BW80

[rustyplymouth]

Can someone help me? I have a 87 Yamaha Big Wheel BW80. I just put a new top end in it and cleaned the carb. I reset the carb to what it was before ¾ turn one the air needle and 4 turns on the throttle needle. It runs great and idles great but according to the spark plug it is running lean and it get hot really fast. I know it’s getting oil because of the smoke but apparently not enough. Do I need to adjust the oiler? Maybe it’s not working 100%? How can I test it? Can I adjust the needles on the carb to make it run leaner? I don’t know what the factory setting are, just going with what the previous owner had. Any ideas?

 

[trezza]

More likely to burn the spark plug white if the air/fuel mix is wrong, oil is just for lubrication, richen things up on the carb and see how you go (More fuel also means more oil anyway). If there's something wrong with the mixer regardless... I say forget the thing and mix the oil with fuel yourself (32:1 should be safe), my brother took the mixer out of his son's PW80 and makes a premix now, the bike runs fine.

 

[rustyplymouth]

I would rather not disconnect the oil. I just want to get it set up right so I don't have to keep mixing fuel. Would opening the air screw richen it up or does tightening it down. Any idea of what it is supposed to be at?

 

[sean01]

firstly you need to work out where in the rpm range its running lean..

my guess is its mid range so i would lower the needle clip on the carb slide which raises/richens the fuel for mid range..

but to work it out exactly you need to clean the plug and do plug chops.
ride the bike at about 1/2- 3/4 throttle for a bit (couple 100 meters) then hit the kill switch and pull the plug and see what colour it is.
also do the same on a full throttle run..

mixture you should be able screw right in and it will want to stall, screw it back out till you achieve the best idle quality..

 

[rustyplymouth]

Ok, looks good on the low end. Mid looked lean so I moved the clip down one notch. Then it seamed like it wouldn't get past the mid range and really smoked. I opened the air needle a quarter turn. Now it seams to hit the mid range good and be able to get to the high. Little hesitation once in a while between mid and high. Maybe needs another quarter turn on the air needle? But It now seams a little lean at the top end. What can I do to help that?

Also it still seams to be getting hot really fast is this normal? Am I just being a little paranoyed? After a 100 yard or so run I can't hardly touch the spark plug to check it. And its in the low 70's to upper 60's when I'm running it. I've never had one of these before so am I just worrying to much? I'm not running it very hard... Does it normaly get pretty hot? Thanks

 

[sean01]

check, double check and triple check for air leaks and check the condition of the reeds (if it has any lol)

but spark plugs will get hot quickly so it could just be normal... but like said above the spark plug colour will tell the story..

normal operating temp for an engine should be around 80 C degrees or 180 F. air cooled bikes run a little hotter than water cooled bikes..
use a IR thermometer gun to measure it or one of those thermo stickers and put it on the head close to the combustion chamber

 

[rustyplymouth]

After doing quite a bit of ripping around with the bike this weekend I think I got it figured out now. Runs great! Quick little bike, could use one more gear.  Think I have to find a new back tire for it before I hand it off to my little cousins to have fun with. Gets a little squirrely on wet grass or on a gravel road. The tires pretty smooth… Thanks for the help!