# 12.5/33 tecumseh BANG BANG quit.



## phantom 309 (Jan 30, 2021)

Hello everybody,.
I just bought a looks like new 12.5hp 33" machine.
I,ve been sorting things out,
I added a new auger belt because it was choking up, and it fires snow a good 30 ft now. i adjusted the scraper blade and the side shoes and now it doesn't try to climb up over everything.
Which brings me to my main issue.
After it has been running for up to 10 mins,. it will start backfiring thru the exhaust, it will start slowly 1-2 then 3-4 bangs and quits.
I took the carb off and found the plastic float had gas in it so changed that.
Machine starts second pull and idles beautifully, throttle it up and it eats and throws really well, even the crap the grader leaves us across the driveways,. until it start the odd back fire and then it quits.
I've been working on cars trucks and equipment for 40 odd years but basically zero small engine experience.
I pulled the rocker cover off and setboth valves at .010 cold. I also ran it with gas cap loose.
Some suggestion would really help
Thanks all.


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## Shovel (Mar 26, 2019)

You could have a spark issue which happens when the engine is warm.
If the plug doesn't ignite the fuel..the fuel air mixture can be exploding in the exhaust with the random sparking.
How long doesnit have to sit before it will start back up?

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## ST1100A (Feb 7, 2015)

Also check your valve clearance. That is enough time for it to get hot enough and not allow a valve to seat properly if it is tight to begin with, and also if your ignition coil is starting to fail from the heat.


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## phantom 309 (Jan 30, 2021)

Shovel said:


> You could have a spark issue which happens when the engine is warm.
> If the plug doesn't ignite the fuel..the fuel air mixture can be exploding in the exhaust with the random sparking.
> How long doesnit have to sit before it will start back up?
> 
> Sent from my SM-A115U1 using Tapatalk


a bit of choke and it fires back up


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## ST1100A (Feb 7, 2015)

Depending on what engine you are working on .010 in is a little bit too much clearance. A lot of them are around .004-.006 intake and .006-.008 exhaust.
Your intake setting would give it a little bit of leanness and bump up your compression a little bit.


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## Preacherman (Dec 20, 2020)

So it backfires then quits then backfires again then quits??
I think the possible intermittent bad coil was my first thought, since it goes away but happens again with load on it it stalls out. But it also could be a blockage in the fuel circuit, if you had the bowl off and replaced the float obviously you set the float level right? Unless it one that isn’t adjustable, I know some are not adjustable. If it has an external fuel filter could be collapsing if it’s old. Just thinking out loud!

I swear I read those motors intake is .010 exhaust is .020.


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## 140278 (Aug 27, 2020)

when you cleaned the carb did you replace tiny green needle seat? you might? have the needle sticking closed in the old one causing a lean. running out of gas issue. 

if you replace it take a good look at the old one before removing it, you will see a ring in it around the center make sure you match reinstalling the new one as while it may not look it, they are tapered, if installed upside down the motor will flood as it won't close when the float is up to full


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## oneboltshort (Dec 16, 2019)

As mentioned above, clearance is .004

https://www.smallenginesuppliers.co...h_4-Cycle_OHV_Engines_Service_Information.pdf


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## Shovel (Mar 26, 2019)

phantom 309 said:


> a bit of choke and it fires back up


I can't see a coil cooling that fast.
I would aim for fuel starvation...Lets say you start with a full fuel bowl and all is well...but you are consuming fuel at a slightly faster rate that it can feed the carb...next thing you know you have a dry carb.
In these cases...a full tank seem let let you run longer and an inch or two of fuel in the tank makes the problem worse..
I would check for good fuel flow from the supply hose going to the carb.Use a jar to catch the fuel of course..you should see a decent stream..dribbles indicate a problem.
I have seen issues where people have installed fuel filters that were to restrictive and cause the engine to use fuel faster than it could supply it.
However with these cases the engine will usually surge for a bit before it quites.
A machine with this age is a good candidate for a fuel starvation issue from crud in the tank..fittings.. petcocks..fuel lines clamped shut from brackets..tight bends in the lines.

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## Rooskie (Feb 12, 2015)

Shovel said:


> I can't see a coil cooling that fast.
> I would aim for fuel starvation...Lets say you start with a full fuel bowl and all is well...but you are consuming fuel at a slightly faster rate that it can feed the carb...next thing you know you have a dry carb.
> In these cases...a full tank seem let let you run longer and an inch or two of fuel in the tank makes the problem worse..
> I would check for good fuel flow from the supply hose going to the carb.Use a jar to catch the fuel of course..you should see a decent stream..dribbles indicate a problem.
> ...


Exactly what I was going to guess.


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## phantom 309 (Jan 30, 2021)

ST1100A said:


> Also check your valve clearance. That is enough time for it to get hot enough and not allow a valve to seat properly if it is tight to begin with, and also if your ignition coil is starting to fail from the heat.


did you read my post,.?

The ignition coil might be my next thing to look at,. i'll have to google up on that.


