Ignition Issues - faulty Pertronix Ignitor? I'm stumped

[ollie]

Hi everyone,

The issue is this; within 500' of pulling out of the driveway and under the first bit of load, say up hill, the car will run great then it will seem to run on 3 cylinders. It will run cut to half power, run rough but not die, then seems to recover provided I keep it under 3,000 rpms after a series of exhaust backfires. I thought it might be fuel starvation but pressure measured after the pump is in the correct range. I did swap the fuel pump and had the same pressure. The tank was boiled and repaired during the restoration. There is no contamination in the filter, which is new.

I have had a Pertronix Ignitor with the stock coil in the car for about 200 miles and all was well for the first 175 miles. Everything is new, the car has is new. The issue seems to get worse when the car is warm. The car will fire up and idle very well, the timing set and idle is excellent. Vacuum advance appears to function correctly.

I have tried multiple stock coils, multiple sets of plug wires, the cap and rotor are new and I have inspected for cracks as best I can. There is a bit of circular play in the distributor but I do not think it is out of spec. I would go and buy a new Ignitor but there are none available here in town. I did send Pertronix a note as well. All wiring seems to be in good shape.

In short, when the car starts to run rough, it seems to be associated with the front carb...carbs are in perfect sync and are functioning well. Again I do not think this is fuel related. When the power cuts to "half" it sputters and backfires out the exhaust, and on occasion out of the front carb. I have not pulled the plugs but I should and I have not swapped the points back into the car.

Any other suggestions I am all ears, this is very frustrating and I am really thinking this is the Pertronix but my car's issues seem a bit different than others.

Many thanks for reading!

[Walter Moore]

I don't see how ignition failure could only affect the front three cylinders, or cause the engine to backfire through the intake. That sounds more like a valve timing issue (which would also not affect only half the engine...) or a problem with the front carb. (Which would affect the vaccum advance by the way.)

[ollie]

I would agree however the issue is nearly binary, as in, one second it is running great then it isn't. The result of it not running well is half power, exahust backfire / popping and the very occasional carb backfire. If there was a carb issue I would suggest it would run poorly all the time...but I am not against looking at the carb again.

I liken the issue to that I have expereinced in my BMW 335i...these cars had extensive fuel pressure issues and when a fault occured the car enters limp mode and has only enough power to make it to the curb.

Anyway I think if timing and fuel seem to be great at the curbside then there is something up with that distributor....and could very well be vacuum related which would make sense. It is pulling vacuum for the advacne off the manifold port of the front carb....there are no emissions on this car and the carbs are 3 screw. They appear to function totally fine as well but I will peer deeply into the carbs when I get back into town from holidays. Thanks for the suggestions...keep 'em coming.

[Mikes Z car]

There was another thread mentioning a sticking carb float valve. Assuming it could be done safely with no traffic or obstructions what would happen if you went up that hill backwards to force the float to swing through a different arc?

[Captain_Zeros]

Hmm, this is a longshot and maybe a tangent, but the only intermittent ignition I had was on my 240Z when it had the stock points & condenser setup. There is a screw that goes through a plastic insulator that holds the condenser, the points, and the ignition power wire all together and the square nut on the inside of the distributor loosed and eventually FELL OFF, all the wires were still roughly where they were supposed to be, but were making poor contact and intermittently losing contact. I wanted to go straight for the carbs because it felt like it was running on three cylinders, but it was in fact running hit and miss electrically.

My symptoms were very similar to yours, I got about two blocks from home and felt like I was running on three cylinders and was able to baby it back home again for inspection and repairs the next morning.

[zKars]

On/Off working/not working is 95% ignition probabilty. About the only exception is random fuel supply cut outs due to plugged lines or sticky float valves that come and go but they tend to act differently. Read on.

Couple of questions to clarify.

1. Given a 30 minute hypothetical drive, what percentage of the time is it running fine vs running bad? You mentioned its good initially then the problem starts up, but does it randomly go back and forth between good/bad over the remainder of the drive?

2. How quickly does it toggle from working fine to working bad? Is it near instantly or does it get progressively worse over over a period of several to 10's of seconds? Near instant = ignition, slowly fades to bad = fuel going away.

Pull the vent hose off the top of the front carb fuel bowl lid and get a thin stick about 3 in long that will fit in the hose barb that sticking straight up now. Poke it in there and see if you can feel a nice freely bobbing float as you poke it up and down. You're making sure the float is free to move with this easy trick. If you feel a dead end, ie no bobbing, then the bowl is empty or the float is stuck.

Pull the top off the front carb float chamber and remove banjo bolt. Check the condition of the filter screen inside the banjo fitting and see what crud is lurking in the float bowl.

Pull the float valve and check the needle tip for deterioration, crud caught in there, and has free motion.

If after a lengthy drive with this problem coming and going, if the front carb is to blame, the front three plugs may look different than the back three. Just a clue here.

Good luck! Don't give up.

Edited August 6, 2013 by zKars

[ollie]

Hi Jim,

In answer to your questions; in a 30 minute drive I can make it about 90 seconds and it will run poorly after that point. The car isn't really safe to drive at all given the lose of power.

As for toggling good to bad, it happens from "good" to "bad" the first time nearly in an instant. Then it takes time to recover in about 2 minutes time or if I pull over...when I pull over it runs rough for a few moments and then recovers and when I pull away it goes to "bad" again within 30 seconds.

It could be a stuck float...the carbs were sold to me by a vendor local in Vancouver in excellent shape, at least they looked very pretty. The claim was the carbs were 100% NOS and had never been used...but take that with a grain of salt as I am seeing evidence these were restored. Anyway I still do not think it is a carb but I will have another good look over these carbs. The floats move very well and pass the "drop" test with flying colours.

One other point; the first time this happened I was cruising along at about 100 kmh under steady throttle...it cut out for a moment's time and since it was warm I blew it off to heat soak.

If I can't sort this out I will post a video of the issue when I am back in town. I am quite convinced this is an issue with the distributor though....many thanks for all your input.

[ollie]

There was another thread mentioning a sticking carb float valve. Assuming it could be done safely with no traffic or obstructions what would happen if you went up that hill backwards to force the float to swing through a different arc?

This is an interesting idea and I will try it for sure. Many thanks.

[madkaw]

" the floats pass the drop test"- your talking pistons.

As mentioned earlier it could be the front carb float . I would examine the needle assembly for smooth operation. It sounds like fuel is being cut off by a sticking needle and seat. The fuel slowly seeps into the float chamber when you stop and fills it for normal operation, then you take off and empty it again.

I would pull the float chamber top after it dies or get a visual method outside the float chamber to check level

Also as suggested - check all connections around the dizzy for looseness

[ollie]

Well this one is closed! After numerous attempts I went back to basics and when I made my way back to the carbs I pulled the float bowls and went to set the floats and could hardly move air through the bowl. Removed the valve and presto found a large amount of contaminate after the filter! The filters had little of it and I have no idea what it is. The tank was boiled and not lined, only powder coated on the exterior. It seems like powder coat but is likely old fuel line decay. Runs great and I now know my carbs all that much more. Thanks for all the help.