SO FRUSTRATED - Run away idle

start with the basics do everything you would do for a tune up, take the carbs back off and re adjust adjust yourfuel screws to stock settings reset your float heights to stock levels readjust valve clearances take your advancer off and make sure it is moving free use some moly grease and relube it double check your cam timing be methodical and also check you fuel filters in line and in the tank dump your gas and put in a fresh batch if you have points make sure they are not arcing set the gap to .014" then when you get it running put atiming light on then set your dwell to about 45 degrees the main thing is dont get frustrated take your time and be methodical and dont miss any steps and i wouldn't be suprised if the problem didn't just jump right out at you.

So WBPDX, tell us... which wire was bad/questionable? :dry:

In re-reading this thread two things appear to stand out... at least to me:

1) The carb holders have not been changed.

2) The carb slides have not been synchronised.

Neither the "Initial Carburetor Mechanical Synchronization" nor the "Carburetor Fine Synchronization" (Vacuum Gauges) procedures, as my manual calls them, have been performed. If these are not done then you have little chance of success.

IMHO, run-away engine control is not an electrical/ignition issue and not a mechanical/electrical timing issue. This is a fuel/air/carburetion issue.

Would suggest the following:
1) Make sure your gas cap is venting properly and the air filter is breathing well. Leave cap open if necessary.
2) Make sure fuel flows freely into carbs. Clean, replace or discard any internal petcock fuel filters. Add or use a new in line filter.
3) Make sure your fuel service level is set to specification using the clear plastic tube method (you're probably really good at this by now).
4) Make sure the throttle cables are free and loose
5) Use a drill bit or coat hanger wire as a gauge to adjust the height of each carb slid as it just comes of idol. See the procedure in your manual under "Initial Carburetor Mechanical Synchronization".
6) Follow up with a set of vacuum gauges to do the "Carburetor Fine Synchronization" as per your manual.

Again, IMHO, I would be astonished if this did not eliminate part and maybe all of these run-away symptoms. If you have a different type of carburetor then just flush the above.

Best of success.

PS
Could you add your year, model and location to your signature to make it easier on us... and it’s considered real friendly too.
Location might get you a nearby member with the equipment you don't have yet.

bill_wilcox100 wrote:

So WBPDX, tell us... which wire was bad/questionable?

#2 Plug wire, which is one of the cylinders I 'lost' at one point. It was actually the plug wire cap - It metered out as having no connection, even on the 2M Ohm setting. Another one of the plug wire caps had over 5k Ohms (in JUST the cap.)

In re-reading this thread two things appear to stand out... at least to me:

1) The carb holders have not been changed.

2) The carb slides have not been synchronised.

Fair. But as I stated in my recent post, the carb holders look 100% fine. I have plans to replace them as a last resort. You are probably correct that synch would be helpful. But these are CV carbs, so the 'slides' would not be synchronised.

Neither the "Initial Carburetor Mechanical Synchronization" nor the "Carburetor Fine Synchronization" (Vacuum Gauges) procedures, as my manual calls them, have been performed. If these are not done then you have little chance of success.

I don't know that my past experiences would agree with you; but I am listening.

IMHO, run-away engine control is not an electrical/ignition issue and not a mechanical/electrical timing issue. This is a fuel/air/carburetion issue.

I agree entirely. It is obviously fuel\air. My ignition woes are ancillary.

Would suggest the following:
1) Make sure your gas cap is venting properly and the air filter is breathing well. Leave cap open if necessary.
2) Make sure fuel flows freely into carbs. Clean, replace or discard any internal petcock fuel filters. Add or use a new in line filter.
3) Make sure your fuel service level is set to specification using the clear plastic tube method (you're probably really good at this by now).
4) Make sure the throttle cables are free and loose
5) Use a drill bit or coat hanger wire as a gauge to adjust the height of each carb slid as it just comes of idol. See the procedure in your manual under "Initial Carburetor Mechanical Synchronization".
6) Follow up with a set of vacuum gauges to do the "Carburetor Fine Synchronization" as per your manual.

1- Flow is fine, I have checked it a dozen times
2- Flow is fine, I have checked it multiplle times, screens are clear.
3- I haven't rechecked it after adjusting float, but it WAS fine.
4- The ONE throttle cable is free and lose
5- CV carbs, sorry
6- Agreed it is not a bad idea, but right now it won't stay running long enough to synch anyway.

Again, IMHO, I would be astonished if this did not eliminate part and maybe all of these run-away symptoms. If you have a different type of carburetor then just flush the above.

Best of success.

Some of it has to be flushed, because these are CVs...

PS
Could you add your year, model and location to your signature to make it easier on us... and it’s considered real friendly too.
Location might get you a nearby member with the equipment you don't have yet.

First post of the thread has all this information, and my username defines my location (PDX is the airport code for Portland, OR.) But, yes, I will add it.

Thanks for all your help.

