Two topics for the price of one this month! What to do with
fouled spark plugs and how to clean and reseal gas tanks are two
subjects that come up quite regularly on the Stationary Engine
Mailing List. Both are problems most engine collectors will have
some experience with at some time or another, so some of this
information should come in handy. The original query came from one
of the young collectors on our list, and the responses were from
collectors around the world, young and old! As ever, the following
comments reflect a variety of opinions that surfaced during this
Fouled Spark Plugs
One of my -inch spark plugs is fouled. It won’t fire, but I
can see it sparking inside the bottom. Can I clean it? These plugs
have lasted a year, until I ran them in the Witte. I soaked them in
some gas, and got one to fire again …. gonna soak them all night
one day and clean them out real well.
Someone told me to soak it in ammonia -said it takes the carbon
out. All it did for me was eat at the aluminum screw terminal.
Someone also told me to use starting fluid – never did though. I
use a needle to dig down inside and scrape it out.
I have been using a long reach Maytag plug in my 3 HP headless
Witte and have not had a problem with fouling.
If you are using a 3095 in that 5 HP Witte, THROW IT AWAY and
get a take-apart plug. I NEVER could get a 3095 to run my 8 HP
Witte for more than two hours. Then had to buy a new one. The
take-apart (I paid $20) saved me LOTS of bucks over the years!
Your fouling is probably caused by carbon buildup on the
insulator. Carbon is a conductor, so now the electricity has a path
that is lower resistance than the air gap between the electrodes.
Douche it out with brake cleaner, ether or some other kind of
solvent, then with a stiff piece of spring wire (such as comes off
a street sweeper), poke a thin rag down there and wipe it off. Take
your time and do it well.
DO NOT sandblast the insulator. You’ll cause pitting in the
porcelain, and carbon will quickly build up again in the pits. DO
NOT wire brush the insulator, as a thin layer of steel will be
deposited on the porcelain, again causing a lower resistance path
for the electricity.
You MIGHT have a cracked insulator and the carbon has filled up
the crack, creating a low resistance path. In that case, you’re
screwed and it’s time to buy a new plug. By the way, Autolite
3095 plugs cost less than four bucks each. I’m of the opinion
that for four dollars it’s not worth it to beat my head against
the wall with a problematic plug. I’ve played with everything
from the $22 take-apart plugs to the cheap Autolites, and cannot
tell any difference except in the thickness of my wallet.
This is standard operating procedure for spark plugs. A lot of
mechanics aren’t aware that wire brushing a plug center
electrode insulator will mess it up royally with streaks of steel
from the brush. I have a final procedure for obstinately dirty
plugs which is A LAST RESORT BEFORE THROWING IT IN THE TRASH. Take
a pinch of saltpetre (potassium nitrate fertilizer) and sprinkle it
down into the recess around the porcelain until the annulus is
full. Gently heat the threaded end until the saltpetre melts and
coats the porcelain. Let it cool, then boil the plug in a tin can
of clean water to dissolve the saltpetre out. This treatment
oxidizes the oil and carbon buildup gunk and converts it to plain
water and carbon dioxide, leaving things nice and clean.
Unfortunately, it is very slightly corrosive to SOME porcelain
formulations and will eventually pit it – that is why I recommend
it only as a final resort. I used to use this on NGK plugs with
impunity, but it was hard on Bosch and AC. I haven’t had to use
this for about two decades, and the porcelain compositions used by
those manufacturers may have changed over the years.
Running slow, my 4 HP headless Witte tends to foul plugs pretty
well. I’ve had excellent success using a take-apart plug. Part
of each day’s starting routine is to take the plug apart and
clean it. It’s good for a whole day of running then. I like to
soak in MEK for hours, then flush out several times. Install and
Every time I visit the dentist I ask for his old discarded (but
sanitized) dental tools. The steel in these is VERY tough and works
great scraping deposits out from around electrodes.
Sealing Gas Tanks
Gas tanks are often a weak point on old engines. As the
metal rusts, the particles get into the fuel system and cause all
sorts of problems, as does old gas. But of course, fuel tanks are
not designed for ease of cleaning!
What is the best way to get the heavy congealed gas or varnish
buildup out of the bottom of a cast iron gas tank?
I prefer Acetone. I know this seems a little volatile and
extreme but it works great! It’s not the cheapest but it’s
what I prefer to get the rotten stuff out. I also use alcohol for
milder cleaning. It’s a lot cheaper and always available.
