Picked up a deal this weekend. 07 400 TRV for $1500, wasn't running, dried mud in the air box, looks like someone's snorkel job wasn't quite watertight. After a new battery, cleaning the spark plug, cleaning the airbox, it finally came to life. Of course, when I got a mile back the trail on my farm, it wouldn't restart. So out with Old Faithful, 02 500i manual that has never let me down, and tow it back home. Still got some kinks to work out on that TRV, but at that price, I'm surprised it ran at all.

It's a lot easier to tow a quad when you have someone else to steer the other quad. If you don't, it gets to be real fun...

 

I had to tow another X2 down a mountain and through mudholes. He was riding and spotted a moose. While gawking at the moose he hit a big log and it got up under his quad and stretched his throttle cable big time. It was stop and jerk all the way down the 5 miles to where everyone parked. Not fun. I hope you get your "new" quad up and running.

 

Had a chance to work with it some more, this is strange.

Got it started again, was running great. So I was running around the yard, and it lost power right as a distinct tapping sound started. It didn't lose power completely, it just lost most power. I could hold it at half throttle, and it would run a little faster than idle, but wouldn't go anywhere. Let off the gas, and it died. Cranked again, and it wouldn't start, but the cranking sounded a bit different. Yanked the hand starter and couldn't feel any 'hard' compression.

Now, I was thinking a sticky valve, but if a valve stuck slightly open, it wouldn't fire at all, would it? The fact that I could keep it running when that tapping sound started up tends to make me think it's something else. Does the 400 have a compression release valve on it?

 

I'm wondering if it got hydrolocked and something got damaged. Water doesn't compress in the cylinder. If it had mud in the airbox it may have got water in the cylinder. I'd do a compression check and compare it to whatever the specs are for your quad.

 

Found the problem. Half of the compression release cam is missing. So it was doing the opposite of what it was supposed to do - instead of releasing compression for cranking, it was releasing compression when the engine picked up speed. That was the rattling sound I was hearing as the engine lost power.

That engine has had people of unknown competence working on it, so it's quite possible they just forgot to put the half moon piece back in place. No wonder it was driving the PO crazy - ran great for a while, rev it high and it just died.

Out with the camshaft, and take the other half off.

 

Actually, the cylinder was scored by the mud. The PO had the cylinder bored and new piston installed, looks like the person doing the rebuilding forgot to put one of the compression release cams back in. Spent yesterday evening tearing out the airbox, ducts and snorkel, and washing the mud residue out.

I can see why the PO was pulling his hair out. It would run great, then every so often, the one remaining lobe of the compression release would swing out at mid RPM's and kill the engine. Take it to a mechanic, it would run great. Was enough to tick off the good humor man.

Got lucky on this one, I remembered something I was told 8 years ago. When I got my 500i new, I heard a tapping sound at mid to high RPM's, sounded like a rod bearing. Was told that this was the compression release cams, it was normal for the 'zuki 500, and not to worry about it. So when this 400 motor was sort of acting like it had a stuck valve, and sort of not, I remembered that. A 'zuki owner on HL gave me a description of what the compression release setup looked like, I pulled the cam cover, and noticed only half of it was there, and there was a spring just sitting in there loose. That doesn't look right.

Only downside of just removing the setup - got to remember not to pull start it. Without that, it'll kick back, yank the pull starter out of your hand, and probably sprain your fingers in the process. Keep a good battery.

BTW: I bought a Diehard Gold battery for it, had the neatest battery acid packing setup, came with six acid bottles molded together and six funnels with piercing prongs molded together. Just put the funnel in the six holes, upend the battery bottle, press it down, and all six cells get filled. No muss, no fuss, no messing with a tube and spilling acid. Good job, Sears. That was easy.

 

For that price its worth to do a some work, when you see a snorkeled ATV you know its been through the ringer,people do not go thought the trouble of adding them if they don't plan on using them.

I pull started a 660 grizzly that have know decompression relief, yes it hurts if the rope rips out of your hand.

 

i know all about the 660 breaking your hand, had a dead battery for a weekend-it sucked.