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JacobSlabach

Yamaha Big Bear 350 carb problem

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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.

Sent from my SM-N920V using Tapatalk

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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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thanks @Frank Angerano!  will do next time.  The float was fine on the oem carb, but the fork (cast aluminum part that holds the float axle in place) was broken off and missing.

anyone know what the valve clearance spec is for this bike?

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was looking online and cant find a definite answer to what the valve clearance should be on a yammy big bear 350.

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the compression was 60psi.  I adjusted the valves to spec with no change.  I'm gonna pop the oem carb back on to see if the aftermarket is indeed the issue.

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Ok well you can spray the engine down with a soapy solution and crank the engine and see if any bubbles show up. Maybe a head gasket leak.  If not then maybe a new piston and rings may be in order. 

How do you plan on putting the old carb back on with a broken float strut? 

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Can’t see the float operating properly with that break in it but give it a shot.  Just don’t burn the bike if a backfire happens with all that fuel. 🥵

 

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90s.  not sure exact year.  thats another thing I should probably do is find the vin and get that nailed down.  anyone know where the vin is on this bike?

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ok.  I got the vin, but left the paper in my shop lol.  I put some WD-40 in the cylinder and retested compression.  now it al 80-90psi.  So it is rings, but also valves prolly.  I'm thinking it ran rich (carb flooding) for long enough that it built up crud in the cylinder and the valves arnt sealing properly and it blew the rings.  I just thought it would be smoking if the rings were shot....

but yea for those out there wanting to know if their low compression is due to rings, squirt/poor 1 ounce of oil into the spark plug hole and hook up the compression tester, then turnover once or twice by hand to make sure it's not going to hydro-lock, then test compression (with electric start).  if the reading is better, your rings are shot.

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