Prestolite Distributor discussion

[Tonka Toy]

I have a prestolite distributor in the "new" Travelall I picked up not long ago. And I have some questions about it, because I know virtually nothing about them. When I brought the truck home, it would randomly misfire and seem to sometimes surge on the freeway. I took them as signs that the internal pick-up might be bad. (especially since the key kept getting left on acc and having the key pulled out by the morons at the car lot it was at. ) my local napa tells me the replacement is over $300! this can't be right. So I go about verifying by replacing it with my Holley/pertronics unit. During the swap, a fried wire in the ignition switch decided to finally let go. Before I figured it out, I had switched the prestolite back in.

Since I assumed that was the problem, rather than the distributor, I decided to leave it in. But I still have the surging. Setting my timing at 0 (tdc), (reduced from my initial 10 degree setting), but it still isn't running right. It has dieseled on me when shutting off a couple of times, and the surging is still there. It feels to me like when you don't have enough total timing advance and it comes up against it. Like the engine needs more timing but can't get it. But I'm not sure. It has also developed an off-idle stumble that it didn't have before. And sometimes I need to crack the throttle to get it to fire up, which I don't believe it ever did before either.

I've never had a distributor without a vacuum advance, so I'm not sure if there is something I need to do or check that I just don't know about. I read that these are the cat's a** in the world of IH distributors, but I had no trouble with my Holley/pertronics. I want to use the best one, but I'm currently skeptical about which one that really is. And "best one" for me also includes affordable, easily accessible parts availability, since I plan on this being our family's backcountry exploration vehicle.

Thanks in advance for your help.

 

[Scooter]

I have a prestolite dizzy in my 345 Scout, and the first thing I did soon after I got it was get the pertronix unit for it. Yes they have one for the prestolite @ $122 and change. Got mine through the kind fellas up at IH Parts America. My stock version actually came with points.

I just completed a 304 motor swap in a 69 Scout 800 with same dizzy but it had the mag pick up. So far this unit is working just fine with out the upgrade to pertronix. When I did the timing on it, I set it at 5* and that seemed to be the sweet spot

as a side note: from what ya discribe, there May be some carb issues, maybe. Having the key left on is never a good thing on these ole heavy irons. So it could be possible the=at the presto mag pick up is showing it's ugly side

 

[Scoutboy74]

I agree with scooter. Your symptoms sound more fuel than spark related. The engine run-on or dieseling is often caused when the the ignition is switched off while the engine is running above spec idle speed. Do you have a tach connected? Your hot curb idle should be roughly 725 rpms in park if auto equipped and roughly 650 with a manual trans.
The acc position on the iggy switch does not feed power to the coil. Leaving the key in this position will not do any harm to the ignition system. That is why it exists, to supply power to accessories while the engine is not running. 10 degs btdc should be almost perfect base timing for your engine, but again this must be established with a correct curb idle speed.

 

[Tonka Toy]

scooter: maybe Carb issues? It's the typical Holley 2 bbl. Of course it has issues. :d lol! It seemed to run fine from the carb aspect before I started messing with it. The only carb related issue I have adjusted is to bump the idle speed up. Once the new wire was on the ignition switch, it ran at about 550 in park. Now it's at about 700 in gear. Idle speed isn't jumping around anymore either. I might just swap the other distributor in and see what it does.

scoutboy: You are right about the switch not supposed To supply power to the coil on acc., but I've seen them do some weird things internally when they wear out. And I think that sometimes it won't fire off until I let off of the key. A couple of times it was just cranking, and as I let go of the key, it fired up. Idle speed is perfect now. About 650-750 in gear. It's a small tach with a large needle, so it's not as precise as I'd like. But it will do for now. I'll try the 10 degree setting and see what it does. In the meantime, I have most of what I need to go GM TBI, so I May not play with this carb very much.

One thought I had last night at work was if my vacuum booster might be bad. If it's sucking enough vacuum from the motor, it can run funny as well. I randomly get the "brake failure" light on the dash, but no apparent change is braking. And when I jumped power straight from the battery to the coil, it lit up, without the key on iirc. So I am leaning towards an electrical gremlin at the moment. Once again, this May be a series of issues that are related that need attention all at once. Man, I hope not!

 

[Scoutboy74]

You said it right. Sounds like your ignition switch is indeed worn out and in failure mode. The next regression is constant power to the coil even with the key switched off, which in your case would also engage the starter automatically...yikes! Hope it doesn't go chernobyl on you before you get a chance to replace it. I think if it were me, I'd be unhooking my battery whenever the truck is not in use and a new iggy switch would be at the top of my grocery list. Good luck.