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John Deere 318 Onan backfiring

Jona Porter A search of the archives turned up nothing relevant on the problem with my 198x John Deere 318 w/condenser ignition.

On its first use after several weeks, the tractor started hard but worked fine until it began backfiring during operation. The revs would drop low, there would be no power, it would almost die, and then recover.

Points, condenser and plugs have less than 40 hours on them (about 2 years elapsed time).

The first thing I blamed was the gas, California changes the formulations on a regular basis. We can tell when this happens because my wife's Nissan shows the "Service Soon" light for the first 50 miles after a change.

The tank was pumped dry (using the electric pump added a few years ago to complement the mechanical) and a gallon of fresh gas was added.

Same problem, ran fine except for intermittent periods of low power and backfire popping that lasted up to 30 seconds or so each time.

My son inadvertently refilled with gas for the chainsaw, which is a 1/40 oil mixture and the tractor ran fine.

Next refill was of pure gas, and the loss of power and backfiring episodes started up again.

After adding enough oil to get a 1/40 mixture in the tank the mowing went smoothly, no issues.

As of now am totally confused.

- If the carb mixture was lean, adjusting the choke would help the engine to recover but it makes no difference until pulled out almost all the way and then the engine dies.

- The mixture smells a little rich, and the black coloration of the plugs that were replaced confirms that the mixture leaned towards rich rather than lean. The new plugs don't have heavy discoloration yet, but the mixture has to be on the rich side because no choke is needed to start in summer.

Running will with a 2-stroke mixture seems like a strong clue as to what's wrong, I just don't know how to interpret it.

Can anybody here help me with understanding why a 2-stroke mix burns smoothly but a straight gas gives me such problems?


thepumpguysc I hope I dont get abunch of backlash from this, but I'm going to tell you the truth.
OIL BURNS and CORN POPS[ethanol]
The only solution is adjust the engine timing OR add octane booster on EVERY fill-up.
FYI the ENTIRE STATE of FLA. has a class action law suit against the us gov't for the introdution of Ethanol gas. CANT WAIT to see the outcome[loose]
The sad part about it is, NOW the stations in the south are selling NON-Ethanol gas at .55c/
gallon MORE than "ethanol ENRICHED"[may contain up to 10% ethanol]
went to the gas station today and REG,ethanol enriched was 3.35 and NON-E was 3.85 and a bag was on the pump handle[out]. Must be a "delivery problem"?? right??!!



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