Random Misfire, Replaced Everything.

[Deneo]

Hey guys

Spent some cash on my Ignition system in the 1990 Mav TB42, Iv'e done Plugs, Leads, Pertronix kit, Flame Thrower Coil, Rotor Button and Dizzy cap and it still has an intermittent misfire on idle and lower revs.
The pertronix kit is all wired properly, Black from the pertronix to the coil and the Red to the ballast resistor.
Can hear it through the exhaust and feel it like when i'm leaning against the bullbar. It's also at random times.
I'm about to take a few liters of ULP and a Zippo too it.
I don't know what to do next, on a brighter note it's running considerably better than it was so I'm a lot happier than i was with it just over it still missing.

Cheers guys for any help.
Deneo.

[chunks]

Is it carby or injected?

[Deneo]

Carby mate, Forgot to add that.

[Deneo]

I'm pulling my f'n hair out over this, Sometimes it's hard to start, Other times it starts straight away, and the misfiring sometimes is worse than others.

[351ciofgrunt]

When you changed the leads did you also change the lead from the coil to dizzy?

Have you checked for vacuum leaks?

Check that the intake manifold and carbie nuts are tight.

Have you considered rebuilding the carb? Most places will do it for around $150.

[Deneo]

When you changed the leads did you also change the lead from the coil to dizzy?

Have you checked for vacuum leaks?

Check that the intake manifold and carbie nuts are tight.

Have you considered rebuilding the carb? Most places will do it for around $150.

Yep, Replaced the lead from the coil to the dizzy.
All the nuts are tight, I'll go over them again just to be sure.
And I have seriously considered it, Just wouldn't know where to take it. Think there might be something wrong with the carb?
Thanks for the reply
Deneo.

[RED60]

Do a compression/leak down test.... easy and cheap.... I smell a bad valve.....

[Deneo]

i just put a new head on it, Had it tested and faced. Where would i get a compression/leakdown test?
Cheers.

[ANDREWGQ 351]

I've had this problem before, i would start by putting all the old leads back on and then the old coil. check that there is not a lead arcing across to the head somewhere. This can be seen in the dark easier
check for a good stable 12V at the coil and there is no wiring or distributor cap damage even though it may be new

[RED60]

i just put a new head on it, Had it tested and faced. Where would i get a compression/leakdown test?
Cheers.

In theory your head should be good then..... you can still get the tests I mentioned done. Any competent mechanical shop will be able to do it... might pay to check the valve clearances beforehand in case you have a riding valve....

[Deneo]

Yeah i did the valve clearances a week or 2 again, I'll check them again just incase.
I played around with the mixture screw and it seems to be running abit better. Don't know if i should of touched it or not though.

[hiy6o]

Just thinking isn't the petronix designed to run 12v if so you should not be using the ballast resistor as they drop the voltage to 9v . Not 100% sure so check the instructions for operating voltage.