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Author Topic: Dohc Cb750f: possibly a valve issue  (Read 2617 times)

Offline teazer

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Re: Dohc Cb750f: possibly a valve issue
« Reply #70 on: Oct 08, 2018, 21:00:54 »
Time to buy a nice simple DYNA S  and see how that goes. 

BTW. how hot is the ignition when it fails?

Offline SquidHunter

  • Posts: 87
Re: Dohc Cb750f: possibly a valve issue
« Reply #71 on: Oct 08, 2018, 22:04:23 »
Time to buy a nice simple DYNA S  and see how that goes. 

BTW. how hot is the ignition when it fails?

I may end up doing just that. I havenít taken a temperature reading, but itís not any hotter than the motor would typically get. I live in the city, so traffic and redlights are the norm.


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Offline crazypj

  • Posts: 13175
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Re: Dohc Cb750f: possibly a valve issue
« Reply #72 on: Oct 09, 2018, 14:02:30 »
Looks like seller of ignition thought it may be power spike although I don't see how a bridge rectifier would help.  If he actually developed ignition *and isn't just marketing something) I would have thought a simple diode bridge and capacitors would work better. It's more than likely one of the 'Military Spec' components  is either breaking down or simple turning off when it heats up. Manufacturer should eb doing more to help you out, so far it's a good advertisement to avoid them at all costs
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline SquidHunter

  • Posts: 87
Re: Dohc Cb750f: possibly a valve issue
« Reply #73 on: Oct 09, 2018, 21:37:54 »
Looks like seller of ignition thought it may be power spike although I don't see how a bridge rectifier would help.  If he actually developed ignition *and isn't just marketing something) I would have thought a simple diode bridge and capacitors would work better. It's more than likely one of the 'Military Spec' components  is either breaking down or simple turning off when it heats up. Manufacturer should eb doing more to help you out, so far it's a good advertisement to avoid them at all costs

You hit the nail on the head. The diode was the last effort to eliminate electrical issues. THE WHOLE TIME Iíve been saying itís a heat issue with the ignition. Itís very obvious. The problem is power arc doesnít want to admit thereís something wrong. Ken at cycle x has been the one trying to figure it out. Now itís been drawn out long enough the warranty is no good, so Iím basically screwed out of 600 bucks. Iím over all the back and forth. I just want it to run right. I need dependability over performance, because Iíll be traveling on this bike. I have been traveling on this bike.


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Online pidjones

  • Posts: 439
Re: Dohc Cb750f: possibly a valve issue
« Reply #74 on: Oct 09, 2018, 21:46:52 »
For dependability, I'd go back to the original Honda system.
"Love 'em all.... Let God sort 'em out!"

Offline SquidHunter

  • Posts: 87
Re: Dohc Cb750f: possibly a valve issue
« Reply #75 on: Oct 09, 2018, 22:40:13 »
For dependability, I'd go back to the original Honda system.

I could do that, but itís hard to believe that nobody has designed anything better. The erratic behavior of the stock ignition, paired with the stock charging system is nerve racking. My stock charging system failed three times since Iíve owned the bike. I went to the cycle x charging system, then my stock ignition failed (whilst riding 600 miles from home). Then I went to the power arc ignition from cycle x, and I havenít been able to achieve reliability since.

The bike runs great, until it breaks down. Iíll check the spark. No spark. Take the ignition cover off..... boom, instant spark. I can ride all day and night with the cover off.

Ken at cycle x tells me heís got one in the shop with the same set up, and he canít even make it fail. I believe him. I just donít know whatís different on his bike than mine. I have to believe itís a difference in the wiring, or perhaps because Iím running an agm battery?

Iíve got to pull everything apart anyway, so Iím thinking I may try wiring the coils straight to the battery, instead of through the ignition switch. I read through some information that suggested that. Apparently the ignition module shuts the coils off with the kill switch, and it isnít necessary to run them through the switch. Power arc even suggests this, due to fluctuations in voltage through the switch. That still doesnít explain why it runs great with the cover off however.


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Offline crazypj

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Re: Dohc Cb750f: possibly a valve issue
« Reply #76 on: Oct 09, 2018, 23:36:17 »
Haven't read all your post yet so may amend this. There is nothing bad about stock ignition system as long as bike is running. It does have problem when ignition is left on and engine isn't running, ignitors overheat pretty quick as they never had a timer or shut off. I would probably get the trigger units and use any of the aftermarket boxes. (even GM can be used at about $20.00 each and about $50.00 for 'high temp' versions) Only time I've seen issue with stock charging systems is when they are used to charge 'dead' batteries.(even brand new ones that were not prepped properly) The charging system can put out about 20 amps but only for very very short period. If the regulator /rectifier tries to maintain high output the internal regulator burns out then the diodes start overheating and often short circuit. Battery goes flat and new battery gets fitted which discharges through charging coils burning off the insulation. A battery will fail if left discharged (10v or less) for about 30 days. You need to get back on Power-X and get them to test ignition at 220f (then get them to replace it when they say it's 'fine') I would also make a lot of noise on their Facebook site (pretty sure they will have one, 'they all' like free advertising) Itonly took 48 hrs for Yahoo to fix my problem when I was locked out, other people had been complaining for 3~4 months and getting run-around with automatic replies I guess negative results on Facebook do carry some weight?
« Last Edit: Oct 09, 2018, 23:44:55 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Online pidjones

  • Posts: 439
Re: Dohc Cb750f: possibly a valve issue
« Reply #77 on: Oct 10, 2018, 15:06:55 »
The voltage regulators in old 50's, 60's cars were electro-mechanical relay type (many had adjustable voltage control), and often lasted for several decades. It's hard to understand why solid state devices can't hold up as well. All they have to do is sense the voltage and turn the field current on/off to maintain it. The diodes in the rectifier could always be uprated.
"Love 'em all.... Let God sort 'em out!"

Offline SquidHunter

  • Posts: 87
Re: Dohc Cb750f: possibly a valve issue
« Reply #78 on: Oct 10, 2018, 23:05:55 »
Iím generally good with mechanics. I understand motors, and I work meticulously. Electrical on the other hand...... blows my mind every time. Especially the technical side of it. Absolutely a pain in my ass. This is the main reason Iíve stripped everything off my bike and made it as simple as possible. Thatís also the reason Iíve chosen the components I have. Simple.

Iím still suspicious the battery Iíve chosen may be the root of my problems. Reason being, these components were designed to work with a lead acid battery. I chose a agm battery (for the warranty, mainly), and didnít really do the homework before hand.


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Offline VintageMBike

  • Posts: 52
Re: Dohc Cb750f: possibly a valve issue
« Reply #79 on: Oct 11, 2018, 18:18:20 »

I think you and i conversed about this. I have a 900f pictured below.

When I first bought it, batteries kept dying, all sorts of shit.

I bought the Cycle X 3 phase thingy (its really a brit charging system) installed it myself with a new battery, and havent had a problem since (well, the battery DID die thereafter when I had to ride 2 up with a friend whose bike broke down in the dead of night. With my headlight on and the extra load, it died just as we got where we needed to go. I ran it a while after with the headlight off and it was fine).

There maybe be an issue in your particular bike that is causing this.

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« Last Edit: Oct 11, 2018, 18:19:51 by VintageMBike »