Yamaha Moto4

rrlund · Apr 17, 2012

Before I go any farther and take off more things than I need to,anybody have any ideas? It just quit on me Sunday morning. Went to start it back up,it kinda fired twice then just whirled like it had no compression. Last fall it acted that waay and had a broken rocker. So I took the tank off,took off the front and back cover,both valves are opening and closing. I still have some gap in the rockers. Took off the carb and exhaust pipe. Blew air in the spark plug hole and it blows out the hole where the carb bolts on even when the valves are closed. Doesn't blow out the exhaust. I stuck a small wire in and can't feel a hole in the piston,I know,that doesn't mean it doesn't have one. Stuck a wire down in the intake valve and turned it over and it grabbed the wire,so the head is still on it.

There was no noise when it died or anything. Just sat there idling while I opened a gate and died like it had idled too slow,not uncommon.

wisbaker · Apr 17, 2012

My pick-up had an incident where it sounded like it had no compression or maybe the starter wasn't turning the engine over. Turns out it was flooded and was so close to running you could not hear any load on the starter.

dr sportster · Apr 17, 2012

Even when the valves are closed maybe should read " the intake valve is allowing air to pass even when it should be in the closed position". Something like that. Intake valve not seating.

rrlund · Apr 17, 2012

There's more tappet clearance there than it looks like there should be on the intake valve. I don't know what could be stuck in it,but I'm thinking I'll try tapping on it a little while I blow a good blast of air in it. Maybe if there is something in it,I can dislodge it. I'd hate to spend half the afternoon tearing it all the way down and then have something just fall out of it.

toadady · Apr 17, 2012

(quoted from post at 14:51:40 04/17/12) There's more tappet clearance there than it looks like there should be on the intake valve. I don't know what could be stuck in it,but I'm thinking I'll try tapping on it a little while I blow a good blast of air in it. Maybe if there is something in it,I can dislodge it. I'd hate to spend half the afternoon tearing it all the way down and then have something just fall out of it.

mabey a piece of carbon stuck under the valve?

teddy52food · Apr 17, 2012

The valve seat may be loose & cocked in the head.

rrlund · Apr 17, 2012

I gave in and pulled the head. Hated to do it because now the timing chain is off of it. Looks to me like a warped intake valve. I'm seeing daylight down one side of it. Doesn't look like the seat. Called my son at the shop,said he'd try to get the parts.

Anonymous-0 · Apr 17, 2012

You may have better luck on an ATV forum..... I have an owner's manual for a bruin/beartracker with a little bit of troubleshooting in it. I can email iot to you if you want. Just shoot me a note..

[email protected]

has it got a rope starter also? Maybe you can pull the plug and see if it's doing what it should...

rrlund · Apr 17, 2012

Took the valve out of the head. Stem isn't bent,just the head of it. It and the piston look like the valve hit it. When I called me son,he said we put a valve and a rocker both in it last year. It kicks back every so often if it stalls or if I let off the starter at just the wrong time. I'm wondering if when it kicks back,it might be jumping timing? I know we had to put a new timing chain tensioner in it last year when we put the valve in. Thought we had it tight enough,maybe not?

Yamaha Moto4

rrlund

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wisbaker

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dr sportster

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rrlund

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toadady

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teddy52food

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rrlund

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Anonymous-0

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rrlund

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