimes I don't. Replaced some wires at the coil and
it improved, but not much. Could this be a bent distributor shaft? Any
ideas would be appreciated.

As I go along, I'll be posting more pics at


Mike Lawrence
Broomfield CO USA
72 MK3 155/5535 Very Orange


I think your car (like mine, 133/5474) has a 383 c.i.d. engine, and 
therefore my experience may be helpful to you.  As a remedy for the stumble 
I'd recommend that you buy a #1406 Edelbrock carburetor and a #1487 
Edelbrock Calibration Kit.  The stumble is most likely caused by a lean 
condition in the transition between the power mode and the cruise mode of 
your original Carter AVS carburetor (assuming that that is what is till on 
the car).  The stage between the larger diameter upper section of the rods 
and the smaller diameter is not right for the air-fuel conditions your 
altitude creates.  Maybe you can remedy that by installing slightly heavier 
springs under the rods.  But, given the difficulty of obtaining replacement 
rods, jets, and springs for the Carter AVS, you will congratulate yourself 
for changing to an Edelbrock, with its ready availability of Calibration 
Kits, containing useful variety of rods, jets, and springs.  To correct a 
stumble such as you describe is a 2-minute procedure if you change only the 
rods; a 5-minute procedure if you change the jets as well.  I speak from 
experience, even Colorado experience.  On our way from San Diego to Park 
City, Utah, last summer, anticipating the climb to the three passes of more 
than 10,000 feet on the Durango-Ouray road, I spent five minutes in the 
parking lot of the splendid General Palmer hotel in Durango setting a 
leaner air-fuel mixture.  The car ran beautifully over the passes, and 
when, near Moab, Utah, we descended to slightly more oxygen-rich altitudes, 
a second five-minute session brought the mixture back to a stumble-free 
condition.  Maybe, if you can find a "strip-kit" for your Carter AVS, you 
can manage such quick and easy adjustments, but I never could find one of 
those strip-kits.  Hence the Edelbrock set-up, with which (as you can tell) 
I am more than satisfied.  These Edelbrock carburetors are, by the way, 
newly manufactured versions of the Carter AFB, the first cousin of the 
AVS.  They are very well made (by Weber!), and they are extraordinarily 
easy to adjust.  Ask the man who owns one!

David Crowne in San Diego
71 Interceptor 133/5474

Thanks David,

I appreciate the info. Sounds quite possible. I do have the Carter AVS
and the 383. Interesting to note the guy who did the rebuild has a
Dart with a 383 and he's running dual Edelbrocks on it. I also noticed
the engine will stumble and die at idle if I remove the manifold
vacuum hose, so I'm guessing it's not running too rich.

What are Edelbrock carbs like out of the box. Are the instructions
sufficiently easy to follow with minimal adjustments? Or is it best
left to a carb person?

What rods and jets did you install for the altitude?

Are you running points still or did you go electronic?

I know, too many questions. :-)




Right out of the box the #1406 Edelbrock carburetor (with electric choke 
mechanism) is set up for economy at low altitudes, which is not exactly 
what we want in an Interceptor, and certainly not what you want at your 
probably 6,000 ft.-plus altitude in Colorado.  Here in sea-level San Diego 
I changed the stock setting (after a good deal of experimentation) so as to 
use a number 1456 metering rod (.073" X .047") and a number 1426 main jet 
(.095"), which is about 6% richer than stock overall.  Consulting my 
records, I find that in the high altitudes of that magnificent "Million 
Dollar Highway" from Durango to Ouray I changed to a number 1449 metering 
rod (.070" X .037") and did not change the main jet.  (These are Edelbrock 
numbers, by the way.)  The change for altitude made for a mixture about 6% 
leaner in the cruise mode and 10% leaner in the power mode, which produced 
no loading up and no stumbling or pinging.  Then, once in Utah, as I said, 
I went back to the previous combination.

The Edelbrock carb is very easy to install (after you buy an inexpensive 
throttle linkage kit).  It comes with an extremely thorough and detailed 
instruction book which includes pages on which you can keep notes on the 
rods & jets you've used, and record the results of changes.  (Obviously I 
have done that with almost religious devotion and regularity.)  Initially, 
depending on your compression ratio, ignition timing, etc., etc., some 
tinkering may be needed to get that good seat-of-the-pants feel that an 
Interceptor ought to deliver.  But once you've found that combination, you 
don't need to change the rod, jet, and spring combinations unless you're 
going up into high altitudes, or wanting to richen the mixture for 
drag-racing (like my friend Bruce Bridges!) or whatever.  The Edelbrock 
Calibration Kits contain sufficient rods, jets, and springs to cover most 
needs (although I must confess that I bought two different kits in order to 
have a greater variety of combinations of rods & jets available).

The #1406 carburetor is a 600 c.f.m. device.  A lot of people think that 
any big-block Chrysler needs a 750 c.f.m. or larger carb, but if you do the 
arithmetic you'll see that there is no way that a 383 cubic inch engine can 
suck in anything like that much air at the revs we normally operate 
at.  MAYBE a 440 could use a 750 c.f.m. carb, but a 383 would definitely be 
over-carbureted with one of those unless you're going to turn 7000 and more 
rpm, and I'm definitely not going to be doing that.

I'm very happily running Edelbrock aluminum heads on my Interceptor, with 
an Edelbrock Performer aluminum intake manifold.  My compression ratio is 
close to 10:1, which is about a point and a half higher than stock, but 
still allows me to use mid-grade gas (89 octane here in California).

And yes, I do use electronic ignition.  Actually, the guy from whom I 
bought the car in 1987 made the conversion, and I'm delighted that he 
did.  Better spark, and nearly trouble-free.  I say "nearly" because a few 
years ago on a trip the electronic control unit began to fail sporadically, 
so that I had to stop every now and then for a few minutes and let things 
cool off before I could go on.  No big deal, though, since I was able to 
buy a replacement ECU at a NAPA parts store in the next town I came to.  I 
don't think you could do that with a Ferrari!  (And, be it noted, the 
383-powered Interceptor is compared very favorably with the Ferrari 330 GT 
in the latest issue of Classic and Sports Car magazine, but of course the 
topic of parts availability wasn't mentioned or the comparison would have 
been even more favorable.)  Anyway, you can buy the Mopar electronic 
ignition conversion kit from a dealer, or from a source like Summit Racing 
or (my favorite) Jeg's.

If you want to post any of this on your web-site, go right ahead.