Poulan18hp Lawn Tractor Problem

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  #1  
Old 11-29-09, 05:47 AM
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Poulan18hp Lawn Tractor Problem

Was mowing lawn, I was running out of gas. Filled up tank, went to start and all I got was backfire. Engine will not start. I have done everything I could think of:

Put new gas in- same problem
Checked Spark- fine
Checked gas flow-fine
Checked flywheel key- fine
Adjusted valves-fine
Cleaned carburetor- fine
checked fuel solenoid-fine

Briggs parts diagram shows a timing key at the end of the crankshaft, did not check that.
Also not sure how to get to it....

Help,
Sgt1166
 
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  #2  
Old 11-29-09, 07:22 AM
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To eliminate a fuel delivery problem, pour some fuel down the carburetor throat and see is it will fire off.

There is only one key that affects timing and that is the flywheel key. Engines in riding mowers rarely shear timing keys but it does happen. Possibly the backfire was hard enough to cause flywheel momentum to shear the key. Inspect key closer or pull the flywheel and replace the key.

Check compression.
 
  #3  
Old 11-29-09, 10:05 AM
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I poured gas in carb, and still only get backfire, just will not start...I did replce the flywheel key.

I am truly puzzled
 
  #4  
Old 11-29-09, 01:20 PM
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Originally Posted by sgt1166 View Post

Put new gas in- same problem
Checked Spark- fine
Checked gas flow-fine
Checked flywheel key- fine
Adjusted valves-fine
Cleaned carburetor- fine
checked fuel solenoid-fine

Briggs parts diagram shows a timing key at the end of the crankshaft, did not check that.
Also not sure how to get to it....

Help,
Sgt1166
Not sure I have seen any specs stated as "fine"
What specs did you verify (valves) and how did you verify the other items mentioned above?
 
  #5  
Old 11-29-09, 01:26 PM
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If you have the float type of carburetor....

I suspect the float stuck in the down position when you ran it out of gas and allowed a flooding of the engine = your backfire.

Check the oil for signs of gasoline. If nothing,shut off your gas from the tank, pull the plug, hold the plug wire away from anything that could produce a stray spark and spin it over a dozen times or so. Then stick the plug back in it with full throttle, gas still off at the tank and see if it will take off. If it tries a couple of times, turn the gas back on and try it with half throttle, no choke.
 
  #6  
Old 11-29-09, 06:42 PM
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Probably would help if you posted the Mfg, Model, type, code and stuff for the engine. You're really asking how long is a rope, and I will say "about that long". Have a good one. Geo
 
  #7  
Old 11-29-09, 07:26 PM
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It could be a carb problem as suggested, or it could be many things. I would check for gas in the oil, and also post engine model numbers since briggs made a lot of different 18 hp engines. I'd also like to hear a little more about the valves.
 
  #8  
Old 12-02-09, 08:01 AM
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Smile Hello

Hi everyone,

I just had this very same issue.

My in laws called me and said it was back firing badly. I cleaned the carb and it ran fine and then back fired again. then stalled.

I then cleaned the carb and adjusted it and replaced the float and it smoke pop and not run.

This thing is 20 years old and the old cast iron 12hp engines.

I struggled and struggled. I reflected back on the back firing issue and decide to pull the fly wheel.

The key was sheared and rotated 30 plus degrees off. I still

I was told intake/exhaust valves and everyhting else and it was the timing. Even had spark and gas and no go.

I replaced the key and first time crank it started.

So it has to be the timing.

Now I have also exprinced recently a Bad plug and or bad air filter as well, not a bad plug when running, but a bad plug trying to start and doing same thing in nature. I tossed a new one in and I be a fool if it didn't crank up. I have had to remove filters before and be darned if it didn't start. Same signs as described.

So the simplist things can toss a wrench in running and be right there in front of you.

Hope it helps!

Henry
 
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