Hi, I am new to the 4 wheeler world. This old Yamaha Moto-4 came into my posession recently. (See pictures) I know nothing about four wheelers but do a fair amount of automotive repair.

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The motor runs pretty good but I believe the transmission is broken. No matter what gear you have it in the unit can be rolled freely and engine doesn't power anything. I pulled back the boot over the u-joint and it doesn't turn with the engine.

When I elevate the rear end and turn the wheels I can hear a chain or gears inside the rear end turning. Which makes me think the rear end is ok?

Can anyone give me some advice? Are there certain likely parts that have failed that I can check and possibly replace or repair? My budget can't constitute spending a lot of money on this old junker but I do enjoy tinkering on things like this. I have acquaintences who repair ATV's that if I need a certain part I can ask if they might have something second hand kicking around but I don't want to go asking for advice on a bunch of stuff.

Lastly, can anyone ID the unit for me. I don't know what year or what it's specifications are. The engine says 1500cm3 on it. I don't know where else to find ID tags or info.

 

I'll give you a few things you can try.

First make sure the sub transmission is in gear. The sub transmission is one you shift with your left hand near the motor. (not the foot shifter). It should have High, Low and Rev.


If that doesn't work I would have a look at your clutches. From the rider view point its behind the right side cover. In this picture look between the big Yamaha cover on the right and the oil filter cover to the left (cover with the paint warn off). Right between them there should be a small cap of some sort. Under that cap (if its still there) will be small shaft with a slot cut in it and a nut. That adjustment is for the force the shifter lever puts on the clutch. You can try adjusting that to see if it helps any.

If the clutch adjustment doesn't help you should pull the right side cover off. With the cover off you will be able to see both clutches. The one near the rear of the motor is a normal motorcycle style clutch pack and the other is a centrifugal clutch. Connected to the crank will be the centrifugal clutch. This clutch has a one way bearing behind it that allows the rear wheels to turn the motor at any speed but the motor will only apply power above idle speed. It's setup this way so you don't lose engine breaking when you let off the gas but you also don't stall if you leave it in gear. It also allows you to get into trouble on hills by allowing you to roll backwords when the motor stalls. Put the rear of the ATV on blocks. Put the sub transmission in High or Low and put the main gear box in first gear. Have someone turn the rear wheels as you look at the clutches. The center of the clutch pack is connected to the transmission, the outside basket is connected to the centrifugal clutch. If you see none of the clutches trying to turn you have a main transmission or sub transmission problem. Shift to another gear and try again. If only the center of the clutch pack spins you have warn friction plates, weak springs or the bolts/screws that hold the boss/springs are not tight enough (be very careful, its very easy to snap the screws if you over tighten them) If the whole clutch pack spins and the centrifugal clutch spins freely, then you have a problem with your one way bearing.... but even if the one way bearing is bad the clutch should still work when reving the motor.. unless the bearing and the friction pads both failed in that case the engine couldn't turn the transmission and the transmission wouldn't be able to turn the engine. Let us know what you find out.

 

Great. Thanks for all that info, I will investigate soon. One question though... when I remove the right side cover is it going to drain a bunch of fluid? (Just want to be prepared).

Thanks again.

 

Ok... update.

Tonight I checked that shifter force adjustment (slotted bolt) and was unable to get the slottet part to turn so instead I used a wrench and tightened the nut.

I then cycled the unit through its shifting patterns while rolling it back and forth. Once in a great while it will grab a gear and the wheel will lock in the forward position and roll backwards with resistance.

I am thinking it doesn't have anything to do with that nut I tightened and probably I just never shifted it enough times to get it to engage.

When I tested the motor yesterday and had it running I had the starter off because it's shot (and it blew oil everywhere). So tonight I reassembled the busted up starter and put it back in place to prevent more oil spewage. I tried to start the bike (with lucky gear engaged and rear end elevated) and it wanted to run and would sputter but wouldn't take off (I am turning it over with a drill and a socket on the pull starter nut). While cranking it over with the drill the rear wheel turned forward ever so slowly.

I am thinking it's not running now because it's trying to turn the busted up dragging almost seized starter motor -or- the load from the tranny is too much. Does the flywheel always turn the starter? I don't see a bendix on it. I guess I should take it outside and try running it without the starter on to learn if the motor powers the wheels???

What do you think?

 

Yes. You should drain the oil first. It will be messy no matter what. Roll it on some cardboard and have some rags ready.

 

Hi, reporting back. I never opened up that cover... I decided not to as of yet. I got the unit running and it seems that once I have the motor running it will sit there and idle for a brief time (less than a minute) and then die. I am assuming this is a carb issue... perhaps the idle mixture screw just needs adjusting?

As far as the transmission goes... if I start the unit when I have it in one of its "lucky" gears (when I finally get it to grab a gear by shifting up and down rolling the unit back and forth) then it goes... and I can drive it around the yard and up the road, etc. It also seems that once the unit is "going" I can shift through the gears so far without any issues. I was tearing around the yard in Low gear and then I kept shifting around until I found a higher gear (I have no idea what the sift patterns are) and went flying up the road and then back down... kinda got scared because the brakes aren't so good.

When It's going, if I STOP, it dies... and is hard to restart (motor is very hard to turn over with my drill & socket). Usually have to let it sit for a long time and then I can get it to start again.

Basically, when it's not running it will rarely grab a gear, when it's running it seems to always shift gears.

I know this is a lot of questions, just hoping someone can take the time to help a newbie learn and troubleshoot the problem.

Thanks!

 

I'm pretty sure it has a starter clutch right on the crank. The motor should not try to turn a stuck starter. As for your transmission problems, if you leave it in a good gear and turn it off will it always work in that gear? or do you have to mess around with it again?

You also said its hard to restart once its warm. Most of the time this is caused by your pilot settings. It also happens to be the first thing to clog up on most carbs. So you will have to clean the inside carb really well before trying to adjust anything. Also make sure there are no cracks in the intake boot between the carb and the motor. A new intake boot is $34. A few coats of high temp RTV can also work on a budget but keep a close eye on it.

Check your private messages

 

I have a moto-4 and i think the trany is going out because some times when i shift it kicks in to netrul

 

on my 86 moto4 225 i know that if the motor/transmission oil needs to be changed the tranny will slip and some times when you go to change gears you pull up on the lever and then it will pop into neutral for a good 3 or 4 seconds than crunch into gear.