Topic: 1976 CB750 k Power loss at higher RMP

[ravexcafe]

 Hello guys newbie here! I have a 1976 cb750k cafe.  I bought with a charging issue, which i believe my new regulator rectifier has solved as the bike starts and runs great, and the battery is staying charged now!  The bike had a dyna ignition installed by PO.  In neutral the bike revs to 7 or 8 k no problem.  But when under power it starts to cut out and bog/loose power around 5500 rpm and is doggy from there up.  The PO put pod filters on which I have seen is a no no, I also have velocity stacks for the carbs would these help my issue instead of the pods?, or is it carbs at all? could it still be my charging system?  At idle the battery reads 11.9 volts and at 4k 12.3 and 12.6 at 5500 to 6000 rmp.  I should also mention the battery reads 12.5 volts at rest.  And I have cleaned the carbs, and the tank is like new inside, the PO creamed it.

Thanks for the help!

Ralph

[iron_worker]

Your voltage levels still seem low. I believe at 5k RPM you should probably be reading closer to 14V or slightly over. I think you still have a charging problem... this could potentially lead to a high RPM ignition problem as well if your coils are not able to charge fully between sparks.

I would solve your charging issue first. You likely just have some bad connections. These bike's electrical connectors do tend to go bad over the years due to weather. Check and clean connections.

I'm guessing your pods are causing your bike to run very lean. A lean mixture is more difficult to ignite than a richer mixture so that may be making your weak battery voltage/charging problem even worse and causing a miss. Setting up a bike to run properly with pods takes a lot of trial and error as I understand it so be prepared to pull the carbs several times and experiment if you want it to run right.

IW

[ravexcafe]

thanks for the relpy IW !  I just went to start the bike bat was flat!!! So  I went through a bunch of the electircal connections before but just the obvious ones.  I am going to tear everything down and go through them all.  Still a charging issue, I tested the resistance between the 3 yellow wires coming out of the stator, and they are all .8 ohms is this a good number, I just want to make sure the stator is most likely healthy too.  The wiring was redone by the PO not to long ago so the connections are not origional, which coulde be good or bad, bad if he didnt wire it correctly and good because they are not to corroded... 
Thanks
Ralph

[BrockSamson]

I had a similar problem with my 1977 750K here are a few things to look at:

1) Air leaks between the carbs and engine.
2) What pilot and main jets are you using?  Do you have the original exhaust or 4-1?
3) Double check that the carbs are clean and nothing else has blocked any of the passages. 
4) Is the petcock pulling fuel efficiently?  Is there an inline fuel filter somewhere?

[iron_worker]

I replaced my regulator/rectifier using parts from this guy:

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

Turns out I think it was just one of my connectors was sh!tty but I would still recommend the site/products. Check out the FAQ (#18), there is tons of info on testing your charging system. He knows his stuff!

IW

[HondaMan]

Hello guys newbie here! I have a 1976 cb750k cafe.  I bought with a charging issue, which i believe my new regulator rectifier has solved as the bike starts and runs great, and the battery is staying charged now!  The bike had a dyna ignition installed by PO.  In neutral the bike revs to 7 or 8 k no problem.  But when under power it starts to cut out and bog/loose power around 5500 rpm and is doggy from there up.  The PO put pod filters on which I have seen is a no no, I also have velocity stacks for the carbs would these help my issue instead of the pods?, or is it carbs at all? could it still be my charging system?  At idle the battery reads 11.9 volts and at 4k 12.3 and 12.6 at 5500 to 6000 rmp.  I should also mention the battery reads 12.5 volts at rest.  And I have cleaned the carbs, and the tank is like new inside, the PO creamed it.

Thanks for the help!

Ralph

Several things, here:
1. The Dyna ignition peaks at 6000 RPM, and the spark dwindles above that by quite a bit. The points setup is good to about 8000 RPM, in comparison. If you use points plus my ignition box, they are good to 12000+ RPM.
2. The stock airbox creates a still-air feed situation so the high RPM flow can get properly mixed, as well as the low-speed RPM, particularly in the 1500-3000 RPM range. Consider using that instead of pods or velocity stacks, as it was well-designed.
3. Don't EVER rev these engines without load above 5000 RPM. When you do, it stops lubricating the piston skirts, and can seize the engine. I have seen it happen several times, though usually on very young engines that have little piston skirt clearance. Just a little friendly advise...

[ravexcafe]

Charging issue fixxed!!! Pulled off the cover for shifter assembly and one of the wired was unplugged, plugged it in and changed the oil, fired it up and 14.2 at 4k accross the battery, now the battery will not hold a charge because a. its a cheap battery, and b. its been cycled too many times, new AGM on the way!!!

[ravexcafe]

Wow sorry for all the typos, lol.  It looks like I am an idiot!!! I just noticed all of them.  I guess its time to proof read my posts!