Mind Boggling issue - the challenge - What its not -

Ok not my xj this time but i know you all are up for this challenge....

1989 Kawasaki 600R ....
ok the the bike fires right up and runs great till operating temp and will idle as long as there is fuel in the tank. before the bike reaches operating temp evertything is exaclty as it should be..... once at temperature boggs and stalls under any throttle... puffing black smoke while doin so.... which i know is unburnt fuel.

ok i have fully rebuilt the carbs on this bike and bench synch pulled the cap resistors , replaced the wires, replaced the plugs, replaced the plugs again with high temp plugs, swapped the coils for known good ones, swapped the Igniter, swapped the pickup coils, disabled the kickstand switch, disabled the clutch safety switch. re-grounded the system and verified the stator and rectifier are operating normally.

i am stumpped at this point.... any thoughts? btw i have some youtube videos i can link in in a bit

 

Midnight,
How long does it normally take before it starts bogging down??

It almost sounds like the vent on the fuel cap is plugged. Try opening the cap and letting it run, and see if it still boggs
Just a thought..

 

Have you got heat resisting pipe on the vac' line to the petcock? if not when hot it can collapse stopping the petcock from working.

 

anytime a engine is cold it wants a rich mixture, when it warms up it wants the normal mixture
is the "choke" shut all the way off ?

 

If the cap vent gets plugged that generally causes a lean condition and then stalls,Does this bike have an ignition advancer either electronic or mechanical.Some times the springs on the advancer stretch or the electronis ones just plain seem to fail the high pass circut .Not to be tacky but the first time I installed my floats i put them in upside down the bike started and idle but as soon as I touched the throttle it would die everytime,Might be one of those day one mistakes we all ocasionally over look.

 

Cap vents? you mean for the tank? this happens using the test bottle as well..

Wizard cyl1 vac line goes direct to the petcock... the issue occurs even blocked off on a test tank... cyl 2 and 3 go the exhaust cool air system.
cyl is blocked off. btw as far as the line type you'll see i am using the spendy blue vacuum / fuel line.

Polok... i thought the same thing so i dropped the carbs and reset the idle mix to the lean side which from factory is 1.75 from bottom (spec is 1.75 to 2.25). it takes a few moments longer but is still present.



youtube videos as promised:

http://www.youtube.com/watch?v=IG8YBzTgPzk

http://www.youtube.com/watch?v=uvw5l4_aGLY

 

ratchetmxr6 - evry thing i see says its just done by the pick up coils... looks alot like the xj ignition setup with wasted spark. i dont see any advancer. i'll keep looking though

as far as the tacky comment let me put it this way i can empty the entire test bottle of fuel and the bowls on the carbs in about 2 min flat at 12,850 rpm i can see the fuel level dropping normally .

 

Shouldn't it idol a tad higher at above 12K so it won't bog down? You said that it puffs smoke from unburnt fuel, so maybe putting the carbs back on the table for concederation is still in order.

 

i'm a little confused by this - i thought running lean means running hot, so shouldn't get to operating temp sooner?

i'm no guru, but is it possible the bike looses compression when it heats up due to expansion of . . . something?

 

It needs a valve adjustment.

 

Fitz, are you saying that because of the audio or the decscription of the issue.... what you cant see in the video is that the exhaust cold air pipe is disconnected ....when its off you get to hear lots of top end noise.. when its on its smooth and quiet

 

Check the carb to head boots for vacuum leaks once it's warmed up.

 

did this problem start before you rebuilt the carbs or after ?

 

bought the bike in pieces .... carbs were completly broken down off the rail ... this bike was a straight up jig saw puzzle .. on the plus side it came will all new hardware... i know it ran before the tear down of the carbs, but i also know there was probubly a reason for him pulling them off in the first place . i was betting on mis diagnosis on his part... he wasnt aware the jets were different for 1&4 and 2&3 on most I4 bikes.

i like fitz's thinking... i better pop the top and check valve clearence

 

Float levels too high? it's acting like it's running WAY rich, check the plugs, see if they're black and or wet

 

float height is good.... ok so the vlaves were a little off not very far ... cyl1 intake was tight by .010, cyl 3 was tight by .020.... on both cyl 1,3,4 exhaust were loose by .025

so basically it was time to do it but it wasnt by any means as bad as i have seen others... i did hear a noticeable difference in the compression after i set the valves....
i havnt bolted it all back together just yet, but am curious if yall think thats waaaay out of spec enough to produce this issue

 

ok i forgot to mention that the intake tubes on this bike appear to be casted into the head ... or possibly pressed
and no leaks thats i can find

 

ok so i hadnt gotten back to it in a few days to re-assemble the bike... i finally got it back together last night.... and had a heck of a time on first start... however the bike runs considerable smoother now... i thought it was ok before but it must not have been... i did spot and replace weak o-clamps on cyl 2-3 intake boots (by weak i mean fully tight to the end of the screw and still can slip around the intake boot a little).... so i replaced them all (12 total) with commercial grade o-clamps from the local auto parts place.

i also found that the PO had upgraded the jets and installed a timing advancer .... yehaw

also i stripped the harness and found more than one patch in wiring and decided to strip and solder each patch... well after 20 mins of run time the bike runs great as far as i can tell buuuuut now i have a temp sensor issue LOL - figures

i think its also worth mentioning that when i set the mix this time i followed the manuals instruction about dropping some thread lock (the weak stuff)
on top the screw once its set....it seals the hole from vacuum leaks.


I'll do more testing tonight.... thanks Fitz!!!! ... i diddnt want to do the valves but it looks like it was worth it