My sisters Poulan lawn tractor would not start when she got it out this year. It would backfire extremely loudly and if it did start it would only run a minute or so and then stall with a loud backfire. She said the first time she tried to start it the deputy sheriff neighbor came running over as he thought it might have been a gunshot.
She never drains the gas in the fall so I was pretty sure it was gummed up and just wasn’t getting fuel. I didn’t see any rodent damage to the wiring or anything. It runs a short time on starting fluid but then stalls with a backfire. I ordered a new carburetor ($20) and it does exactly the same thing. I had suspected the fuel shutoff solenoid on the bottom of the old carb might not be working but the new carb came with a new solenoid and it acts the same way. Is there a way to bypass or jumper those wires to ensure the plunger isn’t the issue? I removed the intake manifold and covering the intake port it doesn’t seem to suck like I expected. It seems to pulsate as if it is pumping both out and then in. I am not sure if that is normal or not?
I cleaned and gapped the coil and pulled the valve cover while my sister cranked it over. The pushrods and rocker arms were working fine but I really couldn’t be sure if the valves were closing all the way. Not sure what to look for here. Is there something I can spray on the valve train just in case that is what is sticking? Thanks for any suggestions.
First, please post the engine model numbers so we have an idea of what engine you are talking about. Second, second, pull the dipstick and check if the level is over the full mark or the oil smells like fuel. Third, you can test to see if the fuel solenoid is working by feeling it between your fingers while someone turns the key from the stop to run position. You should feel it pull in. Post back with you findings.
Thank you for the quick reply, Rivets. The motor is an Intek OHV 18 hp ybsxs5012vp 274826 The engine and valves are horizontal so I don't know what they mean by OHV.
The oil level was actually low and probably has been all last season as she didn't seem to know if she had any oil around for it.
Do I just feel the outside of the solenoid to feel the movement of the solonoid? Should there be power in the wire that will hold the plunger down while the engine is running?
The numbers you gave us are meaningless for our purposes. Rivets is referring to the model, type, and code stamped into a valve cover above the spark plug.
Attached are the numbers off the valve cover. While I was there I watched the valves work as the engine cranked over and they seem to be functioning fine. I also pulled the spark plug and it was black with soot but not fouled. Because this mower was running fine when parked last fall I would guess the proplem is storage related. Maybe a mouse chewed a wire but there are no breaks visible. I did wonder if mice could have got into the muffler and plugged it so I took the muffler off the engine. It started with a shot of either but stalled with a backfire in 30 seconds just like it has been doing. Thank you again for your help.
ok sounds like you've run through your chk list when the valve cover is off one can see the the valve springs going up and down tells you valves are working thats now your problem did you by chance drain that old gas from last yr and start with fresh new stuff straight from pump also replace that fuel filter and new plug then let us know what happens from there.
While I was there I watched the valves work as the engine cranked over and they seem to be functioning fine. I also pulled the spark plug and it was black with soot but not fouled. Because this mower was running fine when parked last fall I would guess the proplem is storage related. View attachment 52287
drain gas out and start with fresh new gas
if that doesnt fix it then reset your valve clearances
if that doesnt work remove the plastic fan and screen on top of engine and use impact gun to remove the crank bolt and look in to see if the key way has shifted out of its slot changing the engine timing
one of the above should fix it, and if not, and all that looks ok, then you just got a bad carburetor and need to send it back and get another replacement.
its not all that uncommon for a new carb to be bad right outta the box
replacing the broke key way will fix your problem especially you have all new gas and usually those carbs new work quite well
#11
TylerFrankel1
I would try and check your valve clearances. My tractor wouldn't crank over (different problem but its worth a shot) and I overlooked the valves. Turns out they were something like .025 when they should have been like .004. They're notorious for getting out of adjustment on the Briggs Inteks
Thank you for all the suggestions! I apologize for my tardy response but I was away for a long weekend.
Yes, I can feel some movement in the carb solenoid when the key is turned off and on so that seems to be working.
It does have fresh gas but I have not yet changed the filter or plug. It has an Insta-fire MGD-89015 spark plug in it. What is a good number for a spark plug and what is the recommended gap?
Today I removed the crank bolt so I could see the keyway. It looks fine. The key is very square and located square in the keyway with no sign of shavings or distortion.
I pulled the plug and rotated to TDC with a screwdriver in the hole. On one stroke both valves remained closed and the valve clearance was .008/.009. On the other stroke the one valve closed at EXACTLY the same split second that the other began to open. At rest, both were ZERO valve clearance - tight! I assume this is normal?
I will change the plug and fuel filter but I really think this must be caused by a mouse eaten wire or something that is throwing off the spark? She swears it was running fine when she parked it last fall. Thanks again for all your comments and suggestions.
#13
Scrubcadet10
691043 is the OEM Briggs plug, champion 946 shows as a alternate.
with a gap at .030"
with the piston at Top dead center both valves closed, it should have the specified clearance, You only want one with no clearance as it pushes the valve down
