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engine miss RS34's 13 Aug 2022 10:36 #872160

  • mark1122
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Hi guys. i need some help to get rid of a miss in my KZ 900 eng. im 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 puls 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.
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.

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engine miss RS34's 13 Aug 2022 11:27 #872161

  • zed1015
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Have you checked valve clearances and done a compression and leak down test to eliminate valve issues.
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engine miss RS34's 13 Aug 2022 17:33 #872184

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 And a quick carb vaccum sync check will tell you something more about your carb problem.....

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engine miss RS34's 17 Aug 2022 15:11 #872405

  • mark1122
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Sorry for the delay.
I rechecked the float levels. they are good all at 17.
The carbs were accurately sync a few thousand miles ago. only about
4ooo on it after the rebuild. it ran great , and then started this miss out of the blue.
I cant do a syc test when 1 cyl is missing

i have a inline fuel filter. the float bowls seam to be filling ok. Its missing right after starting, not like its running ok and then starving.

i have cleaned the carbs again. i found some more bits of the old pilot screw O rings that degraded ,and some bits have may have gone into the pilot circuit . the pulsing is gone. i just have a miss in cyl 4. and a little pop or backfiring. I will try to clean #4 again.

Valve lash is good. compression is 200psi to 215.
I have not really looked into the carb boots. they look fine, as as we know, that doesn't mean much. i have heard that u can test them by running a unlit torch of some kind around them?
76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.

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~ (k) / (z)

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engine miss RS34's 17 Aug 2022 15:53 #872409

  • Ojisan rider
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Pop or backfire USUALLY mean it's running lean. Since you said carb was serviced little while ago, maybe you can scratch that off. Try shooting carb cleaner around the boots. Any change, up or down, you found the problem. Make sure you shoot it from both side of the carb boots. Don't be lazy and just shoot from one side. Don't ask me how I know this.

Don't shoot into carb. Just around the boots.
82' KZ750-R1 cafe racer style. Clip-on, Rear set, Fork-Brace, Mikuni Flat-slide (forgot the size), Kerker.
84' GPz750 (basket case). everything are in pieces.
89' ZX750-H1 (ZX-7 Ninja). Resurrection project are on going with my KZ750. Everything is stock.

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