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Discussion Starter · #1 ·
Hi guys. i need some help to get rid of a miss in my KZ 900 eng.
I'm sure it is the carbs and not electrical. i have switched coils and wires and the miss stayed in the same cyl.
I have cleaned the RS34 carbs a few times and the miss has moved to dif, cyls. after cleaning.
During the last cleaning i discovered the pilot screw O rings have degraded and some bits may have gone into the pilot circuit? I replaced them with new.
I will clean them again and focus here.
I have been testing where the miss is by using a temp gauge on the header .i can tell which cyl is running hot or cool, so i can know which cyl is missing/starving for fuel.
what I just noticed just now is that if i hold my hand lightly in front of the carbs bell mouth(air filters removed) i can feel a slight air pulse on #1 , a very strong pulse in #3 almost like its spitting back, and no pulse on 2 and 4?? At the header, the temps are like this, 1= 300* 2=215* 3=255* 4=175* don't pay attention to the low temps its not completely warmed. just that #1 is running best and 2,4 are worst. they should all be a similar temp.
What is this difference in pulsing telling me??


compression and valve clearance is good is good.
76kZ . gusset work,1200CC.Mukini RS34"s.,ported by Larry Cavanough Racing,1.5mm.over intakes,.424" lift cams ,under bucket shims, pods, Caron Header, undercut trany, Billet 2nd, Earl cooler, Dyna 2000 with 2.2 ohm coils,05 ZRX12 rear end and seat.ZX9 front end.
 

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"compression and valve clearance is good is good"
We hear that a lot that the compression is good, but once we hear the actual numbers it usually turns out the compression wasn't so good, what are the actual numbers on the 4 cylinders? The difference in pulsing suggests the carb are not balanced, but you can't vacuum balance the carbs if the compression values are not reasonable similar values. I take it you did not personally perform the modifications listed.

"hand lightly in front of the carbs bell mouth(air filters removed" <- Air Filters or Stacks removed, if you're running paper or felt pods directly on the carb mouth with no intake stacks, that would be a poor choice on a track bike.

Picture is worth a thousand words :cool:

& ... does the bike have a fuel pump? or does it rely on gravity feed and is it just running out of fuel the further you go from the fuel tap?
 

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Discussion Starter · #3 · (Edited)
"compression and valve clearance is good is good"
We hear that a lot that the compression is good, but once we hear the actual numbers it usually turns out the compression wasn't so good, what are the actual numbers on the 4 cylinders? The difference in pulsing suggests the carb are not balanced, but you can't vacuum balance the carbs if the compression values are not reasonable similar values. I take it you did not personally perform the modifications listed.

"hand lightly in front of the carbs bell mouth(air filters removed" <- Air Filters or Stacks removed, if you're running paper or felt pods directly on the carb mouth with no intake stacks, that would be a poor choice on a track bike.

Picture is worth a thousand words :cool:

& ... does the bike have a fuel pump? or does it rely on gravity feed and is it just running out of fuel the further you go from the fuel tap?
Comp. #s
1=210
2=200
3=200
4=205
Like I said comp. And tappet clearance are good.
The carbs are RS34's, so gravity feed with a pump internal manual accelerator pump. I use K&N filters.
It's not running out of fuel.
Aside from machine work and welding I have done all of the work myself. ;)
 

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Discussion Starter · #4 ·
Ok I cleaned the carbs again. I found a couple of bits of the old pilot jet orings. In #2. Now it seems to be running ok on 1.2.and3. The header temps are around 480 bot #4 is only at 200*. So I will take them off and clean them again. I have only been cleaning the pilot jet and its pathways..
Hopefully it gets it this time. I saw nothing in #4 at the last cleaning.
 

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Discussion Starter · #5 ·
Cleaned them again. Same result. #4 is colder. There seems to be a slight backfire as well. I assume it's #4 but can't tell. I switched spark plugs 3 and 4, no change.
The pulse I was feeling at the carbs is gone now.
If I cover the bellmouth on 4 a bit to choke it a bit, it doesn't help.
 

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KZ900 always had nice long stacks on the airbox, I don't think you're giving it much chance if you are running open carbs and even less chance of improving carburetor efficiency by blocking the intake. Put the almost 3 inch long stacks that came on it back on and it might work a little better.
Plug cap and wires can go bad and easy to over-look, you can meter test them for resistance.
You running high test pump gas or adding any race fuel or octane booster?
 

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KZ900 always had nice long stacks on the airbox, I don't think you're giving it much chance if you are running open carbs and even less chance of improving carburetor efficiency by blocking the intake. Put the almost 3 inch long stacks that came on it back on and it might work a little better.
Don't forget he's running aftermarket carbs, so the airbox runners won't even fit.

That being said, they may need a thorough soak in an ultrasonic cleaner. My CR29s took several passes before they were cleared up of blockages.
 
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The very first model had a really nice cone shaped plenum if one could be found and made to fit.
Sounds like there's not a lot of other things for him to check short of installing intake manifolds with spigots on them and vacuum balancing the carbs. Police KZ models apparently had that extra little touch.
 
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