Xj650 running on 3 Cyl.

Hi guys!
Great forum, learned a lot her. But need help now, out of ideas...

The bike has been running bad with rough idle and racing out of control when throtteling. The 1 cylinder is a lot colder than the other. If I unplug the cap on Nr 1 when running, the engine dies directly. But if started with compression tester in cyl 1 and cap to spark plug it runs (on three of course)

With vacuum tester on its ok vacuum on idle but when revving a little bit Nr 3 draws a lot vacuum and Nr 1 very little.

I have done this to the engine (not exactly in this order, and many steps multiple times)

1. Checked valve clearences and adjusted to specs with shims.
2. Compression test, about 150psi on all cylinders.
3. Checked spark (similar spark on all four)
4. Swapped spark plugs
5. Swapped leads 1 to 4 from coil
6. Taken carbs apart, cleaned everything, did “clunk test”
7. Bench synced
8. Set float levels
9. Vacuum synced all 4 simultaneously.
10. Mixture screws were tampered with so put all on 2.5 turns out.
11. Checked for vacuum leaks with starter fluid (nothing found)
12. Checked air filter

Still same result with No 1 cyl not running/running poorly
If I turn mixture screw on Nr 1 cyl in/out it does not seem to make a big difference.


Spark plug on Nr 1 cyl. Looks a bit black but not oily or completely wet.


Suspect ignition/coil somehow now. But shouldn’t the problem switch to cyl. 4 when switching 1 to 4 leads?


Any help for more troubleshooting would be greatly appreciated.


//David

 

Forgot: The bike is a XJ650 from 1982

 

I was going to ask about plug color, comparing #1 to the others. Swapping #1 and #4 plug leads sounds plausible.
Could you have a vacuum leak leading to #1? Try an unlit propane torch, blowing some propane around the intake boots/carbs.

 

When you disconnect the #1 cap, you're also disconnecting spark from #4, since they fire in series. So, it runs on 3, but won't run on 2, which is not surprising.

It's the carbs. It's (almost) always the carbs. Clogged jet or passage, hole in the diaphragm, bad float height, stuck slider ... ?

You could probably remove the air filter and spray a bit of carb cleaner into the #1 inlet and see a pretty clear indication that #1 starts producing power for a few seconds.

 

Thank for replies, I will test with propane for vacuum leaks.
Will first try starter fluid in Nr 1 Carb. And Then take No1 carb apart again and clean again...
Back on track again with troubleshooting, thanks!

 

Removed air cleaner and used starter fluid on Nr1 cylinder, which makes the engine rev up. Also makes it backfire through carb. Is that normal?
Took Nr1 carb apart, cleaned and checked everything again. It really is super clean inside.

Still same problem though...

 

Did you check service fuel level?

 

You mean the float bowl fuel levels?
I checked them all before. But I will check again tomorrow on that carb.

I only have a side stand on the bike so it is a bit hard to get it perfectly leveled By your self when measuring.
Btw, does that at all affect the engines performance/starting as the carbs are not leveled when standing on side stand? (And the float levels are adjusted when bike is leveled.

 

Update:
Adjusted float level, it was 1mm off, that did the trick. Also vacuum leak from throttle shaft seals, fixed and now runs much better.

Thanks for help, great forum!