'69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHING

[paul blair]

Has this engine ever run good since you have owned it?

[SRT8-X]

Originally Posted by paul blair

Has this engine ever run good since you have owned it?

Off idle it has run better than it is running now but never what I would expect from a 327 in a light truck. My '71 that had a mild 327 would run OK but never to my expectations however it was over carbed and had a 3 spd manual behind it while waiting for a built 700R4, not much expectations from that one. I know they're short on torque but these trucks are light and I've seen plenty of them that run well with a 327.

[SRT8-X]

Just wanted to reply to all those that offered help and suggestions. Unfortunately we had a death in the family and have been dealing with funerals, preparations, etc. and maintaining the normal home life so I have not had much time to work on the '69. I'm posting an update so you guys know you're appreciated and I haven't forgotten. Time off is coming next week so I'll get some wrenches turning and provide some updates then....It snowed here NW of Houston today so we're not exactly in the ideal tuning weather. When this thread was started, it was in the 90's still!

Thanks again and if you guys don't hear from me, Happy Thanksgiving and a day-late "Never Forget" to all you veterans out there!

[SRT8-X]

Just wanted to update those interested. I was running through timing again, adjusting the idle mixture screws and playing with step-up springs after checking the rockers / valves and carb floats. Both checked out leaving me stumped still. At least they're confirmed.

I was able to get Performance Distributor's tech dept. on the line and had a lengthy conversation. There were a few things they asked me to check, (EXCELLENT human communication and tech support by real people who know their products in and out and aren't afraid to talk on a normal level to customers) including the rotor casting, pick-up, stuck weights / springs, coil, voltage to the dist. (as many have suggested), ohm reading at wires, etc.

When I let them know I specifically bought the Live Wires with their 1200° sheathing for protection against headers *under header design*, he stated to make absolutely certain the wires were not coming into contact behind the primary tubes regardless of temperature and other shielding (I have installed boots near 7 & 8 which turned up tightly against the header).

Needless to say the wires were touching in spots and even though there was no arching apparent in the dark, looking from top or bottom, there was some white residue on the plug wires. I decided to go away from the clean aesthetics and give rerouting a few of the plug wires that concerned me over the valve cover and others that were tie wrapped together, I added a tie wrap spacer on each individual wire. He said this was an old trick to make sure the wires don't transfer spark to one another.

After doing this, I have successfully driven the truck for a several hours and over 100 miles without experiencing the misfire or off idle hesitation. She runs great now, it's a 327 so nothing spectacular out of the hole but fun nevertheless....now I can get to fine tuning the carb and idle mixture screws to precise settings to get all I can out of her. Note the idle is set around 650 now and idles smooth, starts with a simple key turn in all temps and has a little more lope than was noticed before. Still thinking it's a stock cam and internals but definitely more fun to cruise.

I'm ordering custom length plug wires from Performance Distributors (can't say enough good about these guys) so that none are tight and I can still run them cleanly under the header. I'll be using 6" boot shields on each plug and the Made For You Vertical Wire Looms 50-710-11 separators with attachments to the block / oil pan so they are routed away from the heat.

I am still having a bit of run-on even with the timing / advance correctly set. I'll continue to play with this and see what happens.

Thanks to all that helped, it ended up being a very simple issue.

Now I do have a dilemma, my new fuel pump is leaking oil at the mount so I'm pulling it off and hoping it's just the plate or the gasket that is a problem.

Again, Happy Thanksgiving to all and I appreciate your help once again.

[Coley]

...so it appears it was an electrical or spark related problem?

ie: you were experiencing some shorting of the spark across the headers etc when running...hence the misfire and stumbling.

Do I have this correct?

C.