Baffled

[roadrunner400]

Hi everyone i am baffled please help. I have a 1972 400 that was bored .030 did the brake in a couple years ago on a stand. Installed in car last year never driven work in progress starts great no issues except when i tried a few weeks ago to lite the tires i discovered i coild not get it to go over 2500 rpm. Changed carbs no difference new plugs and wires no difference. Seems to develope to me an electrical issue. Any help would be appreciated. Its getting fuel no smoking of any kind. HELP

Mike

 

[Photon440]

Make sure the distributor isn't seized and preventing the centrifugal timing to advance.

Is the 2500 limit while under load, or also when in neutral?

 

[roadrunner400]

Drive or neutral no load

 

[Fran Blacker]

Something clogging intake or exhaust? Rags stuck in and forgotten.

 

[roadrunner400]

changed carbs didnt notice anything.

 

[mr. b]

check the ecu i had one do that

 

[roadrunner400]

appreciate all the help guys.

 

[MelroseMopar]

Start with the simple things, do you have a good clean 12v supply to ign? Are your grounds good? Check fuel presser? Try disconnecting exhaust at manifold/collector see if system has a blockage. You have already replaced carb(s?) once ( You said carbs are you running a dual carb setup?) do you have a known good distributor it try? Hopefully you find it in those steps because then you might have to look into things like seeing if the camshaft was installed correctly and check Camshaft timing..


Good Luck
Hopefully its something simple for you !

 

[beanhead]

Coil, ECU, throttle linkage stuck/binding/not opening all the way, bad fuel pump/plugged filter are the first things that jump to mind, good luck.

 

[Master Gunner]

Linkage / throttle cabel problems?

Mark

 

[roadrunner400]

all good on the cables. How about not 180 out but 90. Would that cause rpm to top out low? Or show as a electrical issue like a rev limiter?

 

[Sinitro]

Check the polarity of the distributor, it may be reversed..

Just my $0.02...

 

[Pistol Pete]

Coil is the first thing that came to mind.

 

[roadrunner400]

Changed coil changed cap changed rotor started over TDC same outcome 2500-3000 rpm. Sounds like electrical brake up like it has a rev limiter. Ballast resistor and distributor all i can think of. What is the ohms the ballast resistor should be i am at 1.5. Frustrated in Pa. Thanks for any suggestions. Mike

 

[copper67sat]

Check your ignition wiring. Trace it back from the coil and look for any loose, corroded connections or burned wires, especially at the bulkhead connector. You can try running a temporary wire from the + battery to the + coil to bypass everything and see if it runs better or repeats the issue.

 

[Outsider]

It seems to run well and make power up to 2,500 rpm, or just doesn't run well at all? Idles well and no bog when you punch it, or....

 

[roadrunner400]

yes revs right up to that point and start to cut out. wont take any more pedal no higher RPM idles good. starts right up.

 

[copper67sat]

Mine acted similarly when I had weak/burned wiring in the main power line at the bulkhead - most damaged section was on the dash side so it wasn't easy to spot. Engine wouldn't rev above about 3k rpm without cutting out. It was most noticeable under load - car would starting bucking and stop accelerating.

I finally identified the problem by bypassing the wiring and powering the coil directly after chasing many other potential sources. I was at wits end and called a local auto electrical shop to see about bringing it in. The old timer that ran the place (20 yrs ago) didn't really want to get into it, but but gave me suggestions as above to help diagnose.

 

[roadrunner400]

thanks ill give it a try and keep you posted. the wiring harness on the engine side is all new.

 

[Outsider]

More info needed: initial timing at idle, points or type of electronic ignition, ballast resistor ohms and coil ohms, cranking compression test results, at 2,500 it can maintain that rpm steady or shuts down and dies, miss fires-pops-timing pinging-any sounds?