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Posted by knuttle z7bnc (My Page) on
Tue, May 7, 13 at 9:13

I wish people would qualify their sweeping statements.

It is frequently mentioned that old gas is a problem. Before you can decide if old gas is a problem, know whether the engine uses straight gas that comes in the big over the highway tankers, or an oil gas mixture. If it is an oil gas mixture there will be at least 2.0% residual (50:1 ratio). If old gas is allowed to stay in an engine the gas will evaporate leaving the oil residue in all of the small openings in the engine and with blocked jets and lines, starting will definitely be a problem.

If you evaporate gas from the tanker, there will be less than 0.01% residuals. This means it will be a long time before there are residual levels where there will be an effect engine performance. Octane, hexane, and similar organic compounds are very stable compounds. It would take decades before oxidation products reached a level where they would have any effects. Some of the old enhancer like tetra ethyl lead will increase the residuals, but alcohol, like gasoline, has negligible residuals.

The other statement is that the gasoline will affect the rubber components of the engine. This depends on the age of the engine, or of the part (if a replacement). New engines are designed to handle the alcohol content of current gasoline, so the rubber and plastic parts and diaphragms will not be affected by the gasoline.

Point being if you are having starting problems with a 2 cycle engine which uses gas oil mixtures, look to gasoline residual problems, if it is a 4 cycle engine the problem is else where.

Second point if your rubber and plastic parts are a problem on an old engine (20yrs plus), replace the part with a new one. If you are having similar problems on a new engine check storage condition, and don't jump to the simple conclusion that the deterioration is caused by the gas.

Follow-Up Postings:

RE: gas

Knuttle makes some good points here. There is a fairly simple way to deal with this problem:

Run the engine dry, so that gasoline isn't left setting in the carb - particularly in the case of 2-cycle engines. Easy enough to do: with small 2-cycle eqpt, like a string trimmer, turn it upside down and dump remaining fuel, then start engine and run it until it dies. On larger eqpt., turn the in-line shutoff valve and run engine until it dies; if you don't have an inline shutoff, install one.

This post was edited by javert on Tue, May 7, 13 at 10:44

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