Vapor Lock

Christos · Mar 18, 2009

Hi everyone,

How can you diagonse and fix vapor lock? I've been having issues with my MF 135's carburator - it makes a bubbling noise and then it will backfire.

The guy at TSC said it was either too rich or too lean or the float. I set the float according to specs at 1/4".

(I replaced the condenser, coil, and points. So I don't think its that)

Whatever it is though, I know its something really dumb and if you all could help I'd appreciate it. My manuals don't have anything on troubleshooting the TSX carb for the Z145 engine.

Christos

glennster · Mar 18, 2009

is the tractor running hot? check the fuel bowl when it s bubbling, see if it feels hot. could be ignition timing is retarded, advance weights sticking, or cooling system probems, or carb set too lean. you can try and scrunch up some tin foil and wrap it around the fuel line to insulate it and see if that helps. you also may need to add some heat shielding around the carb to.

John B. · Mar 18, 2009

Make sure you sediment bowl isn't clogged up or something in the tank isn't blocking the fuel flow. I've never heard of a boiling noise come from a carb. Sounds like you hear coolant boiling.

Jerry/MT · Mar 18, 2009

When it's s easy to test, why are you assuming that your spark is good? Putting in new components doesn't guarantee a good spark. If the connections are bad, your key switch is bad, or the points are not set correctly, you won't have a good spark.
You said it back fires so I assume that you've gotten it to start. Is the timing correct? Is the firing order correct.

Vapor lock usuually occurs with high ambient conditions, low fuel flow rates, high altitudes and a fuel line that's too close to the exhaust manifold. Are these your operating conditions?

John B. · Mar 18, 2009

Make sure you sediment bowl isn't clogged up or something in the tank isn't blocking the fuel flow. I've never heard of a boiling noise come from a carb. Sounds like you hear coolant boiling.

Christos · Mar 18, 2009

Overall:
By bubbling noise its more of a putt-putt, timing not so sure of, and I"m in Ohio so its not high-altitude (the guy I asked at TSC offered vapor lock as a suggestion).

I got it to run like it was supposed to last year for 10 minutes before it ran out of gas. I"m not saying the new points/condenser were the cure-all, but I replaced them as a matter of course and I got the fat blue spark.

The thing will turn over, I just can"t get it to fire.

Christos

Jerry/MT · Mar 18, 2009

Get a large container, hold it under the carb, remove the plug from the bottom of the carb after opening the tank valve wide open. You should have fuel CONTINOUSLY gush out like a cow peein' on a flat rock. If it's intermitent, dribles, or is non existent than your fuel delivery is bad. The usual culprits are blocked screen in the carb inlet elbow, hung float(rap the side of the carb with a wooden block to relieve) clogged float valve, clogged filter or scareen in the tank valve, clogged vent in gas cap.

If you have fuel flow, FAT, BLUISH-WHITE SPARK, the color of lightning, then it's either timing or firing order IF you engine is in resaonable mechanical condition. When is the last time it ran?

Christos · Mar 18, 2009

Three years ago. The (new agco) wiring harness shorted out at 13 hours (after rebuild) so I replaced that and I got it to run for 10 minutes a year ago and I thought I had the problem licked. It did the same thing (putt-putting/backfiring sound) then too.

I had back surgery last august and I had to move home temporarily this past January so I"m finally able to try and spend time on getting fixed. Its taken this long for me to deal with it because I used to go home once or twice a month.

Vapor Lock

Christos

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glennster

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John B.

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Jerry/MT

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John B.

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Christos

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Jerry/MT

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Christos

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