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This forum certainly hasn't been appreciative of the Britbike restorations I've taken the time to post AT LENGTH. Maybe a half-handful of replies, and some views without comment.

More of a Jap crowd, and "plank-seat / 2" long front fender / heat-wrapped exhaust" crowd, really. Then there are the people that just flat DO NOT have ANYTHING good to say, and of course SIMPLY MUST inject trite profanities into their criticisms to make it more meaningful...
Simply not true. Yours are posts I look for, because they DON'T become trash fests.
 

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Kerry, was the dead battery the only cause you know of for the starter issue?
The lights come on, but we only get a relay click, but the headlight was dim in Columbus, so I know the battery needed charging. We haven't had a chance to get back to it because of work just yet, I'm just looking for things to check once it's charged if it still won't spin the engine.
Hey, thanks for trying to break up the pissing match. This is a bike thread after all.
 

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Kerry, was the dead battery the only cause you know of for the starter issue?
The lights come on, but we only get a relay click, but the headlight was dim in Columbus, so I know the battery needed charging. We haven't had a chance to get back to it because of work just yet, I'm just looking for things to check once it's charged if it still won't spin the engine.
The easiest way to check if the bike is charging is if the headlight gets brighter when it's revved up. Most bikes produce little to no charging at idle but (should) put out 13-15V at revs.

Obviously a voltmeter will give you more detail, but the headlight will tell you if there is at least some charging going on.
 

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You can do it the "easy way" or the right way.

Charging specs are indicated by a term called "break even". In other words, at which rpm does the system push enough current to power everything plus send juice back for charging. The common spec for break-even is 'at or below idle'. So, if its running, it should be charging. The way to correctly test that is to test battery voltage key off, key on, and at idle. If the voltage doesnt go above the key off voltage at idle, its not charging.

To independently test the components, there are different procedures such as dynamic a/c output and diode checks.

The headlight thing though. Lol.
 

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We'll check it out this weekend, I have a good multimeter, so I can verify charging once we get it running.
David will take the battery and have it charged before I make it over there I'm sure.
 

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The "headlight thing" is the easiest way for a layman to understand if the bike is charging. If it fails this simple test then you know to delve further into testing individual components.

This shit isn't extremely difficult but it can become daunting for someone who is not confident with electrical systems.
 

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I have to agree with that.

Chief, any questions or concerns on the charging or any other electrical system, post a thread. I've had good success helping people test and diagnose over the net.
 

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You can do it the "easy way" or the right way.

Charging specs are indicated by a term called "break even". In other words, at which rpm does the system push enough current to power everything plus send juice back for charging. The common spec for break-even is 'at or below idle'. So, if its running, it should be charging. The way to correctly test that is to test battery voltage key off, key on, and at idle. If the voltage doesnt go above the key off voltage at idle, its not charging.

To independently test the components, there are different procedures such as dynamic a/c output and diode checks.

The headlight thing though. Lol.
The break even spec for that bike if it's an F is 1600 and idle spec is 1000 plus or minus 100, so the headlight would get brighter if it's charging. Yes he should ultimately check it with the appropriate meter. If you are any good at diagnosing over the net, you should start with the correct specs.
 

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I didnt give specs for this bike. I said a common spec is:

Yes some bikes dont charge at idle. I concede that the idle test will not apply. Rev it to 1600 then check voltage at the battery terminals.

Upgrade the charging system. It'll always be an issue if you dont.
 

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Discussion Starter #1,013
... with hundreds of thousands of dollars in production company money, and many months of pre-production preparation including pre-ordering all the necessary parts, tools, and supplies to complete the build, you should be put in jail for a minimum of 7 years....
I am pretty sure that is not how it works. Almost positive in fact. The vehicles filmed in most cases are not paid for by the production company - the costs are the responsibility of the shop doing the work so either they go out of pocket on the car/bike or they get a customer to foot the bill. If there are hundreds of thousands of dollars it goes to pay the crew and the equipment for filming, often the shops are providing the set production value, the projects, and the labor.

While I do agree they do get time to plan and pre-order parts, the schedule is often tight because they need to film a large number of episodes back to back. So often they have two or three projects going for episodes all at once. The episode is cut to look like it is on a tight, 1 week, time frame but likely they have been working on the vehicle for weeks even months along with the other vehicles. They way they justify it is well...if they put 40 hours in it over a month period, well 40 hours is a work week so if they just show you everything that goes into that build it is like they are showing you a week. If you watch the backgrounds sometimes you can sometimes see projects in progress or completed that happen on later episodes. The tight filming schedule is to keep costs down on the crew and editing. It would cost a lot if they filmed one episode, took a break, and then searched for another car/bike and filmed that episode because they would have to pay the crew to keep them on the project in the down time. Often a lot of that schedule pressure is on the shop to keep film-able work churning and projects coming in and out the door.

