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mike costa

2000 KAWASAKI BAYOU 300 bogging down

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Motor starts right up, but when I open it up past quarter throttle it bogs way down while ridding, the longer it runs the worse it gets. If I just leave it in neutral and  give it full throttle it revs up and down. 

Back history:

Bike sat for 3 years,

Installed new plug, cleaned the fuel tank, took it to a shop and had the carburetor gone though.

Picked up from shop, motor bogged down first day and barely got me back to the truck an 1 mph.

Took back to shop after a month I was told it had a bad plug, I told him I just replaced it.

Got quad home and it is doing the same thing!!!!!!!!! 


Thanks in advance for your support!


The carburetor has recently been gone through by a shop

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Sounds like a carb issue, could be jetted wrong.

* Topic moved to kawasaki atv forum

  • Like 1

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Just because a shop went through the carburetor dose not mean it’s going to be good ! We’ve all seen this.  A guy who works in a bus depot as a mechanic can open an atv shop. Does that make him an atv mechanic? No!  Sorry to be so blunt but that’s the way it is. Trust no one until you find the right guy and get to know him or her.     

My guess is the carburetor is not set right. It may have been cleaned and put back together right but If the air fuel screw is not set properly then it’s useless! 

I would get yourself set up right and locate the air fuel screw and turn it all the way back into a snug tight position. Then turn it out two full turns and start the bike.  Then as the bike is running adjust the same screw turning it to where the engine revs higher, and that may be tight or looser until it reaches its best happy place and stop.  And happy place means revs higher as you go, If it’s idling high after this then lower the idle screw. 

See what ya got after this.  

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Thanks for the move, FYI when I created the post the sites main menu it showed machine specific forums was an option for topics, but didn't show them or appear to allow me to navigate to them. 


Just to be clear, I don't profess to be any kind of a mechanic, but I will elaborate on some additional events that may or may not change your comments. 

Trying to ge ready for a trip one of the first things I did in an attempt to bring the quad back into service was pick up a new carb from Amazon, $50.00 and it ran but had similar issues of acting fuel starved past 3/4 throttle. The carb worked for the trip just not well. upon returning from the trip, I changed the spark plug which didn't seem to help.  I admitted I suck as a mechanic and decided to just pay a professional to fix it. I reinstalled the factory carb and took it to the shop. The Carb and Jets are all OEM.  The guy said it was gummed up do to the ethanol in our fuel out here and he had cleaned it.  I put seafoam in all of my fuel cans, boats, and ATVS. My father who previously owned this ATV did not.

Based on how the plug looked the mechanic said if the plug doesn't fix it he thought I should replace the stator next.

To have the carb cleaned, a plug installed, and harbor freight winch installed I am now into this for about $650 in labor.  I already paid for the winch and mounting plate.


Sadly, I think this guy really knows how to do it right, but was is busy and once the machine started he called it good without a test ride or really listening to or revving up the motor. If you hold the throttle all the way down out of gear the motor cycles once avery 2-3 seconds from max RPM to a little less than half. The engine doesn't sound bad when it is doing this, it sounds like a guy is just play with the throttle. If you are riding it, that is a different story, it sounds like it is bogging down, and you can't really run in any gear other than first, at 20% throttle.  

I spent many hours researching this website on stators and the internet, and at the end of it based on several of your posts I thought you "Frank" were going to tell me it was the stator, and to test it!

I did read up on testing stators, and I have the a plug going into the rectifier with 3 yellow wires on it that "appear to be coming from the stator, it matches what I read in the manual. None of the three wires have continuity to ground, If I test Y1 -Y2. Y1-Y3, Y2-Y3,  I get continuity, yet when I changed the meter to Ohms, it reads 0.0. When I read the manual, I expected to see 0.33 - 0.49 ohms.   I was sure you would ask me for these readings!  I was trying to be prepared without biasing you with what the other mechanic had said. I used a Kline new multi-meter, not cheap, but not the best. I was going to dig up my good Fluke 187 and repeat the test.

