new biker with a troublesome nighthawk

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coreyinthewoods
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new biker with a troublesome nighthawk

#1 Unread post by coreyinthewoods »

Hi everyone, I'm new to the site but could really use some help with a 1983 honda cb650 I just bought. I'm just going to list off anything notable since o bought it and any help would be greatly appreciated. I bought it and the guy said it had been parked last fall and stored all winter in a garage that, (from what I could tell wasn't heated) he said it ran great but could maybe use a timing adjustment. I brought it home and kept it in my heated garage until the snow melted and I was released from the army. I started teaching myself how to ride and from what I could tell it was going great. One day not far from my house the rpms started going down and had almost no throttle response. The rpms eventually dropped to zero and died. I tried starting again and it was difficult but it did then only a few minutes later it did the same thing. This time would only stay running for a few seconds. I let it cool down over night and tomorrow the whole thing happened again. Seems to need a few hours to cool down then runs for a while again. So, frustrated and no money for a shop I let it sit for a week or so in the garage. Then I took the tank off and checked out the spark plugs. I forget what they looked like but I just wiped them clean and everything back together. Also checked the oil which was good. Few more days of me cranking on the starter and it'll idle at 2000 forabout 5 seconds then slowly dies. I turned the idle screw all the way in and that helped a bit but same thing. Whenever I turn the throttle it would immediately die. I got the idea it was starving for gas and sure enough my fuel line had a half kink which I fixed and then started it. Fired right up and rpms jumped to about 6k and cared the s#it out of me so i killed it and turned the idle screw out a few turned and opened the choke about half way. Started again and now for the first few seconds it sounds like it won't go but then does and idles at 1.5k but kinda will jump up to 2k or 1k. Not very steady. Side note- imaybe I just never noticed before but after letting it warm up and revving it gently I noticed the whole engine being really hot to the touch and some white smoke out of the exhaust and from the front of the engine somewhere. (Maybe just exhaust ports) it was only like 15degrees and had just finished raining so I don't know but. I'm thinking spark plugs or ignition coil. Maybe carbs? Not sure. Any help is appreciated. Not much money for the shop and theyre booked until July anyway so.

blues2cruise
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Re: new biker with a troublesome nighthawk

#2 Unread post by blues2cruise »

Welcome to TMW.

I don't know about your motorcycle problem....but try Google..for a 1983 Honda CB650 manual.

I saw a couple of places that had them for viewing.
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BRUMBEAR
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Re: new biker with a troublesome nighthawk

#3 Unread post by BRUMBEAR »

Hey first off welcome and THANK YOU for your service, secondly I would lean toward a clogged fuel filter/petcock rust in the tank issue.
Here is what I would do, shut off fuel remove tank clean it and screen in petcock change inline filter if applicable drain and clean carbs reinstall everything and try again. Worst off you cleaned your fuel system and it should be done periodically anyway :)
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Re: new biker with a troublesome nighthawk

#4 Unread post by Hanson »

Corey, welcome to the forum and I am sorry you are having problems with your classic moto. The first things I would try is exactly what Brumbear said, not because I know that much about motorcycle maintenance, but because he does and what he said sounds appropriate.

When you get some time, it would be great if you would post a few picks of your bike. I love the Honda CB motorcycles from that time frame.
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Re: new biker with a troublesome nighthawk

#5 Unread post by GS_in_CO »

It's not at all unusual for bikes that get parked for a long time don't run well upon return to service.
This is because the gasoline can turn gummy and start clogging idle fuel passages (jets).
More recent gasoline is even worse in this regard with the ethanol attracting water and causing corrosion.

Symptoms are consistent with fuel flow problems such as rusty particles in the carb bowls or clogging the fuel petcock outlet. Could be as simple as the gas tank vent is closed/clogged so the gas can't get out of the tank.

I'd remove the fuel line from the tank to the carb and drain some of the gas into a clear glass jar and look at what's in there. While draining look for strong consistent flow. If poor flow, undo the tank cap and try again. If opening the cap allows flow - it's the tank vent not working.

