1971 Ariens Sno-Thro 7HP dies after about 30 seconds. - Snowblower Forum : Snow Blower Forums
 
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post #1 of 8 Old 02-11-2018, 02:18 PM Thread Starter
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1971 Ariens Sno-Thro 7HP dies after about 30 seconds.

I have an Ariens Sno-Thro (100000 series?) 24" with the 7HP Tecumseh engine on it that just doesn't seem to want to run for an extended period of time. I can get the engine to start every time and it will run for about 30 seconds to a minute before starting to sputter and eventually stalling out. I've gone through the entire fuel system and I can't quite figure out what's wrong with this one. The engine will do this whether hot or cold and it will stall out immediately when put under a load, whether it be engaging the auger or engaging the wheels, otherwise it will run for about a minute. After the engine stalls, I can get it to start right back up immediately with no issues and it will do the same thing all over again. Compression seems to be good. There is no electric start on this engine and I'm not sure if it has a decompression mechanism on the camshaft but I would think it feels just like my 8HP engine. No flames out of the exhaust and no backfiring.

I've cleaned and rebuilt the carburetor, adjusted all the screws, replaced the fuel line and gaskets.

Idle air screw is at 3/4 turns from seated
Main jet is 1 and 1/2 turns from seated and I've played with this anywhere between 1 turn seated and 2 turns seated. Seems to run best at 1 and 1/2 turns.

The only thing I can think of is a fuel related issue but the carburetor is definitely getting fuel. I replaced the fuel line with that new plastic crap since that was all I could get my hands on at the time and I'm wondering if this is causing an issue. Fuel gets to the bowl rather quickly but maybe it's just not enough flow? I believe this is a points engine. Maybe there's an air leak after the carburetor somewhere that I'm not aware of? Any input? This one truly stumps me.

Last edited by FlamingSpaghetti; 02-11-2018 at 05:33 PM.
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post #2 of 8 Old 02-11-2018, 08:33 PM
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Its seems to be getting some fuel. Does it run longer at a slow speed? Do you prime each time you start it?
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post #3 of 8 Old 02-11-2018, 09:05 PM
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Just curious how did the float bowl area look when you took it apart to rebuild..any discoloration like green or brown ? and was it running OK last season...did you have to adjust your float when rebuilding and did you use a OEM rebuilding kit ...?

Also if the points and condenser are original, I have seen engines fail under load with bad points. and spark plug.. If all those are good...I would lean towards a carburetor issue though...
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post #4 of 8 Old 02-11-2018, 09:09 PM
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+1 on the points. I bet they're pitted/corroded.


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post #5 of 8 Old 02-11-2018, 09:55 PM Thread Starter
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Quote:
Originally Posted by AL- View Post
Its seems to be getting some fuel. Does it run longer at a slow speed? Do you prime each time you start it?
I do not prime it each time to start it. I only primed it once when I decided to do some work on it today. Every attempt to restart only needed a quick choke and it would stay running after opening the choke up.

Quote:
Originally Posted by Nhpyro View Post
Just curious how did the float bowl area look when you took it apart to rebuild..any discoloration like green or brown ? and was it running OK last season...did you have to adjust your float when rebuilding and did you use a OEM rebuilding kit ...?

Also if the points and condenser are original, I have seen engines fail under load with bad points. and spark plug.. If all those are good...I would lean towards a carburetor issue though...
The carburetor was pretty clean when I took it apart for a rebuild but I had ran it through the parts washer anyway. I used an OEM rebuild kit and the float did not need to be adjusted. It was spot on and level, right where it needed to be.

I did not have this machine last season, it was a trash find. When I first got my hands on it, the machine did not run at all.

That being said, I did not check the points and condenser. I pulled the spark plug out and did a spark test and saw the engine had spark so I just assumed it would run fine.

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Originally Posted by classiccat View Post
+1 on the points. I bet they're pitted/corroded.
Are these points easily repairable? Or better yet, can this be converted to electronic ignition?

Last edited by FlamingSpaghetti; 02-11-2018 at 10:11 PM.
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post #6 of 8 Old 02-11-2018, 10:14 PM
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Little challenge Here is a youtube video of the job...If you have an impact tool/ wrench you don't need to put any rope down the cylinder... Not sure if there is a electronic ignition conversion for internal coil Tecumsehs..

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post #7 of 8 Old 02-11-2018, 10:16 PM
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Quote:
Originally Posted by FlamingSpaghetti View Post

Are these points easily repairable? Or better yet, can this be converted to electronic ignition?
You can sand / file away the pitting but points are cheap to just replace; they're in the magneto module behind the flywheel.

The magneto is slotted so that it can be rotated for the proper spark advance. The timing probably won't be perfect but should be in the ballpark as long as you don't remove the magneto...if you do decide to remove it, be sure to mark the bolt position.

If you want to take it a step further and time the ignition, here's the procedure:

.

I usually do it when I have the head-off...alot easier than snaking the dial gauge through the plug hole.


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post #8 of 8 Old 02-11-2018, 10:17 PM Thread Starter
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Quote:
Originally Posted by Nhpyro View Post
Little challenge Here is a youtube video of the job...If you have an impact tool/ wrench you don't need to put any rope down the cylinder...
Thankfully I do have an impact gun. Both battery and air. I usually work on B&S engines and every time I come across one with bad points, I just convert it over to electronic since that's easily done. Never done it on a Tecumseh engine before. If it can be converted, then awesome. Can't seem to find any information on this though.
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