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Old 20-01-13, 09:33 PM   #11
Alastair643
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ah i get the picture now, thanks chaps :) i have another question, my 75cc has a zenith carb on and i think the needle is worn but not sure. I am using the engine to power another engine (not firing and has all the valve gear removed) as i am using it for a compressor unit to make a petrol powered air compressor. The 75cc will run absolutely fine on its own but as soon as i put the belt on the pulley to connect the compressing unit up to it, it will not start and i don't think it has enough power so i think is the needle worn meaning the fuel/air mixture is not quite right?
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Old 20-01-13, 09:39 PM   #12
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Originally Posted by Alastair643 View Post
ah i get the picture now, thanks chaps :) i have another question, my 75cc has a zenith carb on and i think the needle is worn but not sure. I am using the engine to power another engine (not firing and has all the valve gear removed) as i am using it for a compressor unit to make a petrol powered air compressor. The 75cc will run absolutely fine on its own but as soon as i put the belt on the pulley to connect the compressing unit up to it, it will not start and i don't think it has enough power so i think is the needle worn meaning the fuel/air mixture is not quite right?
Someone please correct me if i'm wrong,

I think that this could mean that you're running too lean. Turn the mixture screw anti-clockwise a quarter turn each time, if it starts running then you may make some more precise adjustments.

The belt could be too tight, giving the engine un neccessary extra load.

Cheers,
Henry
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Old 20-01-13, 09:42 PM   #13
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well i've had the carb off and recently cleaned it out fully with a degreasing agent and fully blown it out with compressed air etc (as it wouldn't flow any petrol before) and now it's all clean it can only be on this one setting that it is at the moment because if the mixture screw is altered ever so slightly, it will not run, its running rich becasue the plug is black
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Old 20-01-13, 09:45 PM   #14
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Originally Posted by Alastair643 View Post
ah i get the picture now, thanks chaps :) i have another question, my 75cc has a zenith carb on and i think the needle is worn but not sure. I am using the engine to power another engine (not firing and has all the valve gear removed) as i am using it for a compressor unit to make a petrol powered air compressor. The 75cc will run absolutely fine on its own but as soon as i put the belt on the pulley to connect the compressing unit up to it, it will not start and i don't think it has enough power so i think is the needle worn meaning the fuel/air mixture is not quite right?
One of my Suffolks powers a compressor, I find it needs full throttle to get going, they really do not have a lot of power at low speed. You can stop them by hand (not that I ever tried that of course.....)

Your carb settings may be a bit out, had similar problems with blocked jets many a time. Worth pulling the long brass jet tube inside the carb out and making sure it's clear.

Phill.
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Old 20-01-13, 09:48 PM   #15
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well at the moment i have a nut and bolt through the hole in the flywheel nut cover and use a drill to start it so its going a couple of thousand rpm and it will run like that with throttle fully open but as soon as i take the drill off, the engine will cut out. I know they dont have that much power but at full throttle it should have enough but like you said maybe the belt is a bit tight
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Old 20-01-13, 09:49 PM   #16
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sorry, like Henry said the belt might be too tight
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Old 20-01-13, 09:52 PM   #17
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Originally Posted by Alastair643 View Post
well i've had the carb off and recently cleaned it out fully with a degreasing agent and fully blown it out with compressed air etc (as it wouldn't flow any petrol before) and now it's all clean it can only be on this one setting that it is at the moment because if the mixture screw is altered ever so slightly, it will not run, its running rich becasue the plug is black
I agree with Phil, you ought to try opening the throttle on starting. Off the top of my head the adjustments are as follows, the main jet screw, thats the one on the float chamber should be 3 quarters of a turn out, the vertical one on the top of the carb should be 1 and one quarter turn out. You need to fully turn in the screws first but be sure not to screw them in too tight to avoid damaging the tips of the needle.

I hope this helps,
Henry.
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Old 20-01-13, 09:55 PM   #18
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yeah the throttle is fully open on starting as that is the only way it will actually run when trying to run it with the belt on. I've also tried those settings you just mentioned straight after i cleaned the carb and various others i found and the engine won't run at all at those
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Old 20-01-13, 10:14 PM   #19
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yeah the throttle is fully open on starting as that is the only way it will actually run when trying to run it with the belt on. I've also tried those settings you just mentioned straight after i cleaned the carb and various others i found and the engine won't run at all at those
I set my Suffolk Colt mower to those settings and it wouldn't stay running, it would just rev up and down then die. I tried with the screws about a half turn out or less, it now runs perfectly.

Henry
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Old 20-01-13, 10:17 PM   #20
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i'll have another play with the screws and see if i get anything (when this snow eventually goes) and try slackening the belt slightly
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