Saturday, January 4, 2014

How to fix an MTD snowblower with a fuel delivery problem

    My 15 year old MTD snowblower ran fine during my pre-season check in October but failed me in late December when I really needed it. I checked the spark plug and it looked OK. As long as it was out, I reconnected the plug wire to the plug and let it lay grounded on the engine and gave the cord a pull. There was good spark. There was no evidence any gas was getting into the combustion chamber. I would have to remove the carburetor cover to have a look at what is going on in there.

Remove the carburetor cover
1) Loosen the slotted 5/16" bolt on the top of the cover.
2) Remove two Phillips screws holding the carburetor cover to the carburetor.
3) Pull the choke knob off the lever.
4) Move the cover out of the way. This one has a key switch on it so I rested it on the wheel.
Inspect the carburetor
5) Inspection revealed the priming hose was completely broken. I removed the rubber left on the barb and pushed the end of the still good hose onto the barb. It still would not start and there was a trickle of gas coming out of the carburetor and hitting the floor. The fuel bowl would have to come off.
6) Put the fuel cutoff in the "off" position.
7) Drain the fuel bowl and the gas line beyond the cutoff. Get a jar and a curved dental pick or other right angle tool. Depress the drain under the bowl with the tool while catching the fuel in the jar.
8) Remove the bowl and needle valve. Use a 7/16" open end wrench to take off the needle valve nut under the bowl. The needle valve does double duty holding the bowl in place.

Removing the bowl and needle valve

9) Inspect the needle valve. This one looked like it might be the guilty party. There is a tiny hole, a fuel jet, that looked plugged.
Cleaning up the needle valve and bowl
10) Disassemble the needle valve. This one has a metering adjustment screw. Measure where it is for proper fuel volume. The screw on mine extended 1cm from the needle valve nut. Record that. It needs to be put back in the same position for proper fuel flow.

Be careful to put the adjustment screw back in the way it was

11) Clean up the parts.  I soaked the parts in a solvent, laquer thinner, for about an hour. An empty pill bottle works great for small parts like this. I put the cover on the bottle and jostled the parts to speed up cleaning.

That very tiny upper port is a good prospect for clogging

12) Run a wire through the ports. I stripped a multi-stranded wire and used just one of the wires. I ran it through the tiny port (it goes at a downward angle) to confirm it was clear.
13) Reassemble the needle valve. Put the needle and metering screw back in just where it was before.
14) With the gasket for the bowl and the needle valve in place, turn the 7/16" nut in till snug. Make sure the low point in the bowl lines up with the low point on the float.
15) Turn the fuel shut off back on.
16) Prime and start the machine. Mine started right up but ran slow. I turned the fuel flow adjustment in (clockwise) to get proper running speed.
17) Put the carburetor cover back on.
18) Go blow some snow.

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