02' Yamaha big bear 400 carb issues

[Wam12905]

Hey all!

I recently acquired an 02 big bear 400 this past summer, carb on it was shot to sh** (pics attached) so my father recommended I just buy a new one off amazon. I purchased the first one that came up as compatible and once it came in, I bolted it in and it fired right up with no noticeable issues. Once I got to the trails with it I realized that on any un-level ground, there's little power output. I checked with 3 different local shops and they all refused to work on tuning up off brand carbs because of how terrible they are. One shop had a motorcycle in with an aftermarket carb and the mechanic said that that would be me if I brought my big bear in. Whoever owned the motorcycle and needed their aftermarket carb tuned up had racked up the bill to nearly $1500. Needless to say he made it clearly obvious that putting any amount of money into an aftermarket carb is not worth it. Now that I've learned all of this, I'm wishing I didn't toss the old carb for a $30 amazon one. In light of this minor f-up does anybody have any recommendations for high quality carbs for my vehicle? I've also attached pictures of the old carb and its condition for your curiosity, although its current condition is likely 6 feet under in a landfill somewhere. 

 

https://www.ebay.com/itm/283488113569?_skw=Big+Bear+400+Carburetor+Oem&epid=10042848409&itmmeta=01JCDWCTMJX5GBC407RF2PPVDD&hash=item42013553a1:g:INUAAOSwn8llquIL&itmprp=enc%3AAQAJAAABAHoV3kP08IDx%2BKZ9MfhVJKkIMhqd%2Fye0vA0YMR5DUzMoCLl0F9GPNRfuAJKaylVqqyVrZCBJVvXQaPrlosjt%2FZnIHyIRPuGiIbxC9o%2B02UqGA4YqXDyyH4bVebnTPz8P5Elg76CvLdu3KyZgwpgpSeYJK2IOWtlo9vtTld7RVjqPwSv1VF26v6kyXGesAB%2BA%2BCHsj3OnqNrHMyKCBuDMSSvUWvOfq%2BKsZKqyHR7yduef%2BHBlXvfiyRJPThHr7Ge9n%2BHBbuxRCb4oF7%2Fp8oZsvajHy9YDitFRfNJeeAssYbgXuhAc7AVvUZZ2YxKW9GzDdxltLMap8orKJtr%2BIk0SRGQ%3D|tkp%3ABFBMsqqzvONk

I found this one on EBAY that advertises as a genuine OEM part for a fraction of the $650 that they're normally worth. Any help would be greatly appreciated, thanks!

[Gwbarm]

Thats ashamed that carb was very repairable, you might have needed some new jets to make it like new but maybe not they would also cleanup. Never throw OEM carbs away , they are valuable. That being said there is a guy on Ebay that is selling new Mikunis  for a fraction of the price that Yamaha sells them for. Dont know how or why and i was skeptical but bought one for my 2000 Big Bear anyway. I have had no problems with it and it is a Mikuni Carb. I think the seller was Nikki Cycle, i will look it up and get the information if you are interested. I think i paid 200 for it. Mine also had an aftermarket carb on it but it was worse than your original all white and crusty from water getting into it and i didnt even waste time on it, just ordered a new one. Looking at your photos yours was not bad at all.

I looked at the link you sent and i didnt see Mikuni anywhere on the carb, i would be skeptical.

[Mech]

Too bad you threw the original away because it looks like it just needed a clean.

Any after market carb might be just as problematic as the one you already have.

Did your new carb come with any spare jets ? They sometimes do.

Since it idled ok, and I'm presuming from your description that you weren't giving it full throttle, the problem perhaps lays in the 1/4 to 7/8 throttle opening systems of the carb ? That range is cobntrolled by the slide and needle, and the discharge tube the needle slides down into. You could try changing the height of the slide needle in the slide. There's a clip on the needle and if you raise the clip  up a groove in the needle it makes it run leaner between 1/4 and about 7/8 throttle, and if you lower the clip it makes it run richer. You can try raising or lowering the clip and as long as you note where it was originally, and whether it runs better or worse in that throttle range after the change, then you will have an idea about whether to move it further or back the other way by two notches. That's an easy job to do in place, and easily undone.

Since you thiink it was sloping ground that made it run bad, as opposed to the load being put on the engine, perhaps it needs the float level adjusting as well or instead of the slide needle adjustment. That's a bit trickier to do, and undo, but you could test the theory by accelerating along the flat, accelerating up hill, and accelerating down hill. If it goes real bad uphill but it's ok on the flat, that would sort of indicate a bad float, but you need to be putting similar load on the engine in both cases to really get a feel for it. You could also try just riding along nice and gentle with hardly any throttle seeing if the engine surges or falters going on the flat or up hill. If it runs a lot different going up a hill, than it does when under power and accelerating on the flat, it might point to the float level as well.. If you read the manual, it may be that that bike's float level can be checked with the carb still on the bike. They might use a clear plastic hose to gauge the fuel level in the carb.

[Gwbarm]

Was you original really an OEM it could have also been an aftermarket. 

[Mech]

Does that new carb in the link have the same throttle cable fitting ? And the electrical dodah.. a choke I presume ?

[Gwbarm]

Good point Mech! The throttle cable may also need to be adjusted to let the throttle plate close all the way, but if its idling good and slow that may not be a problem, but if its idling too fast may want to check that. That electric thing may be a carb heater, mine didnt have one but a lot of them did, and more than likely it was OEM if that is on there.