ST1100A said:


> Depending on what engine you are working on .010 in is a little bit too much clearance. A lot of them are around .004-.006 intake and .006-.008 exhaust.
> Your intake setting would give it a little bit of leanness and bump up your compression a little bit.


manual says .010 cold


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## Rooskie (Feb 12, 2015)

phantom 309 said:


> a bit of choke and it fires back up


After it fires up again, what happens next?


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## phantom 309 (Jan 30, 2021)

captchas said:


> when you cleaned the carb did you replace tiny green needle seat? you might? have the needle sticking closed in the old one causing a lean. running out of gas issue.
> 
> if you replace it take a good look at the old one before removing it, you will see a ring in it around the center make sure you match reinstalling the new one as while it may not look it, they are tapered, if installed upside down the motor will flood as it won't close when the float is up to full


there is no green needle seat,.


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## phantom 309 (Jan 30, 2021)

Shovel said:


> I can't see a coil cooling that fast.
> I would aim for fuel starvation...Lets say you start with a full fuel bowl and all is well...but you are consuming fuel at a slightly faster rate that it can feed the carb...next thing you know you have a dry carb.
> In these cases...a full tank seem let let you run longer and an inch or two of fuel in the tank makes the problem worse..
> I would check for good fuel flow from the supply hose going to the carb.Use a jar to catch the fuel of course..you should see a decent stream..dribbles indicate a problem.
> ...


I do agree with you on a lot of points,. removing the fuel tank and line is on my to do list definitely,.. but i can blow snow for 10-20 mins with no issues,. it will quit whever it feels like it,.idling or pulling hard,. 1 time i started it and with in 30 sec it did the off bang then shut off,. so i restarted and blew snow for at least 10 mins,. then it quit
Just to recap,. this machine has such low hours on it the paint is only slightly worn in the chute,.
inside the carb looked immaculate.
Tank was 3/4 full when i got it,.it ran great for a short demo,. i brought it home and topped off the tank with 94 premium,.it has barely used a 1/4 tank since in two weeks.


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## phantom 309 (Jan 30, 2021)

Rooskie said:


> After it fires up again, what happens next?


It'll carry on blsting away thru nasty snow drifts or will idle just fine,. its so erratic its quite frustrating


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## Shovel (Mar 26, 2019)

phantom 309 said:


> I do agree with you on a lot of points,. removing the fuel tank and line is on my to do list definitely,.. but i can blow snow for 10-20 mins with no issues,. it will quit whever it feels like it,.idling or pulling hard,. 1 time i started it and with in 30 sec it did the off bang then shut off,. so i restarted and blew snow for at least 10 mins,. then it quit
> Just to recap,. this machine has such low hours on it the paint is only slightly worn in the chute,.
> inside the carb looked immaculate.
> Tank was 3/4 full when i got it,.it ran great for a short demo,. i brought it home and topped off the tank with 94 premium,.it has barely used a 1/4 tank since in two weeks.


Well if it quits at idle..low load etc..that seems to come back to an ignition issue as the gravity feed fuel supply will remain the same at idle or full load

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## nwcove (Mar 2, 2015)

Have a close look for any wires that may be chaffed and grounding out the ignition


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## oneboltshort (Dec 16, 2019)

phantom 309 said:


> manual says .010 cold



For Tecumseh OHV engines? I just looked through 4 sites and found my hold in your hand paper copy, all list OHV at .004 INCHES clearance, (.1016 MM)

Flat heads are listed generally as .010 INCHES (range .008-.012 INCHES)


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## phantom 309 (Jan 30, 2021)

well slightly loose valves aside,.

went out with it today,. it pulled like a little train for 10 mins the bangitty ban bang quit.
i said some bad words,..
But ,. i persevered and had an ahah! moment,. i went back to throwing snow at about 7/8ths throttle,. i tried to kill it in the nastiest meanest frozen snow bank i could get it into,. i pushed with all my might and it still kept chewing! Thru the drift into the back yard and it was pulled down good and grunting,.. but i gave up first. Dumb me now i had to back the damn thing out of there😁
So i D doosed that all folks were right with the fuel starvation track,.. i finally ran it out if fuel!
So thinking it over i'm wondering if somebody has screwed the throttle stop open,. less rpm = a richer mixture when the gov kicks in? less advance too? Is that how it works? you can't up the high idle fuel rate just low idle,. and it idles really nice,.
Now i need to investigate wheel weights and chains,. because traction is a real problem if i don't push like hell too.
The adventure will continue,. thanks to all that took time to offer suggestions, much appreciated.

motor part # is 762323
machine # is 536.881121


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## HCBPH (Mar 8, 2011)

I'm not familiar with that model so unsure if it has a Tec or some OHV engine on it. Those bangs and backfires have me head scratching. If it's running out of gas for whatever reason, it will die. Couple of quick thoughts: have you hit the primer bulb right after it dies and do you hear gas being primed? Another thing I've seen is a gas cap that doesn't vent properly. A partial vacuum can develop in the tank preventing gas to get to the engine. Try loosening the gas cap before blowing and see if it still happens. Other things I can think of is a bad gas line, a plugged fuel filter either inline or in the tank, a tank of bad gas.
Good luck.


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