Igniton Question

[Bullzak_83]

The ole 70 C10 will start up on a dime when cold, we have noticed after it warms up and has been running for 30 mins or so there are times you couldn't get it to start with a stick of dynamite. After it sits for awhile it will usually restart.
I have been thinking I had carb issues, but it runs to good when it runs.
I'm beginning to think I might have ignition issues? I converted the old point system over to a mallory electronic ignition 20 something years ago.
And I still have the old large ceramic resistor. Is it possible that, the ignition is getting hot and breaking down?
While trying to start i pulled a plug wire to check the spark and noticed that it did not seem that strong.
The battery was not dead but I jumped started with another truck, and the truck fired right up which makes me think I increased the voltage going to the ignition.
Any thoughts on this, or has anyone ran across this before?

[Palf70Step]

Could Be a starter or a starter solenoid heat soak issue. I have had similar problems like that on the past.

[rockyrivermark]

Do you have headers? If so could be heat soak into starter. They make a defection shield or a mini high torque starter is a good opinion and will resolve the issue. Mine was $124 from summit.
If you have an aluminum intake heat soak will boil the gas in the carb bowl. A phenolic plate will create a heat insulator between manifold and carb and resolve that as well.
I had the same problem and these two changes fixed it.
Not knowing what you have makes it tougher to offer help
Original engine? Any recent changes ?
Mark
Posted via Mobile Device

[HO455]

A couple of questions. When you say it won't start when hot do you mean it won't crank or cranks slow? Or it cranks over fine but will not fire? Two different troubleshooting paths to the problem.
You didn't say what Mallory ignition you have.
Based on your initial information I would start by checking the voltage at the ignition supply. Key on and while cranking the engine. Then the same test at the positive terminal of the coil. If both are good then check that the grounds to both them are good.

[Bullzak_83]

My bad, the trucks turns over no problem, so its not like the starter is dragging after it gets hot. (Been there done that)
The truck turns over fine, no problem, I first thought it was carb issues, I was a little confused on what type of setup I had, been told that it is a quadrajet, wide back large bore in back small in front, with a quad intake (factory).
The reason I bring the carb up is because I have gone round and round with the setup I have, Riser plates, adapter plates etc till finally buying a squrebore holley. But the bolt pattern did not match my intake, SO I removed all plates mounted my carb back down directly to the intake, (don't ask why I had a squarebore adapter plate on my intake) been on there for 20 years.
In other words it was on there when I parked the ruck, Probably never was write. But anyway I thought maybe with the adapter plates I had on it might have been causing the carb to vapor lock.
But now I think that is the issue, only because the truck runs to well while it is running.
By the way the carb on the truck is the one I had o it when it was parked 20+ years ago it is a Carter AFB I did rebuild it, recently.
I'm just thinking now for what ever reason, the voltage may be dropping down low enough to cause ignition problems but only when the truck gets hot

Hope this long post makes sense.

[schovil69]

It makes sense to me. Our truck had the same issue. The engine was old and tired with one cylinder pretty much dead for how low it's static compression registered. Same issue you've described...started like it was fuel injected when cold but it was a crap shoot whether it would start when hot. I would just hold the gas to the floor and keep cranking. It would eventually start or the bat tree would die. Never did find the issue.

However, the potential solution is sitting in my garage right now. The block is fresh from the machine shop and I'm in the process of assembling it.

[68 P.O.S.]

Originally Posted by Bullzak_83

By the way the carb on the truck is the one I had o it when it was parked 20+ years ago it is a Carter AFB I did rebuild it, recently.

I believe your carb is percolating fuel, creating the hard starting. This carb design is notorious for this, as well as flooding when fuel pressure and float levels are incorrect. You're going to need a heat insulating spacer to correct the percolation. It sounds like you have the original q-jet intake manifold, so you'll need an Edelbrock 2732 square bore to spread bore adapter to ensure the intake seals properly with no vacuum leaks. Then, for the fuel percolation, you could put an Edelbrock 8723 on top of the 2732 to insulate the carb from the engine heat. Also, restrict your fuel pressure to 5.5 psi and set your floats to specs and you should be good to go.

