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Author Topic: Dohc Cb750f: possibly a valve issue  (Read 3699 times)

Offline kopcicle

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Re: Dohc Cb750f: possibly a valve issue
« Reply #50 on: Sep 14, 2018, 12:39:50 »
one more time for those that were not paying attention ...


replace the igniter(s) and or pickups until it works
"If a man wants to carry two cats home by their tails, by all means let him. Heíll learn things that he might not have otherwise even guessed, and the experience will be one heíll not soon forget!"
~S. Clemens

If it leaks after all this? I'm gonna pull a "Brad" and bulldoze the fucker!

Quote from: Scruffy;1025553
As an equal opportunity bigot, I'll insult any brand, any style, any time...:wink:
-Scruffy

http://tinyurl.com/TheRedBike

https://www.gofundme.com/nancy039s-final-expenses RIP Nancy

Offline teazer

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Re: Dohc Cb750f: possibly a valve issue
« Reply #51 on: Sep 14, 2018, 12:43:38 »
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.

Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #52 on: Sep 14, 2018, 22:35:58 »
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.

Iím in Birmingham Alabama. The air temperature is hot. 80-90 degrees. Iím running a slight touch lean, Iím almost certain. There was a setback, and I havenít put it on a dyno yet. I wanted to dyno it, and jet from there. However, Iím still running the stock airbox/filter.

The series regulator was supposed to cause less stress on the charging system. Thereís some thermal imaging of bikes running with and without, and apparently it causes them to also run cooler 🤷🏻‍♂️. But, nasa isnít knocking down my door for electrical advice.


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Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #53 on: Sep 14, 2018, 22:38:05 »
one more time for those that were not paying attention ...


replace the igniter(s) and or pickups until it works

Thereís no igniters and no pickups. The ignition is power arc.

Noise interference is the issue Iím having


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Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #54 on: Sep 14, 2018, 22:45:40 »
I wouldn't run a fuse between the regulator and battery, but I'd run them between the battery and everything else.

Well, incidentally, this is how itís now wired. My plan is to get it running right, then break everything down so I can build it right. Iíve got to weld some mounting tabs, and paint the frame and tank/side covers. Suspension etc etc...

So Iíve done a ďtemporaryĒ harness to sort it out. I wanted to start from nothing, and figure it out. Canít even tell you how much Iíve learned.


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Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #55 on: Sep 14, 2018, 22:52:36 »
I'm a little confused by some of the comments.  When you talk about the engine being too hot, do you mean the top end or are you talking about the alternator?  If the whole motor is too hot, then it's unlikely to be the electrical system.  It's more likely to be spark too advanced or running lean.

Have you tried a laser pyrometer to see what sort of temperatures that different parts of thr motor are reaching after a short ride or a longer one?

How was the air temp this time compared to earlier runs.  Up here, it's already 10-15 degrees cooler than it was a few weeks ago and that's enough to make a difference.

The original theory was that engine temperature was tripping a safety mechanism in the ignition. Itís built in to prevent a ďmeltdownĒ.......supposedly. Turns out, itís probably a noise issue due to the regulator being wired to the starter solenoid (ie: like ďstockĒ). Wiring the regulator strait to the battery solves that....apparently 🤷🏻‍♂️

All new information to me, and most of the technical is over my head. But if it works, Iím in.


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Offline teazer

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Re: Dohc Cb750f: possibly a valve issue
« Reply #56 on: Sep 14, 2018, 23:33:00 »
Too many noisy electrons will create issues.  Not sure about the wiring change though.  Battery to starter and wire from that same terminal to the regulator. How does that differ from a wire direct from the battery to the regulator? And what is the noise source?  I don't know about electrical issues to pass judgement - just trying to understand and clear the smoke to see what is actually happening.

I get that the ignition might have some sort of thermal overload protection but it made no sense that the charging circuit was a cause of overheating.  Good to see that theory has been taken off the table.  Keeping in mind that I wouldn't know an electron if I ran it over, I wonder if that new alternator might be generating waves (ripples) in the DC circuits that caused the ignition to freak out.  Maybe the new regulator acts as a smoothing device in some way.

BTW, most bikes now seem to have a 30 amp fuse built into the starter solenoid wiring between the battery and everything else. If it blows, all power to all circuits is cut, so no more engine generating power, so I'd guess that is not an issue. 

Offline irk miller

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Re: Dohc Cb750f: possibly a valve issue
« Reply #57 on: Sep 14, 2018, 23:37:57 »
One advantage to running a fuse per individual circuit vs. a breaker for the whole harness is being able to isolate an issue easier.  If my headlight fuse blows, I know where to look because the fuse told me.  If a circuit breaker blows, I'm checking the whole harness hoping I don't test the headlight circuit last.

Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #58 on: Sep 15, 2018, 21:58:24 »
Too many noisy electrons will create issues.  Not sure about the wiring change though.  Battery to starter and wire from that same terminal to the regulator. How does that differ from a wire direct from the battery to the regulator? And what is the noise source?  I don't know about electrical issues to pass judgement - just trying to understand and clear the smoke to see what is actually happening.

I get that the ignition might have some sort of thermal overload protection but it made no sense that the charging circuit was a cause of overheating.  Good to see that theory has been taken off the table.  Keeping in mind that I wouldn't know an electron if I ran it over, I wonder if that new alternator might be generating waves (ripples) in the DC circuits that caused the ignition to freak out.  Maybe the new regulator acts as a smoothing device in some way.

BTW, most bikes now seem to have a 30 amp fuse built into the starter solenoid wiring between the battery and everything else. If it blows, all power to all circuits is cut, so no more engine generating power, so I'd guess that is not an issue.

My solenoid has a 30amp fuse. My original thinking was that this would be great, considering the stock harness plugs in at the solenoid. But, the stock ignition isnít effected by noise.

Apparently both regulators are producing noise. But, wiring it straight to the battery eliminates that noise 🤷🏻‍♂️. This is the first time Iíve heard this, but......

Tomorrow Iíve got some guys together, and weíre going to shred the surrounding area. Iíll know for sure if itís fixed tomorrow. No holding back


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Offline SquidHunter

  • Posts: 93
Re: Dohc Cb750f: possibly a valve issue
« Reply #59 on: Sep 15, 2018, 22:03:39 »
One advantage to running a fuse per individual circuit vs. a breaker for the whole harness is being able to isolate an issue easier.  If my headlight fuse blows, I know where to look because the fuse told me.  If a circuit breaker blows, I'm checking the whole harness hoping I don't test the headlight circuit last.

You are exactly right. My plan is to run a m-unit. Just trying to work out the bugs for now.

If my headlight fuse blows, my fuse is my headlight.....

Iím going to run LEDS and all that, so Iím not particularly worried about it at this time. Iíve blown that 30amp solenoid fuse about 5 times messing with the electrical. When I say messing, I mean just that. Itís been a total mess. As I expected, Iím walking away with a ton more knowledge though.


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