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Discussion Starter #1
I have a fc420v 14 hp on a 36inch hydro scag mower. The mower will only start when the throttle position is dead center. On the carb the throttle blades are barely open. It idles great until it warms up then dies. It will also die if you give it more throttle seems to be dumping too much fuel.

-has new fuel
-new plug
-spark seems good
-I confirmed valve lash is .06

I have removed the carb several times cleaned all the parts and passage ways. On the last cleaning i used an air compressor blowing everything out. But is still will not allow me to throttle up.
 

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The butterfly needs to open up or you are choking the motor check the linkage to make sure its hooked right sounds like you have it in the the wrong hole
 

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Discussion Starter #3
maybe my original post wasn't too clear sorry i'll try again, if i open the throttle all the way engaging the choke the motor will not fire(throttle blade completely open). If i move the throttle to the middle so the choke blade is open and the throttle blade is open slightly it will idle for a few mins
 

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Discussion Starter #4
I ran a leak down test on the cylinder was 20% leakage so it's pretty good.
I checked lash on the valves again one of them was off by .01 didn't make much difference.
I adjusted the governor that seemed to help a little but i'm still not able to throttle up or start with the choke on.
I checked and cleaned the plug again set to .30


tomorrow i'll get a spark tester and try and put up video that may help you guys see what it's doing

Thanks for you help
 

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It really sounds like a carburetor problem to me. From your description of the problem, it sounds like it's only metering fuel through the low speed circuit of the carburetor and that you are getting nothing through the main or high speed circuit. If the carburetor was dumping an excessive amount of fuel, you should be able to get at least some throttle and speed out of the engine, before is chokes down and dies. From your description, it's running way to lean and as soon as you open the throttle, the engine dies, from lack of fuel.
 

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i tried spraying carb cleaner into the carb when i throttle fast but it kills the motor
While carburetor cleaner may work to prime the engine, it rarely works good to run an engine off of. Try your trick with brake cleaner and you may have different results.
 

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Discussion Starter #9
i had some time so i threw it back together here is a video of the spark

and another of the machine at idle throttle closed, choke open. You can see as i throttle up it blows black smoke and dies.


Still needing to pick up some brake clean.
 

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I don't think you need to try running with brake cleaner. Looking at the video of it running, it really acts like either a valve issue, or ignition timing. Have you checked the flywheel key to make sure it's not somehow sheared? I know you set the valve clearance, did you look at the valve operation and notice if both valves looked like they are opening all the way? It's possible that one of the valve lobes on the camshaft may have wear and your valves are not getting proper lift. Something you might want to look at anyways. Good Luck...
 

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Discussion Starter #11
i'll check the key on the flywheel, and see if there is a way to measure if the valves are opening all the way.
 

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Discussion Starter #12
what is the likely hood that the key sheared and the timing is off? I'm not able to get the flywheel nut off. I don't have a compressor that will run my impact gun.

Is there another way to check the timing?
 

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The possibility of the key being sheared is not very high. It's just something I would want to check to be sure of before looking at the valves or camshaft.
 

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Discussion Starter #14
My brother came over tonight we got the machine to idle then he shut the fuel line almost closed limiting the amount of flow and we were able to get it to throttle up higher (3/4) with out bogging down and blowing black smoke.He is thinking something is going on with the carb it almost seems like the jetting is off.
 

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I don't think the float is adjustable on that carburetor, should be a molded plastic float.
 

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Is the main jet in the carburetor? It's possible it came loose and fell out and this would allow way too much fuel into the engine, however I don't think it would even idle without the jet in place.
 

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Discussion Starter #20
yeah main jet is in place i'm thinking bgbass is correct the fuel level is too high in the carb bowl. but i'm not sure how to check that or what would cause it. Aside from a bad float or needle vavle not seating, i'm Just going by the flow chart in the service manual
 
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