Yamaha ATV forum - yamaha 80 moto would not start

Hi, I have a 1998 yamaha 80 moto atv. I just got it yesterday.
The previous owner said that there was something wrong with trying to start it with the electr..

Hi, I have a 1998 yamaha 80 moto atv. I just got it yesterday.
The previous owner said that there was something wrong with trying to start it with the electric start, so they would roll start it.
When I got it home, the battery was dead so I was just jumping it from my vehicle. The atv turned over, but I could not get it to start.
I pulled the carb and cleaned it. I even tried to get the thing to sputter or start using a starting fluid in the intake, but nothing. I am picking up a new battery today.
Any ideas what is wrong or why it would only start rolling it, instead of the electric start. I definately have spark and it appears that I have gas. Any help would be appreciated, from me and my kids. Todd.

The next thing I would check would be the compression.
Motors will build more compression push starting than with an electric or kick starter.
Hold the throttle wide open and crank the motor until the gauge stops rising. Let me know what the number is. Then put a cap full of oil down the cylinder and retest. See if that raises the number any.

Thanks Doug, I will check that tonight when I get home.
Todd.

The first time I did it, it went to 40 PSI, With oil, it cranked the first time to 175, 2nd time 110, 3rd time 90.

I'm sorry to say but that sure looks like worn out rings to me. There is one more thing to check first before tearing the top end down.
I would set the valve clearances just in case one is very tight and hanging open. Remove the valve caps on the head. Remove the spark plug. Remove the timing cover cap so you can view the timing marks.
Rotate the motor while watching the intake valve open and close. Go to the T mark on the flywheel. Set the intake valve to .002in-.004in and set the exhaust valve to .003in-.005in.
Rotate the motor a few more times and double check your work. See if the compression came up any and if it starts. If it does, you are good to go. If the compression does not come up then you know your rings are done for. You should have a minimum of 120 lbs compression and new would be around 150.
Let me know if you need additional help. If you need to do the top end work I think I have the manual for that machine that I can upload for you.

I forgot to ask how much you paid for the machine. If you paid top dollar then I would return it.

It was free, I am just trying to figure out if it is worth putting money into it. I don't really have any money to put into it, but now the kids are begging to ride it. I hate to tell them that we may never ride it.
I appreciate the help, I opened a cover to expose the fly wheel, and I see a mark on it, but don't see any other marks. I just have no idea how to complete the rest. I opened the cover to the inlet valve, but don't exactly know what to look for. I have the spark plug out, but once again am not sure what to do. Would the manual that you talked about for doing the top end show any illistrations and some other direction.
Also, what would be your best guess at rebuilding the top end.
Thanks
Todd.

It would probably help to have the manual. It will take me some time to upload it and send you the link.
What the intake valve as you turn the flywheel. It will go down and then back up. There should be a T mark on the top of the flywheel that matches up with a mark in the inspection hole. If you can't find any marks you can put a straw in the spark plug hole and when it comes all the way up then you know that is top dead center more or less. At this point you can wiggle the intake and exhaust rocker arm. If not, it is too tight for sure. There is a locking nut on the top with a screw that goes against the tip of the valve. You insert a feeler gauge right there and turn the screw in or out to adjust.
I'll try and hook you up with some photos in a bit.
If it only needs a set of rings and gaskets you can get by for under $50. It's best to check the piston clearance to see if you need a bore job and OS piston. I also recommend pulling the valves and replacing the valve guide seals and lapping in the valves. This will give you a motor returned to factory specs and it will probably still be running when the kids outgrow it as long as you change the oil. If you did the entire works you'd be looking at more like $200 if you did all of the labor yourself.
I'll be back in a bit with some photos.
Doug.

Doug,
I did find a mark, it appears to be on the housing, not under the cover. The mark on the "flywheel" or the gear that has the chain attached. It is passed that point by about 1/4 of an inch when the piston is TDC. I only found one mark. Is the intake and exhaust valve the same valve or is there another valve that I have not uncovered? When the valve is in the up position, which it definately comes up, I can not wiggle it at all. It does appear to come up a good bit, but still not play. Even if it comes up a good bit, do you think that it still is too tight. When you say too tight, I assume you are saying that it is still covering the whole or touching the block.

There is a valve for the intake and one for the exhaust. The rocker arm moves about 2-3 inches up and down. When all the way up the rocker arm should have play in the amount of the valve specifications I posted above.
I am downloading the manual now and will have it uploaded for you in about an hour.
Doug.