Youtube is a dangerous thing especially when you are getting desperate for answers. I was off work today and had time to fixate on this.  I did see a video where a guys bike sounded much like mine where it would run fine at very low RPMs but would sound like it was fuel starved at high RPMS because his CDI was failing. Yet if I am testing the stator correctly than that has to be it? 

I have read RMSTATOR is better than your typical chinese knock off for Stators, CDI Box, and Voltage Regulator Rectifiers. Would like to hear your thoughts. OEM is just sooo expensive!

Sadly I live in California, and the air fuel screw has been made tamper resistant and is not readily accessible. It is a reasonable assumption it is still set to the factory spec.  I have read you can pry off a cap and adjust it if needed. 

I will retest with the Fluke this Saturday, Frank with the additional information about the air fuel screw do you still recommend that as a first step? 


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Great research and work! But I have to disagree on the stator.  If the bike is running and has good spark I don’t think its breaking down.  In my experience the stator is either good or bad. There should definitely be a reading on the ohms setting giving you exact numbers from phase to phase. Why your not getting that is a little baffling. 

You should buy an in line spark tester and plug it in and watch your spark as you rev the bike to see if there is a loss or brake down in the spark. It’s about a $15 dollar tool that’s a big help. 

Back to the carburetor: I would definitely drill out that plug covering the fuel air screw and pull it out. Check it out and clean the port well with cleaner and air.  Before you remove the screw tighten it to a snug position and count the turns so you know where to set it when you put it back. My guess is it’s around 1-3/4 turns out from a snug spot.  The fact that the bike sat, the carburetor was gummed up and that air/fuel screw was never taken out and cleaned leaves a question mark on the carburetor.

I would start with the less invasive stuff right now and do some testing first so your not dumping money into it.  Narrow down the problem so you don’t question weather it’s a fuel or electrical problem.

Fuel tank and valve (petcock) clean and delivering enough fuel, carburetor rebuilt and good to go!  No cracks or problems on the boot connecting the carburetor to the engine etc. if all that’s done then I rule out fuel or carburetor problems and move on to possibly an ignition issue.



Carburetors: Chinese carburetors look great but don’t perform well at all.   If you have the oem carburetor and it’s not cracked or damaged then it’s a good cleaning and rebuild. But it has to be properly done. One missed port or blockage will cause a lot of throttle issues. Floats set wrong, fuel air screw not right etc.

Cdi: oem always. Used from eBay at the very least. Same with regulators

Stators: I’ve used aftermarket RM and Caltric. No issues to date. 

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I forgot one thing. You can put a tester on the battery while the bike is running to see what it’s charging at. This will help you out to determine if the stator is charging properly and if the regulator/rectifier is working.  

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I checked voltage this morning and its at 14.2 when running.

Started to strip the bike, I wanted to get the carb off to drill out the air fuel screw. I decided to start it after removing the snorkel and throttle cable just to see if the symptoms had changed.

It start just fine, a couple of what sounded like backfires but nothing bad and revved up to full throttle and stayed there. Magic the bike is fixed....  I was operating the throttle by hand at the carb. I was amazed at the flow of air coming out of the carburetor air intake, is that normal without the snorkel and filter on? 

I released the throttle and looked at the carb and it had a stream of fuel coming out of the bottom. I switched off the petcok. Humm Frank and Ajmboy might be on to something.... not looking like an electrical issue.

I reinstalled the snorkel and throttle cable, started the back with the petcok off ran the fuel out of the carb, turned on the petcok and started the bike again, same old problem, revs up and down very consistent rhythm. 

I am moving forward with pulling the carb and cleaning the air / fuel screw. 


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13 hours ago, mike costa said:

Thanks for the move, FYI when I created the post the sites main menu it showed machine specific forums was an option for topics, but didn't show them or appear to allow me to navigate to them. 