Wow, you really seem bound and determined not to replace those carb holders until you've tried everything else possible. In an earlier post, you stated that spraying water on the holders caused smoke in the exhaust. That seems to indicate that the water was being sucked in. Visually inspecting the carb holders won't tell you whether they're bad or not unless they are really cracked up because the tubular part of the holders that you can see isn't the first place to go bad. When I replaced mine the old ones looked fine as far as I could see, but when I sprayed carb cleaner around the manifold the bike cut off. BTH, carb cleaner won't hurt anything at the manifold because it's made for cleaning carbs. When I removed the old holders, I found the problem to be VERY fine cracks on the mating surfaces of the holders where they are suppose to seal against the head. These fine cracks could not be seen when the holders were mounted on the head, and the tubular part has no cracks at all. Even with the holders in hand they look good enough to use until you look very closely at the mating surfaces. The mating surfaces of the new holders are more pliable and make a tight seal, the old holders became very hard from engine heat and did not make a tight seal. Ed

650ed wrote:

Wow, you really seem bound and determined not to replace those carb holders until you've tried everything else possible. In an earlier post, you stated that spraying water on the holders caused smoke in the exhaust. That seems to indicate that the water was being sucked in.

Not true. They are expensive, and will take a week to arrive, I am not convinced they are problematic any longer as I have looked them carefully over and see no cracks from the inside. Also, spraying water MIGHT have caused some light smoke, it is hard to tell with the erratic idle and general smoke the bike produces...

Visually inspecting the carb holders won't tell you whether they're bad or not unless they are really cracked up because the tubular part of the holders that you can see isn't the first place to go bad. When I replaced mine the old ones looked fine as far as I could see, but when I sprayed carb cleaner around the manifold the bike cut off. BTH, carb cleaner won't hurt anything at the manifold because it's made for cleaning carbs.

I'll give carb cleaner a go, I'm just not a fan of the idea.

NOW, this all said.

Last night I lowered the fuel level in the bowls SIGNIFICANTLY. after discovering the evidence of gas in the airbox. I just used the clear tube method and found that while two of the carbs have a SLIGHTLY lower fuel level, the other two are exactly the same. This is impossible, as the amount I bent the tang would dictate a MUCH lower fuel level, definitely not identical to prior to bending. I definitely have bad float needles, or way, way mal adjusted float level. I am going to try and determine which it is.

WBPDX wrote:

1983 KZ750 H3, stock...advancer is new...isn't really running on all four cylinders...running hot on 1 and 3, cool on 2, and not at all on 4...fires up pretty much right away...will not rev up (it used to) except when it is sitting there idling and all the sudden it runs away to redline and has to be shut down....

Just pondering some things ---

Hoping the new advancer was undamaged and was lubricated when installed. If stuck or hanging in the more advanced higher rpm position and thereby failing to immediately retard at idle rpm when it's supposed to, a recalcitrant advancer could cause the runaway idle (even with perfectly sealed non-leaking carb holders).

Under the points cover, are there any loose ignition parts or connections?

Which cylinders have no combustion?
Immediately after shutting the engine down following the runaway idle, has water been sprayed onto all 4 header pipes to determine which cylinders have combustion going on inside? Water spray will instantly vaporize off the header if there's combustion inside the cylinder. If water runs off (as it will from a merely warm header), combustion is failing in the cylinder. Am thinking cool on #2 is same as cold on #4.

Confirmation as to whether or not there's combustion in all 4 cylinders, or exactly which cylinders, could be helpful in the diagnosis.


WBPDX wrote:

...bad float needles....

Imo, the runaway idle doesn't result from fuel flooding or mixture issues.

Good Luck!

(If applicable) are the o-rings okay on the pilot screw and pilot jet? Thinking about some other possible air leak source.

For reference, from kawasaki.com


[Click on image to enlarge view]

Well, the float levels must have been some small part, as it is now running better. As were the idle mixture screws. I read the plugs and adjusted the mix screws to match. 1 and 2 are way lean. Three is NOT running now, didn't investigate very much as to why. Four is running, rich, but not as hot as 1 and 2.

Spraying carb cleaner I really couldn't get definite results. 1 and or 2 might have changed, which would explain the lean-ness.

Those o rings have all been 'okay' when taking the carbs apart. The plugs covering the idle jet had kind of crappy orings, but no worse than most bikes I've worked on, and the all seemed to seal tight.

I guess it is time to either get serious and order carb holders, maybe needles and some orings... or bail.

Try backing the idle screw all the way back to make sure it's not pushing on the linkage.Turn the center carb synchronizer screw(clockwise?)1/2 a turn or so.Start the bike and see if there's any change.This should eliminate any linkage issues.You say #3 isn't firing or the pipe was not hot?

The '83 650&750 have BS 34 Mikunis I'm pretty sure.Try this; you should have two vent lines from fuel rail to airbox,right? Turn petcock to prime and blow then suck each vent line-listen for fuel bubbling in the bowls -this will send fuel into the pilot channels and may make #3 come back online.If it does you've got another carb cleaning to do.

WBPDX wrote:

...1 and 2 are way lean. Three is NOT running now, didn't investigate very much as to why. Four is running, rich, but not as hot as 1 and 2....

Thanks for the report.

1 and 2 are way lean -- still casting suspicion toward air leaks, with carb holders being most likely suspects.

Three is NOT running now, didn't investigate very much as to why. -- Sparkplug may be fuel-fouled beyond recovery, and cylinder flooding regardless of possible air leak.

Four is running, rich, but not as hot as 1 and 2 -- could be fuel mixture issue absent air leak.

Good Luck!