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Author Topic: '82 650 Nighthawk fuel problem  (Read 2484 times)

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Chris_in_MI

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'82 650 Nighthawk fuel problem
« on: August 31, 2006, 06:16:51 AM »
I have owned a '82 650 Nighthawk for about a month.  I find that if I ride it every day it starts instantly and runs great.  However, twice now I've been out of town for about a week and when I come back it's extremely hard to start.  The first time once I got it started and it ran fine after that.  The second time I went away for a week I got it started with much difficulty, then it quit 1/4 mile down the road and I pushed it home.  I can get it started with starting fluid and it runs smooth until the starting fluid burns up, but it doesn't get running on its own fuel.  I drained the gas tank last night and I'm going to take the petcock apart to see it it has a screen that is plugged or something.  I am doubtful that the petcock is the problem though, because when I attached a hose to the petcock to drain it it seemed to flow fine.  Does anyone have any ideas?
Thanks in advance,
Chris
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Offline 82CB650SC

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Re: '82 650 Nighthawk fuel problem
« Reply #1 on: August 31, 2006, 06:22:17 AM »
REMOVE YOUR AIR SHUT VALVE ON TOP OF THE CARBS.
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Bob  1982 CB650SC
Never force it just use a bigger hammer

Offline DammitDan

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Re: '82 650 Nighthawk fuel problem
« Reply #2 on: August 31, 2006, 07:09:03 AM »
You mean the vacuum line?

Yeah, it may be causing the problem...  Can you drain the carb bowls and get gas out of each of them?  What does it look like?

Is your tank rusty or is there any detritus in there?

I find that my bike is hard to start if I leave it sitting for a week, but I also keep it outside (damn apartments!).  I'm not sure why though...  Everything on the bike is pretty well sealed.  I guess the gas just magically cooks out of the bowls  ;D
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CB750K4

Offline 82CB650SC

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Re: '82 650 Nighthawk fuel problem
« Reply #3 on: August 31, 2006, 09:05:02 AM »
Thats what I ment to say.  That shut off valve gave me nothing but problems.  I took it apart and cleaned but it would not open some times at random, so off it came.
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Bob  1982 CB650SC
Never force it just use a bigger hammer

Chris_in_MI

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Re: '82 650 Nighthawk fuel problem
« Reply #4 on: August 31, 2006, 09:24:01 AM »
I'm at work right now so I can't look at it.  Are you saying that each carb has one of these valves?  And you can remove them without any ill effects?  Does your bike start better now, even after sitting for days?
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Offline 82CB650SC

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Re: '82 650 Nighthawk fuel problem
« Reply #5 on: August 31, 2006, 12:05:49 PM »
There is only one shut off valve.  Its is in line between your petcock and carb and its only function is to shut the gas off going to the carbs when the engine is not running.  You can remove it with out any ill effect but make sure you plug the vacuum line on the carb.
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Bob  1982 CB650SC
Never force it just use a bigger hammer

Offline DammitDan

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Re: '82 650 Nighthawk fuel problem
« Reply #6 on: August 31, 2006, 03:47:43 PM »
Ya, it's purpose is pure convenience....  Makes it so you don't have to remember to turn on/turn off the petcock.

I've never had problems with it, but they do go out after a time (and prevent gas from flowing to the bowls).  It works by hooking a vacuum line to the #3 vacuum port, so when the engine is running vacuum is applied.  This vacuum in turn opens a valve on a rack on the top back section of the carbs which allows fuel to flow to the main dispensor tube.  So, engine on, fuel flows, engine off, no vacuum and fuel flow is cut off.

This may very well be your culprit, especially if it only happens once in a while.  That's why I say you should also check the next time your bike dies to see if there is fuel in the float bowls.
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Chris_in_MI

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Re: '82 650 Nighthawk fuel problem
« Reply #7 on: September 01, 2006, 02:05:03 PM »
Okay, I removed that automatic petcock and bypassed, but it didn't change anything.  I still can't start my bike except to get it running for a few seconds on starting fluid.  I ran out of time to try anything else.  There is a real small inline fuel filter and I'll change that tomorrow.  I'm quite sure that my ignition system is all in order.  I think my carbs are working okay.  The problem has to be between my gas tank and my carbs.  It can't be that dificult.  I'll work on it tomorrow.
Thanks,
Chris
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Ibsen

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Re: '82 650 Nighthawk fuel problem
« Reply #8 on: September 02, 2006, 03:58:18 AM »
I had the same thing happening to the online fuel filter on my 650 last spring. It was clogged up.
Open the drain screw on #1 carb and see if you get any fuel flowing out of the drain hose. If there is any fuel in there, wait till it's emty, and then open the fuel tap and see if more fuel is coming. If the bowl is emty from the beginning, open the fuel tap and see if yoy get a fuel flow.
If there is no fuel flow with the fuel tap on,my guess is that either the fuel tap, the fuel tap strainer that runs into the fuel tank, or the inline filter is clogged up. If the filter is small, also condensation water can be collected in a paper filter and slow down, or stop, the fuel flow to the carbs.
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