When I started working on my Ideal ‘M’ it had about
-inch of varnish on the bottom of the tank from stale gas. I found
denatured alcohol to be the best for dissolving ‘varnished’
gas and use it all the time for cleaning supply tubes on small
Denatured alcohol dissolves the gum and doesn’t harm the
running of the engine should there be some left in the fuel.
On the Ideal, I put in a quart of denatured alcohol in the tank
and would rock the engine each day to stir up the sediment. I would
dump it out when I saw the mixture getting pretty black. Then
repeat the process ’til you’re satisfied you got most of it
Even now when I start the engine, I can smell the alcohol. But,
I’ve only burned about two gallons of gas running all
I’ve done that with Maytags. I discovered a drawback: The
old gum is plastering over piles of rust chips. Dissolve the gum
and the rust starts moving around.
Then I assume you want to keep the gum in the tank?
Nope. Just a reminder that the job’s not finished when you
get the gum out, just getting started. With a Maytag, the only
effective solution is to take the top of the tank off, scrape, then
blow and rinse it out thoroughly before applying whatever sort of
sealer you may wish to use.
I would get as much gum and rust out as I can. I use nuts and
bolts as an aggregate. Then, if rust is flaking, you might try
coating the tank with Kream, a product you can buy at motorcycle
shops to line motorcycle tanks. You have to be able to
‘roll’ the tank around to coat all sides. Kream has the
consistency of melted ice cream.
I used Kream in a pair of leaking ’56 Harley gas tanks about
15 years ago. No leaks yet. It really is good stuff. The tank has
to be uncommonly clean, though, before you use it, hence the
addition of nails, bolts and chain.
Kwic-Poly is FANTASTIC. It’s a two-part epoxy that has the
consistency of water when first mixed. Pour it in and slosh it
around. It’s an exothermic curing process, so you really gotta
keep sloshing it around ’til it’s fully cured, about 10-15
minutes. The stuff seals leaks, traps and binds any loose gunk, and
One usage recommendation: Use a good degreasing dishwashing
detergent to remove oil films on the surface to be coated and use
the shop vac to dry the tank before coating. It may not be REQUIRED
but it sure will give a better result.
If you’ve got largish holes in your tank, either cover
’em with tape first or JB on some sheet metal, than use the
Kwic-Poly. You’ll end up with a tank that’s armor
I cleaned a 1926 Ford gas tank using heat from a handheld butane
torch. I’d flushed with various things to no avail. The
asphalt-like stuff was thick – I’d bet it had a pint or more of
the crud. I steamed it for an hour. I had to open the top with a
three-inch hole saw in four places. Just the right amount of heat
turned the gum to ash, which was easy to remove mechanically. I
again flushed with MEK, blew it out dry, patched the holes and
applied Kwic-Poly. I’m happy with it. I think the heat did the
trick. Perhaps a good heat gun would work, also – the heat would
not be as local. Be careful!
If you feel the need to agitate (I know I do), use nails, nuts
I use a short length of chain small enough to feed through the
cap. It’s easier to retrieve.
My favorite story is the large full base engine with cast-in
tank. My friend jacked up a tractor and bolted the base to a piece
of plywood, which was bolted to the wheel. Filled it with acid,
nuts, and bolts. Then put the tractor in gear, and just left it on
the spin cycle for a little while. No, the tractor didn’t fall
off the jackstands!
I used a pump jack I rigged up with a variable-speed motor. I
strapped the gas tank to the pumpjack arms, put a few assorted nuts
in, and filled it about 1/3 full with lacquer
thinner. Set the speed to get a nice sloshing motion and let it run
overnight. The next morning the gummy varnish was all dissolved and
the tank was clean and shiny like new inside.
There has been much said about ‘coating’ the inside of
tanks. I’m NOT in favor of doing this unless there is a problem
such as small pin hole leaks. I keep gas in my engines at ALL times
and store them in a garage. I wouldn’t think of coating the
tanks on a Maytag. Once cleaned out, you shouldn’t have any
Current list discussions are about the last shows of the
U.S. season and the first shows of the Australian season. There are
also requests for identification help on newly purchased winter
projects. I’m sure that out of this somewhere some topics will
appear that will interest the readers of GEM next
Engine enthusiast Helen French lives in Leicester, England.
Contact her via e-mail at: Helen@insulate.co.uk. Join the ATIS
mailing list at: www.atis.net.
”There has been much said about
‘coating’ the inside of tanks. I’m not in favor of
doing this unless there is a problem such as small pin hole
A lot of mechanics aren’t aware that wire brushing a
plus center electrode insulator will mess it up royally with
streaks of steel from the brush.’