Rough Idle on 1981 xj550

I have had an XJ550 for about a year finally brought it home from the shop yesterday. The engine fires up well and runs well with the choke and seems to perform well when riding. However, when it idles it slowly dies and stalls. I have cleaned the carbs and replaced the spark plugs, oil, exhaust, air filter and installed new rubber carb gaskets. The mechanic did a compresion test and one cylinder is at 26% - lealy valves. Just looking for some ideas on how to improve idle.

Any help would be greatly appreciated. Cheers, DOug

 

How about do a valve adjustment and see what happens with the soggy pot? It's NOT GOING to idle smoothly on 3 1/2 cylinders, sorry.

 

I was afraid of that. It sounds like another 8 hours of shop labour. I suppose all the valves can be adjusted at the same time?

It seems to run fairly well even with reduced compression on one cylinder other than the idle that slowly runs down to a stall.

Thanks for the help.

Cheers,

Doug

 

It won't do the motor any good running with one jug so far out of whack with the other 3, you will have to address this, as Fitz says get the valves in spec' this might sort out your problem, if not, it's off with it's head.

 

Not sure what this means but he did a leakdown test and measured the following:
Cylinder 1 - 26% (Intake Valves)
Cylinder 2 - 12%
Cylinder 3 - 12%
Cylinder 4 - 12%

Does this mean that three of the cylinders are working at 88% and the other at 74%? Should they measure at 100% Sorry for my ignorance but I am relatively new to engines.

Cheers, Doug

 

Sort of.

What it really means is that the #1 cylinder needs to have the valves checked, and yes they can all be done at the same time, that's the whole idea.

What's involved in a valve check and adjustment: http://xjbikes.com/Forums/viewtopic/t=14827.html

Get the valves in spec and then run a simple compression test. You can perform both of those procedures yourself.

 

where's the 12 % going in the other 3 cylinders? past the piston rings? warm up the engine and check for blowby out of the crankcase breather tube. that'll tell you the same thing a leak down test will if. if you get blowby then you've got worn rings.

you shouldn't have any leakage. #1 intake might be too tight so it's not seating. or it's burned out or some other problem that it's not sealing.

 

Thanks for the great advice and the excellent tutorial. I am tired of shop fees and will attempt the valve job myself. The mechanic had indicated that the intake valves leak.

Was there a specific mileage that the valves had to be adjusted on these bikes? The bike has only 17000km on it and I a surprised that it requires a valve job already. Could this be an indication that it has been abused?

Cheers, Doug

 

I'm pretty sure they're supposed to be checked every 5k miles, lots of these bikes have never had them checked from new.

That's why we always suggest checking them when you buy a "new to you" XJ.

 

If I knew what I know now I would not have purchased this XJ. I had to replace the chain, sprockets, head cover gasket, gromets etc and clean and rust proof the gas tank. Also had to have the carb cleaned. It was dropped and the engine guard was bent and the light cover needs replacing. Now I find out the valves leak. And to think I purchased if from a co-worker. Erggggggggggg! Wouldn't be so bad if I could do more work myself.

Cheers, Doug