classic electrical probs

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kbailey

classic electrical probs

Postby kbailey » Sun Apr 09, 2006 11:29 pm

Hey guys, I'm new to the forum and while I am not a new rider I would consider myself a bit a newbie when it comes to doing more than changing the fluids.
I have an '84 cb650. This is my first bike and I have had it for 6 or 7 years now (I'm terrible with dates). It has had some problems since the day I bought it. I am reading that some of my problems are classic cb650 problems. That's a comfort as there are a wealth of people who have had similar experiences and can give me free advice (no better kind right?). So here are my problems please share your every thought.

1. It is becoming increasingly unreliable as far as starting. It's very electrical in nature. If I have my charger/starter connected to assist the battery i.e. supply the starter with all the amperage it can swallow, it starts right up. Without, it cranks over very slowly. It has a new battery (less than one year old). I just got it out of winter storage today, with the freshly charged battery it cranked over for maybe 45 seconds and started. After maybe 5-7 minutes of running at between 950-3kRPM (mostly the ~1500RPM range) I shut it off and it failed to restart without connecting the charger to it again. I know that below 2k RPM the alternator does not charge but is it really normal to discharge that much? Is it that much harder to crank a hot engine? When the engine started the first time it was still cranking at a healthy speed but when I tried the second time it could barely move the engine. Also, on a related note, when the enging is idling there is a very noticeable difference in headlight brightness with reving the engine. Is that normal or a symptom of a weak alternator?

2. Bad gas mileage. When I first got this bike I took it to the local honda dealer and had them inspect it. One of the things they did was to synchronize the carbs. Assuming they did not do that poorly, I still only get about 40 MPG. The engine seems to run very smoothly. I have not noticed symptoms of overheating. I am not a speed freak and ride what I think is fairly conservatively. Other thoughts on what I might look into?

3. This is a new one to me but in reading someone else's post I found that I seem to have a low top speed. I top out at about 90 mph and others are telling this guy that this bike should scare him out of his socks at WELL over 100mph. I do have a windshield that makes the bike less than ideal as far as aerodynamics. I always figured my top speed was a combination of my windsheid, my size (250 LBS), and the less than enormous engine. am I wrong, should it be higher, how much higher?

and finally, what are the chances that these are all symptoms of the same elecrical ailment? One person said that a significant drop in performace can be seen in an even slightly less than spec elecrical system.

thanks for everything you can share with me. I love my bike I just want it to work a bit better.

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Volker_P
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Re: classic electrical probs

Postby Volker_P » Mon Apr 10, 2006 1:29 am

Welcome, let's see if you can find some help here.
84, is this a Nighthawk? If yes, SOHC or already DOHC?

To your battery problem (so I think it is a battery problem). The battery required the charger support, so maybe it was not fully charged or one cell is dead. For the starter it is harder to restart a hot engine than a cold one. Bad hot starting is usually a sign for me to buy a new battery the next spring. Cold starting is possible much longer.
And do not expect to change anything significant on the charging status of your battery in 5min below 3krpm. Go riding some 10miles to see an effect. Charging seems to be a typical problem of the CB650, but from your description I would not conclude this so far for your case. You also could recharge the battery manually and look if it is able to start better then.
Unfortunately new batteries are not always all right, I was lucky the last years but others reported of dead batteries from the beginning which were exchanged by the dealers without trouble. So there seems to be some expectation of failure and/or dry checking options seem to be not perfect or too expensive.

For the low mpg (60 are possible if you go very easy on the trottle) it might be too rich, check air filter or maybe the carbs had been adjusted for pod filters and you changed back to the airbox? How do your spark plugs (correct heat value?) look like directly after a run at well above 4krpm? (You should not ride another 2-3 miles throgh the town before you check this). Are you sure it runs permanently on all four cylinders? NGK plugs partly tended to fail early when running too rich. So after making sure that you are not too rich, new spark plugs may already solve all your problems.
For optimal power, check also ignition timing and valve clearance (although these should have been checked by the workshop because synchronizing carbs makes no sense without that). Another (improbable) option for insufficient power at extensive gas consumption could be a timing chain displacement by one tooth.

So far for now, good luck.

Guest

Postby Guest » Mon Apr 10, 2006 7:40 pm

it is sohc. yes it is a nighthawk

The battery was well charged, i had charged it about once a month over the winter, checked the electrolyte levels, and charged it for about 8 hours on a 2 amp charger. I was actually concerned that it was discharging over that 5 minutes at 3krpm. I was supprised that it would have discharged that much.

I appreciate your advice. I live right off the freeway so checking the appearence of my spark plugs directly after a long fast ride is no problem. I am also going to get out my multitester and check the charging voltage at ~4k-5k rpm.

I have not changed the air filter style since I got the bike, I don't know what the pod style or air box style refers to.

thanks again.

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Vatch
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Postby Vatch » Mon Apr 10, 2006 8:57 pm

air box style is what came on the bike. It's a black box the filter goes into and then a lid is place over the filter. Pod style filters are after market filters, one small cannister shaped spongy filter per carb.
'99 1500 Drifter


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