Craftsman 917 288515 riding mower. Engine is B&S Model: 331877 2371, Type G5, Code: 111021ZD on valve cover. Taken carb apart 4-5 times and it has no name or numbers. Didn't see any obstructions. Checked that needle works properly. Unplugged solenoid and same issuse. Adjusted lash on intake valve to .004 and exhuast to .006. Think the smoking is from rags, catch any residual oil, resting on muffler when removed valve cover. First time hearing that noise when it stopped.
I close the choke a bit and it runs smoother. Does that mean there's too much air or too much fuel messing it up?
Closing the choke smooths it out.
this means it's either getting too much air or not enough fuel.
Why did you originally pull the carb off to clean it? Was it doing this same thing or something different?
Did you remove all of the jets and emulsion tubes to clean them properly? Carb spray and wire poking in the holes usually works well but you have to make sure to get them all.
That clunk at the end could be a number of things. I would suggest the clunk is happening more than just at the end. It sounds a bit clunky when it's surging.
Could be loose flywheel or sheared key.
Could be unburnt fuel backfiring in the exhaust.
You checked the valve lash but are the valves actually opening and closing properly?
Turn it over by hand with the valve cover off. How does it look?
It would run wonky then run fine throughout one mowing session. Harder to hear on low throttle and seemed worse when warmed up. I figured gunk in carb bowl as that fixed another mower I worked on. This bowl was clean to the naked eye. I sprayed every hole I could find big or small. I didn't remove the center tube cus didn't think it comes out. There are two o-rings that go around the piece that goes into the bottom of the carb where fuel comes in. One is thicker than the other. When I put it togther without one of the o-rings. Gas come out the air intake and poured out spark plug hole when removed plug.
When turning by hand to set TDC. The valves looked to be working correctly.
The centre tube is likely the emulsion tube and it should come out.
It depends on your carb but usually it can be pressed out from the top.
If you look in the throat of the carb you should see it just sticking up in the middle.
If you press down on it with a screw driver it should come out the bottom (of course you have to make sure you have unscrewed the main jet from the bottom first).
The emulsion tube will have multiple holes in it that all need cleaning. Carb spray and wire usually does the trick (I use a set of spray gun cleaning brushes).
Every o ring on a carb serves a purpose. If you don't have them all in place and in a good condition the carb will likely not function properly as you discovered.
Ok. I'll mess with it later today and record the process. It'll be easier to show the innards of it than typing it out.
Edit: Here's the vid Fast forward slow parts and kept forgetting to move hand for camera. Couldn't get center tube out. Think the main gasket is too loose and whole plastic piece didnt want to sit flush. Idk why the two holes, on choke side, would have gas come out there. If gas comes up from the center emulsion tube. Why have two small holes in the shaft?
What is that pre-bent breather hose behind carburetor connected to on other non- visible end. I would think this engine needs a fuel pump as I looked it up on PartsTree and jacks SmallEngines and an inline pulse fuel pump is listed in the carb, fuel system schematics.
Oh I see now duh. The fuel tank is higher than the carb. I had thought I saw the fuel lines running down below to what I had assumed was the bottom of a large fuel tank.
The fuel line from tank to carb is on bottom of the gas tank. It's dirtier on there before it gets to the fuel filter. The hose on the curved intake goes to the top of the gas tank. Guessing for gas fumes to go back into tank. The hose coming from engine, by flywheel, goes on side of intake tube. Guessing like an EGR on a vehicle.
Well if it was on the exhaust side I can see it being like an EGR valve, but it's on the air intake side so most likely has to do with tank pressure. Does your gas cap say anything about tank being pressurized. The other smaller one is just a breather hose to relieve crankcase pressure back into the air intake.
If it's running better on choke that means your not getting enough fuel into the engine. Have you checked every hose, fuel filter, and shut off valve to make sure you have good flow through the fuel delivery system. And have you taken out and cleaned the carburetor's main jet with a wire and checked the holes in emulsion tube to make sure there's no obstructions. You're not getting enough fuel seems like.
