1987-1996 Yamaha Big Bear

[hardlydangerous]

The carb design is a little different then most you will find as I’m sure you are already aware of.

It's basically your carb is a cross between a CV and slide carb. 2 carbs in 1
The main thing to remember is the butterfly valve is not the throttle. The butterfly valves job is to control the volume through the venturi.
On your style carb the throttle cable also activates the throttle slide. On CV carbs it's the pressure difference between the outside atmosphere and the venturi that moves the slide.
Having the butterfly valve will vary the intake volume which provides a more precise fuel mixture over a regular slide carb
With a CV carb the throttle response is slower but at the same time provides a very precise fuel mixture and a very smooth throttle operation.
With your style carb you still get that same precise fuel mixture but with out the throttle lag while vacuum is building in the venturi to open the slide.
This quicker throttle response is much better for off road use where you need heavy bursts of throttle to climb over stuff and maneuver the bike quickly.
A CV carb is usually better suited for road going machines, were precise jetting and fuel economy can be appreciated more.

As for the rear differential bolt... Grab you a heavy ratchet or breaker bar and good 6 point socket. Use a small propane torch and heat the casing about 1" away from the bolt all the way around it. Remember to direct the flame tip away from the drain bolt. After 30 seconds or so put the ratchet on it and giver...
A tiny bit of anti seize on the threads will help eliminate this in the future.

For the brakes you will need to remove the adjuster plugs and back the adjusters off. Also the axle nuts may be SUPER tight if they have never been off before. I remember our biggest impact gun would not touch them; again we had to use a big breaker bar or a ratchet with a piece of pipe on the handle to break the nuts loose.

[mtk]

OK, we have the first ride report.

I took it out on Christmas Eve and used it to drag my log splitter into the woods for a bit of wood splitting before it got dark. It didn't want to accept throttle at first, but I think it was just because it was still cold. Once it got warmed up, it seemed to run OK. At first, if you opened the throttle too quickly, it would bog, but a slow opening had it running fine. Once it was warm, it seemed to accept large throttle openings better. The carb probably needs some fine-tuning as well.

It definitely makes decent power because I got the one wheel of the splitter stuck to the axle and the Big Bear pulled it right out with a bit of throttle. Oh yes, the four ITP Mud Lites throw a decent amount of mud from all four tires.

As for the brakes, the axle nuts came off OK, but I didn't muck with the adjusters. I'll have to do that the next time I have it apart. Now that I'm confident it runs, I can worry about getting the brakes done up properly.

As for the drain plug, the drain plugs on this are socket head cap screws (i.e. Allen heads) while the fill caps are large, hex heads. The fill plugs come right out, but the rear drain plug rounded out on me. I put the large hex fill plug in the drain hole in the front and plan on doing the same when I get the rear drain plug out. I need to replace the boot on the drive shaft anyway so I figure I'll address the drain plug when the swingarm is out of the machine and I can turn it over on the workbench, rather than lay on the floor and try to fix it.

I also replaced on headlight bulb and the high beam still doesn't work. So I guess I'll be tracing the high beam wiring while I'm at it too since it clearly is a wiring problem and not a bulb problem.

The starter relay is also in need of replacement. It works intermittently and that won't do without the recoil starter back-up system. At 589lbs, this thing is too heavy to push if it won't run on it's own.