Are you on a desktop or mobile using the site? If on desktop, was it from starting a new topic like:



Or the main menu:


or from:


Just trying to understand better because if you were confused, other members are as well and I'll suggest to change it around if needed.


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It appears to be working fine this morning, last night the sub menu for ATV Forms by brand didn't seem to load. It could have just been my browser, I use chrome on this machine and it is oddly slow at times. It's a home machine with light use, I need to just drop a SSD in it.  

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28 minutes ago, mike costa said:

t appears to be working fine this morning

Ok cool.

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Fun fact, I’ve only used Quadcrazy via my iPhone! So no clue what you two are taking about lol 😂😂😂😂

Anyway it’s def a carb issue.  A couple of things to look for. One is a crack in the float allowing it to fill up with fuel thus not allowing it to properly float/lift the needle to shut fuel off to the bowl causing an over flow condition as you seen. Two the float is set wrong and it’s a simple adjustment. Or the fill needle  may have a rubber tip or o ring inside that’s compromised. 

The air fuel screw 100% needs to come out and have the asshole cleaned out of it good and blown out. (Count the turns it set at) 

After all is said and done you may have to adjust the air fuel screw with the bike running  to get a final dial in. When you get to that point it’s easy enough to do. 

Get after it! 




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I am not literate enough to just use a phone.... I have to re-read it several times and think about it, plus the pictures are much better on 32" 

The bottom pic shows the needle valve is bent, so I am going to order a carb rebuild kit, any recommendations on who to go with? While I am doing a basic rebuild anything else I should do while I have it apart?

I have been trying to locate any reference to the fuel / air screw. In the picture below I did notice something has been capped above the Carburetor Pilot Screw. 



Below the manual talks about the  Carburetor Pilot Screw Adjustment 2 1/8


IMG_0126.thumb.jpg.d791e3dff86239efce2cf71b869e93fc.jpgI will soak in parts cleaner

IMG_0127.thumb.jpg.39ee12d1c27b1edbe6afa63115e6e8ce.jpgI am going to guess that is not a calibrated factory bend in the needle valve!


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Well dam that’s definitely not a factory bend! The kit will come with new jets that should be the same but compare them and make sure the numbers match.  If you plan on cleaning them use a piece of a bicycle brake cable.  Take a strand off of the cable and use that to clean the small holes out.  

As far as the air/fuel screw it says 2-1/8 turns out. That sounds right.   I would go with that and see how she runs.  I can’t believe how that needle is bent.  Good find! 

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I installed the Carburetor rebuild kit and still have the same issues, after half throttle is just revs up and down, and I have fuel coming out of the bottom overflow of the carb if I turn it off.  

So my guess is:

  • The float, that I just visually inspected, has a leak and I need to submerge it to make sure.
  • I missed something in the bottom the the float needle chamber?


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What kind of carburetor is on that machine.  Reason I’m asking is there is a post out there  about possible print at the needle valve that could be causing a problem. It was on a Mikuni carburetor. Maybe a long shot but hey stranger things have happened.  

This was posted by @Freezeman and some good info. 


As far as the float maybe having a leak I would def check that out.  I just came across this problem on a machine.  

If you haven’t completely broke down the carburetor then do so ASAP.   


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Friday,  cleaned the carb as instructed, well to be honest I didn't put on the safety glasses... Yes, I got carb cleaner in the eyes, and I don't recommend it! 

This has to be the cleanest carb on I've seen on youtube!

I replaced replaced the following:

1) Float chamber gasket

1) Float Needle

(1) Needle jet

(1) Main jet #125

(1) Starter jet #65

(1) Needle jet holder

(1) Pilot Jet, O-ring, washer

(1) Pilot air screw

I've followed all the instructions, tried to purchase a quality rebuild kit, and feel optimistic! So I reinstalled the carb in quad, and it started up fine, after 1/2 throttle it would rev up and down, fuel was pouring out of bottom of carb... I never liked this bike, now is a really good time just burn it in place! 

