Old Tecumseh engine problem has me baffled

baymee(LehighValleyPA)April 8, 2010

Working on this old Tecumseh engine with a carb that still has the adjustable main jet. Changed out all the fuel and I ran it for 5 minutes to warm up the oil, changed oil, ran it some more to make sure it started easy and turned it back to the customer. Customer uses up the fuel in the tank and it stalls. Adds his own fuel and it will start, but only run for 1 second.

I figure dirt or water, so I drain the tank and bowl, and the same thing. I drain the tank, blow it dry, change the fuel line, disassemble and clean the carb, check the float, replace the needle and seat. Go to start it and same thing.

Check the governor, change the spark plug, remove the air cleaner, everything is OK. Go to start it, same thing.

When it starts, it starts easily, revs for one second and shuts down, like it's out of fuel. Loosen the jet, and fuel pours out. Jet was tried at all positions of open.

Only thing left is the coil. What do you think?

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1saxman

Obviously running out of gas - you just have to find out why.

    Bookmark   April 8, 2010 at 11:16PM
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lbpod

Try giving it shots of carb cleaner when it starts,
(you may need a helper for this one). If it keeps running,
then you've eliminated any spark issues.

    Bookmark   April 9, 2010 at 7:44AM
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rustyj14(W/PA)

Baymee: Does the carb have the bolt holding on the fuel bowl to the carb? It sounds like the teeny hole-s are plugged. I use the non-serrated end of my torch tip-cleaner, or a wire tie wire to poke in that hole. Most have 2 holes, one that looks like a speck of dirt.

    Bookmark   April 9, 2010 at 9:52AM
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1saxman

That's right. I assumed it didn't have the more modern set-up, but if it does, a particle has blocked the very small bleed at the top of that orifice bolt. Like Rusty said a soft steel wire out of a strpped wire tie is perfect for cleaning it. It is also a slanted hole. Blast it out with carb cleaner spray after rodding with the wire.

    Bookmark   April 9, 2010 at 10:13AM
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baymee(LehighValleyPA)

You guys must have forgotten my famous picture of the Tecumseh jets and the small holes :)

No, this jet is similar to the snowblowers with a turn screw set at 1 or 1 1/2 turns. I had a jet that is called a bowl nut nowadays and tried that in the carb. It ran for 2 seconds and shut down. Restarting is easy, but only runs for 1 second.

I had the carb off. There are only 3 passageways in it. All 3 are large and completely open. The adjustable jet itself, has one hole drilled in it and the number 106 stamped on the side.

Do I want to waste more time by trying a late model carb? I already see this draining my time when the shop is full of equipment. :(

    Bookmark   April 9, 2010 at 11:02AM
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rustyj14(W/PA)

Could it be the ignition coil? Seems like you have covered everything else.
These things can be maddening! And, when they make me mad, out they go, to sit in the cold and molder!
What does the spark plug checker show? Yes, you have spark, but do you have spark further along in your quest?
RJ

    Bookmark   April 9, 2010 at 2:08PM
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1saxman

'You guys must have forgotten my famous picture of the Tecumseh jets and the small holes :)'

Yes, I did. Thanks for taking it lightly. I guess I'm stumped, but I'll tell you a good one; my son in TX bought a LB 10684 w/Tecumseh 195cc. I recommended it because I like mine. So, he uses it for several years, and suddenly it stops in mid-cut. He couldn't get it going and took it to the shop, where they replaced the coil. He used it twice and it died again, this time while I was there in March. It sure seemed to have no spark, so I told him to take it back to the shop. Yesterday, he told me he never did take it back. He was going to, and tried to start it one more time. It started and apparently is running fine. As a side note, he borrowed his neighbor's Toro to finish the yard in March, also with a Tec 195. It would start but not keep running. Okay, this I know, so I cleaned the 'orifice bolt' and it worked. The neighbor, who is into restoring motorcycles, now thinks I'm an engine wizard. I think my son's mower has an intermittent problem, probably never needed the new coil, and will cut off again.

    Bookmark   April 10, 2010 at 11:19AM
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baymee(LehighValleyPA)

I happened to have another similar Tecumseh carb of known quality. Installed it and it does exactly the same thing.

I can pull the cord slowly and it kicks off, runs for one second and dies. Pull one second later and it does this over and over. Starts so easy a baby could start it.

It might have points. It's a TVS 105. Maybe a bad capacitor? The last thing I want to do is more free work, but this machine is making an ass out of me.

    Bookmark   April 10, 2010 at 7:44PM
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baymee(LehighValleyPA)

I'm bumping my own post to see if there are any new ideas about this engine.

I've gone over all the external parts, even replacing the carb with a known good carb and still the engine runs for a second and shuts down.

What could cause this internally? Condensor? Valves?

    Bookmark   April 20, 2010 at 6:13AM
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gorper99(4a)

I had one like that last year,Toro with Tecumseh.Picked up on CL for $50.00.On mine the bail wire was stretched and it was close enough to make it miss and want to shut off and then rev up.Replaced the cable and everything is OK.

    Bookmark   April 20, 2010 at 9:06AM
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baymee(LehighValleyPA)

That's an interesting option to check.

In this case, the bail is tied fast to the handlebar and doesn't move. I can pull with the strength of a baby and it starts right up each time.

