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high speed miss/ hard start, 1978 b
- JMKZHI
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- tinlizzie37
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Bob KZ 650 E1, En 450
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- KroozR
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I am having the same problem with my 1976 KZ900A4. You can see the bike in the gallery under KroozR. I bought it new in 76 and until now has been running like a clock. Like you decsribe, I too am getting that high speed loss of power but if I open the throttle it acclerates fine, it just won't maintain a steady Krooz at 50 or 60, as you describe. I haven't changed anything in years, just recently rebuilt the catbs back in 2004 but it's been running fine since then and until now. At first, I thought I had water in the gas so I drained and replaced it. I ran it with Sea Foam, a gas additive, but no change. I've also been using a lead additive called 130 Supreme, (real lead, not a substitute), but I been running this too in my 1963 TR4 Triumph. I can't figure it. I does sound like it is leaning out, but why all of a sudden? It does not make sense to rejet since nothing has changed. All I can think of is a fuel passage is getting clogged and less gas is flowing, hence causing it to "lean" out? Maybe, ...but to re-jet does not seem like the answer since I've been running this set-up with the same exhaust since I bought the bike new decades ago. Please keep in touch with me so when and if you find the answer, I will know of it, I will also let you know how I make out. Many thanks in advance, Dominick (KroozR, kdls@verizon.net)
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- Patton
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A too high fuel level in the float bowl can cause an over-rich mixture.
Would test level using quick and easy clear tube method.
Good Fortune!
1973 Z1
KZ900 LTD
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- hap1968
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and it was hard to see but i think the intake valve had oil on it above the seat.
so i will be taking off the heads this winter to check it out.
thanks all,
i thought it was the carbs all this time.if not for the help i got here i
would still think it was the carbs.thanks for all the help.
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- KroozR
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- KroozR
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- Patton
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Am glad to try helping out within this thread, but creating a new topic about KZ900 carb issues, specific symptoms, and suspected conditions, may likely generate more and better responses....having the same problem with my 1976 KZ900A4...bought it new in 76 and until now has been running like a clock...I too am getting that high speed loss of power but if I open the throttle it acclerates fine, it just won't maintain a steady Krooz at 50 or 60...haven't changed anything in years...rebuilt the catbs back in 2004 but it's been running fine since then and until now...ran it with Sea Foam, a gas additive, but no change...does sound like it is leaning out, but why all of a sudden? It does not make sense to rejet since nothing has changed. All I can think of is a fuel passage is getting clogged and less gas is flowing, hence causing it to "lean" out? Maybe, ...but to re-jet does not seem like the answer since I've been running this set-up with the same exhaust since I bought the bike new decades ago....
Where non-carb possibilities as to ignition timing, spark quality, compression, valve clearances, etc., have been ruled out, I would suspect dirty pilot circuits (which may be still having some influence on performance in large Kaw fours at 50~60 mph where throttle may only be barely cracked.
Sometimes Sea Foam isn't enough.
Btw, what are plugs readings, and how long since changed?
Good Fortune!
1973 Z1
KZ900 LTD
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- KroozR
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- Patton
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The carb choke (enrichener) circuit is a distinct circuit separate from the pilot circuit. It's possible to have a choke plunger not completely closing for whatever reason, but am thinking the issue at hand is more likely within the pilot circuit.
Lucky you -- and me -- for still having, riding and enjoying KZ900 bought brand new way back when.
The oem Mikuni 26mm manual slide carbs are imo among the best most user-friendly carbs ever.
Good Fortune!
[Click on image to enlarge view.]
1973 Z1
KZ900 LTD
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- Patton
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Would double-check setting of pilot air screw on the carb feeding whichever cylinder has the blackish looking spark plug....plugs are brand new...good color all tan...but one had a liitle blackish look to it, not excessive, as if that cylinder was slightly rich....
And might help to turn the pilot air screw out counter-clockwise, say 1/4~1/2 turn, for a leaner pilot circuit mixture.
Incidentally, where adjustments to pilot screw don't influence idle speed, there's likely something wrong inside the carb.
Good Fortune!
1973 Z1
KZ900 LTD
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- KroozR
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