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Craftsman self-prop mower primer ineffective

PorscheMeister's Avatar
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05-26-05, 12:02 PM   #1  
Craftsman self-prop mower primer ineffective


I'm not often stumped by silly mechanical devices, but this problem has me scritchin' me pointy li'l noggin.

One of my clients gave me a fairly new Craftsman (American Yard Machines, I'm guessing) self-propelled, mulching mower w/Tecumseh VLV126-502525D.

6 females in that household (3 generations), and no men. Only one of the girls had the motivation and perseverance to start that mower. I was told that after 4 unsuccessful repair attemps, under warranty, it was being replaced with an electric start unit.

Fresh gasoline, clean oil, new(ish) sparkler, plenty of good, fat sparkles, new(ish) air filter, good compression . . . It looked 'good to go'.

A few strokes of the primer bulb, and I was sure I was on to something. Countless strokes of the primer, over the years, on my 30+ year old LawnBoy . . . I'm pretty sure I can tell when the thing is actually "pushing fuel". "Stroke, stroke, stroke, stroke, stroke . . . pull, pull, pull" I quickly understood the girls' frustration. The tiniest little spritz of starting fluid (aerosol silicone lubricant was the nearest thing), and it lit right up.

I popped the air cleaner off, to have a look at the primer function. The air cleaner asm. sort of fell off in my hand. The breather hose was a bit distorted at the crankcase port end, so I'm guessing it wasn't fully seated and has been sucking trash into the intake tract. Anyway, the primer bulb shows no indication of defect. Strangely, I see nothing that looks like a conventional inlet/outlet check valve. I can't, for the life of me, figure out how the thing is "supposed" to work, nor where a check might have been left out, during assembly.

Anybody know if there is, indeed, supposed to be a check valve, and where (air cleaner housing or carb) it's supposed to be located? The parts list illustrations I've found aren't much help.

Thanks for reading, and sorry to be so long-winded.


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05-26-05, 02:56 PM   #2  
First let me say that this is the worst carburetor Tecumseh has ever designed and I've let them know that at the factory technical schools. With these carbs the float bowl is notorious for warpage and with such it will not prime. Bear in mind that common on ALL non-adjustable Tecumseh carbs that it is critical to prime properly...Using the fat of your thumb push in for one second, release for one second, 5 times. In other words, don't go to town on the primer as this has no value in getting the thing to prime. Try this procedure before you start replacing parts as it may simply be this that is wrong. Another notorious area of trouble for priming is the air cleaner gasket. Even if it looks OK replace it.

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05-26-05, 04:10 PM   #3  
Thanks for the quick reply, Mr. Mod.

I think you hit the nail on the head.

>trouble for priming is the air cleaner gasket

I knocked it back down, for a second look: The base of the air cleaner, where it mates to the carb air horn is horribly deformed (from heat, I suppose). I seriously doubt that a new air cleaner will be a permanent fix. I'll try to come up with a gasket material with better heat insulating properties. I'll also look for a simple means to duct a little cooling air at the thing. Maybe that'll keep it from baking itself to death.

(I still can't see how that primer design can possibly function without some sort of check valve. It looks like its doing nothing more than pushing air back and forth. Maybe I can find a simple solution for that, as well).

Thanks again,

P.S. A poor design is a failure only if it doesn't work AND it's expensive to manufacture. LOL

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05-27-05, 12:00 AM   #4  
The check valve is part of the design of the bulb itself, and the housing it is in. When you push it, air pressurises the bowl and forces fuel into the venturi. This pressurization only begins when the bulb is already partway pressed. When at this point, the corrugation, or fold in the bulb, seals around a part of the carb body and then the remaining air in the bulb will pressurize the bowl when the bulb is pressed the rest of the way. Kind of hard to describe.

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