91 CB/Highthawk 250

dsyfunction09 · L Plate Warrior Joined: 22 Aug 2007 Karma :

I have a 91 CB/Nighthawk 250, I've had this bike for about two weeks, logged around 100 miles on it. Ive noticed that when the you accelerate in 1st and second gear there is a bit of hesitation, if you roll on the throttle and give it a good amount of gas it does not have this problem. Ive changed the spark plugs, and just changed the oil, and this bike being somewhat new to me am unable to figure out the problem. Im hoping its an easy fix, and that somebody might be able to tell me where I might look to fix it.
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CB250cafe

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

You have to remember as nippy as these bikes are they are still only a little 250 so they don't take well to harsh attempts at acceleration. Riding smoothly really helps on these.

When you do an oil change you need to take off the right hand crank case cover and clean out the gauze filter. No one ever bothers as you almost always need a new gasket.

If you haven't checked it may well be worth looking at the condition of the air filter, if you need a new air filter there's one here.

dsyfunction09 · L Plate Warrior Joined: 22 Aug 2007 Karma :

The bike does fine under hard acceleration, it is when i am gentle on the throttle that the problem occurs, about 13 mph in first, the problem will happen, and around 20-25 mph in second, if i goose the throttle the problem will disappear. I've rejetted the card up to a 38 on the pilot and a 125 on the main, and the problem still happens. Have not yet checked the gauze filter, will do that monday when I replace the shift shaft. If anybody has any other ideas help would be greatly appreciated.
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CB250cafe

AbiJ · Renault 5 Driver Joined: 27 Jul 2007 Karma :

what color is the spark plug? sounds to me like mixture. Carb boots ok?

Abi.
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'81 Yammi XJ750 Seca, oldie but a goodie.

dsyfunction09 · L Plate Warrior Joined: 22 Aug 2007 Karma :

spark plugs are new, the old ones i pulled out were a little bit black, but were in good shape, no unusual wear on them.

elaborate on the carb boots, the term is unfamiliar to me. and if i need to adjust the mixture where do i go about doing that.
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CB250cafe

AbiJ · Renault 5 Driver Joined: 27 Jul 2007 Karma :

Dsy, I've just replied to your PM. Smile

Abi.
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'81 Yammi XJ750 Seca, oldie but a goodie.

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

thegubner · World Chat Champion Joined: 25 Mar 2007 Karma :

Love it!!!! Thumbs Up

brinniboo2 · L Plate Warrior Joined: 05 Sep 2007 Karma :

Just clean the carbs. Cb250s are pretty touchy about sitting around for a while or just tiny particles in general. Actually the only jet you need to clean is the slow jet (the smaller one) if the hesitation is within 1/8 to 1/4 turn on throttle. Just open float bowl and unscrew smaller jet. Clean with carb cleaner and insert one bristle from a wire brush through it ( do not force) it should slide through. Spray with carb cleaner again then blow with compressed air. You should be able to see a tiny hole through it. If you can't repeat cleaning. After, replace jet and put bowl back on. You should be set to go. Hope this helps.
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Never give up, Never surrender!!

TUG · World Chat Champion Joined: 12 May 2007 Karma :

lol nice, someones trying to help you then you say hes no help, thats harsh mate, paper shouldnt have oil in it (air filter) spark plugs should be a tan colour and you should never put bigger jets in unless you definatly know what your doing.

good luck with your bike, hope you sort it Thumbs Up

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Haz ER-5, innit!