Saturday, May 7, 2011

Tecumseh Primer Bulb Installation Tool

[WEDNESDAY, JULY 27, 2011: I've added a brief note on primer bulb operation and testing. Scroll way down.]

Tecumseh's primer bulbs are long lasting, but eventually they lose their resilience or they become stiff and need to replaced. Here's an installation tool made from copper pipe fittings. I know copper is not an ideal tool-making material, but this works fine and is plenty durable enough for infrequent use. Here's how it looks.

It's a 3/4" x 1/2" coupling, plus a short length of 1/2" pipe and a 1/2" cap. It needn't be soldered together; just glue it with CA adhesive.

I embellished the end of the coupling a bit on the lathe by truing it and chamfering it, but that's not essential. A coupling as you get it from the store will work ok.

Also in the shot is an old single-port bulb and its pushnut-style retaining ring. The part number of that item is 632047A. It comes with a new retaining ring. (I don't have the part number for the two-port style of bulb, but this tool will work with it too.) The mechanic's pick shown is what I use to coax out the retainer little by little.

Once you have the old bulb out, ensure that the bulb's seat is immaculately clean. Put the new bulb in place and push in the bulb and retainer with the tool. Give the tool a tap with a light, plastic-faced mallet to ensure that the retaining ring and bulb are fully seated and you're done. Here's a shot of the finished installation.

Much better. The old black bulb had lost its resilience, and would take its own sweet time to pop back out after being pressed. This new one is nice and springy.

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Addendum -- Primer Bulb Operation and Testing

A push on the primer bulb momentarily pressurizes the carburettor's main fuel well, causing a little spurt of gasoline to emerge from the main jet directly into the venturi. The carburettor has no choke, so that's what provides an enriched mixture for starting a cold engine. Excessive priming will flood the carburettor with too much gasoline -- you'll have to yank on the starter cord several times to clear the condition and get the engine to start. (If the engine has a speed control lever, set it to 'high' to help speed up the process.)

To confirm that a primer bulb is working, remove the air filter and peer inside the venturi with the aid of a flashlight. When you push on the bulb, you should see a little spurt of gasoline emerge from the jet.

It's a very reliable little system. An undamaged bulb that's firmly installed on its seat should work fine. A carburettor that won't prime with a good bulb on it has some other problem, and I wish I had a quick and easy solution to offer for that sort of situation, but I don't.

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