Fresh 1967 Convertible Restoration need electrical help

[Lee B.]

I finally got my father's Sunfire Yellow 1967 Convertible back from the guys that helped me with the restoration. The problem is that it runs great for about 20 minutes, but then starts sputtering and backfiring. Thought I had figured it out, but took it out tonight and it ran fine unless I really got on the gas. When it gets full throttle, it sputters and slows down. All the electrical checks out best I can tell. I figured someone has run into this before and would know what to do. Please help, the car is too beautiful not to run strong.
Thanks
Lee

[John H.]

Re: Fresh 1967 Convertible Restoration need electrical help

I finally got my father's Sunfire Yellow 1967 Convertible back from the guys that helped me with the restoration. The problem is that it runs great for about 20 minutes, but then starts sputtering and backfiring. Thought I had figured it out, but took it out tonight and it ran fine unless I really got on the gas. When it gets full throttle, it sputters and slows down. All the electrical checks out best I can tell. I figured someone has run into this before and would know what to do. Please help, the car is too beautiful not to run strong.
Thanks
Lee

Lee -

Which engine, trans, correct parts (carburetor, ignition, etc.). Need more info.

[Lawrence S.]

Re: Fresh 1967 Convertible Restoration need electrical help

John I will answer for Lee since I was with him tonight. It is a 300 HP AC car, M20 100% original car just beautiful. Original carb, distributor with points etc. Convertible car.

[William C.]

Re: Fresh 1967 Convertible Restoration need electrical help

Look for an obstruction in the fuel system, for starters, when it quits if you pull the aircleaner off and hit the throttle do you get a full shot of fuel?

[Anthony P.]

Re: Fresh 1967 Convertible Restoration need electrical help

I have run into a similar situation way back in the day when I was a line tech in a Chevy dealer, a 66 Corvette 427. ended up having a very low rear float setting, adjusted the float up to the sight hole and it ran perfect, Check fuel delivery to the carb and the float levels.

[Edward J.]

Re: Fresh 1967 Convertible Restoration need electrical help

Lee, Larry, I believe Bill and Tony are on the right path, I myself have seen this many times over the years It sounds like it is running out of fuel. I would look at the fuel filter and pump and maybe do a pressure test on pump Look at the spec.s but generally it is about 3to 5 lbs..

[Lee B.]

Re: Fresh 1967 Convertible Restoration need electrical help

I will check the float level when I get home tonight and let see if that works. I hope that is the problem. Here is the whole story (was on my tablet last night and could not type a whole lot). I went to pick the car up 3 weeks ago and got about 10 miles and it started backfiring and eventually cut off. I towed it back to the shop and he found out the condenser had gone bad. I picked it back up Saturday and this time made it about 15 miles before it did the same thing. While I was waiting on the tow truck (for 2 hours in the rain) the car cooled off and ran fine when the tow truck got there, actually drove it on the truck. I towed it home and replaced the ballast resistor. That seemed to help, and I might be chasing 2 separate problems. Hopefully that fixed the electrical and now it is the float level. Lawrence answered John's question last night, but the car is as follows:
327/300 hp Convertible
M-20 Trans
Restored to completely original condition with points
Original Holley Carb
One other thought Lawrence had was the date coded reproduction spark plug wires might be bad. Any thought that might be the problem?
Thanks for all the help,
Lee

[Timothy B.]

Re: Fresh 1967 Convertible Restoration need electrical help

Lee,

Go to NAPA and get a ignition coil for the car. If you have a known good coil to swap in you might try that first but IMO the coil is bad.

[Terry M.]

[Lee B.]

Re: Fresh 1967 Convertible Restoration need electrical help

Tried several things tonight. Took the working coil off my 68 GTO and put it on the Corvette. Drove it around town and sure enough around mile 9 or 10, the Corvette started sputtering and backfiring and I barely made it off the road. While I was waiting for it to cool down, I was checking the plug wires and found 3 loose on the distributor cap. I pushed them back in and the car fired right up. On the next 2 miles home, it still sputtered but was better. When I got home, I got my wife to mash the gas and yes fuel was plentiful going into the carb. Several observations, the coil was hot as hell when I got back, could not hold it, the car drove great for 8 miles, but when it went bad, it would not run at all. I am going to buy a new coil tomorrow and give it a try. Any other suggestions or ideas???

