I have a customer car that I overhauled the HD8 carbs. Not my first set. I can not find a vacuum leak. Distributor new Pertronics. Had problem before and after new dist. Adding starter fluid while misfiring does not help. Timing 7*BTDC. To my knowledge the problem started after rebuild. Sometimes it will have flame blow out of the carbs while this happens. Runs good until full throttle. Fuel flow through filter looked good when I emptied the bowl. I'm stumped!!

 

Petronix can be great, BUT do you have the petronix wires to match?
Old copper wire will send surges to the unit and eventually burn it out.
Also are the bowl levels set.....many over look this and trouble begins.
Good luck other than a bad coil, the petronix can work but you have to tweek.
gtjoey134

 

Had this problem on a MK VII, petronix tech recommended their wires, immediately went away.

 

Try (temporarily) running power direct from battery to coil, bypassing the battery-ignition-fuse-coil wire. The Pertronix is very sensitive to voltage drop.

 

Thanks for the replies. The misfiring began after? carb rebuild. (As far as I know) I"m replacing front crank seal at the moment and will change wires after that's done.

 

What is not clear is what air filter syste are you using. 4k stop on revs is typical of non OEM filters (boy racer filters)

 

The air filters are not installed (OEM) at the moment. When I'm done with front crank seal I'll get back to it. I'm going to change the plug wires before I do anything else. The rpm range will vary sometimes. And it will run ok sometimes to 5K. Just not under load. (boy racer filters) Funny.

 

 

Air cleaner back on. No improvement. Suppression wires from Welsh installed. No improvement. Changing mixtures does not help. I'm headed to check valve clearances. Thanks for all of your responses.

 

Also substituted a different fuel pump. No improvement.

 

Its the tank now and line.
Take a gas can and connect it to the fuel pump in the back with high grade fuel ,I bet the ranch in two minutes you see a complete change, barring you dialed in the floats.
ETHANOL IS KILLING THESE CARS
Good luck

 

To eliminate one other item, is the upper timing chain properly adjusted?

 

I just checked valve clearances. 7 out of 12 are too tight. 2 intakes are .002". Even have 1 exhaust at .002". Wish me luck!!

 

I have set valves to spec. It idles great but still pops through the carbs when revved. I have no more hair to donate!! Cams are in time perfectly. The tank was drained and filter checked. ok

 

Run gas from another bottle, crap in the tank and moisture a killer....good luck.

 

1968 XKE: I had a fuel filter in the bowl on bulkhead that look OK, but would only flow enough fuel for cruise on hot California day, when I starter up long grade engine would loose power. Stop several times to investigate, found nothing. After 5 minutes started off again and was fine for a while at moderate speeds only. On way back I took out fuel filter as pure guess, as I had no tools with me. Sure enough engine performed normally up the grade going home. Installed new filter and was OK.

Curious if you Carburetor overhaul included new piston spring, new jet and new needle? If piston is binding and not going all the way up, you will have lean mixture at high RPM ???

 

Finally!! After valve adjustment I replaced the jets again. Car runs great now. Suspect that after valve adjust I hadn't refitted the complete air filter assy. and that contributed. I don't know for sure why BUT at this point it's not important. Now it can go home when the rain stops. Thanks for your help.