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Discussion Starter · #1 ·
FD590V - 18 hp engine stalls abruptly 5-10 seconds after start.
New carb, new plugs (wet), removed and cleaned gas tank, fresh fuel, new fuel lines, fuel pump good, compression good, crankcase vacuum good, choke plate good, as gas tank cap vent good, clean air filter. Will test cylinder leak-down next, but feel like I'm missing something more obvious to cause such an abrupt stall. Can't see how safety circuit could be involved. Typical exhaust smoke at start - but could could muffler be partially clogged?
 

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If plugs are wet, tooooo rich. Could be choke issue or mixture screws. If starting with throttle near/at idle, close idle mixture screw 1/8-1/4 turn. If starting at half or more throttle, close high speed mixture screw 1/8-1/4 turn. Before adjusting mixture screws, "play" with choke if manual choke. As soon as engine fires once, slowly open choke. If automatic choke, sorry, can't help.

Different engines start at different choke settings. My 314 will start ONLY with choke closed and I have to immediately start slowly opening choke. My 317 starts with closed choke, but if it fires once, I can quickly open choke. My 322 starts on closed choke and after that fires, I can just barely open choke and it'll run...rough, very rough, but it'll run! Bob
 

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Discussion Starter · #3 ·
Thanks Bob - May have overplayed the "wet" plugs. Intended to convey just that they are moist v. dry. Anyway, I start mine like your 314 with a manual choke. Assumed the factory carb settings would be best, but I'll try adjusting (once I figure out which is which).

Dave
 

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Exhaust obstructions unless severe, won't cause engine stalls. They tend to cause excessive heat, loss of power but not much in terms of "sudden stalling". When there is an exhaust obstruction, it causes excessive back pressure, which results in slow throttle response, "stumbling" and the engine acts very disconnected to the operator input. Also, when there is an obstruction in the muffler / exhaust the engine sounds very .........different, often with a thumping / rattling sound.

I would have to say its a possible ignition issue, especially since you have replaced the carb with a new one. Is the stalling now exactly like it was before the carb replacement?

Safety circuits generally don't cause sudden stalling, they either prevent engine starting or even prevent cranking at all.

Does the choke input do anything to keep the engine running when you reach the 5 to 10 second stalling time frame or does the choke do nothing to prevent the stalling once it begins to occur ?
 

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This may be a long shot, but if the new carb did not come with a new fuel shut off solenoid, the old one may be the problem. If I remember correctly, when the key is on, there is voltage to the solenoid to open it. Key off, a spring makes the plunger seat to stop or limit fuel flow from the bowl to the main nozzle. You should be able to hear or feel it click as the key switch is cycled on and off. Might have to have someone in the seat with the brake on to try this. Best way is to remove it from carb and observe whether the plunger operates correctly. Just open the bowl drain screw first and catch the fuel as it runs out, then remove the solenoid. Don't try to start it, just cycle the key.
If no voltage to the wire, trace back to switch for problems.
I don't think the original carb will have anything but the idle adjustment (pilot air) screw, which shouldn't cause it not to keep running. Oh how I miss the days of fully adjustable carburetors!

tommyhawk
 

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Discussion Starter · #6 ·
Thanks for all the insight and suggestions guys. The carburetor adjustment did not help Bob, but I don't think it's really adjustable anyway. The original Mukuni is just like the new Mikuni with just a single screw that adjusts a pilot orifice on the manifold side of the butterfly valves - which I assume is just for idle adjustment as you note tommyhawk (the new one utilizes a plastic thumb screw adjuster that has a stop that limits movement to a max 1/2-turn/180 deg. total). SulleyBear, the same stalling problem began before I replaced the carburetor, and after replacement I had a short amount of operating hours before the engine began to stall randomly with and without load, until now where I'm back to an immediate stall. And the choke seems to have no appreciable effect on preventing the stalling - maybe just the slightest momentary delay when I fully choke quickly when I know it is about to stall. Though it would have been a nice solution tommyhawk, the carburetor does not have a fuel shut-off solenoid, just a manual valve before the in-line fuel filter.

I'm wondering if I need to open up the carb and to see if it somehow got fouled?
 
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