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ignition help needed

930 Views 11 Replies 5 Participants Last post by  handyhand
Was driving the mustang to work this morning, car was running perfect, stopped to get gas, a few miles later, noticed the engine started stumbling real bad at idle, and would surge when driving, I pulled over to see if I could see anything obvious, nothing, I had to turn the idle way up to get out of there because I kept stalling everytime I would slide it into drive. I got it home, barely, and started pulling the plug wires, #'s 2,3,5, and 8 did not have any effect on the RPM or engine running. I pulled the #2 spark plug out, looked OK, . I have been running the pertronix ignition, flamethower wires, and coil for about a year now, spark plugs are bout' the same age. I am thinking at this point my pertronix unit is shot not firing the 4 plugs, but I wanted to see if I missed anything, or maybe I am way off, what do you guys think?? any another input or help would be appreciated.
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I wonder if you've got a chunkie in your carb??

Most of my weird engine problems have come from debris in the carb....the notable exception was an off-idle stumble that ultimately was the result of premature wear of the point rubbing block which caused the points to close excessively and create a dead spot.

Unless your Pertronix has gone wonky, I'd look at the carb...

Also, remote possibility is a tank of bad gas, given your description of when the problem began...
Ya, I was just out in the garage, and sprayed some carb cleaner like everywhere, checking for a bad vacuum leak, I did not notice anything, except when I sprayed some direclty into the carb throat, it seemed to idle higher and smooth out a bit, is that a good indication that it might be carb related you think?
Bad gas. I've had it happen to me before. You could try some gas additives that remove moisture. If that doesn't work you could try draining the tank and starting over with a fresh tank from a different station. I use the same gas station 98% of the time to try and avoid this situation. Once I get bad gas, that station never sees me again.

Good luck.
Close your idle mixture screws (engine off), noting rotations until seated (gently), then back off to original setting. Start engine and turn screws in slowly, one at a time, until idle gets real rough. Note rotation. Then, back off past original setting and see if idle smoothes out. Sometimes I'll back the screws way out and rev the engine up...natural vibrations, combined with a more open orifice channel, can sometimes dislodge and flush debris (if that's your problem)...just note what you do so you can find your way back if you get lost. Ideally, the idle mixtures screws should be about equally open and somewhere between 1.5 and 2.5 turns open..

Don't forget about the possibility of bad gas...your diagnostic leads me to believe debris or mixture, but it still could be gas...

Good luck!
Thanks camachinist, I did try that idle mixture screw trick just about a half an hour ago, still ran rough. I have been running my new carb at about 1 1/2 turns out. I just got a rebuilt Pony carb a couple of months ago. A couple of questions if you dont mind, if there is debis in the carb, what is the procedure or best way to clean it out, and if that does not do the trick, how can I dispose of 14 gallons of gas at my house??? I have been running Premium 91 octane from Mobil latly, this was a new gas station I used today however. Thanks for all your help! James.
Did you happen to check you vaccum level on your engine? If the Distributor and timing set properly?

I had a rough ride after Carisle...and my timing was off...and I learned a trick using the vaccum guage as a quick way to get the engine to run much smoother than it was. Just loosen up the distributor bolt and look at the vaccum guage (attaches to the intake maniford in the rear) and see what the guage says.

For a 351W its about 20 psi or so...give or take a degree either way...and then turn the distributor slightly and see if it races or gets rough...depending which way you turn it?

Pony Carb..said the Distributor should sit w/ Vaccum Diaphram in the seven o'clock position (normally) but it really depends on how it was installed and where your engine wants to run...good luck!
Do the obvious checks like Yukon mentioned (I tend to overlook the obvious because most of my mechanicing is done instinctively) and then focus in on the carb....

Are you running a 4100? I've had chunkies pass on their own (kinda like kidney stones *G*) before with the one on the D-coder...couple of WOT blasts on the freeway (happened to me when I was in town...suddenly started idling like crap and sounded like it was running on 6 cylinders, except at WOT) and the problem disappeared as mysteriously as it had appeared.

Exact procedure is something I know when I see it...I haven't done any major work to my 4100 so I can't visulize the details of the carb to instruct, if it were a Holley...*G*

Lastely, IME, generally, ignition problems (other than sporadic/poor connections in primary wiring and/or components) are consistent and progressive, whereas carb problems can come and go.....your observation when spraying carb cleaner leads me to believe ignition is not the problem here...

Gas...hard to know...I'd square the carb away first, being watchful for funny debris in the bowls or strange optical glitches when looking down into the bowl, which might be a sign of water (water is heavier than gas and sinks)....I guess you could kill a bunch of weeds or ants (you didn't hear it from me...hehehe)

Keep us posted!
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The last thing you did before things got hinky, was get gas.

Bad gas.
Bad gas is definitely a possible, but with these old gas tanks I tend to look towards the filter and carb for trash first.
Thanks for all of the input gang, I must say it was all to strange for that to happen right after the gas was filled. I slept on it and what I am going to do is run my 2 gallon gas can over to my regular gas station I usually go to, then disconnect the hose to my gas tank on the car, maybe get some more hose to reach my gas can, stick the hose into the gas can and run the old gas out of the fuel system and see what happens with the car running on the good gas from the can. If that doesnt do the trick, I still have my old carb, its still worked o.k, i'll stick it on there and see what that does. All you guys are awsome, thanks again for all the help, i'll keep you all posted as to what we find out, this should be interesting.
Follow up to the engine problems I had. I bypassed the gas tank by running the fuel line from the car into a 2 gallon gas can, with gas from a different gas station. Problem still present. I still had my old carb, so I pulled my brand new Pony Carb off of there, and installed my old one, ran fine. I put in a call to Pony Carbs that Friday afternoon, all of the techs had left for the day, so I called back on Monday, I guess I needed to get with them as to what I was doing or the warrenty on the carb would be voided. He simply told me to take the top off of the carb and clean out the needle and float area with air and or carb cleaner. When I pulled the top off, I noticed the clip that holds the needle to the float was missing!, it cant go anywhere, so I am sure it was overlooked and not installed during the rebuild at Pony Carbs. Ran to AutoZone and picked up a rebuild kit, slapped the clip on there, car runs fine now.I am glad I figured this out, and thats all it was, but Pony carbs is going to get a letter from me. Thanks all who helped me with this. Take care gang! James.
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