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Finally figured out why my kz 400 bobber run's bad
- oldkaws4ever
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So now i know what my problem is, i need to get new rubber intake manifolds. Does any body know were i can buy them, i thought i remember reading some wear they are a real PITA to find. I remember also seeing them on ebay some were, they were brank new and made by a company that was selling them, i will see if i can find them. Thank's Jim.
74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- oldkaws4ever
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cgi.ebay.com/ebaymotors/_Motorcycle-Part...C39%3A1%7C240%3A1318
74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- Patton
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...it will idle really good...run's smooth as silk up to say 5000 rpm's.........then its like hitting a wall. It drops off onto one cylinder and run's like crap... replaced the coil with a green 3ohm dyna...new dyna copper wires, new spark plugs, new points and condensor, new battery, and cleaned the carbs so many times i can do it with my eyes closed...my dad mentioned it sounds like a vacume leak...sprayed carburator jet cleaner on the left and right intake manifold, the rpm's dropped and it died.
So now i know what my problem is, i need to get new rubber intake manifolds....
Meanwhile, if not already done, would assure there's no fuel starvation issue from such as:
clogged vent in fuel tank cap (experiment by running with cap ajar--not snapped down);
grit/crud clogging screens on petcock pick-up tubes inside fuel tank;
clog in other petcock filter screen;
clogged in-line fuel filter;
floatbowl vent being blocked;
floatbowl vent hose being kinked or blocked.
AND assure valve clearances being to specs.
AND read the sparkplugs to aid further diagnosis.
Good Luck!
1973 Z1
KZ900 LTD
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- oldkaws4ever
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74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- Patton
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If running without airbox (or other support at intake side of carbs), it creates additional stress on the carb holders which may lead to earlier failure, as the carbs "bounce" against their grip inside the holders.
Added weight of pods increases the stress.
Running without any rear-end suspension would likely cause even more stress.
Concur with need to resolve leaks in carb holders (presumably not due to loose clamps or faulty vacuum caps), and hope it eliminates the problem. But thinking air leak more typically causes idle issues as opposed to suddenly dropping a cylinder at 5000 rpm in an otherwise smooth running engine.
Thanks for the progress reports.
Good Luck!
1973 Z1
KZ900 LTD
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- oldkaws4ever
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I took the little poop cycle from the devil out for a couple mile run tonight. Although it isnt running perfect, it ran a ton better than previously, i was able to cruise at a steady 4500 rpm, with the occasional bog, but if i tried to accelerate from 4500 rpm real qiuck it would drop onto 1 cylinder. Earlier i also drained the float bowls and sprayed carb jet spray cleaner in there, and some little gold squares flushed them selves out. Then i started it, it ran stronger and had better throttle response.
74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- Patton
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- Thank you received: 2098
Good Luck!
1973 Z1
KZ900 LTD
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- Patton
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A non-carb possibility could be a weak or broken valve spring in the affected cylinder. Could cause loss of compression at the higher rpm.
But still hoping it's something simpler, like maybe a clogged air filter, or maybe a partially blocked air filter (shop rag, tool pouch, or something), or maybe an over-oiled K&N. Tough call (for me anyhow), especially without sparkplug reading.
If not already done, is the advancer unit clean, lubed, and properly functioning?
Is there a good flow path for air into the airbox?
Good Luck!
1973 Z1
KZ900 LTD
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- Patton
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...occasional bog, but if i tried to accelerate from 4500 rpm real qiuck it would drop onto 1 cylinder. Earlier i also drained the float bowls and sprayed carb jet spray cleaner in there, and some little gold squares flushed them selves out. Then i started it, it ran stronger and had better throttle response.
Perhaps some little gold squares are clogging the main jet.
Clogged main jet would be expected to produce a too lean spark plug reading at the higher rpm road speed. Perhaps aggravated by the air leak.
Insufficient air supply for whatever reason would be expected to produce a too rich spark plug reading at the higher rpm road speed.
Good Luck!
1973 Z1
KZ900 LTD
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- oldkaws4ever
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74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- oldkaws4ever
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- Have no regrets...... You only live once.
- Posts: 1648
- Thank you received: 12
74 Z1a 900 (Apart and making it better than ever)
77 Kz 650b (Threw a rod, going to sandwich in a 900 or 1000 motor)
76 Kz 400d
05 ninja zx-636
81 Kz 750 Ltd
Darien, Illinois
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- Old Man Rock
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Now that I'm thinking about it, your posting (fixes & results) would help at least 10 of the carb postings recently put on the forum...
You reviewed & analyzed the situation and symptoms, tore into the carbs and cleaned them up, asked intelligent questions, listened to the advice provided and did accomplish the recommendations and low & behold, "hauls ass".....
Have to love it!
Way to go young man,
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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