Author Topic: cb650 problem (Read 8242 times)

sfcb · « **on:** January 18, 2007, 10:43:57 PM »

hello all. hope someone has an answer for me or at least guide me into the right direction. i have a 79 cb650 w/ 28,000 miles. i cleaned carbs a couple of times. i haven't synced them, but i did a bench sync. all jets are clear and i set the float height. the plugs and coils are working fine, and it is getting fuel from the petcock. i put a clear hose there so i can see. the problem is i can warm it up and drive it about 10 minutes (or like 5 miles) with no problem, but after that it will start to bog when i roll on the throttle. it loses all it's power. before that it has no problem accelerating and it has GREAT power. i double checked my fuel line, and it's still getting fuel to the carb. i opened up the bowl drain screws, and there is fuel there. i pulled out the plugs, and it looks like it running lean (brown, ashy color). the engine gets really hot when it starts to bog. so basically it runs great for about 5-10 minutes and then it loses all power. i drove it around the streets going about 40-50mph. anybody have an answer for me? thanks.

Dennis · « **Reply #1 on:** January 18, 2007, 10:55:46 PM »

I'm not familiar with your model, electronic ignition isn't it?

Sounds like a heat and electronics problem to me. Ignition becoming unstable after the electronic components warm up.

Sorry that I can't help any more than that. Maybe someone who is familiar with that ignition can comment.

750goes · « **Reply #2 on:** January 18, 2007, 11:25:54 PM »

it could also be starving for fuel - check the float height...........that may explain the lean condition..........

oldbiker · « **Reply #3 on:** January 19, 2007, 01:25:29 AM »

Make sure the vent in the gascap is clear as a blockage here can cause exactly those symptoms.

Dennis · « **Reply #4 on:** January 19, 2007, 01:43:53 AM »

also good suggestions, check those first
easier to check than ignition
eliminate the simple stuff first

Rsnip988 · « **Reply #5 on:** January 19, 2007, 02:20:26 AM »

may seem like a stupid question but did you cut the choke off?

sfcb · « **Reply #6 on:** January 19, 2007, 08:18:55 AM »

i set the float height to 12.5 mm as the manual suggests. the vent tubes on top of the carbs are clear, and the choke is working correctly and is pushed in after warmed up. i've also tried running the bike w/ the gas cap off, and no help there.

dusterdude · « **Reply #7 on:** January 19, 2007, 08:26:57 AM »

to check the electrical,buy a can of that freeze stuff at your local electronics/computer store.take a ride and when it starts running bad,spray the ignition unit and see if it runs better.

sfcb · « **Reply #8 on:** January 19, 2007, 12:52:27 PM »

i'll try that. thanks

Ibsen · « **Reply #9 on:** January 19, 2007, 03:31:46 PM »

Checking the vent hole in the fuel cap is a good idea.
Normally, if everything is working as it should, the 79 650 should act the other way round when it is started cold. They need full choke when you start it and you will have to run it with the choke partially on for 3~5 miles before you can turn off the choke and the engine will pull without bog down.
Have you checked the spark plug colour btw? That will tell you if the carbs are running too lean or not. You should also check for air leaks in the intake system, and have the carbs properly synced. And it is correct that this bike have got an electronic ignition system with a mechanical advancer mechanism, and sometimes the ignittors located under the seat goes bad, or the timing advancer could be stuck. Also bad coils can make the engine act like this.

sfcb · « **Reply #10 on:** January 19, 2007, 08:20:24 PM »

well i just got done riding my bike around for about 5 miles and no problems. i ran it w/ the ignition unit cover OFF for that whole ride. i stopped and put the cover back on and it ran like crap. it started bogging and had no power. then i took of the cover, and it ran like a champ. so do i need to replace that part (ignition unit) or is it serviceable?

750goes · « **Reply #11 on:** January 19, 2007, 09:15:57 PM »

Is the ignition cover somehow shorting out the electronics

...is there any bare wires or pinched wires that may cause the problem ??

Pinhead · « **Reply #12 on:** January 19, 2007, 10:27:04 PM »

What do you mean the ignition cover? I've got a '79 CB650 and I don't have any cover over the top of my ignitors... Do you mean the cover on the side of the engine??

rab1dwolf · « **Reply #13 on:** January 19, 2007, 11:19:16 PM »

on my 82 650 I had similar problems thar were caused by some sort of malfunction with the spinny magnet parts under the right hand side ignition cover on the engine.

sorry about the vague description. I havent worked on my bike in over 3 months and it seems my brain is loosing the specific terms...

750goes · « **Reply #14 on:** January 20, 2007, 12:20:15 AM »

I meant the pulse generator under the right side engine cover... are the wires coming out of that being pinched somehow???

Ibsen · « **Reply #15 on:** January 20, 2007, 12:34:18 AM »

Quote from: sfcb on January 19, 2007, 08:20:24 PM

well i just got done riding my bike around for about 5 miles and no problems. i ran it w/ the ignition unit cover OFF for that whole ride. i stopped and put the cover back on and it ran like crap. it started bogging and had no power. then i took of the cover, and it ran like a champ. so do i need to replace that part (ignition unit) or is it serviceable?

