Misfire @ 2000-2500 is RPM

[obredneck]

I've got a 66 coronet with a 68 Superbee 383 MSD ignition new plugs gapped to .035 that is having an issue with a misfire at about 2000-2500 rpm. It feels like it's only one cylinder and I can only feel it in that range. Already checked all plug wire connections at the distributor and the plugs. Ensured that there were no fouled plugs etc.

I don't have a garage to work on it and am only able to access a work area on Sat and Sun so I want to have the parts I will need in hand before I go and don't just want to throw parts at it until the problem straightens out. Are there any of you that have come across this issue and might have a fix? I'm thinking it may be the distributor cap either going bad or the distributor itself but I don't have enough experience to be say for sure.


Appreciate your help.

 

[bigmanjbmopar]

Cracked spark plug insulator? bad wire? Have you pulled each plug wire off one at a time while it's running to see if you can find the one?

 

[obredneck]

Possible insulator, #8 plug didn't hard stop when I reinstalled after cleaning/gapping plugs. Will look into the plug wire issue, just didn't think that direction because of it being limited to certain rpm range.

 

[bigmanjbmopar]

The more rpm the more spark up to a point and that range is about right for peak spark from an msd unit. so spark is arching on something.

 

[Cranky]

How many miles are on the plugs, cap, rotor, carb tune etc?

 

[obredneck]

How many miles are on the plugs, cap, rotor, carb tune etc?

Plugs/carb tune have no more than 1000 miles on a fresh rebuild (so says the guy I bought it from) As for the cap and rotor I honestly have no clue.

 

[STREETREBEL]

I had a similar problem.
It was my Eddy carb. Turns out that they have little
screens at both ends of the fuel inlet, and clog very easy.
My engine wouldn't rev past 2000.
Just a thought!

 

[watermelon]

I had a similar hesistation when I would get up around 50mphs or so. I thought my points style ignition system was the issue. I did a whole MSD upgrade and still felt the same thing.

It turned out to be a clogged fuel filter and a gunked-up Edelbrock.

I ended up dropping the fuel tank and cleaning that out along with blowing out any remainin fuel in the lines. Took apart the Edelbrock and cleaned it out and added fuel filters before the fuel pump and before the carb.

The thing runs strong now. 1966 Coronet/440 ci/727 trans.


Does your car run nicely at low speed?


I don't have a tach on my setup so I can't say what rpms I'm doing.


watermelon

 

[obredneck]

It ended up being the fuel filter/crappy fuel line. Figured this out after changing plug wires, distributor cap and rotor..........live and learn. Appreciate the help.

 

[tpodwdog]

The more rpm the more spark up to a point and that range is about right for peak spark from an msd unit. so spark is arching on something.

id say the BIGMAN nailed this one. some cracks in the insulators can be so minute that youll not be able to see them. replace all the plugs and plug wires and i bet your problem is solved. its arcing someplace.

when its dark out...fire it up and rev it to 25oo RPM and i bet youll see a cool light show!:headbang: