XJ650 Difficult to Start and Fast Idle

Hi,

I recently bought a 1982 XJ650 Maxim. The previous owner took it out after four years in the garage and tried to get it running. He was able to get it to run, but inconsistently and had trouble starting it. It sat for another year before I bought it. When I got it home the battery was dead so I jumped it. I set the petcock to prime, and it started right up. At first it idled fine, and revved fine. It seemed to run well. After a fourth or fifth rev however, the rpm's didn't die back down. The engine stayed idling at 4-5k. I killed the engine, and started it a couple more times but it kept idling high. The idle set screw and choke didn't help.

Before I had tried to start it I had checked compression. Two of the cylinders were low (and improved with some oil in the cylinders), but after I had run the bike I checked again and they all read fine.

Two days later I came back and tried to start it, but it wouldn't start. Most of the time it would fire, but not catch and run on its own. Sometimes it would just crank as if it didn't have gas. Eventually I sprayed starter fluid in one of the vacuum ports on the intake manifold (on the engine side, so as to bypass the carbs) and it started right up. I killed it and was able to start it up just fine without starter fluid. This time, the idle speed screw worked and I was able to set a decent idle. But when I revved, it was reluctant to come back down to idle and would sometimes creep up and idle at ~4k. Sometimes when I tried to rev it would die as soon as I touched the throttle, but it always started back up just fine. I'm pretty sure the throttle was a little unresponsive as well.

My two ideas have been clogged carb and vacuum leak. I took off the carbs, and removed bowls and diaphragms. The previous owner had had the carbs rebuilt 1-2 years ago. There was a little bit of green goo in the bowls, and some sediment, but otherwise seemed fairly clean. The jets where a bit corroded but totally un-clogged. Overall much cleaner than I expected. Seems to me that if the jets are clean the circuits can't be too bad, but perhaps I'm wrong? Tonight I'm going to attempt to clean the circuits thoroughly.

On the vacuum leak front I've inspected the intake manifold. The engine-side seems pretty new and un-cracked. The pipe clamps were old and loose when I took of the carbs though, and the covers on the vacuum ports seemed a little loose too. The air-cleaner side seems old, and the manifold looks like it might not be seated in the box right. If back pressure is an issue, I'll try and fix this.

This is my first time working on a bike, so any advice would be greatly appreciated! Thank you.

 

vac caps want to be tight or will leak .

if your choke was on that would account for the 4 to 5 k rpm

 

Good to know, thank you. I'll tighten the vac caps.

The choke wasn't on, I turned it off to smooth out the idle.

 

I cleaned out the pilot and choke circuits. I was able to spray carb cleaner through jets and see it spray out in the venturi. They seemed pretty clean.