And who would have guessed. Glad you might have found the problem.
My guess will be the wires running from the pulser generators. Check the insulation at the point where they are in contact with the engine case and the cover.
And no, the pulser generators are not serviceable.

This is how the system looks btw:

CB650 IGNITION SYSTEM

rab1dwolf · « **Reply #16 on:** January 20, 2007, 10:21:21 AM »

Thats what was bad on mine. Luckily I had a spare on hand that I swapped it out with and its worked fine ever since.

Mine didnt have any pinched wires that I could see and the condition of everything looked fine as well. My electrical system had tested fine as well on a multimeter. Took me several months to trouble shoot that problem.

From what I remember it wasn't exactly cheap to buy a new one...hopefully yours is something simple like the wiring

sfcb · « **Reply #17 on:** January 20, 2007, 01:35:13 PM »

yeah i do mean the pulse generator on the right side of the motor. i checked for any bad wires or anything pinched, and everything looks cool. so i guess i have to fork over the cash and buy a new unit. now that i discovered that problem, i also have a faulty charging system to diagnose. gotta love these old bikes! thanks all for the feedback.......

rab1dwolf · « **Reply #18 on:** January 20, 2007, 08:13:31 PM »

my charging system was bad too:
check the rotor on the left side in the alternator arear. Mine was bad as well. Replaced it and it ran fine.
FYI: the rotor is a pain the the ass to remove. get the removal tool (has screw threads on one side and hex on the other) and if the rotor is bad then who cares if you damage it getting it off...so I suggest holding it with a pipe wrench as mine ate two different strap wrenchs

oh and get someone to hold the wrench that holds the rotor...your going to need all the muscle you can get:)

Pinhead · « **Reply #19 on:** January 20, 2007, 10:31:55 PM »

If you need a new regulator/rectifier check the link in my sig.

sfcb · « **Reply #20 on:** January 20, 2007, 11:22:44 PM »

hey guys. i did some tests on the rectifier today, and according to my haynes manual, it's defective. i tested resistance from one wire to the other, and there is resistance. but when i reverse the test wires, there is no resistance. i ran the bike w/ a fully charged battery (13v) and the voltage on the battery while running is 11 volts. at higher rpm (5000) it still reads 11 volts. could it also be possible that the alternator is bad too?

hey pinhead. i read your "homemade" rectifier/voltage regulator and it's pretty cool. my question is the wiring. the 4 wire from the regulator is connected to the wires from the 4 pin connector on the bike right? but how do you wire up the other wires that are from the 6 pin connector on the bike. if you have pictures then that'll be greatly appreciated.

Ibsen · « **Reply #21 on:** January 21, 2007, 02:05:40 AM »

You can also get an aftermarket reg/rec unit made for the 650:

http://www.oregonmotorcycleparts.com/Reg_rec_units.html

CB650 Wiring Diagram

Dennis · « **Reply #22 on:** January 21, 2007, 07:55:33 AM »

Quote from: sfcb on January 20, 2007, 11:22:44 PM

i ran the bike w/ a fully charged battery (13v) and the voltage on the battery while running is 11 volts. at higher rpm (5000) it still reads 11 volts. could it also be possible that the alternator is bad too?

Well it's definitely not charging. Can you meter the alternator components? Again, not familiar with your particular model so I can't help any more than that.
Eventually you need to check for output from the alternator somehow.

Quote from: sfcb on January 20, 2007, 11:22:44 PM

hey guys. i did some tests on the rectifier today, and according to my Haynes manual, it's defective. i tested resistance from one wire to the other, and there is resistance. but when i reverse the test wires, there is no resistance.

This sounds like the definition of a rectifier. Conducts electricity in one direction only.
Why does Haynes tell you it's bad?
I'm confused!

Could it possibly be the regulator?

sfcb · « **Reply #23 on:** January 21, 2007, 09:39:33 AM »

hey dennis. from the test procedure in the manual there should be resistance from one wire to another (green o yellow), and if you switch the test wires from the multimeter, there should also be resistance, but there isn't. i'm going to throw the battery back on the bike and check the alternator output. i didn't check that yet, but i read how to last night.

Pinhead · « **Reply #24 on:** January 21, 2007, 11:19:21 AM »

Quote from: sfcb on January 20, 2007, 11:22:44 PM

hey pinhead. i read your "homemade" rectifier/voltage regulator and it's pretty cool. my question is the wiring. the 4 wire from the regulator is connected to the wires from the 4 pin connector on the bike right? but how do you wire up the other wires that are from the 6 pin connector on the bike. if you have pictures then that'll be greatly appreciated.

The alternator output is the three yellow wires. These three wires are the three-phase AC output that needs to be rectified with the rectifier (rectifier changes AC voltage to DC voltage). The output of the rectifier ties straight to the positive battery terminal through a 30 amp fuse. *In the original R/R the regulator and rectifier is all in one unit.* The rectifier regulates the alternator output by varying voltage across the field coil, which is the two "other" wires in the 5-wire connector. Maybe this diagram will make it a little more understandable. I'll go out later and take some pictures and label them to correspond with the diagram.

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Author Topic: cb650 problem (Read 8242 times)

sfcb

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Ibsen

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Ibsen

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