Saturday, Can't work on it have to BBQ for friends. BBQ.jpg.e0eb4270f8c2a47f727e156dc3745f1d.jpg

Sunday, Tried to just rotate the carb to make adjustment to float,  Float, float needle, and other misc parts in up on garage floor, Removed carb, located missing parts on floor, and cleaned parts. Used a very un-scientific approach to adjusting the tab on the float needle, bent up until it looked good. Started up quad and died shortly, would not start again. loosened the bolts on the bowel, no fuel poured out. Pulled carb again and continued with my non scientific approach and reduced the bend by about half. Re-installed carb, no fuel leak and it runs! I am a fuel float GOD! Air box is not connected, give it full throttle and  revs all the way up and but a little backfire. Yah, its going to work!  Getting late, have to stop paying or risk pissing of neighbors,

Monday,  Starts fine, air box is still not connected, can run at full throttle with little backfire.  Verify snorkel is clear, and re-connect air box,  starts fine, no leaking fuel, revs up to 1/2 and then rev up and down. Pilot screw was backed off 2 1/8 turns from bottom per specs when replaced, backed out another 1/8 turn and now revs up to about 3/4 throttle.  Backed out another 1/8 turn no change.

Any Ideas? Burn in place, or tow to firing range and put down with 300 Winchester Mag to the  Cylinder Head!

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Lol well it looks like your better at the bbq then rebuilding carburetors!!!! Lol just kidding.  Food looks amazing, call me next time I’m coming over ! 

Seriously though you did some good work.  Unfortunately you have what is called a flat spot in the carburetor , it’s going to take some more time to adjust the carb and test.  Did you replace the air/fuel screw ? This could be a problem if the screw is worn or damaged.   

Maybe adjust the needle on the throttle slide by moving the clip into a different notch. Check the spec for where it needs to be or move it and test ride.  

You will get it dialed in.  It’s just one of them pain in the ass cranky carburetors.   

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Bike is running really good, below are a few things I did wrong.

In an effort to try and help others like myself who have NEVER worked on a bike, I am sharing my mistakes, and making some mechanical statements based on my observations and experience troubleshooting. Frank please review and correct me if some of my conclusions, or terminology are off.  I never did reply to your question as to what model carb, keihin cvk32

I took the following shortcuts:

I assumed my air intake was fine, filter was clean and the air box looked almost dust free,  I thought the air entered the air box from two what look like rear facing scoops on top the the airbox. I was wrong, it enters from the snorkel that you don't really notice until you pull the air filter off and look underneath. Mud daubers had built a nest in snorkel all but plugging it.

After having to take the carb off a dozen times I stopped fully assembling it when I tested. I was NOT tightening the hose clamp on the boot between the head and the carb. This allowed air to bypass the carb reducing the vacuum, when I would open up the throttle all the way, the butterfly valve was opening but not creating enough vacuum in the vacuum chamber to overcome the tension of jet needle spring, so my main jet would never open all the way. the reduced vacuum prevented the main jet from opening up all the way.

Since I was not fully assembling the bike I was not test driving after installing the carb each time. This last time I completely assembled everything, engine would still rev up and down a little at full throttle. Well when I took it out for a ride, it ran faster and stronger then it ever has, no issues at full throttle.

My carb has probably been fine since I rebuilt it, I just didn't know it because my testing was flawed. Lesson learned.

At the end of the ride I noticed my choke was on about a 1/4 when I closed the choke the bike would die. recommended position for the fuel / air screw is 2 1/8 turns and as I recall the last time I adjusted it out about 2 3/4 turns. So now I have what I think are just a few minor adjustments to get things dialed in.

Thanks again for all of your help Frank, I leaned far more than I ever thought I would troubleshooting this, If you were closer I would buy you a beer!

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Haha well maybe if I’m ever near you I would take you up on the beer.  

I’m glad everything worked out good, hopefully your good to go for a long time. 

Your adjustments and final dialing in sound right on point. 

Well done! Ride safe brother. 

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