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Yes, that is true. I do need to pull the carb and rebuild it, at some point. I did spray some cleaner in there, and the uphill stall-out was identical to before, for what it's worth. Also, when I put on the new fuel pump yesterday I used a clear line from the filter -> pump, and I see about a 1-inch long bubble in there. I got the bubble out, but once I ran the hill again and it nearly stalled, the bubble was back. To me this says I'm pulling air back into the fuel pump from the crankcase.

@MarkinARthanks, I picked up some carb cleaner this morning and will give it a spray and see if any symptoms change. In the service manual I have for this model it says "float height not adjustable." You are right that I jumped ahead of myself with the fuel system parts, but seeing multiple folks saying that they had issues with the fuel pump and switched to electric really got me convinced that that was my problem too. I ordered a cheap electric 12v pump and will have it on hand if the carb cleaning doesn't help...

Well, after tinkering on my last project (a 2003 Kawasaki Bayou 300) I ended up putting it on Craigslist and it sold within a day. Then about two weeks after that a 2005 Mule 610 with 40 hours on it popped up, for about 1/3 the cost I usually see them, so... I didn't have much of a choice. The Mule's first issue was idle, it would die if you didn't keep a light toe on the accelerator. Turns out the idle screw had never been touched, five minutes after I got it off the trailer it idles just fine. 🤦‍♂️ As of today, it runs great on flat land. And it climbs like, well, a mule. But it has one issue. Sometimes uphill it will suddenly lose power like the fuel isn't getting delivered. It never dies completely, it just sputters and won't go until you let off the gas pedal and let it recover. It tends to do it more with 2 passengers or some cargo and wide open throttle BUT occasionally will do it at only partial throttle and with just me on it. I read a lot about how the fuel pumps on these Mule 610's suck, so I put in a new one today and a new fuel filter. It still had the same symptoms immediately after, so that was $40 wasted. Any ideas? I keep seeing folks saying they replaced the pulse pump with an electric fuel pump. This thread said so, and it gets brought up in this thread and also here. In each case somebody says "12v fuel pump solved my problem!" and then they promptly disappear from ever posting again, lol. I have some questions for y'all: 1. Do you think fuel delivery is the problem? I have a hunch that it is, given the hill + throttle symptoms. 2. The pulse pump on the Mule is located ABOVE the gas tank. Can an electric fuel pump pull fuel UP in this manner? 3. What would I do with the spare line that goes from the fuel pump to the crankcase? Every electrical pump is just in & out, they don't have that third line... 4. Any idea what kind of flow rate I would need or which pump works for this application?

I just sold my 2003 Kawasaki Bayou 300 (KLF300B) last week. Pretty sure it is mechanically similar to your new quad. When I got mine the front brakes would start sticking after being used 2-3 times – I cleaned out the brake fluid return port in the master cylinder with a little guitar string and that solved that problem, seems like that port is smaller than some others I have seen. Another thing with mine was that the centrifugal clutch would not engage at low revs - I did this trick with a dremel tool and it actually completely solved the problem: https://nicholasfluhart.com/2015/01/08/project-bayou-300-4x4-clutch-repair/

Updates: Adding some Dremel grooves in the very very worn out centrifugal clutch worked wonders, it pulls much sooner & stronger now. I changed the oil for some Shell Rotella 15w40 diesel oil and that also seems to have helped the wet clutch and helped the smoking at low revs. I still get smoke at high revs but since I'm just putting around on it, I think I'm going to leave it alone for a bit and just enjoy this quad that I got for a few hundred bucks. No sense in rebuilding it given the type of use it is going to get. I'm not confident in my ability to replace the rings or valve seals myself, maybe in a few months I'll take it to a shop. The one thing I will probably still need to do is get some tires. Factory it's supposed to have 22x9x10 on the front, but 22x8x10 seems more readily available online. I can safely go down an inch in width I assume? Rims are 6" wide. On the back it's supposed to have 24x11x10s, but I thought if I went down to 22x11x10s I would gain a little low end torque, is my thinking here correct or am I being a dummy.

Fired it up after work and it seems slightly happier and quieter than before the valve adjustment. It's still smoking but not *quite* as bad as before. Smoke is during uphill acceleration, or parked in neutral at high revs. (Does this mean rings more than valve seals?) And I will take your advice and seal up those bolts & covers. Waiting on a new oil filter before I drain it again and check out the clutch and try this whole honing / grooves trick. By the way, what do you recommend oil-wise for this situation.. a well worn engine, and slippy clutch. I live in an area where it rarely drops below 40° and will probably always be riding on warm days, I'm thinking 20w50 mineral to seal things up a bit and give the clutch the friction it needs.