If it doesn't flow, should remove petcock and see what kind of rusty gunk is in the tank.

If tank checks out good, reinstall with fresh gas and apply to the carbs. Carbs often have drain screws so you can drain the bowls without removing the carbs (Both my Hondas, my Yamaha, and my Suzuki had these). Drain into the clear jar again. (should come running out some small diameter rubber fuel lines at the bottom of the bike (try to follow them from the carb to be sure they are there). Rusty flakes, water or other junk might be from the ends of the lines but could also be crap in the carb bowls. Sometimes just flushing the junk out is all that's needed.

I put 80% odds on the issue being old/bad fuel rather than broken parts. Carbs are elegant for their simplicity but they don't like bad fuel any more than any other fuel delivery system.

BTW- white smoke out the exhaust at cold temps (such as 15F) is just water vapor. Burning gasoline produces CO, CO2 and H2O. You can see the H2O.
Ron

Current: 1988 BMW R100GS (the 'numberplate' model)

Past: 1987 Yamaha XT350
1983 Honda CB900F
1980 Honda XL185S
1979 Suzuki GS425E

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Re: new biker with a troublesome nighthawk

#6 Unread post by BRUMBEAR »

Hanson thanks for the props and GS spot on with the protein sludge from newer gasoline it's a nightmare I now have to run my generator every 2 or 3 months just so it doesn't get all wonky!!!! I only used to have to do it once a year.
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coreyinthewoods
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Re: new biker with a troublesome nighthawk

#7 Unread post by coreyinthewoods »

Wow thanks everyone for the help. Im not having trouble starting it anymore since I fixed the kink in the fuel line (also drained some gas and it looked clean thank god) I let it idle for about five minutes and after another minute felt the exhaust pipes carefully. First two (from left to right) seem normal, the third is twice as hot and has oil around the thing that holds the bolts that connect the pipe to the port, and the fourth is completely cold, so I'm assuming that ones not firing because it also had a wet plug while the other ones were dry and black. Could ALL of this just mean I need new plugs or should I worry about a seal or gasket somewhere?
Thanks

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Re: new biker with a troublesome nighthawk

#8 Unread post by GS_in_CO »

Temperature differences between cylinders could be as simple as unbalanced carbs. (you were messing with them before so may have disturbed their settings)

If you are checking this at idle and warmup it's not as significant as if you were to check it right after a good hot road run.

Syncronizing carbs means making them all the same. It's a fiddly job and requires a special tool to just read what's going on. Idle and mid-throttle settings interact and with 4 carbs there's a lot of action between the cylinders with adjustments.

I wouldn't worry about the oil seepage unless you're in danger of running out of oil or causing a mess on the driveway.

Work one problem at a time.
Ron

Current: 1988 BMW R100GS (the 'numberplate' model)

Past: 1987 Yamaha XT350
1983 Honda CB900F
1980 Honda XL185S
1979 Suzuki GS425E

GS_in_CO
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Re: new biker with a troublesome nighthawk

#9 Unread post by GS_in_CO »

Simple test for the cold cylinder with wet plug is to remove the spark plug, connect the wire, lay it on the cylinder head and crank the engine. Look for spark jumping the gap.

Without unscrewing the plug the test for spark is to remove the plug wire at the plug end, put a small screwdriver in where the spark plug goes and hold the metal of the screwdriver near the cylinder head to give the spark someplace to jump to. Then crank the engine.

SOME systems will be damaged by this so - service manual is important. (my BMW is one that would be damaged)
Ron

Current: 1988 BMW R100GS (the 'numberplate' model)

Past: 1987 Yamaha XT350
1983 Honda CB900F
1980 Honda XL185S
1979 Suzuki GS425E

coreyinthewoods
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Re: new biker with a troublesome nighthawk

#10 Unread post by coreyinthewoods »

Alrighty thanks everyone. Good point on working one problem at a time. I switched the plugs around and found that one is just dead because the cold cylinder moved. So I'm going to run out tomorrow and replace all 4 and keep you posted.

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