Lost... 2000 Yamaha Big Bear 400 4x4 Need Help

[redneckinker79]

i just picked up this atv and now its smoking and knocking hard i thought it was piston and rings but was told i might just be the timing can anyone help me out

[redneckinker79]

i also was wondering what the bolt on the pull start side the one that says increase or decrease what does it do ? i turned it towards increase and it helped a lil bit and dosent smoke as bad but still knocks

[marioweldinginc]

On my yamaha 200 moto4, the increase/decrease bolt was for the auto clutch

Sent from my SGH-T959V using Xparent Blue Tapatalk

[oxidized_black]

you're absolutely right mario, clutch pressure only with that adjustment.

the knocks might be the valves, if they are out of wack it'll knock and smoke.

Edited March 25, 2012 by oxidized_black

[cheriah]

agreed with Oxy, check your valves and their clearances as well as the springs, make sure they are not bent, broken or weakened, and the timing...before you replace the piston and rings, check your compression.....eliminate the easier stuff first:wink:

Edited March 25, 2012 by cheriah
uhhh duhhhhh

[oxidized_black]

here is the complete manual ... :cheers2c:

 

 

[redneckinker79]

thank you very much this will def help me out otherwise i would have prob just sold it

[oxidized_black]

most welcome... never give up on a good yami, most all can be troublesome, but bullet proof too.

you'll have 'er runnin' top notch in no time

[redneckinker79]

hope so will try in the am plus i live about a mile away from a mud bog racing place and want to def check it out until then i made a lil play area in my parents back property its got 2 mud pits one is about 3-4 ft deep and the other is about 2-3 ft for the kids and about 4 jumps

[redneckinker79]

hey i dont have a timing plug area under my pull starter what do i do ?

[oxidized_black]

in the manual, section 3 page 11 they show a plug there, i think most are all yamahas have them. might be dirty and covered with dirt/mud/oil, but it is there ...

[redneckinker79]

yeah i found it its on top well i checked the timing and it seems fine so i went to adjust the valves but i dont have a feeler gage but both intake and exhaust valves were really loose so i just measured it by hand or feel should i say and it seemed to work great i will adjust them again when i get the right tool lol i doesnt smoke anymore but sill knocks just not as bad and over all it runs better than when i first go it before it started knocking and smoking

[oxidized_black]

probably once you get the feeler gauge and set them right, it won't knock anymore. good news !!

[redneckinker79]

yeah it will be great thats what i was thinking im sure the rings are def worn out but thank you for the info

and it def made a huge difference in performance and it actually idles better now as well

[cheriah]

YAY! Glad your getting everything adjusted!! Feeler gauges are invaluable and a cheap investment you'll always need as long as you own a 4 stroke!! Piston rings are not hard to do either....Happy trails to you!!