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Author Topic: Bike won't run all of the sudden  (Read 1313 times)

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Offline jkot55

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Bike won't run all of the sudden
« on: September 26, 2009, 01:53:53 PM »
I tried to start my CB750K5 (1975) and it would not start well or run with out the choke on.  At that it ran like on less then 4 cyclinders.  I rode it about a week ago and all was fine.  This week only starts after much turning over with full choke.  As I shut the choke down, even just a little it immediately stalls.   Whether held at 1500rpm or 4000rpm  (did not want to rev much higher.   I bought the bike last October and besides changing fluids and filters I have not done anything to it.  I do not know much about it's history but while I have had it the engine would always start right up and while "cold-blooded" it would run well after a few minutes running.  What could have happened all of the sudden?
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Offline OldSchool_IsCool

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Re: Bike won't run all of the sudden
« Reply #1 on: September 26, 2009, 02:10:58 PM »
Clogged fuel filter starving the engine for gas or maybe a kinked fuel line?

May want to take a stab at the 3000 mile tune-up. 
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Offline Old Scrambler

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Re: Bike won't run all of the sudden
« Reply #2 on: September 26, 2009, 02:49:01 PM »
Clean the petcock........drop the carb bowls.........turn on the fuel to see if fuel flows to all carbs..........Use a mirror and clean the pilot and main jets.........if your into this - remove the jets and emulsifier tube and give them a thorough cleaning.......can be done with the carbs on the bike but its a pain unless you have a bench........if the fuel does not flow remove the floats and clean the needle and seat.........don't drop the parts........reassemble and it should work.  I use a set of welding tip cleaners to clean the jets......you must see air through every hole.....do not use a drill bit.
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Dennis in Wisconsin
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Offline stickman

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Re: Bike won't run all of the sudden
« Reply #3 on: September 26, 2009, 03:09:16 PM »
Sounds like the gas in the tank may be getting old also.  Only takes 5-6 months for gas to degradate and start jelling.  Suggest you also drain all gas from the tank, flush the tank and replace with fresh gas; replace or install inline fuel filter.  good luck.
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Ed Jones, Lenoir, NC
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Offline BVCB650

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Re: Bike won't run all of the sudden
« Reply #4 on: September 26, 2009, 04:18:23 PM »
I'd like to suggest that gas starts to degrade in as little as 3 weeks. Flame away.........
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Offline Hush

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Re: Bike won't run all of the sudden
« Reply #5 on: September 26, 2009, 04:32:29 PM »
Just had exactly same problem with my 650, started but rattled and wouldn't idle well, did the "touch-ouch" test on the pipes and found #4 was just warm.
Pulled the plug lead off a bit from top of plug and she fires on all four again.
Solution, replaced plug, starts right up, no vibration or rattles....did 30 miles just to check  ;D any excuse eh.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline myhondas

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Re: Bike won't run all of the sudden
« Reply #6 on: September 26, 2009, 09:34:05 PM »
Quote from: Old Scrambler on September 26, 2009, 02:49:01 PM
Clean the petcock........drop the carb bowls.........turn on the fuel to see if fuel flows to all carbs..........Use a mirror and clean the pilot and main jets.........if your into this - remove the jets and emulsifier tube and give them a thorough cleaning.......can be done with the carbs on the bike but its a pain unless you have a bench........if the fuel does not flow remove the floats and clean the needle and seat.........don't drop the parts........reassemble and it should work.  I use a set of welding tip cleaners to clean the jets......you must see air through every hole.....do not use a drill bit.

whoa.....dennis.....lets try some easy stuff first.... check pipes for cold.... check spark plugs and wires....points and condensers......timing........then check fuel lines.....etc.....
no offense dennis....but I always try the easy stuff first.... just lazy I guess.....
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Offline TwoTired

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Re: Bike won't run all of the sudden
« Reply #7 on: September 27, 2009, 12:03:34 AM »
Even easier...
switch the fuel tap to "reserve".

However, the bike is well overdue for its routine 3000 mile/3 mo. tune-up.  Some might even say the bike has been neglected.
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline Hush

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Re: Bike won't run all of the sudden
« Reply #8 on: September 27, 2009, 02:26:31 AM »
My guess....one dirty plug. ;D
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline jkot55

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Re: Bike won't run all of the sudden
« Reply #9 on: October 03, 2009, 06:18:47 PM »
I checked the spark plug wires basically pulling them off and putting them back on.  I think one of them seems to be a loose fit.  I then put the fuel valve on reserve.  It fored right up and ran like it did before.  Thank you for the suggestions.

The fuel is not old as I ride it once or twice a week and use about a half tank before filling it.  Probably could use a tune up.  Anyway, thank you all for the suggestions. 

JK
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When I ride my CB750 I'm a teenager again
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