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JacobSlabach

Yamaha Big Bear 350 carb problem

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Posted (edited)

got a big bear I'm working on for a guy and it was flooding gas out into the air box, but still running.  I pulled the carb and its beat up just like his other bike I worked on for him (the bayou 220).  Its a weird carb tho:  the throttle comes in at two locations.  it has a plunger and a butterfly.  Is this necessary and could I just switch to a butterfly carb?  The problem with it is it has a broken float fork (the metal piece that holds the float pivot in place.  I'm assuming it is causing the flooding.  also the rest of the carb is well worn out and most of the screws are stripped telling me that it has been fiddled with too much by someone who didnt know what they were doing.  Also, the oil temp light is turns when key is turned and then goes off after a second- dont know if thats supposed to happen or not.

Edited by JacobSlabach

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Its not uncommon to have 2 cables at the carb. It acts as a send cable and return cable. First and foremost. Replace the carb. You may find another float but you said the other is pretty beat up.

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I believe you can get a round slide carb but have to replace the throttle cable. Try to get close to jetting as you can. Also, make sure they are the same bore size

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I just got one on amazon that was for the model.  I will update everyone when it is in.

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2 hours ago, JacobSlabach said:

got a big bear I'm working on for a guy and it was flooding gas out into the air box, but still running.  I pulled the carb and its beat up just like his other bike I worked on for him (the bayou 220).  Its a weird carb tho:  the throttle comes in at two locations.  it has a plunger and a butterfly.  Is this necessary and could I just switch to a butterfly carb?  The problem with it is it has a broken float fork (the metal piece that holds the float pivot in place.  I'm assuming it is causing the flooding.  also the rest of the carb is well worn out and most of the screws are stripped telling me that it has been fiddled with too much by someone who didnt know what they were doing.  Also, the oil temp light is turns when key is turned and then goes off after a second- dont know if thats supposed to happen or not.

You were right in getting a new carb.  If it's the same style as oem, the one cable operates the throttle valve/butterfly and the other cable is the choke/enrichener.

Oil temp light is supposed to do that.  I guess just to show you it's working...????

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haha ok thanks @Frank Angerano and @wanrep!  give you an update soon

the thing that gets me is when you push the throttle in, both cables pull- one twists the butterfly and the other pulls the plunger up..  I'm just curious who thought that was a good idea :nah:

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I was thinking of the later model Big Bears with a vacuum slide carb.  The early models did indeed have a dual cable.  One operated the butterfly and the other lifted the slide.  The choke is a manual, plunger type.  If I remember right, you adjust both cables so the butterfly and slide start to open at the same time.

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new carb in, bike runs, but really rich (doesnt need or want choke cold and bogs if you goose the throttle)  I'm not sure how to adjust these types of carbs yet so any help would be great.  @wanrep, This replacement carb has one cable to it and that operated both slide and butterfly.  It has an adjustment for the slide (so you can have the slide down more or less than the butterfly open.  I just removed the second cable in the box where the throttle splits.  I will try to upload some pics later-  main issue is its starving for air (air filter is dirty in places like it got into some oil, but not bad)  I will try to run it without the filter on and see if it makes any or much difference.

Also, the clutch is too tight making it hard to shift.  I have tried adjusting it out as far as it will go (with the adjuster on the side of the clutch cover), but it still lurches forward when put in gear and doesnt want to disengage when you let off the throttle for shifting.

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Posted (edited)

checked it out again and the air screw is out all the way (had to screw it back in some so it wouldnt rattle lose and lose itself..  So does the slide need to go up more or stay down more?  

Edited by JacobSlabach

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I figured out how to adjust the needle and adjusted it down (leaner), and it doesnt change the way it runs except that now it backfires too.  I'm thinking the issue isnt carb related?  I checked the timing- good, it has a new spark plug in it, brand new carb, maybe valve clearance?  I will check compression.  Anyone know what the clearance spec is for this bike?

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compression at 60psi.  problem found.  What next?  this is reminding me a lot of the bayou....

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next on the list.  the thing that gets me was that it was running ok (had trouble starting and bogged a little), but now it dies with throttle but starts easy as my polaris...

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Posted (edited)

yes.  it was noticeable before, but it wouldnt idle before.  now it idles great but wants to die with throttle

Edited by JacobSlabach

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Are you sure the gaskets are correct? Did you pressure test the motor?

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Are you sure the gaskets are correct? Did you pressure test the motor?

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By correct I mean in good shape

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Head gasket, cylinder gasket, case gaskets. Just because it's not showing a leak doesn't mean it's okay.

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how do you check those without tearing it down?

And i left it sitting with the compression tester for a minute and it the needle stayed the same (didnt edge down like it was leaking)

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So let’s back up here and recap for a second.  

1. It’s a Yamaha big bear with a dual actuator carburetor.  

2. You added a cheap aftermarket carburetor AND eliminated the secondary throttle cable at the splitter.  

3. Did all of this without checking compression and valve adjustments first? 

@JacobSlabach you should know by now  that the work you did was completely backwards! 

Basics first!  After that then the technical stuff. And furthermore you put a cheap aftermarket carb on a bike that will not run properly without the oem carb! 

You were better off finding a used oem carb and rebuilding it and putting it on the bike.  

Sorry if it sounds a little harsh but the only reason I’m saying this is because your smarter then that! 

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Good point Frank. Even I know better than to buy junk carbs. But in a pinch ya gotta do what you do.

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yea I should have checked compression and valve clearance.  all the issues screamed carb to me so thats why I jumped to the carb.  the airbox had gas in it (carb flooding) and I took the carb bowl off and saw that one of the float forks was broken off.  so it did need a carb.  the owner is cheap like me (lol) and doesnt want to spend money on oem parts, hence the aftermarket carb.  I had already fixed his bayou with an aftermarket carb and it worked a lot better than with the oem.  and the aftermarket carbs on my polaris and bayou (sold) work perfectly.

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I hear you but a float comes with the rebuild kit for $60 bucks.  No modifying of throttle cables needed and the valve adjustment and compression test costs nothing.   Unless the compression comes back low after the valve adjustment! Just saying you have to think before you attack.  Saves more money, time and frustration. 

 

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