Help needed - 1983 KZ750 L3

I'm currently finishing a 1983 KZ750 L3 that I want to sell but it does not run correctly yet. During the restoration process, I took the carbs apart, cleaned them (ultrasonic cleaner), cleaned also the MJ and PJ. Three weeks ago, I posted the following on FB:

1983 KZ750L3
Engine turns but exhaust pipe #4 is about half the heat of the 3 others. And by the sound, something’s missing for the engine to purr.
Also, revs sticks and engine hesitate when throttle is turned from idle.
Suggestions please.

Following the comments written, I took the carbs out again (they are OK) and adjusted the valves. #4 intake was quite tight and #1 intake a bit tight. They all now are within specs. I also put some RTV sealant between cylinderhead and carbs adaptors. Now that everything is assembled back (had to wait for valve cover to arrive), the engine started pretty well and seem to idle and respond OK to throttle input.

I let the engine idle for about 15 minutes. I was to the point that I intended to put my helmet for a short test ride around the house when I got some problem again. Now, I can't get the engine to start correctly. It does start but only on full choke and seem to be running on 2 cylinders. I replaced the spark plugs and checked for spark on the 4 plugs (there is).

While the engine was idling, I was earing something like an air intake. I sprayed some brake cleaner on the carbs (at the cylinderhead to carbs rubber boots) and the idle raised immediately. I torqued tighter still the clamps on the carbs but nothing changed.

Well, that's about all for now. Engine do not start correctly and I'm about to throw some lighted matches in the fuel tank...

Any guru here can help me please??
Many thanks!!

Definately sounds like an air leak, are the carb to head rubbers new ? If "yes" are they OEM? If "no" they are probably age hardened and cracked (could also be leaking between the manifold and carb) I guess the best solution if they are old is to replace with ideally OEM manifolds

Nothing last forever. Old cracked, brittle and leaking carb rubber boots cause most of the carb related tuning problems here in the forum!

 

You should go back and check the basics (fuel, compression, spark, timing)

Are the plugs wet? (fuel) What is the compression on all 4?

If you have a OEM Kawasaki electronic ignition the Igniter box can often be the issue putting out weak spark (happened to me) - there are ways to check the spark output.

Sounds like you have a vacuum leak somewhere (negative spray test)

Wookie58 wrote:

Definately sounds like an air leak, are the carb to head rubbers new ? If "yes" are they OEM? If "no" they are probably age hardened and cracked (could also be leaking between the manifold and carb) I guess the best solution if they are old is to replace with ideally OEM manifolds

No, those carb-to-head rubbers are the 1983 originals. You really think those can create the problem I wrote?
I think I'll have to replace them. However, this bike will be sold as soon as I'm done with it and 4x new OEM rubbers will cost about $200 CDN!! I've see some chinese units on eBay for about $20!!! CDN including shipping. I don't care how long they last as long as the bike runs OK after I fitted them. However, they will take 1~2 months to arrive here...

Any source for those after-market but priced between OEM and chinese?

Scirocco wrote:

Nothing last forever. Old cracked, brittle and leaking carb rubber boots cause most of the carb related tuning problems here in the forum!
 

Geez, those are old! I suppose mine are quite like that. I'll remove them tomorrow to be sure. Any source you are aware of for non OEM (ie: cheaper than OEM) but better than chinese's ?

Injected wrote:

You should go back and check the basics (fuel, compression, spark, timing)

Are the plugs wet? (fuel) What is the compression on all 4?

If you have a OEM Kawasaki electronic ignition the Igniter box can often be the issue putting out weak spark (happened to me) - there are ways to check the spark output.

Sounds like you have a vacuum leak somewhere (negative spray test)

Plugs are wet but #2 and #3 seems darker.
I took compression in january and it was not so bad. From memory, 3 cylinders were at at about 135 psi and one closer to 120 psi.
Thanks!

Having it running well will add more than $71 to the sale price 

Wookie58 wrote:

Having it running well will add more than $71 to the sale price 

 

Seen that way, I can hardly argue with you...
I'm more toward eBay and I've seen OEM there so I'll give it a look. Thanks!

Well, I just did my old routine again… Removed seat, fuel tank, carbs and carb-to-head rubbers. They all seem to be still relatively soft and pliable. I "folded" each of them at 6 places around the perimeter and did not see any crack. They are not at all like those Scirocco posted the pictures of. I will order new units pretty soon but I'm far from convinced that they are the culprit…

FWIW, I compared them to KZ1000J's I have in my garage and they are the same, except for a +/- 3 mm larger distance between mounting holes. What make me wondering is that on 1000J's, OEM p/n is clearly molded in the rubber (which is also quite harder to flex).

On the 750's, there are a few numbers but nothing close to a p/n. Because of this and their remaining flexibility, could they have been replaced a long time ago with aftermarket units? Possible but I would be quite surprised.

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I looked at Z1 Enterprises pics and their 750 rubber do have the same 749 and 819 numbers (as well as OEM p/n) as mine so, I assume mine are 1983 originals.