valve issues I think

so i bought a 99 wr 400 this winter. i have done a bunch of maintenance to it. its running strong. I havent had a chance to get it out on the trails yet, but i have ben putting around the neighbor hood a little. the thing seems to have a ton of power and dose not blow smoke. the issue is that when i start it now after about a minut of running it stalls out. its not a fuel or spark issue. it revs strong than dies. than i cant kick it over. there isnt alot of compression. i can repeatedly kick it over without the compression release lever. once it cools down it starts back up. i have checked the compression release cable its not to tight. i checked the valve clearance and i need to install thiner shims. intake tolerances are .15-.2mm i have .1mm on all 3. the exhaust tolerances are .25-.3mm i measurd .15mm the shims that are in it i can still read the numbers and doing the math i can get new shims that will bring it back to within the tolerances. the samlest one i need is a 155 and i think the smallest one they make is a 125 so i am not in the lower end. my question is will the tight shims( valve clearance ) make it lose its compression when it warms up or do i need to look for something else. its not blowing smoke i dont think its the piston but the stalling i am pretty sure is a compression issue. i am going to pick up new shims tomarrow but if i need to look further into this now is the time so i dont have to spend the money on shims i dont need and spend the time to put it back together to take it appart again. thanks much

i cant kick it over. there isnt alot of compression. i can repeatedly kick it over without the compression release lever.

I'm 140 lbs and with out the decomp lever I can put all my weight on the kick at TDC and it holds me for a while. Even when it warms up after riding it still has too much compression to kick on TDC. I put it slightly past TDC the kick,

You absolutely have to have the correct clearance for those valves! As they heat up, they will no longer be able to close off the combustion chamber, and will get way too hot and will in effect, "burn" and you will have to replace them!! The only way those valves can shed the heat that develop within them during combustion, is to seat on the head and shed there heat back into the head via the valve seat. Without the correct clearance, you will have some major engine maintenance to perform in a short period of time, costing you lots of money!!! Now, having said that, I think you have other issues going on too. When you said, "It revs strong, then dies. And I can't kick it over." then right after that, you say "there isn't alot of compression". Well, which is it? Can you kick it over, or can't you? This will help us help you in the diagnosis. Maniac

when i first start the bike it has to much compression for me to kick it over with out the compression release. than it starts first or second kick. it reves and sound great no issues with this . it runs strong than it dies all at once no sputter nothing. after 1 or 2 minutes of running. than i can kick it over and over with little resistance. until it coolsdown. what i meant is that it wouldnt start again until it cools down. not that it wouldnt kick over. sorry for the miscomunicatioin. iwent and picked up the new shims and am installing them. the dealership agreed that they were to far out and this would cause the low compression. but they didnt mention burnt valves. what is the danger of this. or will it just not build compression and not run. thanks for the response.

If you run the engine too long with the valves out of spec, you stand a chance of ruining the valve, and it will never seal against the head completely. This will cause all kinds of issues, such as poor running (if at all!!), running hot, backfiring thru the carb, etc.,etc.. Lets hope you caught it in time! Maniac

nope. i didnt catch it. at least i got the bike for a decent price. i changed the shims. it did the same thing, i started it with the seat off this time and i could hear a little backfire through the carb when it died. oh well. i got it all apart and at least the cylinder and piston is good the dealership was kind enugh to measure them for me.. i got the valves and new rings on order and the valve seats are getting inspected this week. there was a bunch of carbon on the valves and head but the piston was fairly clean in comparison. not as thick with deposits. i guess that this may be the fuel mixture and a bad plug? I bet that i have only ridden it for 15 min. how fast can you burn out the valves it seemed to be ok untill i changed the plug out. its also the correct one i got it from the dealership and it matches with my manual. i got the bike in december and went around the block a few times no problems. once it started to warm up i did the plug, oil and filter, breaks, chain and sprockets , got it street legal. went around the block a few times and than it started to die. i had read about the valve clearance and the shims but i know a few people with the wr and they said that the valves havent ben an issue so i didnt check them until i started to have this problem. I am pretty sure its a valve ishu i have spark have fuel. but no compression once it warms up. i am doing a leak check on the head tomarow. so i will see. so my real question if how fast can you damage the valves did i do this or was it most likely damaged before? live and learn. thanks

My guess, and that's what it is, is that the previous owner probably had already done it, that was why he was selling it cheaply. If the valves are out of spec, it doesn't take long to burn them up, depending on how hard you ride it. And yes, the WR is stone reliable, but the valves will tend to tighten up on clearances if run really hard at high rpm's, and also if the maintenance is suspect. Sorry to hear you didn't catch yours in time. Just go thru it and get it done proper, stay off of the rev limiter, and do your oil changes religously, and you won't have anymore issues. Were here to help!!! Maniac

Maniac... I understand that good oil is the life blood of any rotating machine. However in the case of the valves here, how would oil contribute to reduce the amount the valve clearances close up by. Could it only be through cooling of the parts? Obvoiusly shit oil will cause the cam lobes and buckets to wear increasing valve clearance. Do you guys run any sort or upper cylinder lubricant. I put valve saver in my fuel and have never had issues with my valve clearances (touch wood) although i try to maintain them as best as possible and tend to short shift rather than bounce of the limiter ( 450 has gross power anyway, no need to bounce imo)? But got to agree the yamaha is a super reliable machine for the level of performance you get.

Appreciate your input


Edited by aussieklx

aussie, your right. The oil has a minimal effect on valve clearance issues, except as you stated, in the cooling effect it contributes. The rev limiter has the most effect I would guess. As for upper cylinder lubricant, I don't use it. And I don't know of anyone that does around here. If it has some lead in it, it probably does wonders in helping those valves!!! Damn American Beaurcratic crap!!!! Maniac

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