Fouled Plugs!!

[drolston]

Took the '41 coupe on a 300 mile out-and-back trip this past Saturday, almost all on Interstate 64. I ran 65 to 70 mph there and got 16 mpg. Engine temp went up from the usual thermostat 170 degrees to about 180, and 195 going over Afton mountain, a climb of about 1200 feet over 4 miles. Ran 55 - 60 mph on the way back and got 17.5 mpg; temperatures about 5 degrees lower. Pretty good; but not without incident.
The last 10 miles to my destination included coming down the Afton mountain grade at over 60 mph but very little throttle and then a few miles through traffic in Staunton. It stumbled a little but no great concern.
Then I parked on a steep hill, facing uphill. When leaving about an hour later the engine started okay but was missing terribly. Like, no way it would get over that mountain. I limped into a shady spot at Sheetz and discovered that three cylinders (3, 5 & 7) were getting spark, but not firing. Replaced those wet and black NGK B6HS plugs (1/2 reach for Offy heads) with new NGK B-6L (3/8" reach). It ran much better, like on 7 cylinders instead of 5, and after half an hour at highway speed was hitting on all 8.

So, why did the plugs foul so easily? Maybe sitting on the hill allowed fuel to spill over from the three carbs into the manifold, and flood some cylinders?

I need to get back to plugs with 1/2" reach. Is there one that is hotter than the NGK B6HS? Any brand, as the NGK B6HS is now obsolete. Any other suggestions on how to avoid fouling?

 

[38 coupe]

I suspect part of the reason is the low throttle high speed run down into town followed by low speed driving. With little to no air moving through the engine at highway speed you can get a lot of un-burnt fuel going through the cylinders. Driving around at low speed will not clean all that out. Do you have idle circuits in all three carburetors? If yes, that is a lot of fuel with no throttle at 60 mph. The old "Italian tune-up" method for muti-carb engines may be your friend...

 

[solidaxle]

The lower the NGK plug number the hotter the plug which is opposite from Champions. I have found the NGK plugs to better then other brands for a Ford flathead.



It could be your fuel pressure is to high or float needle valve is not operating correctly.

 

[drolston]

I suspect part of the reason is the low throttle high speed run down into town followed by low speed driving. With little to no air moving through the engine at highway speed you can get a lot of un-burnt fuel going through the cylinders. Driving around at low speed will not clean all that out. Do you have idle circuits in all three carburetors? If yes, that is a lot of fuel with no throttle at 60 mph. The old "Italian tune-up" method for muti-carb engines may be your friend...

The end carbs do not have idle circuits. I am not sure what an "Italian tune-up" might be. May adding some olive oil to the gas?

 

[drolston]

The lower the NGK plug number the hotter the plug which is opposite from Champions. I have found the NGK plugs to better then other brands for a Ford flathead.



It could be your fuel pressure is to high or float needle valve is not operating correctly.

The floats are not sticking and the fuel pressure is regulated at 2.5 psi.



I do not find a hotter plug at NGK with 1/2" reach. The NGK B6HS is obsolete, as is the hotter B5HS. The listed replacement is the BR5HS, but that is a 5,000 Ohm resistor type plug, which I cannot use with stock Flathead ignition.

 

[Tim Ayers]

NGK B-4L's & B-6L's are commonly used in flatheads of all types.

 

[solidaxle]

I would check the float height, just to confirm the fuel level is not too high. After that, check the spark once the coil is warmed up, if all good, install new plugs with proper gap.

 

[drolston]

NGK B-4L's & B-6L's are commonly used in flatheads of all types.

Quite true, but they are 3/8" reach; fine for stock heads, but for the Offy heads I am looking for plugs with 1/2" reach. Even that leaves the plug a bit more than one thread from reaching the bottom of the plug hole in the head.

I made it home using B-6L to replace the fouled B-6HS but having the plug shrouded by over 1/8" inch is not something I want to run with, long term

 

[drolston]

I would check the float height, just to confirm the fuel level is not too high. After that, check the spark once the coil is warmed up, if all good, install new plugs with proper gap.

I will check the float height, just to be sure the float hasn't leaked and dropped down a bit.

