Question about 1991 Honda CB 250 Nighthawk

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1991 nighthawk won't start. battery is drained so jumped it. cranks fine. At first it would start for a few seconds then die. Now it just cranks and cranks. I cleaned spark plugs. Checked plugs for spark. Sparks fine. no help. I waited a day then I drained practically all the gas out of tank then added fresh gas. Checked spark again. Again cranks and cranks but does not catch. Removed and reinstalled spark plugs (in case they had been improperly installed.) Same thing. Took seat off to facilitate airflow. Same thing.

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  • ejoell Sep 28, 2010

    I attached the old battery to the car with jumper cables. I then let it charge for 20 minutes. Afterwards I checked the indicator lights on the bike. They were very faintly lit. The next day, all of that charge was gone.`This leads me to believe battery will not hold a charge and is therefore dead. The bike did fire until I pulled the spark plugs to clean them. Subsequently the starter just grinds. A spark is being sent to the plugs which I verified. That leads me to believe the electrics are working just fine. On a car you cleaned the carb by removing the air filter and spraying a cleaning solvent into the body of the carb. In addition you werre able to prime the carburetor when it would not start. This carb appears sealed. So I can't figure out how to clean or prime. As for removing it, if the job gets that complex its off to the shop as my experience in doing serious repairs has taught me I would only make it worse.


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Foremost This will require strong dependable battery, starter and plugs. if any of the above is a fail, don't bother with what I said or you can try. Good luck.
First: Make sure you got a strong and or fully charged battery before you do the following.
1- Make sure your gas line petcock is in the ON position.
2- Empty your tank. and remove air filter temporarily.
3- Add an ounce of seafoam fuel stabilizer/conditioner to the tank, then add 2 liters of HIGHEST grade fuel you got.
4- Crank the engine few times with 15 seconds wait intervals so you don't wreck the starter. If the battery dies and the bike won't start, let it sit and charge it and try again later on or wait for a day so the seafoam works itself into the carbs and loosens them up. meanwhile put the charger onto the battery for the next day.
keep doing this. Eventually the bike will start. When it does clean air filter and re install it
5- Once you did all that, fill it up with highest grade THEN MMEDATELY add another 2 ounces of seafoam.
6- For maintenance, Add one ounce with every fill up
7- and for winter storage add 3 ounces to a full tank. run it for 20 minutes, fill it back up with fuel then kiss it good night. always use high grade fuel pure gasoline.
I hope this helps you and others in solving and maintenance.
Keep the shiny side up.

Posted on Feb 17, 2015

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Test battery for holding a charge-must hav over 12v to run rite-thats the problem with batt-coil ignitions--they dont run off alternator like a car once started--r ur carbs clean-thats an old bike--mite need a compression test too

Posted on Sep 27, 2010

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  • ejoell Sep 27, 2010

    OK have ordered new battery. But after firing then stopping, has not fired since I cleaned plugs. I thought about carborator but carborator appears sealed. How to clean?

  • Arnie Burke
    Arnie Burke Sep 28, 2010

    any carb can be takin down and cleaned-its put in a special solvent to dissolve the varnish caused by heat--lets stic with electrical-did u test old batt-cause the alternator may be the issue or the coil any discount place can chec these things on a machine for free If u have a kickstarter then u can replace the batt with a capaciter which is sold at harley stores-makin it like a lawnmower

  • Arnie Burke
    Arnie Burke Sep 29, 2010

    20 min does not charge or test a batt-take it to a auto zone and reread my last comment--carb cleaner isnt real cleaner--dont give up buy a clymer repair manual and enliten urself

  • ejoell Sep 29, 2010

    Its going to be pouring down rain over the next couple of days so I can't do anything until Saturday afternoon after my morning meeting and when the sun is back. I will let you know result of battery test. As for learning everything you wanted to know about Bike repair but were afraid to ask; there are several very good reasons for me to not attempt anything complex. Number one is that for the last 33 years in anything mechanical more complex than an oil change, I will end up screwing up a vital part due to lack of proper tools and/or knowledge and end up paying a professional 10 times the money to fix what I broke than I would have paid to have them do it in the first place. (I can give you a long litany of things like blown head gaskets, seized engines, broken toilet tanks, burst pipes, electrical short circuits, and the list goes on.) So I just don't do it any more. Friend of mine says the defininition of insanity is doing the same thing over and over and expecting different results. I can take the battery out and find someplace to have it tested, but previous experience with this bike has shown that when it sits in the garage for a few months and the battery is over a year old, it will not hold a charge.


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