    Bookmark   April 20, 2010 at 11:23AM
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rustyj14(W/PA)

How about the breather hole in the gas cap? Those leetle bugs can lay an egg in there as quick as a bunny, and clog the cap that fast! The bugs are flying about, mating, and laying eggs in any little hole!
I used to wonder when i'd see an old machine lying out in the weeds, why every hole in it was filled with mud! Until i found out about Mud-wasps, i always thought some kid had patiently filled up the holes with mud! And, your gas cap hole is just the ticket!
The whole thing goes like this: You start the machine, run it for a minute, and it stalls. So, you take off the gas cap, which allows air to enter the tank, peer in, see it is full, replace the cap. start it up, runs a bit, stalls out, you remove the cap, peer in, tank is full, and restarts--for 60 seconds--on and on! Sound familiar?
Breather hole in cap is plugged! BT, DT!

    Bookmark   April 20, 2010 at 3:44PM
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baymee(LehighValleyPA)

I'll check the gas cap too, but since it runs for only a second, I don't think so.

The owner has now abandoned the mower, so if I ever find spare time, I'll look at it again.

    Bookmark   April 21, 2010 at 6:28AM
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rustyj14(W/PA)

Gee--i was hoping to hear that the problem was solved! Don't quit now, and leave us hanging on tenter-hooks!

    Bookmark   April 28, 2010 at 6:44PM
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baymee(LehighValleyPA)

I wish I knew too, Rusty. It's sitting down at the warehouse. With a different carb, perfectly clean tank and new gas hose and having the same symptoms, I done looking at the fuel system. Maybe I'll hook up a drill to the flywheel and see if it sparks for 30 seconds.

    Bookmark   April 28, 2010 at 7:11PM
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babongo

I am dealing with the same issue on my 6 HP Tec.

I did notice that the spark plug wire was shorting to the shroud.

I tried some plastic sheathing, but could still see some sparking. Tomorrow the shroud comes off.

Also, the float bothers me on this unit. But, you swapped
the carb with a known worker.

This engine starts to rev just a bit before it dies.

Have you tried it with the governor disconnected?

Is the plug wet after it dies?

    Bookmark   April 28, 2010 at 10:19PM
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babongo

Baymee, I've been reading the Tecumseh tech manual regarding the cleaning of these carbs. Did you check for movement of the metering rod (emulsion tube)?

    Bookmark   April 28, 2010 at 11:54PM
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baymee(LehighValleyPA)

The engine revs up to full speed for just one second and dies. One funny thing....when I put on the new carb, it ran for 2 seconds before dying and then back to one second thereafter. I'll have to look at the old carb again for the metering rod.

Now that the mower is abandoned, I can throw on a primer bulb carb as long as the linkage matches. Currently the carb is under a plate with linkage and throttle cable.

    Bookmark   April 29, 2010 at 6:23AM
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baymee(LehighValleyPA)

Problem solved. This was the weirdest set of circumstances I've ever seen.

The mower is old as dirt. The owner keeps the bail wired up to the handlebar. I remember that from when it came in.

Over the years, from keeping the bail wired up, the cable stretched along with the springs in the flywheel brake assy. Everything was at the point where the ignition circuit would be grounded/ungrounded just by putting my hand on the bail to pull the cord. The cable was stretched to the point where the bail was barely ungrounding the circuit.

When I pulled the flywheel, everything was coated with heavy clay dust and the mechanism that moved the kill wire, under the flywheel, no longer moved easily. I tied the cable in one knot to shorten it, re-installed the cable, lubed the brake mechanism, bent the kill wire/spring a bit and viola, it works!

    Bookmark   April 30, 2010 at 8:43PM
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andyma_gw

Good catch. So what are you gonna do with this orphan? I rescued 2 freebies last fall. A few bolts and they were right as rain.

    Bookmark   April 30, 2010 at 10:52PM
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baymee(LehighValleyPA)

I'm going to sell it to a guy whose 15 year old MTD transmission failed.

    Bookmark   May 1, 2010 at 6:36AM
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1saxman

Wow. I'm glad you got to the bottom of that. That engine/blade control switch/bail/cable deal has caused a ton of hair-pulling on every kind of mower and is the least-understood and most-missed cause of no-run symptoms. Your experience should emphasize to all of us the importance of checking for 'fire' FIRST, including the remote possibility of cranking fire but no run fire. One of those in-line spark testers would work for this, and I think I'm going to get one today.

    Bookmark   May 1, 2010 at 10:26AM
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osbormd_gmail_com

I'm at a similar point here. If I give it 10 shots or so of the primer button and pull the cord, it will start for 1 second and die.

I've tried just about everything I can find. Changed out gas, replaced plug, replaced air filter, tried w/o gas cap, cleaned out carb and the little bolt with the needle hole.

Any other things worth trying before taking it in to examine the flywheel?

Thanks

    Bookmark   May 9, 2010 at 7:51PM
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baymee(LehighValleyPA)

Unplug the coil's ground wire and try it. Turn the motor with an electric drill on the flywheel nut. If it makes spark, you've isolated the problem to the flywheel brake linkage or switch.

    Bookmark   May 9, 2010 at 8:51PM
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backman01(nc pa)

WILL IT RUN ON CHOKE?WILL IT STAY RUNNING ON 3/4 CHOKE?
IF SO CARB IS STILL DIRTY,BOWL SEATED GOOD ON CARB?GASKET GOOD? IF ALL IS PERFECT THEN INTAKE NOT SEATING COMPLETELY,GRIND VALVE STEM DOWN. RICK

    Bookmark   May 9, 2010 at 9:40PM
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