# Runs strong for 5-10 minutes then sputters out.



## chapel

anyone have any suggestions for my snowblower: it runs fine for like 5-10 minutes... then it starts sputtering and dies... it'll refire for 3-5 minutes but run rough and die. Bad gas?

It's an Ariens ST724 with a Tecumseh HSK70.

It has a new carb. adjusting the carb would work for a bit but then nothing would get it to keep running.
What's a good baseline for the carb screw? Turn it all the way in and then back it out how many turns?

Found this:
http://handymanwire.com/ubbthreads/ubbthreads.php/topics/508271/Tecumseh_HSK70_runs_fine_then_


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## JRHAWK9

vapor locking?? Try running it with the cap loose.


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## chapel

I'll give it a try.


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## chapel

yep.
also it might have been low on gas too. I topped it off and it ran flawlessly for 30 minutes.


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## scipper77

I don't think running with the cap loose will help with vapor locking. 

It sounds like it could be a few things...

Vapor lock: where your fuel expands into a gas in the before it enters the carb. This results in gas (not liquid I mean) entering the carb and the carb running dry before the liquid fuel behind the vapor gets in.

Vent plugged: this is where loosening the fuel cap is telling.

Restricted fuel line: Gas is leavingthe carb bowl faster than new gas is coming in. After resting a few minutes it should start up just fine but will quickly shut off again.

Ignition coil shorting: Usually the coil works fine at first and after it heats up it begins to short out. To check this (properly) you need a spark plug gap tester. You have to check for this immediately after the engine fails while the coil is still hot. You should be able to arc across a 1/4" gap. You can try shorting the plug to ground and pulling the rope also to see if you have spark but if the gap can be made larger than the plug gap a bad coil will be more likely to arc to ground.

EDIT: Just saw that you added gas and got it running.


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## JRHAWK9

scipper77 said:


> I don't think running with the cap loose will help with vapor locking.
> 
> It sounds like it could be a few things...
> 
> Vapor lock: where your fuel expands into a gas in the before it enters the carb. This results in gas (not liquid I mean) entering the carb and the carb running dry before the liquid fuel behind the vapor gets in.
> 
> Vent plugged: this is where loosening the fuel cap is telling.
> 
> Restricted fuel line: Gas is leavingthe carb bowl faster than new gas is coming in. After resting a few minutes it should start up just fine but will quickly shut off again.
> 
> Ignition coil shorting: Usually the coil works fine at first and after it heats up it begins to short out. To check this (properly) you need a spark plug gap tester. You have to check for this immediately after the engine fails while the coil is still hot. You should be able to arc across a 1/4" gap. You can try shorting the plug to ground and pulling the rope also to see if you have spark but if the gap can be made larger than the plug gap a bad coil will be more likely to arc to ground.
> 
> EDIT: Just saw that you added gas and got it running.


Yeah, I was referring to a venting issue. I guess we always referred to it as vapor locking. My friend in HS had a '62 Falcon that would stall. He had to pull over and remove the gas cap...lol Obviously he had a gas venting issue....he always referred to it as vapor locking.


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## scipper77

JRHAWK9 said:


> Yeah, I was referring to a venting issue. I guess we always referred to it as vapor locking. My friend in HS had a '62 Falcon that would stall. He had to pull over and remove the gas cap...lol Obviously he had a gas venting issue....he always referred to it as vapor locking.


Well I suppose the negative pressure in the line from a blocked vent could cause vapor lock. I think.


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## chapel

I noticed it started to sputter when I was going uphill. I can only guess it was just low on fuel... stupidity on my part.
if the vent is plugged, do I just need a new gas cap?


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## CO Snow

Gas caps on older Tecumseh engines have a metal disc for venting and can become defective. I had a similar problem. You can replace the cap but I heated a sewing needle with a propane torch a pierced the cap with a tiny hole. Worked great.


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## chapel

There's a new cap apparently that fixes this. Does anyone know the part #?
I'm still getting some issues here and there and running with the cap loose helps.


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## Pathfinder13

chapel said:


> There's a new cap apparently that fixes this. Does anyone know the part #?
> I'm still getting some issues here and there and running with the cap loose helps.


Pretty sure it's tecumseh# 37845.


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## driz

Till you finally find one drilling a small hole in the upper side of the cap so it can get air will get you by. If it was me i would take the cap with me when I went looking. They aren't all that specific and you shouldn't have to resort to ordering one unless you are unlucky.


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## chapel

filled my jerry can with 2 gallons of gas, a dose of stabil and a dose of seafoam
I then put a dose of 'Start your engines' into the blower tank and filled it with the jerry can.

That should do it.


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## chapel

Pathfinder13 said:


> Pretty sure it's tecumseh# 37845.


got this, the threads are too thick and it won't screw on at all.
Dealer even thought this was the right part.


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## Pathfinder13

chapel said:


> got this, the threads are too thick and it won't screw on at all.
> Dealer even thought this was the right part.


thats the one that i got on Amazon. It screwed on harder for sure, but I got it on partway and works fine.
I actually slimed the threads with a little motor oil to get it going, I thought I had just got a defective one, it's weird that you got one tight too.


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## chapel

I got it from a dealer. it jams almost immediately.


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