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Discussion Starter · #1 ·
i picked up an older craftsman II model # 917-254611 . it's a 12hp. i think tecumsah but not sure. anyway squirted some starting fluid in throat of carb while cranking and seemed to be "blowing back thru carb. pulled plug and checked for spark ... has spark. squirted some fluid down plug hole ,re-installed plug... cranked it over and POW ! it backfired thru plug. i pulled flywheel and key is not sheared, but it seems like a timing problem. guy said it ran last fall and would not start this spring......??? any feedback on troubleshooting this is appreciated . thanks in advance
 

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could be a stuck valve? im not really sure or the keyway is in backwards making it do that
 

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Discussion Starter · #3 ·
well i just thought if it sheared and slipped some on crank it would be out of time , but it's fine. any thoughts on freeing the valve? off the cuff i'm thinking pb blaster down plug hole?
 

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Discussion Starter · #5 ·
yeah yeah i know. trying to be contructive here. i'm not a big fan of them either. i have another tractor just like this. i got this for free for parts. but it's complete, and in some aspects better condition than my runner, so if i can get it to run right..... i'll have a back up
 

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yeah yeah i know. trying to be contructive here. i'm not a big fan of them either. i have another tractor just like this. i got this for free for parts. but it's complete, and in some aspects better condition than my runner, so if i can get it to run right..... i'll have a back up
My first thought before reading your entire post, was sheared fw key or intake valve sticking, but you ruled out a sheared fw key. did you pull the head? spin the valves once opened or try to spin the valves once closed at TDC and see if they spin.
 

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may want to check valve clearances also.
 

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Discussion Starter · #8 ·
i've done nothing else other than what i posted. guy said it was fine in fall when parked then ng come spring so i'm leaning FIRST toward stuck valve.will post back what i find:thanku:
 

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IMHO, needs a carb rebuild. Had a 13hp Enduro that did the same thing, and it just needed Carb rebuilt to correct. Backfiring is due to plugged main jet or some other related passageway. Do a good soaking carb clean, and then follow all the passageways with a "shipping tag" wire. I even use spray penetrating oil with the spot tube (red)and follow the passageways with a squirt of the oil, and look for the exit of the oil.
 

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Do you have any compression? No compression, with the backfiring, strongly indicates a stuck intake valve. Easy enough to free up, especially if you pull the head.
 

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Discussion Starter · #11 ·
okay, pulled off the valve cover . intake valve is definitly hanging open.not positive if it's hanging up due to debris at valve seat or if spring is collapsed . i took 2 quick vids. they speak for themselves. tell me what you think ? be patient as they take a moment to load



 

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Discussion Starter · #13 ·
i dont see how it's an adjustment issue being the rocker is as loose as it is. i mean i could see if the required clearance was too tight and causing the valve to hang open a bit, but thats not the case here. i know it's kinda hard to see in vid, but rocker is pushing down on valve and coming completely off quite a bit. i'm thinking it's either the spring or buildup on valve seat. only reason i thought maybe the spring is it looks more "compressed" at all times than the lower exhaust valve spring does. can you make it out in pic or vid? never seen a collapsed spring to know what one looks like. thinking if it's not obvous i'll pull head. was hoping not to. do you have a vid for that. looks easy enough to pull, just want to make sure i put back together right.
 

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Do you have the Model # handy? If you want to make sure it's put back together right..take pictures, as many as you can.
 

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Discussion Starter · #17 · (Edited)
:fing20::duh: just took this off the flywheel cover, close to sparkplug..........143 406512ser 00929

is that it ?

fwiw, i did find the owners manual in the link in the stickeys and faq, but no fsm which would be nice to have
 

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:fing20::duh: just took this off the flywheel cover, close to sparkplug..........143 406512ser 00929

is that it ?

fwiw, i did find the owners manual in the link in the stickeys and faq, but no fsm which would be nice to have
can you take a pic of the entire engine?
 

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Agreed, it looks like something is holding the valve open, either a bent stem or the seat came loose. You're not missing any parts of the choke or air cleaner that might have gotten sucked in and caught, are you?
 

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Discussion Starter · #20 ·
i can take pic of engine. i can say while looking at owners manual it showed that number on the engine breakdown page only it was 152 intead of 512. tried to copy and paste here but could'nt it's on page 42.

to fcubman- i picked this up and air cleaner , engine cover were in a box. really cant say. anything is possible
 
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