Topic: 81 CB650 Pulse Generators Bad?

[gilesclement]

Here's the scenario, 15 miles at 75mph after which the bike starts to lose power. Pulled over and checked the plugs for spark. The two inner ones aren't getting any. When the bike is cold it runs pretty well and if I leave it sitting for an hour or so after riding hard it's back to normal. I've replaced the coils. What's the next most likely thing to go bad?

[Mattbastard]

I've been told the coils go bad when they get hot as well.  Maybe check the resistance when they're hot.

[Hush]

I've been down this road before and so have a few other 650 owners.
I replaced my stator=no change relaced the regulator/rectifier=no change replaced the rotor=battery now charges and hold charge. Untested conclusion, rotor died but tested fine.
De-rusted the advancer mechanism and greased it=increase in top end power.
These bikes need pretty much full battery charge to run well, I guess firing the pulse generators takes some load so battery gotta be in tip-top order.
To test coils I believe you can swap the two plug leads for the other two and see if the problem follows the swap.
Pull your plugs, what do they look like? What plugs are you running?
Bike could also be running lean, means bike will perform OK until you push it for some effort then she may stumble, can cause major internal damage if left for any time, plugs should be slightly brown but not bright white/blue on the insulator.....black and fluffy indicates flooding which could also occur if two cylinders weren't firing but unlikely following your story.

[joeb]

The issues I have had with pulse generators on my glod wings are massive back firing and complete stall out at highway speed when they got heated up.  Let the bike sit for a couple of minutes and away you go.  You will need to check with an ohm meter to see if thay are within specs with the engine cold.  The manuel should give the readings you need for that bike. 

[Soos]

I hate to say it, but I would seriously read through kit's (and others) threads on 650 problems.

It does sound like a few possible things.

Bad wires(?) to one or the other inner spark plugs from the coil
pulse generator(s)
coil(s)
spark units(marked MPS200 probably, under the seat, there is a pair of them, the things with the black goo in them)
Even possibly a spark plug(??)

Oh, missed that you had changed the coils.
What to? A used or new set?


I would put my money on either the spark units, or the pulse generators though.(and between those two, my money goes on the pulse generators)
Where you located at?
Might be another 650 rider near that could help with parts/testing if need be.

l8r

[gilesclement]

I should have mentioned that I've got a brand new battery which is charging fine, new plugs and plug wires which look to be fairly new as well. Normally the bike cranks over quickly and fires right up, when I'm having the problem after running and I shut the bike down it does crank over harder, sometimes pretty slowly but it's enough to fire it up on two cylinders. People keep mentioning stuff with low power etc and that somehow relating to loss of spark. ?

The thing's also got a bit of a vibration going on at about 5000rpm, up till then it sounds fine, past that up to about 7k it snarls and just sounds like it's sort of fighting itself, I've never ridden another 650 so not sure if that's normal. It will go 0-60 in about 5 seconds and cruises right up to the end of the speedo at 85. Cruising at 70mph there's kind of a resonance going on, a low wooob-wooob-wooob noise, dunno if that's engine or the #$%*ty ass tires I'm rocking. Low end torque seems reasonable.

The bike is hot right now and I checked the resistance of the two blue leads and the two yellow leads coming out of the PG's. Between blue and blue it's 930 and between yellow and yellow it's 640. Should these match up or is that an indicator that the blue PG when hot has much higher resistance and thus potentially not generating enough energy for a clean spark?

Checked again with the bike a bit cooler and they're now both about about 600. The yellow runs the 2&3 cylinders... I could see the connection between those cylinders not firing at temp if that PG had the higher resistance at temp but it's exactly the opposite with the 1&4 cylinders running at high temp and the two inners not....

Poo.

[Hush]

As both inner plugs fire from different coils I'd be loathe to blame them.
This "hot start issue" which Kit dug into pretty deeply seems a 650 thing, I still don't think Kit knows how she cured it she just did.
If you haven't had the carbs synchronised yet that would be my next move, they sound like they are pulling against each other at speed, this also gives a pretty crappy idle but if you've never seen or heard a 650 on-song then you wont know if your is good or not.
That starnge exhaust note could also be carb sync related, if they don't pull as a team you wont see the best out of your bike, the difference once done is amazing...like someone just gave you a new bike.
Another thought occurs, if the carbs are out of whack with each other there will be residual gas unburnt at stop, this will give a pretty rough start up again as the mixtures will be off.
My Clymer bible doesn't give any test for the pulse generators sorry, I guess if you have spark then you have PG's working.
Did you look at my suggestion of realigning the PG plate or rotating it slightly either way to improve your bikes' issues?

[Frankenkit]

no, 2 and 3 are on the same coil.  1.4 are the left ignition coil (or the blue/ blue/white pulser coils) and 2.3 are the right ignition coil (or the yellow/ yellow/white pulser coils)

your pulser coil resistance seems to be too high. it should be around 530 +/- 50 ohms. 

I'm going to agree with Soos that it's likely pulser coils or spark units (actually I'd guess spark units more because they seem to get weird easily) I'm not sure if we've completely ruled out your ignition coils but I'd think so if you have new coils on and the problem continues.

Cheap assurance is readily available, too, in the form of new plug wires.  They help anyway and can't hurt. 
 
My honda manual doesn't have any test for the pulse generator beyond resistance.

BTW, I never fully cured my hot-start issue, because I don't think I'm charging the way I really *should*.  The new starter I have drags less on the electrical system, though, so now I finally can start when hot.  ...different issue, though.

[Hush]

Damn, Kit you are right...I must stop relying on my suspect memory for such details of course #1 and #4 are from left coil and #2 & #3 are from right coil duh!

[Frankenkit]

i wouldn't remember if this stuff weren't beaten into me.

[gilesclement]

New (used) pulse generators and problem solved! Whee hee!

Of course now I've got a plug cap going bad, out in the rain tonight and it started arcing... will it ever end?

[Frankenkit]

plug caps are cheap, score one (or a new set, cuz they're cheap) off Z1.  I think they're only $2 each.

[Bryceo]

To rule out the OKI MPS-200 spark units check resistance with from the black to white wires.  Both my spark units overheated and #2&3 spark unit failed after the epoxy / tar melted and dripped out.  All other resistance values were similar to one another.

Resistance for the failed #2&3 unit was 148 ohms, the #1&4 spark unit that overheated read 76.1 ohms. I got two MPS-200s from a Goldwing that read 75.3 and 75.1 ohms, had no indications of heat damage and work perfectly.

Prior to the #2&3 spark units failure I had been leaving the ignition system energized and using the starter excessively while I tried to get the carbs functional/tuned.