[Richard M.]

Re: Fresh 1967 Convertible Restoration need electrical help

I've been following this and have a few suggestions now that you know, kindof....that you have fuel and spark. But not conclusive it's either one yet to me. Could be 2 intermittent problems, a tough diagnosis for sure. I'm gonna rule out fuel at this time as your fuel test passed and backfiring tells me you have too much sometimes.

A hot coil is normal, as it's mounted on a hot engine. Since you changed it out you can probably rule it out. As Tim mentioned, it's always a good idea to keep a spare in the toolbox. When they fail it's usually when they get real hot. I carry points, cond, coil, regulator, misc wire bits in my '59 always.

To me, it seems you're loosing your ignition somewhere, obviously intermittently. If it's backfiring, that tells me you have lots of fuel, but intermittent spark. When the spark comes back, too much fuel built up in there to get fired off and it backfires.

Tough when it ain't broke hard as they say. Intermittent problems are a real PITA. It could be one or more of several things. I'd diagnose the electrical this way.

1- Loosing electrical due to a bad connection, fault, short, etc....namely at:
a- Starter solenoid battery connection
b- Main feed from starter to Horn Relay Buss Bar
c- Fusible Link wire plug at Horn Relay Buss Bar (It's a black soft rubber wire with a round plug on the end which plugs into the #12G Red wire to feed the entire car) (a member here a while ago fried his due to a miswire in a thread not long ago) HERE See posts 17 & 21 for pics of it
d- #12G Red wire(from c) going through the Bulkhead Connector "Twin-Lock" terminal, intermittent due to corrosion/heat(this is a very common problem)
d- Intermittent Ignition Switch or Harness wire terminal at the switch or faulty wire in the Ign/wiper harness to the ballast. (makes/breaks contact going to the Ballast/Coil)

2- If all of the above check out:
a- Intermittent Coil+ feed from the ballast, bad connection, slightly shorting top ignition shield, etc
b- Intermittent Coil- going to the distributor points
c- Bad points
d- Bad Condenser
e- And this tricky one to find....A bad ground on the distributor breaker plate or bad distributor ground(very rare)

Now, how do you rule all this stuff out.....This is what I'd do. You could physically check and eyeball each of the above. I'd do that first. If nothing is obvious, then you'll have to get into it......

Using a Digital Voltmeter, connect it up to the ballast input Pink wire(12v+), and a good engine ground. Run the meter leads so the meter is in the cabin. Go for a ride around your neighborhood for whatever miles until the car dies out, hopefully in front of your house. Keep an eye on that meter.

When it dies,
If the voltage is gone, it could be from the ballast back to the solenoid feed. You have then start probing the circuits back to the source with the meter to find the fault.
If the voltage is there, maybe bad ballast, coil, points, breaker plate ground, condenser etc.(you've ruled out a few with swapouts already)

Good luck, hope it's simple.

----
Rich

[Edward J.]

Re: Fresh 1967 Convertible Restoration need electrical help

One more thing to add to Rich's post is take a peak at the inside of dist. and the feed wire coming from coil to points, sometimes when the vacuum advance is rotating the breaker plate it can ground out to the metal plate and cause a problem as what you are experiencing. along with the ground wire inside as Rich eluded to.

[Richard M.]

Re: Fresh 1967 Convertible Restoration need electrical help

Yup, good catch Edward.

[Lee B.]

Re: Fresh 1967 Convertible Restoration need electrical help

Thank you for these ideas, as usual, will be rushing home to start working on it. Will post later tonight with what I find.
Lee

[William C.]

Re: Fresh 1967 Convertible Restoration need electrical help

"Hot as Hell" on the coil is not a good sign, the wiring in the car is set up to bypass the ballast resistor when cranking. When the solenoid is disengaged this feature is deactivated.and the ballast resistor controls the current to the coil. Make sure the wire from the solenoid is not mis-attached to a hot feed at the solenoid.