Craftsman Tractor Blowing Smoke, Backfiring, and Runing Poorly

thompsdw(Zone 6)April 28, 2009

We have a Craftsman lawn tractor with a Briggs 15.5 I/C Platinum 28N707 engine. Never had any engine problems, but this year after servicing (oil, plug, and cleaned filter) - the problems began on 2nd cut after servicing. Here are the observations:

- Blows white smoke when heavy load is applied (engage blade for example).

- Backfires when idle speed is low.

- Runs very rough at low idle (but became better the longer I ran the tractor).

I did some diagnosis last night and installed another new plug. I did find that there was too much oil in the engine. It was overfilled by about a half quart. The mower ran fine at normal throttle, but would not run well at low idle (missed, almost died, etc.). The mower would smoke intermittently under load. The more I ran the tractor the better it ran and the less it smoked (even when under load). It ran fine at normal throttle for about 15 minutes up and down grades. The low idle speed operation improved over time and I was able to get the mower to run at low idle after a while. When I pulled it into the garage it "dieseled" and backfired again.

Can the oil level cause this type of behavior? I am going to do a compression test on the mower tonight, but if the fault is related to service I did (oil) - I find it strange that it mowed fine one time (full yard cut), before it really began to act up. I find it hard to believe it has lost time (shear pin) because of how normal it was running at throttle. BTW - I did NOT turn the mower over on its side to change the oil.

Any help would be appreciated........

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canguy(British Columbia)

Does the oil appear thin and smell of gasoline?

    Bookmark   April 28, 2009 at 9:51AM
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thompsdw(Zone 6)

No, the oil seems normal. I didn't literally smell the oil last night. I can do that tonight to see if there is gas in the oil.

    Bookmark   April 28, 2009 at 11:20AM
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thompsdw(Zone 6)

A couple of follow-ups. The oil appears to be normal with no gas smell. The compression tested out at ~130 psi and actually held well. I used a borescope to view the top of the piston and everything looks very clean with no cylinder gouges or marks. Guess the catastrophic failure is now behind me.

Any ideas on what to look for next? I don't know if it is a route or not, but I was going to pull the carb bowl and look for signs of oil or pluggage.

Any help is appreciated.

    Bookmark   April 28, 2009 at 6:01PM
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thompsdw(Zone 6)

Well hell. You guys/gals are gonna love this. Goes to show that you need to focus on the simple things first. Well, after not finding anything obvious - I call my wife into the garage (she mows the lawn). I say "is there any chance you used weed eater gas in the lawn mower?". She says No. I used the gas in that blue can. I say "what can?". She says the "blue can". I say "doesn't the fact that it is blue and says Kerosene on the can seem to mean anything to you?". She says "no, you shouldn't have that in the garage." Hummm says I .......... at least I am consistently wrong.

Well, that explains a lot of things at this point. Why it was so HOT (hope it didn't completely fry the internals - but they are CLEAN). :-)

    Bookmark   April 28, 2009 at 7:28PM
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esemilio(Z5 WI)

Does Kerosene burn hotter than gasoline? (I assume Kerosene is the same as Fuel Oil #1.)

    Bookmark   April 28, 2009 at 9:28PM
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canguy(British Columbia)

Kerosene will detonate, it will sound like dried peas in a can, and will really clean any carbon out. The detonation will damage the piston and head if prolonged.

    Bookmark   April 28, 2009 at 9:40PM
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esemilio(Z5 WI)

Canguy - didn't know that - thanks! Learned something new!

Would it make sense to burn, say a 4 to 6 oz of kerosene once a year to de-carbonize the cylinder head? Is that was is in "SEA FOAM"?

    Bookmark   April 28, 2009 at 10:04PM
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thompsdw(Zone 6)

It was amazing how clean the piston and cylinder were when I looked at them. Luckily she quit after it started acting up. I don't know that it was actually hotter, but it sure seemed to be.

    Bookmark   April 29, 2009 at 7:44AM
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mownie(7)

"Does Kerosene burn hotter than gasoline?" Well.......yes, but just barely. The real issue about kerosene (as a fuel in IC Engines) is the violently explosive manner in which the kerosene "combusts" after being compressed and spark ignited. The gasoline formulae are all blended to perform at a specific "Octane rating" (which relates to the "rate of burning" of that fuel blend). Higher Octane rated gasoline burns SLOWER than low Octane rated gasoline. The octane rating specifications of motor fuels are based around the design parameters of the engines which will be burning the fuel. One of the primary considerations in fueling internal combustion engines, is to make sure that the fuel combustion is not violent enough to damage the combustion chamber components of the engine. With this aim in mind, gasoline is blend of various compounds and additives so that it does not actually EXPLODE in the combustion chamber, but instead it only "burns very rapidly". Kerosene, in contrast, is not formulated to be a fuel in the average, piston type, spark ignition ICE, and so DOES NOT contain any "Octane rating improvers" or "anti-knock" compunds. Consequently, when kerosene is used as a fuel in a piston type, spark ignition engine, detonation (instead of a rapid burn) will occur at the moment of the spark. Because the crankshaft and connecting rod (of a given cylinder) are nearly (but not quite) straight up, the detonation has the EFFECT of trying to force the crankshaft to stop and turn in the opposite direction. Because the reversal cannot actually happen, the effect of the detonation on the piston, rod, and crankshaft is very much like a fencepost being struck by a sledgehammer. The piston and all the other components of the engine were never intended to withstand the forces produced during detonation. For those interested in further reading, click the link below. There is a paragraph that deals with early attempts to use kerosene as a fuel in motor vehicles. It pretty much sums up what canguy posted.

Here is a link that might be useful: Gasoline history

    Bookmark   April 29, 2009 at 10:49AM
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