1990 Trail Boss acts like it has engine breaking

[carguydave]

Hello, I have a 1990 Trail Boss 250 that is in very nice shape. I think it has been very well maintained from all indications. The problem I am having is that the four wheeler seems to take an inordinate amount of throttle to make it go. Once rolling, the second I take my thumb off of the throttle it slows down like it has engine breaking instead of just coasting. The brakes aren't binding, as it rolls easily in Neutral. I have changed belts to see if that would help. The belt also seems to have correct deflection. The transmission has the correct fluid, and is full. When I pulled the clutch cover and found a green spring so I replaced it with the blue/green that is recommended. The primary clutch seems to work correctly. I have not watched the secondary. The other thing that I am curious about is that the input shaft seems to be tied directly to the output shaft even in Neutral. If I put the ATV in neutral and rev it up the rear disc spins, which in itself may not be too unusual, but if I pull the brake lever it decreases the rpm like it is putting a load on the engine. So as it sits, it looks like I have an issue with either the secondary clutch or the transmission. My gut says transmission, but I hope not. I would appreciate any insight as to wether this is a normal condition or, if not, how to fix it. Thanks in advance, Dave

[Frank Angerano]

Have you checked the tires for wear? 4x4 bikes have to have the same size tires all around obviously. But i had  a friend that had a similar issue. He rode the bike on pavement and concrete etc. turns out the front tires wore down pretty good and it put a strain on the four wheel drive due to the size of the front tires being smaller then the rear tires.  The revolutions were not the same. And the gears had a good amount of stress on them.  

I would put the bike on some blocks and put it in gear and let the tires spin. See if it happens while all four wheels are in the air.  

[carguydave]

I can see why you might think that, but this four wheeler isn't in 4wd unless you put it in.

[Frank Angerano]

Ok I’m sorry I thought it was full time 4 wheel.  I would still lift off the ground and see what it does in gear just as a starting point.  See what happens. 

[wanrep]

How's the chain/tension?  If it's too tight or has tight spots it'll put things in a bind.  Should be about an inch of free play just sitting.

[carguydave]

The chain tension is correct, and it rolls fine in neutral.  Another weird thing I found today after I took the belt off and put it in gear is that it will roll with resistance for about four feet and then the rear tires lock like it has hit the compression stroke on the engine. This isn't the case because the belt is off, but that's what it acts like. If I rock it a little it will free up again and roll with resistance for another four feet and repeat.  And I still wonder wether the secondary clutch should spin independently of the rear disc. As it is now, if I rev it way up in neutral and hit the brakes hard it takes the rpm out of the engine. I thought I should be able to hold the brake and rev the engine at the same time, I just don't know for sure. Oh, and I made a mistake, it's an '89 not a '90, if that makes a difference. I really don't want to dig into the trans. but it's looking like that may be what I have to do.

[wanrep]

The rear brake disc is on the same shaft as the driven clutch so with the belt on, stepping on the brake will slow the engine.

If you have a 4x4, you'll have 3 chains turning at the same time.  Try to isolate where the binding is taking place. Take the middle chain off, jack up the rear and run it to see if it still binds.  If not, the problem would be in the front chains or front diff.  If it still binds, then it could be the rear axle bearings but more likely in the transmission. 

[lagomu]

I am not familiar with this model but I would think you have a transmission problem. I would not think the brake would have any effect no engine rpm if the machine is in neutral.