Hi, fe 390. looking for a hotter plug than stock plug. can anyone give me a suggestion on this? 390, auto, stock dist. with points & condenser, stock intake, holley 4 barrel carb. 600. had problems with the stock carb. switched to aftermarket carb. just looking to install hotter plug. thanks.

 

Can you describe what you mean by "hotter" plug? What problem are you trying to solve?

If you mean, "plug capable of facilitating a higher-voltage spark," that's not so much a function of the plug itself rather than what's generating the spark. The plug gap simply has to match the spark voltage range. But there's not much value in changing this behavior on a stock engine.

 

In the past I had a 351c that required a hotter plug when I replaced the carb. Just not wanting any fouled plugs. I am currently running the original plugs I believe. 62,000 miles on it.

 

You always want to run as cold a plug as possible, not hot. In Motorcraft I'd try 42's

 

It's not about the spark.
The heat range of the plug refers to the plugs ability to dissipate heat from the electrode.
A hotter plug with retain more heat.
A colder plug sheds heat quickly.
In very general terms higher performance engines need colder plugs in order to cycle cleanly and not keep heat around that may pre detonate.
The lower performing engines need more heat to make lower cr's and slower air velocities work (clean out the garbage).
I happen to use a little hotter plug (Autolite 45) because I idle in traffic a lot and my cr is only 9.5/1
Hope this helps.

 

What do the plugs look like right now? A pic would be helpful.

A colder plug is probably a good plan for sustained high speeds (interstate highways) but a stock plug is pretty much perfect for general use. I would suggest there is something else going on there.

My 292 engine was problematic till I got the carb setup right - float level, idle mixture, etc. the plugs looked like they had been sprayed with black paint. Hotter plug didn't do anything. If you look in my album there are some shots of my plugs after adjusting float, but even before really dialing in the mixture settings with a vac gauge. Waay better. Hope this helps.

 

I had a previous thread about having the carb rebuilt. I had the stock two barrel Motorcraft on it when it started idleing badly. Had to stay in the gas at stop lights and sitting in gear. Had the carb rebuilt, ran great for a couple of weeks (daily driver 14 miles per day) then it just stalled while driving home from work. Felt like it ran out of gas. Towed it home, put a leaking carb on it just to see if it would run. It ran but I couldn't let run too long due to a bad leak. Sent rebuilt carb back to the shop, couldn't find anything wrong. Put it back on and it ran for maybe two minutes before it felt like it was choking down, then it finally died and wouldn't start again. Replace plugs, cap and rotor, points, coil, fuel pump, fuel line and finally bought a new Holley 4160 street carb. Put everything on, it ran about two minutes and choked down to finally not starting. Pulled plugs and cleaned, re installed. Ran a minute then choked down. Not starting again. I remembered a 351C I had that needed hotter plugs. Just trying to figure this thing out. I also replaced / spliced in a new wire from dist. to coil that had looked a little rough. No blue smoke from tail pipe. Just black. Seem like the best carb out of the three was the one that leaked fuel. Seems as though I am getting too much gas but I don't have enough time in the day to get anything figured out. The old plugs were black but not wet. Maybe one was showing a little moisture.

 

I put in Autolite 45's in. Made no difference
Also, I cannot keep it running long enough to try to adjust the carb.

 

Thanks for the clarification; I wasn't sure what that meant. Plug temperature should not be the difference between a healthy engine and fouling so bad it won't run. It sounds like you're facing a cracked throttle body or blown power valve. Are you blowing black smoke out the exhaust?

A Motorcraft 42 plug will be fine for just about anything you ever want to do. But realize that spark plugs are not where you should be looking. Your carburetor has a problem, but you're obviously aware of that.

 

Ok
So you're trying to fix a tuning problem with the plugs.
That's not gonna work as you found out.
Sorry I can't sit with you and work it out as I'm on vacation with very spotty connections.
But first, once you get a carb you're happy with, while it's not running, turn the idle mixture screws all the way in and bottom them out lightly. Then turn them out 1 1/2 turns. Start your tune from there.
Are your float adjusters adjusted correctly and tight? That could be a leak point.
Is your choke adjusted correctly?
Here's a page to get you started with info.
Holley Performance Products Technical Library
Also, have you checked your timing?
Have you checked for vacuum leaks?
It sounds like you have a few problems to lick.
Go at it slowly.
The guys will chime in with help.
Good luck.
Edit
Just saw that fmc400 answered.
Good

 

I have put on 3 different carbs now. Rebuilt original Motorcraft, another 2 barrel I had sitting around that has a leak, and a new Holley 4160 that I just bought.
Pretty sure that one of them should be good. Is there any other direction I should be looking at? Could the distributor be causing a no spark issue? I get spark at the coil with the wire off and grounded on the block while cranking. I am stumped.
I do get black smoke out of the exhaust.
I will turn the adjustment screws in and back them out 1 1/2 turns and try that but it hasn't been running long enough to try anything carb related.
Thanks to everyone for your suggestions
Also, points are getting a spark. Not sure on the voltage but visually I see it.

 

If the engine runs, you're getting spark. You can use a spark tester to help gauge the "strength" of the spark, but if you're blowing black smoke, that's a sign that you're dumping fuel. I'd check for a blown power valve and make sure that the float is set correctly. Do you see fuel pooling in the intake?

Also check choke and timing. It sounds like TH and I are saying all the same stuff. You've got a laundry list of things to check.

 

I'm with TH and FMC400 on this. I say its timing. The fact that you have had 3 different carbs on there and they have done the same thing leads me to think this. Have you checked the timing?

 

I see fuel moving thru the clear fuel filter.
It wants to start but just wont. I agree with you all. I mentioned that the original carb was rebuilt and it ran fine for about two weeks. Out of the blue it just stalled and needed towed home. Now all of a sudden I am having these issues.
Have not check the timing. Won't run long enough.

 

I've never experienced a timing jump out of the blue. Was running perfect after carb rebuild. I guess I need to check the timing. I did experience a carb backfire with flame yesterday while cranking it for about 10 seconds. Sorry, I would have mentioned it but forgot.