I was curious about plugs and plug recommendations. The heads I have on the Bronco were set up from the factory to have a really high lift, high rev solid lifter cam. The springs that came with it were enormous and tripled up. The manufacturers website had a plug recommended for the heads. I am running a much more mild roller cam with the heads.

That being said I am still having some run on problems after the motor is shut off and I am at 10° BTDC on the timing. So I am curious if the plugs are too hot and causing this issue?

I also read something about the alternator feeding back and causing this problem as well. There was something about adding a diode to the wiring to stop it from doing this.

Comments/suggestions??

 

If you have one of those HEI distributors I would add an ignition relay.
Once it opens there is no way for power to get to the coil.

Look at the plugs.
There's likely no problem going to a colder plug.
See if it helps.
Check them in a couple of weeks and see of they need to be hotter to stay clean.

 

Are the DSII's hall effect? Thats what I have on it now.

The stock setting for the timing is 8° BTDC as far as the sticker under the hood claims. James' 400 says 6° BTDC. I dont know if I should go with less advance than 10° with the cam or not. The idle is set fairly low now. It was around 800 RPM. Now for some reason it has settled to about 600 RPM. So I am pretty sure the throttle plates arent open too much at this point. The run on isnt awful, but nevertheless it's hard on the motor and more than I would like.

Does more or less advance cause run on? Seems like it would be less to me.However, once the key is off there shouldnt be any power going to the dizzy so it shouldnt be lighting the fuel. It doesnt rattle or ping under acceleration. 12° BTDC gave up some pinging under acceleration so I went down to 10°.

An article I read was claiming that hot plugs have less ceramic than a colder plug. A colder plug having more ceramic will dissipate the heat better and not contribute to the run on syndrome as much. Thats why I have been wondering if the plugs for the heads were too hot. The idea that the heads were equipped from the factory to deliver a lot more radical performance sort of lead to me think that maybe they were a hotter than average plug.

 

In a hot plug the ceramic pocket goes deeper into the plug and the path heat has to travel is longer.
With a cold plug the heat is carried away to the head more directly.



The only effect timing has on 'run on' is how hot the combustion chamber runs.
Like you said, the ignition is off.

Illustration from; NGK Spark Plugs USA

Spark Plug Facts

 

Jim, that link was extremely informative. Thank you for posting that!

 

I agree - a colder plug can't hurt and may well help. But, that doesn't mean I volunteer to change them. Lemme see - change plugs with those headers on or replace the rear seal? Close call.

 

The electrode has to be really hot to ignite the charge all by itself.

You can forget about whatever 'stock' timing settings either you, your buddy, or any of us have.
You have non stock ignition, heads, cam, pistons, carb, etc...
Set the distributor for whatever gives best performance without detonation.

Use a hotter or cooler plug to adjust how it wears.
You don't want the electrode melting (too hot) or the ceramic insulator so dirty it allows voltage to bleed off (too cold).
There are extreme pictures in most generic manuals.

 

James doesn't know how difficult it is yet.

I will have him help me with it. He has every kind of tool there is so it might be a little easier this time. I will make it happen one way or another. He has a collection of wobble , wiggle and flexy extension stuff.

 

You had to buy shorty plugs for that setup, didn't you?

 

Yeah, a regular length plug will put the boot right on a header pipe.

I sent an email to NGK to get a cross for the Accel plugs and find out what letter/numbers designate a short plug in there coding.

 

We went through this in your thread when you first fit up those headers.

Here's the key again.
http://www.ngksparkplugs.com/techinf...tnumberkey.pdf

 

Thanks Jim! I saved it to my favorites this time.

 

Lets use the key and figure out the cross here as far as what is what.

These are the NGK plugs a generic cross reference says cross with the Accel 276 and 276S. The "S" designates "short".

• NGK UR4
• NGK 5950
• NGK BPMR6F
• NGK 1270
• NGK BPM6F
• NGK stk 6630

 

I got a call from James on New Years Day saying he was just calling a friend to wish them a happy new year. So, I'm supposed to bite my tongue and let a friend of mine walk into that buzz saw? Yeah, right!

 

The "M" designation is the compact.So the BPMR6F is a compact. The 6 seems to be the common heat range. I am trying to decipher some of the others on the list also. The BPM6F is the same, but non resistor. That may interfere with the radio so it's out.

I need to find out what Accel's heat number is in their coding.