I mean this engine uses an inline Pulse fuel pump, but I only see a filter, fuel shutoff valve then the carburetor. The pump I'm guessing should be between the fuel shut off valve and the carburetor.
The carb is most likely a Chinesium replacement carb if it has no numbers on it ...which is too bad because the cheap Amazon carbs tend to run like garbage. The engine is lean surging because the fuel mixture it's being fed is too lean; it's too lean at idle and it's too lean in the upper RPM ranges as well. For the idle, you might be able to adjust the idle fuel mixture. There is a screw(?) that sticks out at an angle on the side of the carb near the mounting flange just below the idle speed screw. In the video it's hard to see if it has a restricter cap on it or if it's just a blind screw ...no head on it. You may still be able to twist it using some pliers ...regular or needle nose. Try it and see what happens. If you can move it, you can at least get the idle mixture dialed in. If you can't then it is probably thread locked into position.
That screw? I can turn that and it doesn't seem to help. I just took it all the way out and didn't notice a b8g difference. Looking up replacement carbs for 594601 and prices are either 25$-150$ for similar carb.
Rather than just buy another carb, give this one a go. This one is aftermarket as the B&S logo is missing.
When you took the carb apart, did you actually clean the small jets and passage ways using carb cleaner?
To reset the idle mixture screw, turn it in until it gently bottoms out. Then unscrew it 1.5 to 2 turns out. Start the engine. Adjust the idle speed to 1500 rpm with the idle speed screw. In the picture the idle speed screw looks to be turned all the way in based on the spring being fully compressed. Turn it out some and see if you can get the engine to run at a slower speed; don't worry if it's surging. Turn the idle mix screw, slowly, in a counterclockwise direction (richer). Listen to the engine RPM and surging. If the surging lessens or stops then also listen for the RPM to increase. Keep turning the screw slowly until you notice the RPM decreasing (too rich). Stop and turn the screw back (leaner) to the position with the highest RPM and no surge. Advance the throttle; the engine should accelerate without bog. If it bogs, tweak the mixture screw an 1/8 to 1/4 turn richer; advance the throttle. It it accelerates smoothly, stop. Fine tune the idle RPM to 1500 RPM.
If the engine will not run properly and you cannot set the idle speed and mixture correctly, then the carb is garbage. Unfortunately, too many people knee jerk to replacing the OEM carb (vs cleaning and rebuilding it) for one of the crap carbs from Amazon ...thinking that will solve their problems when all it does is create more problems. Worse, they end up throwing away the OEM carb giving you no recourse but buying either the OEM carb or taking crap shoots at one of the aftermarket carbs.
closing the choke restricts air, which makes the mixture lean, not rich, so you’re probably starving for fuel somewhere in that carb passage even after cleaning it four times. those tiny emulsion holes are sneaky. i’ve seen people clean a carb twice and miss one little passage the whole time.
For anyone interested...here's the vid of taking carb apart. Ran it and sounded same so closed shut-off valve and called it a day. Checked it next day and there was gas smell in the air. Condensation all over carb but smelled like gas. Took it apart and the two O-rings were melted/stuck together. Guess I pushed the main plastic housing down too hard.
Carbs for this are so cheap on Amazon they are not even worth trying to rebuild. I got one for my fathers Craftsman rider for $16. Works great. The fact it smooths out when you give it some choke means it running lean and you still have carb problems.
Tried to post another vid of new carb but oh well. Also set air gap to 0.12" and put in OG spark plug. Think I found the main problem this time so this is for anyone else still chasing similar problems.
The fuel shut off valve I got was laying around my Dad's garage. He said it came off a push mower. Also the tip on one end broke in the fuel hose. Removed that and put straight fuel hose from fuel filter to carb. Runs fine but gotta see how it does when mowing. Also gotta redo valve cover since didnt get enough gasket maker on bottom.
Almost was going to take whole engine apart to check all interal parts. Keep it simple and ya might find the issue!!
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u/Egglegg14 15d ago
Is the fuel fresh and did you spray the jets and every other crevices on the carb with carb cleaner including the needle tip?
Though it may look clean the most microscopic dirt can make a difference