C/3 breaking up

[Wally A.]

have a 73 here with a base eng. 350 car has had new points plugs dist. cap plug wires and condenser
installed, correct dwell and plug gap. timing set at 12 deg. advanced. car runs great up to about 3800 rpms
then starts breaking up real bad. does not feel like its starving for fuel, or is it. carb is original quadrajet
has all imissions in place..... thanks for your input. wally

[Thomas H.]

Re: C/3 breaking up

Wally,

Was it running fine before the new parts were installed? If it was then I might suspect the new wires.

I'd try a new coil also.

Tom

[Wally A.]

Re: C/3 breaking up

car ran before the same way. no progress , also new napa coil installed during tune up.

[Mike E.]

Re: C/3 breaking up

Fuel filter perhaps?


Mike

[Wally A.]

Re: C/3 breaking up

new fuel filter installed first thing...car runs the same as if nothing was replaced.

[Rob M.]

Re: C/3 breaking up

fuel pickup in the tank maybe blocked (partly)? Bad fuel pump?

[Joe R.]

Re: C/3 breaking up

Wally,

When was the last time your distributor was serviced?

Joe

[William C.]

Re: C/3 breaking up

A little secret from a guy who did a LOT of work in the 1970-1985 timeframe, in the very early 70's the distributor rotor was shortened slightly to require a larger buildup of energy before the energy in the coil was allowed to travel to the plug. Delco Remy rotors of that era ALWAYS had an "E" stamped on the brass part of the revised rotor, and when an owner complained of lack of high RPM, that was the first thing we replaced. Get an NOS version or possibly one of the "hot rod" versions, although I'd check them tip to tip with yours before purchase as more than a few of the aftermarket "high dollar" stuff is made to the second design, (although without the stamping) and don't do SPIT to help the problem you are hiving.

[Duke W.]

Re: C/3 breaking up

With a dwell meter attached bring revs up to 5000. If the dwell changes more than two degrees the distributor is sloppy - excess end play, wobbly breaker plates, etc.

Better yet, drive the car with the dwell meter in the cockpit and watch for variation.

Duke

[Edward J.]

Re: C/3 breaking up

Wally, Do you have the ignition shield in place? I have seen wires jump spark to the shield, since everything is sandwiched under the cover. another thing is to make sure each wire is in the correct spot in the holders, the rubber groment holders are marked with the cylinder no.s for each wire on left and right banks. this is a small detail but the reason for this is to prevent the wires from cross firing.

[Wally A.]

Re: C/3 breaking up

thanks for all of the response. rather busy gathering all the input.....dwell right on, fuel delivery in line, plugs looked great.
after all of that. pulled the exhaust immisions belt, definitely helped. with that, found deverter valves at thermactor tubes
were not working properly. as per owners request, removed complete smog system. BINGO not only solved breaking up at
hight RPM but also cured poping on de-celeration. obviously smog system malfunctions caused the issues...
again thanks for all your input wally