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xr 600 lacks power, dont know what to do.

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Hi all

hope I can get some help here for my '92 xr 600.

I think I need to tell the whole story so here goes:

I've bought my xr with a defect engine.

When I got it home and cracked it open, I discovered that one of the exhaust valve seats had been eaten by the engine, and had bent the valve too.

I bought 1 new exhaust valve, and took the head to a specialist who installed a new seat, and re-cut all the seats and valves.

The piston didnt seem too bad so I just honed the cylinder and reused the old piston.

After assembly it was running really lean, and I started to suspect false air getting in. After narrowing it down, i figured it was the valve guides, because I had seen some play when installing the valves.

I took it apart again and installed new OEM valve guides, and stem seals and reground the valves.

After reassembly the bike ran 500m and bent the other exhaust valve. I found the reason to be a wrongly reamed valve guide, so I bought a new valve and guide and this time installed it correctly.

Now the bike is running, but it really lacks power. I have no reference to how it was driving before.

I dont know what to do now, I really could use some help.

Here are some specs:

Orginal Carb with

160 main

68 pilot

ABP racing exhaust with loud silencer

K&N filter, no snorkel.

it seems that its mostly lacking bottom end power, doesnt lift the front wheel at all.

thanks

- Karlo

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How much compression do you have? I would have replaced the rings at the very least after honing the piston. Get us a compression reading, Plug wire off, throttle wide open and three kicks.

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thanks for the input

It feels like it has good compression when im kicking. But i will try and get a hand on a compression tester, to get some numbers on it.

I was thinking that if its not compression maybe it could be a worn camshaft ?

or could the bending of the valves have caused stretching of the camchain ?

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1.) It feels like it has good compression when im kicking. But i will try and get a hand on a compression tester, to get some numbers on it.

2.) I was thinking that if its not compression maybe it could be a worn camshaft ?

or could the bending of the valves have caused stretching of the camchain ?

1.) A stock cam with the automatic decompressor will only produce around 90-100psi(~6bar) of compression in a normal engine.

2.) Other way around: a stretched cam chain will tend to produce bent exhaust valves.

At the very least it appears that your jetting could use some attention. The 68 pilot is really big; a 62-65 would probably clean up the lower throttle fueling. The 160 main is also on the small side. I would try a 162 and see how it responds.

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I have now changed the pilot jet to 62, but it didnt change anything.

I have also done a compression test, with the auto decompressor active I got a reading of ~ 3 bar/43.5 Psi

Without the auto decompressor I got ~ 7 bar / 101.5 Psi

Seems quite low on compression ?

I have just received a new overbore piston, so im already looking in to a rebore. Something I should do while I have the engine open besides new piston, rebore and a new camchain ?

- thanks

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