Yep I used feelers, intake I set at .15 and exhaust at .20 ... I did not check compression before, that was dumb, I should have. And I haven't checked it after but I have an old compression gauge somewhere which I will dig up and have a look. Also, Attached is a pic of the exhaust valve cover - can't tell where that somewhat fresh oil is originating from, but it seems to me to be originating from the bolt that goes in where the decompression lever is. The valve cover itself was on really good and seemed sealed up so I don't think it was coming from there.

@MarkinAR this is valuable info!! Thank you! Googled and found this really good write up of a mod for the centrifugal clutch https://nicholasfluhart.com/2015/01/08/project-bayou-300-4x4-clutch-repair/ I will give it a shot and see if it fixes my low-rpm clutch slipping issue. I adjusted the valves last night but had to run to work before I even got a chance to fire it up, so not sure what the results were yet... The intake seemed a bit loose and the exhaust seemed a bit tight... I also found once it was on the nice level garage floor that it was overfilled with oil. We'll see where things stand after all these little tune ups, I suspect I will end up finding a mechanic to do the valve seals when all is said and done.

Will look at the valves tonight.. Interestingly I found this post https://www.kawasakimotorcycle.org/forum/showthread.php?p=2403491#post2403491 Which describes exactly two issues I'm having with my KLF300: "How well/smooth should the centrifugal clutch work? This one will start to drag with a few revs then with a touch more will drag slightly more for a couple of seconds then jump to full engagment." Yep, yep me too "There is some smoke from the exhaust and quite a lot till its good and warm.. Some of which may still to burn off with a good ride as the exhaust looks black from rich running. " Yep, also exact symptoms "About valve seals and we have been told that it is quite common on these quads for the seals to harden and it may get better with good oil and some riding time." Hmm, that would be nice

I guess I could start by just opening the valve covers and seeing what's in there... maybe it needs a good cleaning (he said, hopefully)

OK, choke cable is on its way. And a new air filter. In the meantime I have the air filter completely out of the air box and I'm still getting smoke, now I think the smoke is probably from burning oil. And there's some oil in exhaust, so I'm thinking this might be ... valves? Either adjustment, or replace the seals? Guess I can start with an adjustment - it does sound a bit "clackity clack" ish so maybe that is a logical next step. What's the best oil for this situation - high mileage w/ smoking? I'm wondering what the last guy put in it, and if that could be part of the problem.

Thanks (as always) @Frank Angerano ! So the plunger is moving, I just wonder if it is not seating all the way and allowing extra fuel to sneak by.. the way the cable looks I feel like it could be twisted or messed up and not have enough play to allow the needle to "fall" all the way into the hole. However my first fixes might be on the air side, I pulled out the air filter last night and found it was using a homemade PVC pipe filter "holder." The pipe used was much too long and extending all the way into the rubber manifold and hitting the other side, probably cutting off a significant % of the incoming air. So I'll try a new filter first and see if my mix gets a bit better before messing with the choke!

Just picked an '03 Bayou 300 2WD. It runs ok, needs a little help though. Maybe someone can answer some questions for me. 1. The choke "off" position is the lever all the way right, correct? 2. The choke seems mechanically... funky. It has a little valve clamp around the rubber boot where it goes into the carb, seems kind of janky, I don't think there's typically a valve clamp on that part? The engine seems like its running really rich, smoking a bit, so I wonder if I can just completely remove the choke cable to see if that's part of the issue? But I don't fully understand the choke needle setup. Is "choked" when the needle is being pushed in, or pulled out? Like it I chopped the cable just outside the rubber boot by the carb, would I be permanently choking it or permanently unchoking it. 3. I've read that I can tweak the air/fuel screw and maybe fix the rich mix. Where is that even located, and if it's behind a cap that I have to drill out... where is that? Thanks for any tips

I just picked up a 2003 Bayou 300. A cheap Craigslist find. Funny enough I'm having the same problem, it sat in the sun all day today in 90 deg heat, and it was flooding and wouldn't start. I pulled the fuel line with the petcock in the "off" position, and lo and behold gas came pouring out. Seems like these Bayou fuel valves go bad. And as it sat all day the fuel slowly flooded the engine (not sure if that's even possible?) Anwyays I put an inline fuel valve on it so I could be SURE that the gas is off when it sits in the sun, and a new plug, and it fired right up... So you might check your fuel lines and make sure they aren't dumping gas into it while it sits. Mine is also running really rich, which is a story for a different thread