'84 xj550 Strange idle behaviour, colder no. 1 exhaust

Hi everybody,

I've recently bought an old (70000 km.) XJ550 to get into the world of motorcycling.
In getting the bike roadworthy and cleaned up, i've encountered this here problem.

When idling with the lights turned of, the rpms rise to around 2000-2300. When I turn on the lights the idle drops to 1100 (normal).
When cold the bike will idle (lights of) at 1100 rpm but the voltagemeter will show 14v (instead of the expected 12v).
when I turn on the lights the voltage will drop to around 12 volt and rise with the rpm's (normal).
And when giving it a squirt of throttle the rpms don't come down to idle fast enough, it's rather slow.

I've also noticed that the number one (when straddling bike the first from the left) exhaust pipe is warm but not as boiling hot as the other 3 pipes.

All this I've noticed after changing the plugs (btw, the no.1 does get spark) and oil (+filter). I've also noticed the air filter smells a bit of gas.

Is it time for a carb cleanup, or do I have more serious problems here? Is my no. 1 carb to lean?
I'm a diesel guy myself (volvo 240 diesel) and am not familiar with gas carburetor engines, so any advice would be welcome here.

Thanks in advance.

Dietbrand Vandenberghe

1984 XJ550

 

the 14v with lights off and 12-13v with them all on should be normal at low idle... as for the slow idle down, colder exhaust pipe, and gas smell, I had the exact problem with my 550, turned out that #1 carb had a broken emulsion tube (AKA main jet tube) and gas was just pouring unto the motor instead of spraying, hence not firing right, and some gas was getting back into the air box, I bought a new tube off chacal (on this site) and the problem seems to be much better (I just got to free up the mixture screw now)... I would say get the Carbs cleaned and completely checked out !

 

Thanks for the information.

One question:
Am I right in thinking no 24 on this diagramme (att) is the afformentioned tube? (just to know where to look first)

 

no, looks like #37, it's the tube the needle goes down into and your main jet screws up into, made of brass, mine was split in half, but didn't know until I took it out to clean it.

 

YOu could also have one float out of adjustment. I had the same problem when starting (one header did not warm as fast as the others did)
So I removed the varbs and after inspection, I coudln't find anything wrong with them, so I just adjusted my floats (it never was done before) and it took care of the problem. It's worth a shot. PD

 

Just reading through the posts, and came across this one. I had the same problem. Tried the carbs, but failed to see if it was getting enough spark. I was baffled to find I had one dead coil wire. The coil ohmed out to specs. Come to find out, one of the 12v wires was broken out of the pig tail goin to the coils primary. Stripped it, reattached, and all my problems went away. By any chance, is it the number four cylinder? I have had 2 buddies, that this happened to, and it was on the same cylinder. Anyhow, it is worth a shot.