New Truck - Problems - help

[jlolson]

Hello All,

I'm new to this board and have been working on my new '71 LB C20 w/5.7L 350 for about several weeks now. There's a couple of problems I haven't been able to nail so I thought I'd ask here:

1) The spark wires and rubber caps near the exhaust manifold were melted but functional when I bought the truck. I just bought a new set of Duralast plug wires today and after a 10 minute drive I smelled the burning rubber. They are melting again. Do I need to buy better wires or am I getting super hot headers for some reason?

2) The truck has a new carb and I've spent quite a bit of time dialing in the idle speed, idle fuel mixture, and timing. It's an automatic 350 and idles in drive with the AC on at 550RPM and the timing is set perfectly according to the service manual. It still diesels badly when I shut it down. What else can I do?

Thanks,
Jarrod

[68gmsee]

Welcome from Texas...

For the dieseling: If your timing is set correctly and it's not overheating, I'd go to the auto parts store and buy 2 or more cans of your favorite fuel additive and pour both cans in the tank. Fill it up with good quality gasoline and do that for 2-3 tanks full. Some people prefer seafoam but I have always had good luck with Chevron or even STP.

My 68 GMC would do it real bad because of old gas and carbon buildup. After several tanks of good quality gas and a can or two of treatment it is no longer doing it... Oh, and choking it (manual choke) when I turned the ignition off helped until it stopped on its own.

I can't help on the header/plug melting problem.

[big mike71]

Are your plug wires touching the headers? if they are you need to reroute them. Also they sell sleaves to go over the wires, but I think they're pretty high dollar. Welcome to the broad and show some pics of your truck.

[rwolf9653]

For the plug wires there are different types sold. You should look at them and see which set or mix of sets works best for you. There are some that are made to be routed under the exaust manifold at the block, and there are some that are meant to be run up by the valve covers. There are covers, some are good quality and some are bad, but getting plug wires with the right boots will help a lot.
You can make your own if you feel like taking the time and youu have a good set of crimpers.

Deiseling I have never figured out myself. My 85 blazer never did it for 12 years, but then one day it started and I haven't got it solved yet.

[GruntMoanCough]

Welcome, from Spud Valley.

Like rwolf suggests, you can run a mix of straight and angle boots as required to clear your headers.

As for the run on you're getting, I'm thinking that maybe your engine's running a little warm, since you live in Arizona, the plug boots are melting and that your timing is probably set too late for the way that your engine is modified (headers, new carb, etc.)
Just my toonies worth.

[unclewatts]

You never mentioned whether you are running headers or cast iron exhaust manifolds. If you are running cast iron, then you should check to see if you have the stock spark plug wire heat shields. There are 4 of them. Classic parts sells them for $24.95 a set part#83-389 or get some at a wrecking yard. If you have headers, I would recommend what RWOLF9653 suggests.

[jlolson]

Thanks for the advice.

Re: Unclewatts and Bigmike - I'm running stock cast iron manifolds and no, they aren't touching the manifold, the boots melt in place on top of the spark plug. They aren't angled boots and there's no way to get them further away.
I'm planning on getting a performance set. Apparently you can take a blow torch to these so I hope the work http://www.accel-ignition.com/

I will also try the gas additive for the dieseling. FYI the truck has a new gas tank, new gas, new filters, I flushed the fuel lines with 100% alcohol until it ran clean. If there's any carbon it's internal and hopefully the additive will clean it up.

Thanks again

[mclairmo]

I like use BG44K to remove carbon. Use metal heat shields for the plug wire boots.

[jlolson]

Someone requested pictures... here u go... It's a great looking truck, 54K original miles, AZ vehicle so no rust. Unfortunately it sat in a garage for a long time and has a lot of mechanical issues.

[Sinister]

Nice truck!

[GunnyRob]

Have you tried the "shorty" sparkplugs?

[highperf4x4]

Post a good pic of the engine/plugs/wires.

What distributor are you running?
What size wires are you running?
What spark plugs are you running?
What temp is your engine running at?
If you're using stock iron manifolds is the metal heat shield in place?

Dieseling is caused by carbon buildup inside the cylinders. It creates "hot spots" that will continue to ignite the fuel.

It sounds to me like your plugs are getting too hot and melting the boots and this could also cause the fuel to continue to ignite after you shut the engine off. I'd check the plugs and make sure you have the right ones installed.

Installing more durable wires isn't really a solution. If something is melting your stock wires and it's not the manifolds then you have a problem that needs to be addressed. You could actually burn a hole in a piston.

[jlolson]

Sorry for the delay in my response, some really good advice in this forum. In response to the questions above:

What distributor are you running? - HEI Conversion
What size wires are you running? - 7mm
What spark plugs are you running? - Just replaced with autolite platinum
What temp is your engine running at? - reads normal on the gauge which appears to be functional.
If you're using stock iron manifolds is the metal heat shield in place? - stock ramhorn style manifolds in place. There is no heat shield and from what I can tell there should not be a heat shield (am I wrong?)

Basically those new plug wires got a little smokey at first but never melted like the old ones. I'm of the opinion some more durable wires would have prevented that at this point. I think I jumped the gun a little and assumed they would melt like the old ones.

[highperf4x4]

Ok, now that we have some info, I see 2 problems

The melted wires are caused by the distributor. This is because an HEI distributor needs and 8mm wire. If you have a high performance coil like 50,000 volt or more then you should run 8.8mm. HEI stands for High Energy Ignition. It's alot hotter and you can't use a 7mm wire.

2. You don't want to run a platinum plug in a carbureted engine. I know people do it alot but the electrode tip is just too small. They will foul easily just from a rich carb. Fuel injected motors don't have this problem as the fuel is atomized coming out of the injectors and you get a much more efficient burn. If you're burning any oil at all then you can write them off with the first oil change or two.

With your engine I'd run an AC delco R44ts. You will immediately notice the difference with the large well exposed electrode. Hope this helps.

You can run some Shell 91 octane fuel and some lucas oil fuel system cleaner to help with the carbon buildup and it may help with the deiseling. Shell premium fuel already has all the additives you'd want in your fuel. Cleaner, upper cylinder lubricant, etc and Lucas makes the hottest fuel system cleaner too.