Topic: What the heck part 4

[cb650 bobber]

I am consolidating all the what the heck series into this final installment. I havent had that much time to work on the bike I changed out the fuel filter this weekend. And took it for a short ride to the store. Ran fine. Came out from the store wouldn't start. So I ran home. Not that far and drove the car back a half an hour later jumped on the bike started right up ran the bike home. Took it for a spin for a little bit and parked it. Later that day jumped on it agian went to get gas in it ran fine once I was done pumping gas wouldnt start parked it in the parking lot. Ran over to my car which was still parked in the next parking lot. Drove home later that night got my wife to drop me off after we went to eat started right up and drove the bike home. So pretty much once you ride it and it warms up it wont start....I need to start doing stuff to try and fix this as I like riding better than running and I cant take it anywhere far. It can be a fairly long ride 15-20 min or a short 5 min. ride and it still does it.

I need some ideas of best places to start........and I will go down the checklist untill it gets fixed.
These are some of the ideas guys have given me so far....I am looking for the most likely cause of this weird condition.

Solenoid
Coils
Pickups
venting fuel cap
battery.

[cb544]

That small list seems pretty right on... so as my first "blind" diagnosis on a motorcycle, I'm going to say that it's all electrical. I really doubt it's the battery, or the fuel cap...

I'd first test those coils per FAQ instructions, then the solenoid.

Are your plugs proper?

Of course, I may be way off base here...

[mlinder]

My guess is battery or other charging system device (rect and/or reg).

Sounds like either your battery isn't holding a charge, or isn't getting charged while running. You have a multimeter?
Whats your battery showing? What's the multi do when hooked up to the battery and you hit the ign button?

[cb650 bobber]

FOUND THIS ON YAHOO ANSWERS >>>>SAME PROBLEM AS MINE>
My CB650 won't start when at operating temp, even with a fully charged battery.?
I have a 1980 Honda CB650c. My problem is that when the engine is at operating temp, if I shut it down, I cannot get it started. This is after a 15 minute ride or so, various rpms, running flawlessly. (synched carbs sound very smooth.)


In failure mode, on pressing the starter button, the starter cranks very, very slowly, as if on a depleted battery, even when the battery reads 12.5-13v.
The battery is new and delivers 165 measured cranking amps. Voltage dips to 12v then returns to 12.4, signifying a good battery.

New starter solenoid, no trouble with the starter clutch. The starter cranks effortlessly when cold and I have very good startups both when the bike is cold and when the bike has cooled for 20 mins. Still won't start when hot. It *will* bump start, though, and once started, runs fine if a touch roughly. It will eventually smooth out, though.

I've taken out the starter motor itself and cleaned the commutator, replaced the brushes, checked continuity on the commutator and to the field coil in accordance with my Honda service manual, and everything checks out okay.

The charging system checks out alright, too. I generate 13v at 1600 rpms, and 14.6 at 5k (where the regulator keeps it in check) Haven't had the guts to measure without the regulator, haven't felt the need to.

I haven't found a definitive answer yet, though I've seen other 650 owners with this problem, which makes it more maddening.

[bryanj]

Hot starting can have many causes as you have found so i will try and be psycic here

(1) When hot does it crank as fast as when cold, faster or slower

Same is ok

Faster is OK suggests good battery and charging

slower suggests bad battery and or main connections

Have you checked for spark when cranking hot?

If you have slower cranking i would suspect weak spark due to voltage drop.

I know its a pain but you need to check battery voltage under the following conditions

(1) Static cold

(2) cranking cold

(3) static hot

(4) cranking hot

If Hot and cold conditions give same readings i would suspect the ignitors and or electronic box

[cb650 bobber]

I will have to see if I can check it tonight. I really need to try and have this fixed by Saturday I am going on a bike ride with my friend this weekend and need a bike that starts on call. I saw in another post to check the ground and coil connections as well.

[mikethejeepguy]

If you're going for a ride and don't get it fixed by then, I would suggest Don't shut if off? 

Just a thought... have you checked your ground wires? I used to have an old Oldsmobile that kind of did the same thing when hot. I cleaned the ground wires that developed the white/green powder oxidization on the brass fittings. They seemed to work when cold but heat somehow increased their resistance. A shot in the dark really.

M

[Hush]

If you have ever ventured into forum member Kits' "hot start issues" thread you will see what a world of pain you are about to embark on.
My CB650Z developed the exact same issues so i was working closely with Kit to find a solution.
Kit has yet to totally cure her issue but I found mine, I swapped out the regulator/rec but it wasn't that, swapped out the stator but it wasn't that either, finally when I replaced the rotor with a borrowed one the issue disappeared.
Not saying it is your rotor but that is how deep you may have to look, oh yeah and just because your rotor passes the ohms continuity test between the rings don't think you are OK, my old one (which is now a door stopper) still tests fine....but does not work!
Another forum member found same issues and he swapped his rotor and all good again....they must have a shelf life and they get damn hot in there so I'm guessing heat causes a catastrophic failure.

[martino1972]

if starter solenoid has been replaced,i would suspect either the thick ground cable from battery to engine block or the rotor..with  rotor meaning the hump of steel that sits on your crankshaft behind the left engine cover...

[cb650 bobber]

I replaced the rotor a year ago not that that means anything. But I know how to do that.

[cb650 bobber]

ok so if I want to see if it is
battery,reg.,or rectifier how would I test each...

I figure that if the reg. bad it would over charge to up in the 16's but not sure about rec. or how to see if the battery would be bad if the rotor is bad it would drop even at 4 or higher rpm.

[cb650 bobber]

I was reading kits page ...yep this sounds like a world of hurt im in for.