I do agree with you that reality TV is responsible for a lot of misconceptions in the hobby right now, but some of that is on the viewer too. TV is for entertainment purposes, unless you are watching actual technical school videos it is no instructional. It's up to the viewer to take some responsibility and do some research and be honest with themselves before they go out and spend $500 on a cx500 before they even own tools because they saw how easy it was on reality TV.
 

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Discussion Starter #1,014
I didnt give specs for this bike. I said a common spec is:

Yes some bikes dont charge at idle. I concede that the idle test will not apply. Rev it to 1600 then check voltage at the battery terminals.

Upgrade the charging system. It'll always be an issue if you dont.
2100 not 1600. Please do your homework. Honda break even charging is at 2000 rpm (10amps). If you are testing the charging system you should check it at idle, At 2000-2100, and then watch the meeter all the way to redline. If you are above 14 volts at redline there is a good chance you are boiling the battery in a SOHC cb750. The original round top voltage regulators are adjustable, the later ones are not. I believe this one still has the original round top separate VR but I could be mistaken.

The upgrades that exist for the SOHC cb750 are:
- Magneto, a used one but they can be rebuilt as jaguar has shown
- A smaller charging rotor because the stock one has some mass to it and if you are road racing it helps the crank spin up faster. Often you lose the e-start running one of these as it only charges enough to keep the bike running
- upgraded voltage regulators from oregon motorcycle. Doesn't get rid of the not charging below 2000 rpm but provides a more stable charging curve than the old junk.

and that's about it.
 

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The magnetos that I have rebuilt in those threads here do not charge anything.
 

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Discussion Starter #1,017
The magnetos that I have rebuilt in those threads here do not charge anything.
yes but they are an upgrade as they do provide enough energy to provide spark independent of the charging system, meaning there is less strain on the charging system. Unless you are referring to the distributor you rebuilt in which case it's not a magneto but still an upgrade.

- - - Updated - - -

Dude fuck off. Cyorg provided that spec while calling me stupid.
another reason why you should never trust anything on the internet.
 

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Discussion Starter #1,019
The break even spec for that bike if it's an F is 1600 and idle spec is 1000 plus or minus 100, so the headlight would get brighter if it's charging. Yes he should ultimately check it with the appropriate meter. If you are any good at diagnosing over the net, you should start with the correct specs.
That is the honda factory manual specs, but can I be a dick here for a minute? For the NON-US bikes this would be true because of the switch to allow the headlight to turn off....but....in 1975 the bikes received a control switch that kept the headlight on full time for the US market. From Clymer, Haynes, and personal experience, the extra draw of the headlight and tail light tend to bump the charging RPM up.

here is the factory manual (page 98):
http://www.classiccycles.org/media/..._1653604/24a1fc97eff08d37ffff84ddffffe41e.pdf

unfortunatly there is no link for me to post for the clymer. This is a good illustration as to why you shouldn't rely on one single source for this and exercise common sense and an understanding of how the charging system works.


At the end of the day, whether it starts charging at 1000 or 2000 doesn't matter, what matters is you see over 12 volts but under 15 volts for the majority of the rev range.
 

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That is the honda factory manual specs, but can I be a dick here for a minute? For the NON-US bikes this would be true because of the switch to allow the headlight to turn off....but....in 1975 the bikes received a control switch that kept the headlight on full time for the US market. From Clymer, Haynes, and personal experience, the extra draw of the headlight and tail light tend to bump the charging RPM up.

here is the factory manual (page 98):
http://www.classiccycles.org/media/..._1653604/24a1fc97eff08d37ffff84ddffffe41e.pdf

unfortunatly there is no link for me to post for the clymer. This is a good illustration as to why you shouldn't rely on one single source for this and exercise common sense and an understanding of how the charging system works.


At the end of the day, whether it starts charging at 1000 or 2000 doesn't matter, what matters is you see over 12 volts but under 15 volts for the majority of the rev range.
You aren't being a dick. The spec I quoted is from that American Honda Publication and it lists 1600 break even with high beam on for the F. Granted I haven't worked on a SOHC 4 in a while and don't see one in my future, so I can't bet my left nut that the spec is correct.
 
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