Another baffling Tecumseh engine problem on a snowblower

12 years ago

My friend left his 40 year old Ariens, with a 4HP Tecumseh, out in the recent ice storm. It ran well up to that point.

He changed out the gas in the tank and then in the bottom of the carb and it was a no-go. He called me to look at it and I didn't find any water in the tank or the bottom of the carb. The spark plug was wet and I thought that would be the fix.

He called me later and said it wasn't the plug.

I bought it home and suspected that it might be electrical because it attempts to fire and might go 2 revs and then dies. These old units are not easy to take apart to check anything.

Checked the spark with a tester. Jumps a 3/8 gap consistently and bright blue. Point gap perfect, all ignition parts look good. Flywheel key good. Pulled the head and both valves are opening fine and the compression release is working. Didn't check the valve lash because the engine was running fine before this. Took the carb apart and cleaned all the orifices and jets. Put it all back together and just knew it would start. It didn't.

Symptoms are the same. Attempts 2 revs and quits, gasps, and sometimes kicks back like a timing problem. Carb cleaner in the carb doesn't make it start any different.

I can't think of any other exterior motor problems. Coil is under the flywheel. Used my own good gas after thoroughly drying out the tank and carb.

Any thoughts, please?

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Comments (8)

loger_gw
12 years ago
1. Did you check that the CarbÃ¢ÂÂs needle seat is not stuck or seat swollen??

2. With the kickback and age, IMO at least ck the valve clearance.

3. Did you lightly dress the points, even with good looking fire there could be small trash affecting contacts/timing?

4. The Tecumseh Engs are very Picky Eng compared to B&S and Specs that makes them Tuff.
tomplum
12 years ago
Out in left field- do we have a valve that is just sticky enough not to return as quick as it needs to, loose valve seat or possibly enough ice in the muffler to plug it? What do you expect for free advice? ;)
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baymee
Original Author
12 years ago
When I had the head off, everything looked good, but the sticky valve idea is a good thought. I didn't check the valve clearance because it worked well in the past and the valve rose in the compression release phase.

I'm wondering if something inside broke at the exact time it rained.
loger_gw
12 years ago
1. Did you check the compression to see if it would climb per stroke? I doubt it would climb to an acceptable level if you have a sticking valve.

2. What could the weather have affected if no moisture was present? But you mentioned rain! Where could rain water have collected and expanded to cause a problem?

3. Would freezing cause enough contraction that some carbon c/h turned loose to cause resistance?
baymee
Original Author
12 years ago
The compression was 100#. I was going to give up on Thursday, take a loss, and give it back.

The large-gap spark tester would produce sometimes a spark every revolution, and then would skip some, and then every rev.

I decided to go over the ignition with a fine tooth comb. Removed the head and installed a dial gauge. The points should open at .89MM btdc. Used some flexstone on the points and gapped at .020 Brought the piston around and the points opened about .070 btdc, close enough. I adjusted them to .89 btdc.

With the coil tester, I checked the coil (under the flywheel) and condensor. Put everything back together and it started.

Maybe the water (3" ice storm) made corrosion on the points ?? I didn't find the problem. It sparks more consistently now.
ericwi
12 years ago
Intermittent failure mode is the hardest to find and fix. Life would be simpler if things would fail completely, and stay failed. Maybe you removed and re-attached a wire, and that action got rid of some corrosion, making a better connection. Or maybe the gremlins don't like being left out, exposed to ice and rain.
loger_gw
12 years ago
Good Work! Plus, more patience than I w/h with a Tecumseh today.

I took some whippings from a few Tecumsehs in the 70s. We had all types of special equipment related to troubleshooting Tecumsehs as mentioned vs ever needed on B&S. The good part was that we d/n see as many Tecumsehs with problems.

I know the feeling of wanting to load it up vs the trial they can put you through. I welcomed a challenge from a B&S vs a Tecumseh. I would load a donor Tecumseh for scrap quick if a routine checkup d/n fix it. Strong Engines Though!!
ericwi
12 years ago
I have another guess, regarding the cause of engine not running. Some component in the ignition system, perhaps the coil, got wet, and failed intermittently, due to moisture. You brought the engine indoors, and warmed it up to room temperature. Eventually, the part dried out, and began to function as it was designed. Just a guess, but that would explain why the engine came back to life after a few days of tinkering.