Exhaust #3 is warm and #4 is cold

After cleaned the carbs the bike strated up with choke and it will run rough and die in idle. The throtle is not reponding quick and I think ist' because the brass piston of the diaphragm assy are dragging (I didn't do the clunk test). Today I started it up again and cylider 3 and 4 started backfiring (ocacionally) and I touched the exhaust pipes and 3 was worm and 4 was cold (1 and 2 were hot).
I don't think the coils are bad because if on goes bad it will affect 1/4 or 2/3.
I think I still have fuel supply issues and I will take the carbs apart on Saturday and clean them again.
Do somebody knows how to check a coil?
Do you think I'm in the right track?
Thanks in advance

 

Before you pull the carbs back off, Check the fuel level in the float bowls. Mark them on the sides of the carbs so you know how much if any adjustment you need to make when you have them open again for cleaning.
Make sure you have all the jets in their right places.
If you have some stiction on the slides, polish the slide bores not the slides.
Make sure you take out the main jet and clean the emulsion tube...

Other than that, make sure you have spark on all cylinders.
Maybe put some new plugs in.

 

Make sure that the #4 spark plug is firing. If it's not firing then check the plug cap and the connection from wire to cap.

Sean

 

All the jets are in the right place, carbs fuel levels are decent (I have a picture in my gallery when they were at the bench).
I have spark on all the plugs. I will measure the coil resistance on Saturday before remove the carbs. The plugs are 1 year old but only have 100 miles on.

 

After you are sure that your carbs pass the clunk test AND that the enrichment passages squirt carb spray several feet, then you should synch the carbs.

My bike would not take throttle until I synched the carbs with the differential bottles. I found the meters to be useless.

 

Halfcentury, did you do bench sync first?
Did you use the YICS tool to balance the carbs with the bottles differential method?

 

Yes, I bench synched with 1/4" strip of business card.

Yes I used the YICS tool. Without the tool don't bother.

After the bench sync and re-install the bike would still not take throttle. The engine would die with throttle applied.

My #3 and #4 were horribly out of balance to start.
All of the water was sucked to the #4 carb bottle.

Any imbalance is IMMEDIATELY displayed using the diff bottle setup.

Make sure to re-install the YICS passage bolt. Without the bolt in place the engine will not start. Duh

 

Hey I did a bench sync with the business card strips and it wouldn't start or run right. After backing off ALL throttle butterfly sync screws (butterflys now closed & using 3.5 turns out on pilot - idle screws) and full choke it started fine.

Also the bike would not idle properly until I took the same sync screws counterclockwise again; this was after I tried adjusting them to get more idle speed.

Apparently xj carbs need NO (or almost zero) idle air volume to allow the YICS engines to start & run right.

Yes, it will need a full carb synch afterwards but this method may get it going.

 

taildragger,
Are you sure you were not getting air in via a leak? That seems odd..

 

I took the carbs apart again, did clunk test (passed), cleaned all passages again, pu them back together and started up.
Ride her for a mile and when came back checked the exhaust pipes temperature, #3 cold and #1 very hot. I will buy new plugs this week and tested again. Also I noticed that have back fire in the right exhaust (#3&4) I assume is # 3 cylinder. I started thinking that for some reason #3 is not getting a healthy spark.

 

Agree about the zero air. If you cause the butterflies to be open with choke on the revs will go through the roof.

You have to set the idle at least a little high after a carb cleaning or the bike is not gonna start unless you luck into a perfect adjustment before you start it tune it. Yeah, right.