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Qualcast 35S carb.

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MSWilliams Fri, 14/06/2024

I have searched through the history of the forum issues but have not found specific help for a problem with  my otherwise in good order mower. The basic problem is a very rich mixture, giving me a black sooted plug after a short run, and 'lumpy running' at mid revs. The mixture adjustment screw can be all the way home and the engine will still run. The governor arm seems to be working ok. Symptoms include blue smoke, and periodic slowing of the engine which causes the regulator to open the butterfly, which results in the engine pick up with blue exhaust.

I have not yet taken the carb to pieces to check. Could this problem be caused by the level in the float chamber being too high?

Any help would be appreciated, thank you Kindest regards to all. Michael Williams.

 

 

 

Forums

wristpin Fri, 14/06/2024

Too much fuel as with a punctured float or leaking needle valve or too little air as in blocked air filter element . Try running without the filter. Could even be too little spark !!!
A pic of your carburettor would be helpful, they’ve used several types over the years. 

sparkymike Sat, 15/06/2024

See my posts on Qualcast SPP 17 S carb problems. That was also much too rich and other problems. That was the Dellorto carb. 

Mike.

MSWilliams Sat, 15/06/2024

I might have spotted the problem……I was very curious as to how the engine could keep running with the mixture screw all the way in. Looking at the pictures I took of everything, I see that two o rings have been put on the mixture screw not one as I would expect. This means the screw cannot go in far enough which would result in a rich mixture. Tomorrow I will re assemble the carb and test my theory, and will revert.

best regards,

Michael Williams.

 

MSWilliams Mon, 17/06/2024

Gentlemen,

Took off the carb, stripped it and refitted it. Found no obvious fault, but the engine now runs much better probably as good as it gets. Still curious. Starts without the choke, mixture screw all the way home. I suspect the float valve was not working as it should, it is the only moving part. Tick over is fine. Tried to buy a replacement mixture screw but the 11E model screw is not available any more. The double o ring mentioned in my previous email was a false alarm.

thank you for all the comments.