Carb or Ignition Problem?

[Anonymous]

I actually used to be pretty good with cars 20 years ago...now I guess I'm rusty, and looking for help. I have a 1969 Mustang w/250, dual Clifford headers, port divider, and I have the Ignitor II and Flamethrower II coil. I just put a Demon 350 cfm on my 250 a few days back, and at first it ran really well, then when it got real good and hot, it ran rough/died - choke setting I thought, so I adjusted that. Then last night it started missing real bad and didn't want to get over 40 MPH...finally got it up to 60, but running rough. Now when I put it in gear, it dies. I've tried setting the air/fuel mixture several times now. Other possilby related stuff: 1) when I rerouted the line from my gas pump I got a bunch of crud in my gas filter (see through type), and have changed the element three times. 2) I tapped off of the ignition input to my coil to supply power to the Demon's electric choke. 3) My timing mark has somehow been off for years, so I have to set it by ear. 4) There's some black, almost powdery stuff coming out of my exhaust pipes and collecting on the floor - no smoke whatsoever though.

Any suggestions please, on what I should try?

Thanks so much,
James

 

[addo]

Try a set of points in it, and see how it goes. The Ptx II is famous for malfunctions on these motors!

Cheers, Adam.

 

[Lazy JW]

What Adam said. Not much sense in splitting a pile of kindling if your matches don't work.
Joe

 

[CobraSix]

I'm torn between 2 pieces of advice:

1) If something is broke, it's usually caused by the last thing you 'fixed'. So that would point me to the carb. if it was running fine before the carb switch, the only variable to change is the carb. Try to switch back to your old carb and see what happens.

2) The P2 does have a lot of complaints. it is worth looking into that as a source of problems.

Unless it is a real pain, I'd switch the carb back and see what happens. That will at least either confirm the carb as the problem, or point to the ignition.

Slade

 

[Anonymous]

Part of it sounds like it is starving for fuel. Does it seem to start missing at wide open throttle and smooth out if you back off on the acceleration? If so, it could be a fuel supply problem. Given you mentioned the debris in the filters, it could be plugged. A choke that is staying on too long would also prevent reaching top speed.

The black soot could either be the an improper choke setting, or the carb may need rejetting. Its rare that carbs fit a non-stock application right out of the box.
Doug

 

[Anonymous]

Thanks for the great advice, guys! Unfortunately, I've thrown my back out (I have a bad one, and leaning over a fender so much didn't help)...so it will probably be a couple of weeks before I can work on it again (while I'm doing the physical therapy thing).

One of the first things I want to try is checking the voltage at the (+) input of the coil. That's where I tapped off for the electric choke, and I don't know if that is a resistor wire feeding the coil or not...if it is, then I've unintentionally lowered the voltage to the P2. That would be a relatively easy fix (running a non-resistor wire from the ignition switch to the coil).

Since the carb ran really well to start with, wouldn't that mean that it shouldn't need rejetting? And here's my real dumb question - what is rejetting? Is that just changing out the air/fuel jet screws, or does it involve taking the carb apart?

Thanks again,
James

 

[mugsy]

My guess is that the coil is not getting enough volts/amps. I *think* the Pertronix units can handle 12V; read the distructions! . If you connected the original coil feed then that is your problem I bet. I have had issues with higher speed performance issues when the coil/dwell was all messed up. You could also pull a spark plug wire, stick the business end of a a screwdriver in where the plug goes, and then place the shaft of the screwdriver close to ground and see what kind of spark you are getting (make sure you are only touching the plastic handle of the screwdriver ). That will tell you if the voltage is right. Also have some one rev the engine and see if the spark quality changes. And lastly, I would find a different source of 12V to the carb choke, regardless of the spark test.

Thanks,
Mugsy 8)