[Bullzak_83]

Hey all wanted to touch back, 68 POS when you say percolating are you say that the fuel continues to drain into the intake after the truck is off?.
schovil69, wish I had the funds to drop a new old engine in it, but at this point I just want to keep it running long enough for my boy to be able to drive it..
I have included some pics of the mystery intake and carb, I have been told that I have a quad/spreadbore carb. And yes this is the original intake to the engine. But I can tell you the holley 600 I bought will not work with the bolt pattern on the intake you could say I have a 4x4 square but the holley is a 3.5x3.5 bolt pattern

Well, I tried to upload some pics but I am being told I'm missing a security token?
so I'm unable to upload

[tim_mc]

I had a bad HEI coil and/or module that would cause problems when warm. At first I thought it was an intake leak. Truck had an occasional backfire or load up when driving. It progressively got worse to where it would start OK, but would die when put into gear. It would idle and rev OK, but ran badly under a load, or when stopping at a stoplight. I had to put it in neutral a few times to keep it from dying at intersections. Later it would lean out and backfire after it warmed up and eventually would not restart when warm. Installed a Davis Unified Ignition coil and module and haven't had a problem since. Starts faster, idles better. Maybe try a replacement coil since you don't see a good hot spark? Also, should that Mallory ignition have a full 12 volts to it? If so, then maybe remove the old points ballast resistor.

[HotWheelsFan]

It could be weak spark or carb heat soak problem. I'm not sure what type of ignition set up you have or if it's wired correctly. Points and condenser type of systems use a resistor to lower the voltage to the system. GM style factory electronic systems do not.

Heat soak can cause fuel to leak into the intake causing a rich condition or it can boil all the fuel in the carb causing a lean condition.


You could check to see if carb accel pump shoots a shot of gas during the no-start condition. You could add a little gas into the carb to see if it help fire up...



Bob

[Palf70Step]

Originally Posted by Bullzak_83

Hey all wanted to touch back, 68 POS when you say percolating are you say that the fuel continues to drain into the intake after the truck is off?.
schovil69, wish I had the funds to drop a new old engine in it, but at this point I just want to keep it running long enough for my boy to be able to drive it..
I have included some pics of the mystery intake and carb, I have been told that I have a quad/spreadbore carb. And yes this is the original intake to the engine. But I can tell you the holley 600 I bought will not work with the bolt pattern on the intake you could say I have a 4x4 square but the holley is a 3.5x3.5 bolt pattern

Well, I tried to upload some pics but I am being told I'm missing a security token?
so I'm unable to upload

Get the adapter for the squarebore carb like the edlebrock/holley. You may have to adjust your throttle rod compared to the quadrajet.

BTW that error normally happens when the photos you are trying to upload are too large for the system to handle.

[Bullzak_83]

Hey everyone, I think I've found the Gremlin.
I went ahead and picked up a new HEI distributor, and while changing it out once I removed the old ceramic resistor from the firewall, I found this on the back of the resistor (notice one end of the resistor). I only wish that I had,the correct plug wires so that I could have finished up tonight. Needless to say I now have a HEI distributor in place where the old Mallory contact-less once was.

[Accelo]

The HEI systems use the full 12V and does not incorporate a ballast resistor?
Possibly the Mallory contact-less did. Unsure on the application.
Wire it for the full 12V by leaving out the resistor.

By 1970 the resistance needed for a points distributor was built into the wire. This system replaced the ballast resistor. Obviously the resister was added to your truck. If the added ballast resistor was installed on the factory resistance wire the voltage available at the HEI would have been extremely low.

Typically when I change SBC over, to an HEI, I unwrap the harness and pull the ignition wire out of the harness. It has a funny coating and doesn't look like any of the other wires. Color is kind of an off white. Cut the wire off about an inch from the firewall. Solder a new 14G wire to the terminal and re-wrap. Do no reconnect the wire from the starter it isn't need with the HEI system.
Your good to go.

[Bullzak_83]

Hey Accelo,
Can you explain why I needed the extra wire going to the starter in the first place. I read something about if the starter shorted out, some how it would feed back through this wire and prevent anymore damage. Don't really understand the concept.
I rewired the truck with Painless wiring, and have included the wiring diagram for the engine.

[BigBird05]

That yellow wire was used to get 12v to the coil during cranking. Normally the coil gets 9.5v because of the resister wire. But during cranking that voltage drops to below 9v. so you don't get any spark or very little. With an HEI distributor you have the full 12v at the distributor so that yellow wire is not needed. That is also why you need to replace the resister wire with a new one so you feed 12v to the HEI distributor.

[Bullzak_83]

Thanks for the info and help.
Amazing what a new carb and electronic distributor will do for a engine.

[68 P.O.S.]

Glad you got it figured out