View Full Version : Old gas turned to "varnish".....

06-28-2007, 12:03 PM
The situation is a 1925 Johnson A-25 outboard motor given to me by the widow of the owner. Apparently it hasn't been run for 30 to 40 years according to her.

The tank still had gas in it, but it doesn't smell like any gas I've seen. Dumped that out, refilled with new gas.

No gas flows out of the tank to the carburetor , the outlet and quarter turn shut-off are totally plugged with "varnish". When I say plugged I mean it, the varnish is the consistency of very hard wax. So the question is how to clean it out, what's a good solvent?

The good news is the shut-off to the carb was turned off so from the tank forward the lines and carb are open.

The best thing of all is after putting gas in the float bowl it came to life on about the 5th pull of the rope. But, it only runs out the gas in the float bowl then quits, no feed from the tank.

06-28-2007, 12:13 PM
I'd get a can of carb cleaner and soak it in that (outside) or if you can get a path through them then just spray it through them.

06-28-2007, 12:51 PM
If the tank is steel there's probably a lot of rust in it and that can flake off for years to come. Pinholes are not impossible. There's a lot of tricks that motorcycle restorers use to salvage as many original parts as possible including tanks. Might be worth googling for more info.

When I was a teen I used to think "40 years ago" meant something ancient. Now it just means "when I was a teen".

06-28-2007, 01:03 PM
Thanks guys.

Okay, carb cleaner sounds like the ticket.

The tank is aluminum. This one of those cool old motors with aluminum and zinc castings and the horizontally opposed cast iron cylinders sticking out the sides. I don't see anything steel, except bolts and those seem to be heavily plated, even the muffler is cast iron.

06-28-2007, 01:15 PM
Just went through it with a motorcycle that sat since '79.
In that though the carbs were a varnished up too.

carb cleaner needed a lot of scrubbing and soak time to soften the edges of the varnish, ended up mixing castrol super clean 1:1 with HOT water, then dumping it in the tank and putting the carbs in a bowl to soak for a bit.

Don't go much over 1:1, dumped extra superclean in with the carbs and it roiled (not boiled) for a while, made me nervous.
came out shiny clean though. rinse well with hot water afterwards.
what varnish was left wiped off with my thumb, or while rinsing them.

Now if I would have remembered to change or clean the hoses I wouldn't have had to pull them again to clean the needles

they came out so well, and ran so good afterwards that I took the carbs off my bike and subjected them to the same treatment.


06-28-2007, 02:14 PM
Use the 'dip' type carb cleaner, sometimes referred to as 'stripper'. It is powerful stuff and will help to remove rust or scale from any metal with a few hours' soaking. You do have to remove any non-metallic parts first. The aerosol stuff is weak by comparison.

06-28-2007, 03:14 PM
I'd be careful with the Castrol Super Clean on aluminum, it's got a fair amount of sodium hydroxide in it. There appear to be some buffers as well so it might be OK, but NaOH usually eats aluminum pretty well and on something old with some folds and cracks might be fatal.

06-28-2007, 05:25 PM
I would agree about using a dunk-type carb cleaner. Solder Seal (Gunk) makes one that is a basket in a 1Gal paint type can for the purpose. Be sure you can get parts for the carb :)

I had an old Lawn Boy 2 cycle snow blower that had a very rusty tank. I took it off and first used some hot soapy water and some gravel and gave it heck. I then cleaned the inside with acid and rinsed. I followed that with Oxi-Solv (one of those phosphate coating things). I rinsed it in water and dried it by heating gently to drive out all moisture. I followed that with a couple of coats of Eastwood's fuel tank sealant. The key, however, is all the prep work to get the internals really clean so the sealant will stick.

The sealant is nasty stuff that is acetone based and is about the consistency of Elmer's school glue. Its snow white too, so you can see what you have hit with it as you tip it around and wait for it to spread its way around the inside.

good luck!


J Tiers
06-28-2007, 11:39 PM
That "Johnson Waterbug" has another cute item you may run into trouble with.

The float is, like many old floats, varnished cork or the like... In the first place, it may be saturated and not float. And, if you re-varnish, use something that modern gas won't dissolve..... Some carb cleaners may be deadly to it.

They are neat little engines, A friend has one, and I assisted him in the rebuild. We had to pump the pistons out with grease, but they cleaned up OK and its now a good runner.

I particularly liked the opposed pistons with the bent connecting rods! An interesting solution to the problem of balance and opposed strokes.

06-29-2007, 12:55 AM
In similar circumstances (1930-ish Stewart Turner marine, IIRC) I found that dishwasher detergent worked well (dishwasher powder, not washing-up liquid).
Dissolved in near boiling water, then soaked for a couple of days, heating occasionally, carby and jets came up as new.

J Tiers
06-29-2007, 01:15 AM

Most dishwasher powders are alkaline, and may eat cast alloy parts to a greater or lesser extent.

Rusty Marlin
06-29-2007, 09:28 AM
I used to run around garage sales and pick up old boat motors, get them running and then turn them around.

I tired everything on the shelf to cut the varnish.

The NUMBER 1, absolute best thing going is....

DYKEM Solvent.

What ever that mix is its fantastic on removing gas/oil varnish.

06-29-2007, 09:55 AM
To effectively remove old "varnish" deposits you need a gum solvent. A very effective gum solvent that won't attack metals is an equal parts mixture of gum turpentine, methanol and laquer thinner (acetone). The gum turpentine can be purchased at an art supply store. It should be kept sealed as turpentine will oxidize when exposed to air, the same reaction that causes the gasoline to form gum.