kz650 carbs--lean issue

here's the story.....78kz650b2, stock airbox, Jardine 4 into 2's(unbaffled of course), dyna ignition and coils....went for a ride today and usually at cruising speeds when I twist to WOT, I have to hang on for dear life....not today......it just stumbles a couple times then nothing.....back of the throttle some and it takes off.....or if I just roll into the throttle at cruising speeds it will go....also at idle if I blip the throttle, idle drops so low it damn near shuts off then comes back up to normal idle...bt I did hve to raise te idle on it too..pulled the plugs and they are lean.....real lean.....put new plugs in and the same thing......real lean.........NOW....I did adjust the valves the other day...I have adjusted them before and nothing like this has happened......am I just paranoid about my valve adjustment because the carb situation or what??? Would a valve adjustment have anything to do with this? sorry for being so long winded...........

I'd start with pulling the carb bowls off and checking all the passages. My bike sat for only a few weeks and then ran like crap, running on only two cylinders. I was surprised to find jelly-like gunk in the carbs. It didn't take long to build up. I guess we need to ride regularly or drain the carb bowls if it's going to sit for more than a couple weeks. Good luck.

Fugitive

Sorry for not trying to insult here but what adjustments to valves did you make in a KZ650 head?

i.e. new shims, cut & grind on the valves themselves, seats, guides etc....

Did it run well or at least better since you opened up the head for the valve adjustments?

If so, had you removed the carbs at least off the intake manifolds to slide the valve cover off the head?

NOTE: Good chance this is where the problem lies, intake manifold leak....

Did you remove the cam cap bolts by chance for shim replacements?

If so, are you sure you have the correct alignment marks and number of tooth count and cam lobe orientations correct?

Had you changed, bumped or anything with the pilots or air screws in the carbs... not sure of your carbs so....

Possibly as jiggling the carbs around to remove the valve cover your floats gunked up or shifted internally...

Do you have the means to test your carb settings and perform a vacuum check for this will inform you of quite a bit.... Meaning piss poor vacuum equates to piss poor air/gas mixtures into the combustion chambers....

In answering your question, if something isn't correct in your head due to leaks, timings, intakes etc... then yes, it can make a HUGE difference in performance...

OMR

EDIT: Not saying this is your problem but your question was "can this effect it"....

all I did was under bucket shims.....no carb removal....I only move one cam at a time as to not mess up cam timing......but just to be sure, I made sure timing mark was right and arrows on cams pointed in their respective places, and counted the number of teeth on the cam chain between cam arrows......I triple check these readings before buttoning everything up........

Thinking possible fuel starvation and maybe advancer unit needs cleaning and lubing.

Could test for clogged tank vent by running with cap ajar.
Possible inline filter clogged, or petcock pickup tubes inside tank clogged, or petcock otherwise clogged.

Would doublecheck timing with strobelight, and to also assure advancer unit is moving freely.

Good Luck!

Perhaps a leak or kink in vacuum hose to petcock or poor vacuum hose fitting at carb nipple or petcock nipple.

Could test by running with petcock set in PRI position to help rule out vacuum issue.

Good Luck!

when was the last time you rode the bike if it was longer than about a mopnth ago then chances are the gas went to crap in the bowl's if they werent drained prior to storage pull them off and clean all the jets and passages and please be meticulous for your own sanity and please use compressed air on them as well because that will be the only thing that will blow the passages clean for sureget an air gun with a rubber tip so it will seal on the jet or port.

How many shims did you replace and were they intake, exhaust or both? How long since you last checked or adjusted them? Unless valves had been misadjusted before it seems highly unlikely that you would need to change very many. If the bike was running ok prior to these adjustments, I would start by using the manual to very carefully check the valve clearances again and check the valve timing (cam positions at TDC). It's possible that some simple mistake was made during the adjustment. Ed

well..........I got bigger problems now.....started with the simple stuff...checked inline fuel filter and petcock screen....was going to check timing advancer to see if it was hanging.......pulled the dyna ignition out, grabbed a 13mm socket on an impact to take the bolt off and.............SNAP.......hellshitdamn!!!! had it on righty tighty instead of lefty loosey.....broke the bolt going into the end of the crank anlong with the little dowel pin........mudderfukker!!!!!!!!!and the bolt snapped about 1/4 inch inside the end of the crank...........how the hell am I gonna get that outta there????

Should probably await other suggested options before deciding, but I would center-punch the broken bolt, and begin slowly and without much pressure using a reverse-cut drill bit, being extra careful not to snap off the drill bit inside the bolt. Gradually increase size of reverse-cut bit and re-drill. Repeat, but avoid cutting into female threads inside crank. Hopefully the broken stud will come out. Might also need an easy-out, again being very careful not to snap off the easy-out inside the drilled hole.

Could possibly help to heat the crankshaft end while attempting to twist out the broken bolt.

When using a strobe-type timing light, it's easy to see whether or not the advancer is readily moving back and forth as rpm varies by blipping the throttle. No need to remove the advancer to "check" its operation. If the advancer is seen to be sticking, then it's usually better to remove it for thorough cleaning and lubing.

Thinking the advancer, if not readily retarding at lower rpm, could be an issue with the reported idle problem, and not so much with the ultra-lean higher speed issue.

The ultra-lean higher rpm problem may well be clogged main jets, as already suggested by others. But my thinking is looking for something that would cause all four plugs to simultaneously run ultra-lean, such as some sort of fuel starvation problem.

Good Luck!