Do you know of a hotter plug with 1/2" reach? All plugs were have proper gap at 0.025"

 

[tubman]

Quite true, but they are 3/8" reach; fine for stock heads, but for the Offy heads I am looking for plugs with 1/2" reach. Even that leaves the plug a bit more than one thread from reaching the bottom of the plug hole in the head.

I made it home using B-6L to replace the fouled B-6HS but having the plug shrouded by over 1/8" inch is not something I want to run with, long term

We had an extended discussion about plug fitment with Offenhauser heads on this very forum a couple of years ago. I think the consensus was is that there is no direct match with any production plug made and that proper solution was the next longer plug and a spacer.

 

[drolston]

I found a source for the discontinued NGK B-5HS, which is only a little over one thread from reaching flush with the chamber. Hopefully the hotter range will avoid recurrence of fouling problem.

If I wanted to go with the spacer approach, what plugs might I try?

 

[tubman]

I found a source for the discontinued NGK B-5HS, which is only a little over one thread from reaching flush with the chamber. Hopefully the hotter range will avoid recurrence of fouling problem.

If I wanted to go with the spacer approach, what plugs might I try?

I don't use Offenhauser heads, so I hesitate to make a suggestion. I believe it was "flatjack9" who came up with the proper combination.

I apologize if I'm wrong about that.

 

[Bored&Stroked]

The spacers should be made out of solid copper bar stock - for good heat transfer. You can buy the bars at McMaster Carr. If I'm doing this, then I setup the spacers to run 3/4" reach plugs.

There are a TON of plug options in 3/4" reach - including all sorts of heat ranges. This is one reason that Edelbrock changed their head patterns to use 3/4" reach plugs (sometime in the last 10 years). I don't know if they now use 3/4" reach plugs on ALL their flathead heads, but they definitely have them on the block letter ones.

I would download the NGK PDFs for plug availability and it will give you all the information you need. You cannot run a 'projected tip' plug in almost every head (excep the Edmunds where they moved the plug location).

Also, stick with non-resistor plugs - they deliver a lot more spark energy and help prevent "spark jump" on our early distributors.

 

[alchemy]

Pretty sure the term Italian Tuneup means to take it out and floor it. I recently took an OT pickup that usually gets only around town driving on a long distance at interstate speeds. Did wonders for how the truck runs. I’m guessing it burnt some crap off the plugs in it too.

 

[Tim Ayers]

Pretty sure the term Italian Tuneup means to take it out and floor it. I recently took an OT pickup that usually gets only around town driving on a long distance at interstate speeds. Did wonders for how the truck runs. I’m guessing it burnt some crap off the plugs in it too.

Sounds not politically correct (LOL), but back in my Alfa Romeo days, most manuals instructed you to run the car hard in 3rd-4th gear to do exactly that; blow out some of the cob webs.

Most Italian motors are built to rev, so I can see how low speed is not good for them.

 

[Zeke3]

Pretty sure the term Italian Tuneup means to take it out and floor it. I recently took an OT pickup that usually gets only around town driving on a long distance at interstate speeds. Did wonders for how the truck runs. I’m guessing it burnt some crap off the plugs in it too.

That is my understanding of the phrase also.

 

[alchemy]

The term isn’t related to the people, it’s related to the cars. Who wouldn’t want to floor a Ferrari?

 

[Tim Ayers]

The term isn’t related to the people, it’s related to the cars. Who wouldn’t want to floor a Ferrari?

Totally and, yeah, I hear you.

Unfortunately, not many Italian cars around. Those that are, tend to spend some time at the shop.

 

[drolston]

To wrap up this thread, - Is there anything I can do to restore the fouled plugs to useful life? Like maybe burn off the black stuff with a propane torch?

 

[Tim Ayers]

To wrap up this thread, - Is there anything I can do to restore the fouled plugs to useful life? Like maybe burn off the black stuff with a propane torch?

https://www.amazon.com/Pneumatic-Spark-Plug-Cleaner/dp/B004SBBNX0?tag=atomicindus08-20

These type of spark plug cleaners were very common. They blast the plug with a fine abrasive.

Since the NGK plugs I use are relatively inexpensive, I just replace them.

I'm curious if others had luck cleaning them with a brass tooth brush and sometime of solvent.