[Wam12905]

1 hour ago, Gwbarm said:

Thats ashamed that carb was very repairable, you might have needed some new jets to make it like new but maybe not they would also cleanup. Never throw OEM carbs away , they are valuable. That being said there is a guy on Ebay that is selling new Mikunis  for a fraction of the price that Yamaha sells them for. Dont know how or why and i was skeptical but bought one for my 2000 Big Bear anyway. I have had no problems with it and it is a Mikuni Carb. I think the seller was Nikki Cycle, i will look it up and get the information if you are interested. I think i paid 200 for it. Mine also had an aftermarket carb on it but it was worse than your original all white and crusty from water getting into it and i didnt even waste time on it, just ordered a new one. Looking at your photos yours was not bad at all.

I looked at the link you sent and i didnt see Mikuni anywhere on the carb, i would be skeptical.

Never throwing an OEM part away again, bummed out I learned the hard way. Thanks, I will definitely look into the Mikuni carbs

[Wam12905]

1 hour ago, Mech said:

Too bad you threw the original away because it looks like it just needed a clean.

Any after market carb might be just as problematic as the one you already have.

Did your new carb come with any spare jets ? They sometimes do.

Since it idled ok, and I'm presuming from your description that you weren't giving it full throttle, the problem perhaps lays in the 1/4 to 7/8 throttle opening systems of the carb ? That range is cobntrolled by the slide and needle, and the discharge tube the needle slides down into. You could try changing the height of the slide needle in the slide. There's a clip on the needle and if you raise the clip  up a groove in the needle it makes it run leaner between 1/4 and about 7/8 throttle, and if you lower the clip it makes it run richer. You can try raising or lowering the clip and as long as you note where it was originally, and whether it runs better or worse in that throttle range after the change, then you will have an idea about whether to move it further or back the other way by two notches. That's an easy job to do in place, and easily undone.

Since you thiink it was sloping ground that made it run bad, as opposed to the load being put on the engine, perhaps it needs the float level adjusting as well or instead of the slide needle adjustment. That's a bit trickier to do, and undo, but you could test the theory by accelerating along the flat, accelerating up hill, and accelerating down hill. If it goes real bad uphill but it's ok on the flat, that would sort of indicate a bad float, but you need to be putting similar load on the engine in both cases to really get a feel for it. You could also try just riding along nice and gentle with hardly any throttle seeing if the engine surges or falters going on the flat or up hill. If it runs a lot different going up a hill, than it does when under power and accelerating on the flat, it might point to the float level as well.. If you read the manual, it may be that that bike's float level can be checked with the carb still on the bike. They might use a clear plastic hose to gauge the fuel level in the carb.

My Dad rode it and suggested it was the float, haven't heard anything else from him but I don't quite know for sure yet. First off, yes, the problem is in the mid range of the throttle. Going uphill, throttle dumping it seems to be the only way to receive the power I need at those demanding moments while going uphill. However, towards your second point of it being the floater; I have a trailer that the quad towed just fine at all throttle ranges from 1st to 2nd gear on level ground but those gears never lose power on graded terrain so it's not definitive that its the floater yet. I have about a 300 yard straightaway, I should probably get to those upper gears with the trailer (load on flat ground) and see if that does it. I will get back to you on the results of this little test.

[Gwbarm]

Just looked it up. He did have one, you might want to talk to them they are very knowledgeable and kept me from ordering the wrong one, i gave him my Vin and he told me which one to order.

https://www.ebay.com/itm/154609803212?epid=13049274481&itmmeta=01JCF2HDKYTK2PYDHBZ1YER326&hash=item23ff765fcc:g:d8kAAOSwbZ5m~wvt

[Wam12905]

1 hour ago, Gwbarm said:

Good point Mech! The throttle cable may also need to be adjusted to let the throttle plate close all the way, but if its idling good and slow that may not be a problem, but if its idling too fast may want to check that. That electric thing may be a carb heater, mine didnt have one but a lot of them did, and more than likely it was OEM if that is on there.

Since the throttle adjustment screw is easily accessible, I took the opportunity to play around with it while I was out riding last. It didn't seem to fix the issue 

4 minutes ago, Gwbarm said:

Just looked it up. He did have one, you might want to talk to them they are very knowledgeable and kept me from ordering the wrong one, i gave him my Vin and he told me which one to order.

https://www.ebay.com/itm/154609803212?epid=13049274481&itmmeta=01JCF2HDKYTK2PYDHBZ1YER326&hash=item23ff765fcc:g:d8kAAOSwbZ5m~wvt

Will do, thanks!

[Mech]

I was questioning whether the throttle attachment was the same on the one in the link and the original. I thought one had male threads and one had a hole for a cable to fit into. Might be bad eyes.. or brain.

[Mech]

And yeah good test Wam, towing the trailer.. That's the way to figure it, be methodical, pay attention to what changes. Figure if it's load or bike's angle causing the problem, and/or adjust the slide needle, that will compensate some for a bad float height. You will likely still end up with a flat spot if the float's wrong, but as long as you roll the throttle on at a speed the engine can keep up with, it will test whether a mixture change is helping or not. If the needle adjustment does fix it, and you don't get a flat spot, then that might be all that's needed.. I'd try the needle.. it's so easy to do..