For all of you Hemi diagnostic gurus..... 1970 Hemi built to factory specs and has been on the road for about 12 years without any issues until now. After about 15 - 20 mins of driving it starts to spit back through the carbs intermittently while cruising. Under hard acceleration the car falls on its nose and can't hardly break the tires loose. good power when cold idle and revving in neutral sounds ok. Timing good, replaced fuel filter, checked fuel pick up Mopar Performance fuel pump replaced about three years ago. Carbs rebuilt two winters ago.

Thoughts/

thanks
paul

Have you checked the length of the fuel pump push rod? Might look at it to see if it has failed on the end and worn down. I had a friend a couple years back that had a similar issue as you describe almost like a vapor lock issue and it was his fuel pump push rod. It just took him a while to find it. Good luck!
Matt

I assume it has a hydraulic cam if its a 70. But a solid cam motor will behave that way if the lash is way to tight. Also check the float levels.

Maybe coil, pickup or ecu once hot.

Replace the points and condenser.....

If it's nothing major (bent valve, flat cam, etc.) It could easily be something relatively minor. Even though the carbs are only 2 years after a rebuild, bad gas or other fuel related issues could easily cause problems with the accelerator pump rubber and the needles & seats. Popping and backfiring could also point to a distributor or timing chain issue, give everything a really close look.

Sounds like ignition, change the condensor and change or clean the points if its a point ignition. If not check for a leaking coil.

pull the valve covers and check it out

original point setup correct? (1) coil or ballast (got spares you can sub in one at a time for a quick test?) (2) block all (4) metering rod pistons up so you're on the power circuit and take it out again for a quick test (vac leak)

Make sure the chokes are fully open after the motor has reached temp.. Hemis are notorious spitters

if not maintained or set-up right

Bad tank of fuel? Bad or burned plug wire? If still points, check dwell(or condenser as someone suggested). Retarded timing for some unlikely reason. More obscure might include ignition wiring including ignition switch connection or connector from steering column wiring to general under dash harness that includes turn signals, starter circuit and positive wire to coil. Vacuum leak or really rare slipped timing chain/ gear. Coil failure.

Any news as to what the problem was?

Not yet, I replaced the condenser and checked the points. Points looked good and gap was ok. Will take it for a ride tomorrow. I fired it up tonight sounded ok carbs seem to be functioning correctly at idle and after warm up. will post results tomorrow

Really appreciate everyone's input!!!! Thanks again.....

You say "after warm up" is your choke functioning properly?

Did you find the problem yet?

Not Yet, I replaced the condenser and checked the points. Verified the choke function. Finally had a chance to take it for a ride last night and the same thing happened after about 20 miles of back road driving(40 mins). Acting like a bad vapor lock? With about a 1/4 throttle and a very little load (flat road) seams to be ok but as soon as I give it more throttle it spits real bad back through the carbs. Will be replacing the coil tonight if I get a chance, just trying one thing at a time to pinpoint the issue.

Again Thanks for everyone's input!!!!! Will keep you posted.

Thanks
Paul

Had a 77 Gran fury doing that back in the 80s turned out to be the fuel line was rubber that had turned porous and was sucking air threw up by the floor of the car Check your fuel line going back to tank and by the way only did it when car warmed up ???

Well replacing the condenser and the coil did not work.... Replaced coil tonight and let it warm up my normal 5-6 mins or so. But this time instead of acting up after 30 mins of driving, it started spitting back through the carbs within 30 secs of driving. Did not even make it out of the neighborhood. So far replaced fuel filter, checked pick-up and sock, verified choke set up, new fuel, replaced coil, condenser and cleaned checked points...... onto the fuel pump/rod....