Tecumseh Surging problem

[lefty]

LH318SA-156582H

This is on a 926001-022942 Ariens snow blower

Came in for a service with some vicious surging. What I've done so far:

I cleaned the carb.
Two new after market carbs. Both still surge.
Drilled out the idle jet on the original carb.

Drilling the jet did improve things slightly. I guess I could keep drilling.

The engine smoothes out with choke. Compression test yeilds 60 psi.

I put a new plug in this and it has only run for about 10 minutes total since. I noticed the plug is a little black and has oil on it. Here's a couple pics.

https://photos.app.goo.gl/mkQy4CvnJDUPQ9FS7
https://photos.app.goo.gl/KvendZM1qRgJNsxW7

I'm at a loss on this as far as eliminating the surging. Any help is appreciated.
Thanks.

[Skywatcher]

Hi Lefty

What is the date code on the engine? I ran into several of these surging Tecumseh engines on snow blowers a few years ago where the exhaust valve was barely seating with zero or less than zero valve to tappet clearance. Cleaned up the valve faces and the seats, set the valve clearances to the upper end of factory spec and the problem went away. Valve to tappet clearance for Tecumseh L-head engines is .008" to .012" both valves. Hope this helps,

Sky

[lefty]

06263CB0072

So I think 2006?

If I remember correctly, the flathead valves wear and end up tightening the clearances? I think I filed the end of the valve to open up the clearance a bit the last time. Am I on the right track?

I don't see a compression release on the parts diagram for the engine. Would my compression results be meaningful at all to determine whether or not valves are sealing or
is a leakdown in order?

Or should I just bypass the leakdown and just check my clearances? And then go ahead and adjust?

Thanks

[38racing]

Have you tested for an air leak?

[lefty]

I have new gaskets but no, I have not. I'll check that first thing in the morning. Thanks.

[Skywatcher]

Hi Again Lefty

The date code says the engine was the 72nd engine built on the 263rd day of 2006 (September 20th). With the engine being built that late in the year, the machine itself was probably sold a a 2007. The machines I ran into would have been the same sort of vintage. The valve faces and seats showed almost no wear, so I'm convinced the valves were never set properly in the factory. Once I'd ground the valve stems shorter to get the correct clearances, the customer said the engine had never started that easily right from new.

Generally snow blowers never see many hours of use and the electric start tends to hide hard starting problems caused by improperly set valves. Check the valve clearances before taking anything apart, let us know what you find and we'll go from there,

Sky

[38racing]

I had an old snowblower with a tecumseh engine. It would start and run fine but die under any snow load. Someone suggested that it had no clearance on the exhaust valve. Turned that was exactly the issue.

[lefty]

It's definitely difficult to start. I was just attributing it to the fuel issue, or what I thought was a fuel issue. I never use the electric starts except to test them and I almost needed a nap after pulling this over 20 times before giving in to the electric start.
I'll check the clearances today Thank you.

[mr-moe]

Sometimes --- an engine will surge when it is running above rated speeds. Will act just like a carb. that's lean on fuel, but it's not a fuel problem.

Because snow blowers run at top speed to operate, that speed is mechanically set.
People like to increase that setting "to throw the snow further" that will affect how the governor operates.
Check out the max. speed.

[lefty]

It's running at about 3400 per my tach. The surging is less at lower rpm but still apparent.

I just checked the valves. I have .004 on exhaust and .006 on intake. I think the spec is .008-.012 for both. So I'm definitely out of that range.

What is the operating range? Meaning, once up to temp, is there still a minimum required clearance for operation? And how long does it take for the valves to start stretching? I ask because the surging doesn't start right away. I'm not saying it's minutes but it seems to run well long enough for you to say...oh, this looks good....then the surging starts. About 15-20 seconds when cold (going from memory but I could check that if someone thinks it's important). I would think the exhaust valve is the first to start growing but does it eat that clearance up that quickly? If so, valves may be the culprit.

Thanks.