Problems with XR400?

[Syris D Indomitable]

I know they are hard to start but this one takes the biscuit.

Riding along today holding the throttle on steady at around 40 and 50, the power and speed lowered even though I didn't wind the revs down, so opened throttle again slightly to keep speed then the bike sped up really fast.

My plug is really black too which is rich.

Anyone know what the carb setting are on the XR400 or why it's running rich?

Also I set all the valve clearances at their widest points, when I put it all together there was no compression, so the valves were out.
Anyway I have set them back the way the manual said aligning the "T". The problem with this is that the valve clearances are quite tappy/noisy. Someone mentioned to me the shim wear, I have no idea what this means.

I would be greatful for any help.
Thanks!

I am currently cleaning the carb.

[Suntan Sid]

[Syris D Indomitable]

Thanks for that, I will do. Fitting a new carb next week too.

[Syris D Indomitable]

Are the valve shims for the XR400 expensive and difficult to replace?

[.....]

The XR's have lock nut adjustment valves. When rotating to the 'T' mark make sure you go anti-clockwise only as turning clockwise can activate the auto decompression leading to incorrect measurement of the gap.

Motion Pro do great little feeler gauges that fit through the tapper cover and are angled so you don't have to bend them - it makes the job much easier.

What specs did you set the valves to?

It should be

IN: 0.10 +- 0.02mm (0.004 +- 0.001 in)
EX: 0.12 +- 0.02mm (0.005 +- 0.001 in)

[Blue_SV650S]

Have you checked the air filter?
____________________
The purpose of life is to fight maturity.

[Syris D Indomitable]

Cheers for that, I have done that but the head is still very tappy.
I really struggle starting it because of this as well as the carb be knackered. i am fitting a new carb next next.
I have looked for valve shims on the XR400 and can't find any, have you any idea what components are likely to be worn from this pick.
Thanks!
https://img27.imageshack.us/img27/4057/oie26141130vkrsgfev.jpg

[Syris D Indomitable]

[.....]

I remember from my XR days the folks over on Thumpertalk used to say "Slappy valves are happy valves" meaning a bit of valve noise is normal. Is there an actual tapping noise or just valve train noise?

XR's can be difficult to start from cold or after being on their sides - make sure you're using the right technique.

Just had a thought, the choke lever on the XR can be confusing - are you sure you have it in the right position ?

[Syris D Indomitable]

Yeah Iv'e mastered the choke, got the bike started once but couldn't start it again after. It runs like a trooper when it's going, really powerfull but just very tappy. Also keeping a steady grip on the throttle at 40 and 50 the power dies, I give it throttle then fly's off again. Carb trouble. Iv'e just stripped the bike as well as the carb. Most of the screww heads on the carb are threaded, it's been well molested.
Running rich too as teh plugs black.

Just going to replace the carb next week.

[.....]

Can't you just clean and check over the carb instead of replacing it? Put the jetting back to standard and replace the screws for small allen bolts.

If you really must replace the cab have a look at the Mikuni pumper carbs. Makes starting a doddle.

[Syris D Indomitable]

You must be reading my mind. I am going to give it one more go tomoz. I have just read that the mixture screw on these should 2&1/4 to 2&1/2 turns out from it's fully screwed in seated position. When I checked mine it was only 1&1/2. I have cleans and replaced all jets and adjusted mixture screw.

I have one more problem. i don't know how bigger gap to leave through the slide to set the idle speed.
does this look about right??
https://img823.imageshack.us/img823/1021/oie261556nc6azfab.jpg

[Blue_SV650S]

[Syris D Indomitable]

Ok thanks, Il'e do that.