I have carb issues this Spring. First, needle was gummed up causing float to stay down and although the engine ran, fuel was flooding the float bowl and pumping out. Got that fixed.
Next it was surging or hunting. No doubt a lean condition. I removed the carb, removed the float, needle and main jet, and that's as far as I could go. Seems pilot jet is under a welch plug so a complete carb kit would be required. So what I did was to soak it for about 1 hour in an ultrasonic tank, then blow it out with compressed air alternating with some carb cleaner spray. Re-installed the carb. Some improvement. At full speed it seems "almost" normal but at half speed it hunts very badly. It was surging at all speeds before.
There is no pilot jet. The pilot circuit is drawn off the main circuit via the idle fuel restrictor. This is the little brass tube that runs through the venturi. It is not removable. You would need to remove the small welch plug at the top of the carb and hope you can get the old fuel cleaned out of it. You can remove the welch plug, with the main jet and emulsion tube removed, you should see light through the tube when shining from the top. The passage way is very small. It’s hard to find something small and rigid enough to try and clean it out. The larger welch plug is the transition port. This is easily cleanable.
The discount carbs on eBay are cheap for a reason. Not intending to be harsh, improper maintenance has a cost. Always drain or in this case, run your carb out of fuel at the end of the season. Adding Stabil or equivalent prior to the season end is also a great idea.
T-Y for your reply. The mower is about 12 years old, so it's no surprise that my lack of maintenance caught up to me. It's rarely a problem when I can clean a carb, but this one is a problem. Oddly, the exploded view of the carb calls out a pilot screw under the welch plug closest to the rear of the carb, so naturally I thought there would be one there.
Yes, normally you get what you pay for. I did have a bad experience with a cheap e-bay carb for another engine. It wouldn't work right and could not be adjusted. I finally made one using parts from the old one and the new one and it worked fine. Sometimes though, aftermarket parts can be good. That's why I asked.
The “pilot screw” is the idle port adjustment. Typically there is no need to remove this. When you get the welch plug out for the transition port, just spray carb cleaner in the passage towards the screw. If cleaner comes out the little hole in the venturi, you are good to go. Good luck.
Ultra sounds do not clean out badly gummed uppassageways unless they are filled with a solvent for fuel gum
What does work if the gum is really thick is to soak in a solvent cleaner over night then a couple of hours in very hot ultrasonic cleaning tank filled with a strong detergent .
On some cube carbs they end up needing multiple runs through my tanks at 60 minutes a hit .
Story so far: I did remove the welch plug that hides that screw. Screw looked brand new, clean and wet from gas. Havn't replaced that plug yet as I playing with tuning, but so far not really much of anything from adjusting that screw.
Next I removed the next plug forward. It reveals 4 little holes; transition holes no doubt. There was a small piece of something black in there... appeared to be a small bit of gasket material. I removed it and cleaned the holes. Had a new plug from another carb kit and sealed it off.
Next I sprayed carb cleaner through everything, then air, then the ultrasonic tank again, repeated the carb cleaner and air blast. Re-installed carb and same surging.... terrible below full throttle.
Still assuming it's a lean, I tried the choke and a small amount of choke and the engine ran fine. So.... if the carb "isn't" gummed up, could the float bowl level just be low? Well, when I first start the engine, it runs fine for about 10 seconds before it starts surging. I removed the fuel line at the carb and started the engine. Not much fuel cam out sort of a trickle.
Next, checked the fuel filter. I couldn't blow through it, but a few drops of gas came out so some air much have been getting through. Not having another filter handy, I just connected the two hoses together to try it. Not really any change. I then blew air back through to the tank and I could hear it bubbling up through the gas. Tried it again and it ran fine for quite a while, but then started surging again. Just sitting there, surging would drop off, then start again.
Not sure what next, but think I will inspect the tank for debris that could be plugging the line.
Well, it's fixed, although I'm not sure why and don't have much confidence it will stay fixed, but it's running perfectly now. Seems a combination of problems, but I'm a little vague on the last one.
1/ Cleaning the carb. This did help, but only the first time I cleaned it. Subsequent cleaning didn't help.
2/ Fuel filter was is very bad shape. Replacing it must have helped, but it didn't right away.
3/ Fuel pump. I had previously watched the output of the pump and it was a trickle. I checked it by removing the hose from the carb. Today I checked it again. Now I had already changed the filter without any improvement. So with the engine running (and surging) I pulled the carb line off the pump and fuel blasted out the way it should. I connected the line back up it started to run better. I put the clamps back in place. The last clamp to be put in place was the line feeding the pump from the tank. As the clamp was released in place, the engine started running fine.
Could be some sort of airlock in the pump, but I suspect rot or some sort of hole, crack, etc. in the hose and the clamp must have covered it up or something when I put it back in place. I need to check that out, but not quite yet. I have a little mowing to do.
Thanks to all for your advice and help. I learned quite a bit about this carb, fixed a few things that probably should have been dealt with under routine maintenance, successfully installed a welch plug and eventually got it repaired, although I do admit to being left with a question or two.
I was just informed the other day after using my wife's pots for carb cleaning, I could buy my own hot plate and pot for a few dollars. So now I got my own mower carb boiling rig. Not as much fun now sneaking a pot out of the kitchen.
I should have known that it was running right as a fluke as I never really found anything wrong. It started surging again after about 10 minutes or so of running. Quite bad at times... almost stopped. So this morning I cleaned the carb again. This time I managed to remove the emulsion tube and it had a lot of what I can only describe as floating black bits of mold in it. Same as the little piece I found earlier under the middle welch plug. Same stuff that seems to be coating part of the bottom of the plastic gas tank. Anyway, I cleaned it out. Also removed the welch plug over the small tube that fits inside the emulsion tube. Couldn't get it out (actually scared I would break it trying), but forced a lot of carb cleaner down it and was vicious with the compressed air. All back together and I just finished using it for about 1.5 hours and it ran like new.
Ah... a new reply. Quite apropos as I've been thinking I ought to add to the thread for a couple ff reasons. First of all, I think it may be noticeable that my surging issue was consistent for a while but eventually changed to intermittent. When I went to clean the emulsion tube, it had those black deposits on it. I noticed they wern't stuck and would slide around and came off quite easily. This matches up with intermittent. Sometimes those little holes were covered, and sometimes they wern't.
But what about before when the surging was consistent? I assume those black patches were stuck and didn't move around. So why's that? My best guess is that I added SeaFoam to the fuel tank and it was gradually cleaning things up. All speculation, but it matches the facts.
So what is that black stuff? Somewhere on Youtube I found a video that says it's carbon from a filter usually inside the fuel tank cap. Hmmm... I will admit there's a lot of this black stuff inside the tank.
Anyway, SeaFoam may have eventually fixed the problem... maybe. And a carb can't be too clean! Sometimes it takes an extra effort.
