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I replaced the carb on my ST724 and thought I had it dialed in, but not after using t for awhile. Once it is fully warmed up (I have been using it for 10+ minutes) at WOT it will stall as soon as a heavy load is applied that requires the governor to "throttle up". It will NOT restart by hand at WOT, but will restart by hand at a lower throttle setting. Also, if you "throttle up" quickly it will stall.

I have been closing down the high speed jet thinking it is running too rich. Is this correct ? It seems to idle fine so I have not touched the low speed jet.

I know I need to check the valve clearance, so should I just put off tweaking the carb an further until I do that ?
 

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Not starting at a higher throttle setting makes me think the main is too lean, not too rich. Lower setting are on the idle circuits . . . Failure to take load is also consistent with lean.

Could also be a bad carb. What was the problem that motivated you to replace it? You could always clean the old one and try that again as well . . . .
 

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in my tweaking of the carb the low speed screw should also be adjusted, im not talking about the idle speed set screw sitting beside the throttle plate linkage.
on a warmed up engine, at wot adjust your high speed , when it sounds good lower throttle to just before kill switch and adjust your low speed. bring it back up to wot again and use slight increments in either high or low speed screw to achieve proper mix. at wot, and maybe everything below wot, carb uses both jets to achieve fuel mix
imo, ymmv
 

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Discussion Starter #4
Not starting at a higher throttle setting makes me think the main is too lean, not too rich. Lower setting are on the idle circuits . . . Failure to take load is also consistent with lean.
I am sorry, I am not following you. Too lean on the high speed jet or too lean on the low speed (idle/primary) jet.

Could also be a bad carb. What was the problem that motivated you to replace it? You could always clean the old one and try that again as well . . . .
I am pretty certain the carb is good. The old one had a sunken float. A new float and carb kit cost cost more than the replacement.
 

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Discussion Starter #5
in my tweaking of the carb the low speed screw should also be adjusted, im not talking about the idle speed set screw sitting beside the throttle plate linkage.
on a warmed up engine, at wot adjust your high speed , when it sounds good lower throttle to just before kill switch and adjust your low speed. bring it back up to wot again and use slight increments in either high or low speed screw to achieve proper mix. at wot, and maybe everything below wot, carb uses both jets to achieve fuel mix
That is what I am struggling with !
 

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I am sorry, I am not following you. Too lean on the high speed jet or too lean on the low speed (idle/primary) jet.


I am pretty certain the carb is good. The old one had a sunken float. A new float and carb kit cost cost more than the replacement.
Too lean on the high . . .

And cheqper is not necessarily better . . .

- Tim
 

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Have you done a compression check on the motor. With full throttle you may not be getting enough suction of fuel & air, to start. With partial throttle the position of the throttle blade may help with enough to draw the mixture in. I've seen when Tecumseh's have really poor compression, the plug will be bone dry, not enough of vacuum to draw the mixture in.
 

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Just a thought! I had a 7 Snowking doing similar things. After a year or 2 I found some drag marks on the flywheel. Adjusted the air gap and all better... Just a thought!
 

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Maybe I missed it, but assuming this is a TEC engine I didn't see where the jets were adjusted (assuming this is an adjustable carb). Pulling this off the top of my head so forgive me if it's not quite there. IIRC the low speed jet (by the throttle plate) is turn it in all the way then out 1 1/2 turns. High speed jet (bottom of the bowl) is turn it all the way in then out 1 turn. On the low speed jet, start the engine and when the choke is off turn it in till the rpms start to fall, note that position then reverse and the rpms should increase then eventually start to fall off and note that position. Split the difference and that should be your low speed setting. Next run the engine and do the same thing with the high speed jet on the bottom of the bowl.


If that is set then you can go onto your next steps in your check out but if the carb isn't adjusted right then none of the other tests will be valid.
 

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Maybe the carb gasket is bad. Check by spraying starter fluid or wd40 at the base of the carb, If the engine surges (when the engine is running as you do this) the gasket is bad.
A bad gasket is sucking air and not fuel and that for sure won't run.
 

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Could be an air leak . Manifold to block, carb to manifold gaskets . With engine running, spray [ spray bottle, not hose ] water on gaskets, if engine briefly speeds up, you have air leak, engine speeds up when leak is sealed by water .
Not common, but they do happen when vibration loosens bolts .
 
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