Major Malfunction at the junction

What a great day, I just wish my motor didn't go south, I could of had fun riding today. But no, I'm stuck trying to figure out what happened to it, and I have the head off inspecting it

Let me tell my story, it started after a good ride where the bike was ripping it up. Just a few minor problems came up as I was inspecting things: 1. front wheel bearings; 2. jetting(pilot circuit to lean); 3. wanted to know how many free mods were done to the bike(yz cam timing, yz throttle stop, Grey wire,etc.)

Well after putting the carb back together, front tire , head cover, gas tank on, I tried to start it.

I was gonna fire her up after I fixed(inspected) everything. I started to push on the kicker to hit the compression for the starting procedure, but the kicker just went all the way down with no release! I did it a few more times before it started registering (in my brain)what was actually going on. No :thumbsup: compression!!!!!

I don't know what the hell I did, but I have the head off the bike as of tonight. I run out of time on diagnosis tonight, but nothing appears visually out on first inspection. :bonk:

Tomorrow ill do a solvent valve test, head warp check and from there not sure. Gosh, I wouldn't think the compression ring blew :confused:

Well this is my first time having her apart, and would appreciate any advice and tips from you guys :thumbsup:

check the compression release, it could be stuck in the open position.

I would say you have a hole in your piston.

If you've not altered cam timing and it was running ok when you last used it I can't see why anything could have changed. I would certainly be looking at the decompressor in case you've jammed it in some way (you're not holding the decompressor lever whilst kicking it over?). I wouldn't be taking the head off until you've rechecked the cam timing etc. (Did you change cam timing or just inspect it?) If it was head gasket, warped head etc. then you'd have some obvious signs (water leaking, gas escaping).

Keep us informed, I'm interested to know what's happened!!

Maybe the ratchet mechanism in the kicker is not engaging.?

Hard to tell what the symptoms are.

What a great day, I just wish my motor didn't go south, I could of had fun riding today. But no, I'm stuck trying to figure out what happened to it, and I have the head off inspecting it

Let me tell my story, it started after a good ride where the bike was ripping it up. Just a few minor problems came up as I was inspecting things: 1. front wheel bearings; 2. jetting(pilot circuit to lean); 3. wanted to know how many free mods were done to the bike(yz cam timing, yz throttle stop, Grey wire,etc.)

Well after putting the carb back together, front tire , head cover, gas tank on, I tried to start it.

No offense, but unless I missed something, I think you were a bit premature in tearing the head off the bike.

It sounds like the bike was running just fine, and that you didn't touch the inside of the engine. What could possibly have gone wrong while the engine WAS NOT running that would lead no compression to having to take the head off the bike?

I am guessing that the compression release was stuck open. It sounds like a lot of work to figure that out...

Thanks for the replies :bonk:

Ya believe me, the last thing I wanted to do was pull the head off But I already checked the compression release and that wasn't the problem, my thoughts kept coming back to one conclusion, its internal. :bonk:

Well I think I found the problem and have an idea of what caused it. Alittle stupidity mixed with a 12 pack of cheap beer :thumbsup:

I followed the manuals recommendations on a solvent test(only I used gas), where I filled the ports up with gas and could visibly see the gas leaking past the valves. :bonk:

what I think happened is when I had the carburetor and head cover off, I pulled the spark plug to check its color and condition. Well the plug hole was full of dirt, dust, and sand. Before putting the plug back in I come up with this brilliant idea to kick the bike over and blow the crap out of there. Man there was a huge dust cloud. I think that dirt got in through the intake and plug hole and got stuck in the valves. :confused:

I think I'm gonna get some valve grinding compound and try lapping the valves and put her back together. :thumbsup:

Sounds to me like maybe you should quite while you're ahead and take the bike to someone who knows what they are doing. No offense of course.

If it's just dirt in the seats and the motor hasn't run since then you probablly don't even need to lap the valves but it probably wouldn't hurt.

If it's just dirt in the seats and the motor hasn't run since then you probablly don't even need to lap the valves but it probably wouldn't hurt.

Actually, if it has Titanium valves they will be damaged by lapping. I don't know if you have stainless or titanium but first just clean them, make sure the stems are straight and test them again.

Good point. I believe all the 426's had titanium valves.

Thanks for the replies :thumbsup:

Well I think I found the problem and have an idea of what caused it. Alittle stupidity mixed with a 12 pack of cheap beer :thumbsup:

That is an expensive 12 pack. The poor WR--once it was a highly tuned piece of racing equipment.

You mention carb work, did anything slide down intot he inlet? Ever some fuel can knock loose some carbon and hold a valve open enough to lose comporession, but will usually come back with several kicks. Even small amounts of debris/dirt falls inside, same deal, but like I said, it wull usually clear right up

Something that happened to me whilst having this CDI problem with my WR400 gave me this symptom!! I've had all sorts of things apart on the bike now including the carburettor trying to get to the bottom of the fault. When I had the carb apart, I backed the idle screw right the way off. I was going to adjust it when the engine was running. However, I went to kick it over with and without the decompressor and it suddenly had zero resistance!! I made sure the decompressor lever was returning but still nothing! Opened the throttle and kicked it and hey presto, I had compression. It appears that it couldn't suck any air in while the throttle was closed completely. Had me worried for a minute!!

That probably wasn't a good idea to kick the bike over and blow the crap out. As soon as the piston hits TDC and goes back down it's going to suck air and dirt back in the sparkplug hole regardless if the valves are open or not. Make sure to check the piston and rings really well since you already have the head off. make sure she goes back together CLEAN! :thumbsup:

I finally got the time to put her back together today and shes alive, it fired off on the first kick :ride::ride:

I had already lapped the valves by the time I read not to, but it didn't seem to hurt them. I only did it alittle to polish the seats.

Well at least I got the chance to get familiar with the beast and it was actually pretty simple. I didn't pull the cylinder because then I would have wanted to put new rings and a hone on it.

I had thought it was yz timed but it wasn't, so I had to put her at the yz specs to see if there will be a difference :crazy: . I haven't been able to ride it yet cause its been raining steady for 2 days :lol:

since when has rain stopped anybody? :crazy::ride:

Pulling the cylinder off for inspection doesn't mean honing it and replacing the rings, but just replacing the cylinder gasket if all data inside the cylinder is in spec.

02 has titanium valves valve lapping will remove coating (not reccomended) if you have to very lightly the most important thing is to clean the compund completely adjust shims after lapping

02 has titanium valves valve lapping will remove coating (not reccomended) if you have to very lightly the most important thing is to clean the compund completely adjust shims after lapping

I just polished the seats because the sand left some nicks. The seats were polished very easy and I could see know change in the titanium valves. In this situation, it worked very well because it cost me nothing. I paid nothing for a machine shop, Im using the same vavles, and they are now seated properly with no compression leak :crazy:

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