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Hesitation / lack of power around 5k rpm
- Fergie
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Things I have tried.
1) New carb/engine rubbers.
2) Cleaned out carbs, tank filter and petcock.
3) New air filter.
4) New plugs and leads.
5) New carbd diaphams
5) Set and balanced carbs using Colour tune and Carbtune tools
6) Upsized main jets (from standard 102.5) to 107.5
7) Experimented with different needle heights (currently on mid position.
Any suggestions
Sorry, should add that the problem is worst on full throttle. Ease off a bit and it improves, but still low on power.
Thanks in advance
Stewart
Z650-F4 1984 UK Spec
JMC Aluminium swingarm.
Harris 4-1 exhaust.
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- Fergie
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Z650-F4 1984 UK Spec
JMC Aluminium swingarm.
Harris 4-1 exhaust.
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- rstnick
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There's a similar post (or more) on kz650info at the moment:
forums.kz650.info/index.php?topic=3729.0
Rob
CANADA
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1978 KZ650 C2, 130K kms, Delkevic ex, EI, CVK32, PMC easy clutch, ATK fork brace, steering damper, braced swingarm, 18" Z1R front wheel.
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2005 z750s
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- Patton
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--- after throttle chop at problem rpm.
Valve clearances to specs?
Ignition timing advancer functioning properly?
--- watch action under strobe timing light.
Fuel starvation issue?
--- from any of several possible causes.
--- Might be simply a clogged vent in fuel cap.
--- Would test run with loose fuel cap.
--- In any event, need ample clean fuel supply to carbs.
Clear tube test?
--- otherwise perfect carbs suffer from incorrect fuel levels.
Good Fortune!
1973 Z1
KZ900 LTD
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- Patton
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Could remove tank, shake, and fast-dump fuel out open filler cap. Add some fresh gas, and repeat shake and fast-dump.
Good Fortune!
1973 Z1
KZ900 LTD
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- TeK9iNe
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- What did you do!?!
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Check the exhaust for an ubstruction, like a nest.
Motorcycle Shop Owner/Operator
79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors
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- Fergie
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Spark plug reading?
--- after throttle chop at problem rpm. DONE THAT. SEEMS OKAY
Valve clearances to specs? DONT KNOW. REPLACED GASKETS LAST YEAR AND SET CORRECT THEN.
Ignition timing advancer functioning properly?
--- watch action under strobe timing light. I HAVE HAD IT OFF AND CHECKED OPERATION BUT NOT UNDER STROBE.
Fuel starvation issue?
--- from any of several possible causes.
--- Might be simply a clogged vent in fuel cap.
--- Would test run with loose fuel cap. DONE
--- In any event, need ample clean fuel supply to carbs.
Clear tube test?
--- otherwise perfect carbs suffer from incorrect fuel levels. NOT SURE WHAT YOU MEAN. DO YOU MEAN CHECKING FLOAT LEVELS. CHECKED THESE AND ARE CORRECT.
Good Fortune!
I have checked most of these out. Would going up to 110 main jet help.
Z650-F4 1984 UK Spec
JMC Aluminium swingarm.
Harris 4-1 exhaust.
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- Fergie
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Might be crud inside fuel tank, suspended and hovering about petcock pick-up tubes inside tank, and obstructing pick-up screens at higher throttle.
Could remove tank, shake, and fast-dump fuel out open filler cap. Add some fresh gas, and repeat shake and fast-dump.
Good Fortune!
Have had this off (at least 3 times) and checked for debris. The tank filter was pretty clean.
Z650-F4 1984 UK Spec
JMC Aluminium swingarm.
Harris 4-1 exhaust.
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- Fergie
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Set your fuel heights perfectly, then go back to the stock mains. Increasing the fuel, decreased the power.
Check the exhaust for an ubstruction, like a nest.
I have had the carbs off (at least 3 times) and checked the float levels seem okay. 18.6mm in the Clymer manual?
Fuel heights. Do you need a special tool for that or can I measure it with a tube from the drain pipe.
Can anyone also confirm the spark plug gap. On searching the internet there seems to be a bigger gap recommended for 3ohm coils??
Thanks
Stewart
Z650-F4 1984 UK Spec
JMC Aluminium swingarm.
Harris 4-1 exhaust.
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- Motor Head
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- FIX UP YOUR BIKE RIGHT AND CHEAP
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As far as the washer at the needle position, you can check your manual to be sure of it's inclusion or position. When tuning carb's try to get a plug reading when operated under the same condition, bring you plug wrench and pull over and pull them all out after running at the problem area. Motors are Air Pumps, 4 into 1 means it will pump more air, so more fuel needed to keep the correct air/ fuel ratio. Sounds simple right? It may take 1 adjustment of jets or it may take several, be patient.
1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...
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- Old Man Rock
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"Upsized main jets (from standard 102.5) to 107.5"...
Why was this done for this is a fairly large jump in mains jets...
The symptom you're describing seems the term "Falling on it's face" when describing carb issues. Based on the Jett charting graph below... running Lean! @ 5Krpm, this would be ~ 3/4 range right between needle and main operations.
As mentioned, go back to 102 jet and take for a test ride, hit the 5Krpm range and make note of performance. If all good, then tackle mid rpm range needle clip position/jet.
Good luck...
OMR
1976 KZ900-A4
MTC 1075cc.
Camshafts: Kawi GPZ-1100 .375 lift
Head: P&P via Larry Cavanaugh
ZX636 suspension
MIKUNI, RS-34'S...
Kerker 4-1, 1.5" comp baffle.
Dyna-S E.I.
Earls 10 row Oil Cooler
Acewell 2802 Series Speedo/Tach
Innovate LC1 Wideband 02 AFR meter
Phoenix, Az
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- Old Man Rock
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1976 KZ900-A4
MTC 1075cc.
Camshafts: Kawi GPZ-1100 .375 lift
Head: P&P via Larry Cavanaugh
ZX636 suspension
MIKUNI, RS-34'S...
Kerker 4-1, 1.5" comp baffle.
Dyna-S E.I.
Earls 10 row Oil Cooler
Acewell 2802 Series Speedo/Tach
Innovate LC1 Wideband 02 AFR meter
Phoenix, Az
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