Small Engines (Lawn Mowers, etc.): Tecumseh carburettors, water in the fuel, float bowl

Question
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Followup To
Question -
I have a second hand lawn mower that doesn't run very well.  Can you give me a general idea of how to make sure the carburettor is set up properly.

Thanks
Answer -
Hi John,

The large, high speed mixture screw is initially set at 1 & 1/2 turns out.  Then adjust it to give good acceleration and top speed, while not closing the screw more than you need to.  The smaller, low speed mixture screw is set at 3/4 of a turn out.  Adjust that, to give a smooth idle.  The 3rd screw, the idle speed screw, is set to give a low idle speed without stalling.  

If no change, then the carb most likely has dirt, debris or gummed fuel inside. You will need to remove the carb, disassemble it, clean all the small internal openings and blow it out with compressed air.   Probe each and every hole with a small wire.   Adding a carb rebuild kit wouldn't hurt either.  

Another possibility if the problem is fuel related: Check the gas cap to make sure it is venting and not causing a vacuum in the tank.  Also check for water in the fuel.  

Let me know how you make out.
Michael


Thanks for that.  Progress!!  It runs.

I assumed that the 'inset' screw was the high speed mixture screw, and set it accordingly.  However, the other screw is'nt really smaller, but it is fixed in position by a spring around the barrel of the thread.  Screwing it out increases the engine speed, but screwing it in doesn't reduce the revs to a gentle tickover.  And easing the throttle stalls it.

Any suggestions?


Answer
Hi John,

Some progress is good!  

The high speed screw should be on the bottom of the float bowl and the low speed screw on the side.  Some carbs don't have a low speed screw, as the jet is fixed.  The idle screw acts as a stop and limits the throttle from closing.  Clockwise increases the speed.  Look for that screw at the end of the throttle cable or lever.

Keep me posted.
Michael