Yet another brain twister!? Craftsman 917.203901

[dart451]

Well, thought I'd ask some of the experts on here for some clues as to what's happening with this motor 44R677-0021G1 in the Craftsman 917.203901 tractor. Customer brings the tractor to me because when it's running, it surges. I have tested this by choking it a bit where most of the time it will clear up. However sometimes it won't even try to start unless I spray some starter fluid in it! So, it's rather intermittent...sometimes it runs smooth. I have tried this: Thought: (Water in gas) drained gas out of the bowl (in case there's still water inside), by-pass fuel tank with fresh container of fresh fuel...No cure! Changed out fuel pump, installed new fuel pump vacuum hose, (old one was cracked)...No cure! Fairly new tractor...carb not dirty. I think my next step is to throw a new carb on it but I thought I'd ask you guys what you're thoughts might be!?

[bgsengine]

check valve clearance , maybe do cylinder leakdown test (burned /leaking exhaust valve?) check flywheel key, try a new plug (or two) and see if it is governor related (stop throttle from moving and see if it smooths out, if it wants to die, its fuel, if it stays steady, maybe do a static governor adjustment, check for weak gov. springs, check for worn throttle shaft)

[KE4AVB]

Try adjusting the base idle speed up a little and see that helps. I had few engines lately that where the minimum idle have been set too low cause surging and since these engines run off the idle circuits when off load it causing problems.

As for starting it maybe that it is not choking fully. The IPL show this has an auto-choke setup though it may have been channged over to a separate manual choke.

Jst a couple thoughts but take with a grain of salt as I have a splitting headache right now.

[dart451]

check valve clearance , maybe do cylinder leakdown test (burned /leaking exhaust valve?) check flywheel key, try a new plug (or two) and see if it is governor related (stop throttle from moving and see if it smooths out, if it wants to die, its fuel, if it stays steady, maybe do a static governor adjustment, check for weak gov. springs, check for worn throttle shaft)

Ok, tried the "hold throttle from moving" and noted that the engine does smooth out! So, if it's not a gas problem, I need to do a static governor adjustment, check weak gov. springs...INTERESTING!

[dart451]

Ok, Static governor adjustment made...didn't move at all...engine seems to have cleared up again but I assume it won't last. Will check the valve clearances tomorrow...

[KE4AVB]

Could always be like a couple Kohler Courage engines where I had put a gauge in place so the throttle vane didn't fully open and do the static adjustment to the remove the surging.

[dart451]

Valve clearances were a little off on left bank...re-adjusted them...no change in engine surging...also cleaned the plugs, not very dirty! Here's another thing I tried: While running, I pulled a plug wire one at a time...smoothed right up! I thought...ah ha! I found the problem! So I do the same thing on the other side...runs smooth! What?? So I'm back to square one. I do have a carburetor coming...might as well throw it on see how the damn thing runs!

[KE4AVB]

It looking like you a have partial plugged idle port or as I suggested that throttle plate is just closing too much at no load speed. I know it sounds crazy but I have seen this 3x this year alone where the throttle plate was closing too much. By operating on just one cylinder you are putting just enough load for the governor to crack the throttle plate open a little more as the engine fights the non firing cylinder compression.

[hanz63]

Interesting observation on the throttle plate. I see that this is a twin barrel carb. I had a single on one of these that I couldn't do anything with but replace it. Thought the same on the idle bleed but no dice. Ever run into one of these with surge on an Intek twin?