1999 Yamaha bear tracker 250 Carb problem

[Yamaha250]

I have a 1999 Yamaha bear tracker 250 that needs  carburetor but I really can't afford a new one right now $650 at the dealer is there an older style o could use that would work 

 

[davefrombc]

I'd tell  the dealer where to place his  $650  carburettor.  You can buy one online for  ~ $165  and a rebuild  kit  for your old one  $16.    both are  offered  with free shipping   in the  US.

http://www.ebay.com/bhp/yamaha-bear-tracker-250-carburetor

[Ajmboy]

You can buy it on Amazon brand new for $165

* Added ATV info into topic title.

[Rebel50]

I just got one from justgastanks

[sheba2012]

99 beartracker 250

replaced carb and intake now when it cranks up it is at full throttle

already disconnected throttle cable and checked all screws to ensure they are tight to help rule out a vaccum leak

what is it i am missing?

[Mech]

Where'd you disconnect the throttle cable ? Did you check the slide's going right down ?

Is this an old fashioned carb with the cable straight onto the slide, or a more modern sort with a diaphragm on the slide ?

[sheba2012]

Disconnected cable from under the cover on the side of the carb.

It's a flat slide with a diaphragm that actuates it the slide moves freely .

When it fires up the slide goes up without opening the ventury

[Mech]

Yeah I had a look at the parts book.

Well the obvious question is, and don't take offense here, are you sure the butterfly is going right closed, have you wound the idle speed screw right back ? If the butterfly's right closed then it doesn't matter what the slide's doing, no fuel's going to get in. If the butterfly's closed then the slide shouldn't rise. If the butterfly's closed then even if air was getting in through a fuel tap vacuum hose or a manifold vacuum leak, it would take a combination of problems, like the vacuum leak, and excess fuel from somewhere like a hole in the diaphragm of an auto fuel tap or the choke.

Is the choke in and working ? That bypasses the butterfly.

I can't think how or why but perhaps a breather pipes swapped with an auto fuel tap hose.. if it has an auto fuel tap..

 

 

[sheba2012]

Idle screw is backed out completely and even double checked the butterfly.

As well as  checked the spring on top of the slide.

[Mech]

Hmm..  Well as you no doubt know, the slide gets lifted by vacuum.. So how is that vacuum getting to the top of the diagram I wonder..

That aside for the moment though, even if the slide lifts, nothing should happen if the butterfly's closed.. so.. somewhere there's air, and fuel getting in..

Is this a knock off copy carby ? Have you looked at all it's drilling to make sure there re no unusual ones ?

The yamaha doesn't have a fuel pump Huh ? Does it have a auto fuel tap tapping on the carb, or a pump tapping ?

All I can think of without inspecting it is that the choke's causing this.. it bypasses the butterfly.. If the plunger was open, and if the aircleaner was badly blocked, the choke passage could let vacuum to the inlet side of the venturi, and so to the slide diaphragm.. perhaps ? Or, a combination of the choke supplying fuel(way more fuel than they are meant to, plus extra air getting in somewhere.. 

Some choke plungers have a tapered needle to alter the amount of fuel going through as you use less than full choke, and some plungers dont.. Maybe something there.. 

[sheba2012]

It is an aftermarket carb.

Could it just be the wrong carb?

[Mech]

A wrong one wouldn't do it, but a badly made or assembled one might be able to.. But I don't see how.

If the butterfly is shut then there's only the idle circuit operating.. If there was no air jet for the idle circuit perhaps ? Or the idle mixture screw not there at all.

Also.. do you have an emission diagram on the side of that carb..Could check that.

[sheba2012]

On 5/24/2017 at 1:53 PM, Yamaha250 said:

carburetor

No emissions on carb only a fuel feed and a bowl vent

[Mech]

Well on the air-cleaner end of the venturi there are one or more brass air jets, one of them will be to restrict air to the idle circuit. It might be way to big or missing.

And the idle mixture screw I hope you are familiar with. That might be missing..

[sheba2012]

ok so mystery solved......simply the carb was just a cheap chinese pos . replaced with a higher quality aftermarket and there ya go

now onto my next one is a 2004 polaris spotsman twin efi any ideas on a replacement fuel pump and sock ?

[Mech]

It must of been an unusually bad one. Most of the aftermarket carbs I've seen have been ok made, but not tuned for any particular bike or market, and so needed retuning. They generally run after a fashion though, and don't have that problem.

And nope, I don't know where to get parts..  I'm in New Zealand.. We just fix everything with number eight fencing wire.