YZ400 barely starts and will not idle

Clean the carb? Did you open the acc pump?

If not, do that.

I cleaned the carb very well. I did find some dirt under the acc pump diaphram. Also, the tiny rubber o-ring around the starter jet broke and i only found 1/2 of it. I found a suitable replacement at an auto parts store. I think the carb should not be the problem now.

Originally posted by Osmond:

Clean the carb? Did you open the acc pump?

If not, do that.

Oh yea, one more thing. When I came in off the track, two of my buddies said they smelled a strong hot/burnt oil smell. Does that make it more likely to be the valves?

Finally, I just replace my head gasket two months ago and popped the head off last night to check things out. Do I really need to wait for new head gasket to show up to put it back together given the newness of the one I just took off? I sound lazy I know but that means missing this weekend's ride.

Something is sounding a little toasted.

You may want to drain the oil and see what comes out, including any odd odors. It and the color of the plug will tell all.

Originally posted by Tom Krause:

Do I really need to wait for new head gasket to show up to put it back together given the newness of the one I just took off?

You mean head cover don’t you? If so then yes, reuse it. I bought a new one for my ’00 and never put it on until about a year later when I managed to put a small tear in the original one, which I must’ve had off there five or six times. It is rubber and should be fine.

From experience with other motors, I would definitely wait for a new head gasget. You could have the dealer over-night ship it if you really want to ride. The old one may work, but is it worth the risk when so many other (and more expensive) problems could arise if it didn't work?

Also I would definitely check your valves, the sooner the better. If you do have one leaking then riding it could cause a valve seat to get burned from the hot gasses leaking past it. Fixing a burt valve and valve seat is much more of a pain and more expensive than just replacing the shims if the valves are out of adjustement. I haven't checked mine yet, but it looks pretty strait forward and I don't think that it would take very long. If/when you check let us know what you find!

If it's the valve cover gasket, you can re-use it. If it's the head gasket DO NOT re-use it.

Bill

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99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, EKP #4, 50PJ, 175MJ at 500-1000' Thanks James Dean!

Last weekend I was hearing a funny noise and then after three sessions on the track, it took me forever to start and wouldn't idle at all...still doesn't. To get it fired, I had to keep kicking and trying different combinations of hot start/choke combinations. I had to force it out onto the track where the mid range and top end still worked very well. Afterwards,I put a new plug in and cleaned the carb very well and am still having problems. I am embarrased to say that after three years I've never checked the valves other than I checked them for leaking 6 months ago. Any thoughts on what's causing it to not start/idle? Thanks much for any replies.

Check valve positioning. I have seen posts here where the gears spun on the camshafts. Could also be electric related.

Originally posted by sirthumpalot:

From experience with other motors, I would definitely wait for a new head gasget. You could have the dealer over-night ship it if you really want to ride. The old one may work, but is it worth the risk when so many other (and more expensive) problems could arise if it didn't work?

Also I would definitely check your valves, the sooner the better. If you do have one leaking then riding it could cause a valve seat to get burned from the hot gasses leaking past it. Fixing a burt valve and valve seat is much more of a pain and more expensive than just replacing the shims if the valves are out of adjustement. I haven't checked mine yet, but it looks pretty strait forward and I don't think that it would take very long. If/when you check let us know what you find!

Oops. I think I sent you a blank email. I have the thumper running. The valves were pretty tight but adjusting was very simple after reading the manual. After completely dis-manteling the carb, we found the tiny o-ring that goes on the needle jet was broken and in the oriface of the needle jet. It now idles and hopefully will run for Millville this weekend. Thanks for your help!!

Originally posted by sirthumpalot:

From experience with other motors, I would definitely wait for a new head gasget. You could have the dealer over-night ship it if you really want to ride. The old one may work, but is it worth the risk when so many other (and more expensive) problems could arise if it didn't work?

Also I would definitely check your valves, the sooner the better. If you do have one leaking then riding it could cause a valve seat to get burned from the hot gasses leaking past it. Fixing a burt valve and valve seat is much more of a pain and more expensive than just replacing the shims if the valves are out of adjustement. I haven't checked mine yet, but it looks pretty strait forward and I don't think that it would take very long. If/when you check let us know what you find!

Great news that it was an easy fix! Have fun riding. :)

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