Topic: Basket Case after Rebuild

[CarmOgden]

Guys I need some help here;
- 1971 cb750
- Bored over to 850
- Rebuild top end with exception of valves being lapped

The bike ran great after rebuild and showed charging at rpms as it should. Then she started smoking but I'll leave that for another post. Then on a short ride the other day I lose all power and my dash goes haywire. Had to push her home, that sucked! 

So here is my need; I tested all the components off the bike and this is what I have. I am having a hard time knowing what is bad, I assume I had some sort of short but can't find what failed.

Stator:
-  .6 ohms over all three yellow
-  Book says .2 but watching a few videos some people consider this good

Field Coil:
- 7.7 ohm
- Book says 7.2 so I assume this is ok

Reg/Rec:
- Diode test over 3 yellow lines from BCL ( BATTERY CHARGE LINE)
- s1 453
- s2 441
- s3 443
- Diode test over 3 yellow lines from ground
- s1 448
- s2 453
-s3 453

So what I need first is some help from the pro's, what is bad? Any idea what could have happened?

Carmon

[calj737]

http://www.electrosport.com/technical-resources/library/diagnosis/pdf/diode-testing-guide.pdf
http://www.electrosport.com/technical-resources/diagnosis-center/fault-finding-guide

Start with a full charged battery that's been rested overnight. Verify the actual full resting voltage. Then walk thru the links above. No guess work involved.

[CarmOgden]

Thanks Calj

That is how I did the testing above.

So far from my test I can conclude that there is nothing wrong with the reg/rect but the other two have me confused because of the fact they are not to the spec in the book but others say those numbers are good.

Cm

[calj737]

Your rectifier diode tests leaves me confused. You should only see current in 1 direction. I also do not see any voltage measurements from your "tests".

[Bodi]

The diode test (on multimeters with it) reads millivolts across the device and those readings look OK with a forward drop of around 1/2 volt. It's not likely a diode with a normal forward drop will be bad reversed, but hopefully you did check that. Bad diodes generally read wither open - no conduction both ways - or short with no resistance either way. Different meters read differently for open but probably it would say "ERR" - whatever you see with the leads apart, short is what you see with leads touched together.
The coil readings seem OK too, make sure you measure each coil lead to ground and get no connection.
What does going haywire look like?
Check for any frayed or damaged wires contacting the frame. This is not uncommon where pod cables go into the bars or inside switchpods where repairs leave wires poking against the bars or the entry hole.
Confirm that the battery ground cable has a really good connection to the frame and engine case - this is often compromised by frame painting or powder coating - the terminal should contact clean bare metal, and the engine case should be sanded clean where it also touches bare frame metal. Also that the battery connections themselves are clean and tight. Find where the main harness power connects, may be at the battery or at the solenoid, make sure it's secure.
Generally a good going over on the harness - checking, cleaning, retightening all the connectors and dealing with any obviously overheated ones - solves a lot of electrical problems.

[CarmOgden]

Your rectifier diode tests leaves me confused. You should only see current in 1 direction. I also do not see any voltage measurements from your "tests".

Sorry Cal

I did do the test both ways, the diode test you are seeing are from ground and battery lead from reg/rec. Then I reversed on both and got the OL or no reading so it was fine. I didn't add it as it was all clear.

I did do voltage testing before I tore apart the bike. It was losing voltage during the ride, start at 13.1 fully charged and then slowly drain to 10.9 and my battery sensor would flash. Isolating the circuit yielded no better results so I started testing charging system components. The issue is I couldn't isolate the stator for some reason, I assumed I had a bad connection but after pulling it off the bike I got the results you see.

[CarmOgden]

The diode test (on multimeters with it) reads millivolts across the device and those readings look OK with a forward drop of around 1/2 volt. It's not likely a diode with a normal forward drop will be bad reversed, but hopefully you did check that. Bad diodes generally read wither open - no conduction both ways - or short with no resistance either way. Different meters read differently for open but probably it would say "ERR" - whatever you see with the leads apart, short is what you see with leads touched together.
The coil readings seem OK too, make sure you measure each coil lead to ground and get no connection.
What does going haywire look like?
Check for any frayed or damaged wires contacting the frame. This is not uncommon where pod cables go into the bars or inside switchpods where repairs leave wires poking against the bars or the entry hole.
Confirm that the battery ground cable has a really good connection to the frame and engine case - this is often compromised by frame painting or powder coating - the terminal should contact clean bare metal, and the engine case should be sanded clean where it also touches bare frame metal. Also that the battery connections themselves are clean and tight. Find where the main harness power connects, may be at the battery or at the solenoid, make sure it's secure.
Generally a good going over on the harness - checking, cleaning, retightening all the connectors and dealing with any obviously overheated ones - solves a lot of electrical problems.

Bodi

The harness was replaced with a custom one I made, fused on all circuits and all new with the exception of stock ends off components. I reused those, that maybe my issue as I was getting odd readings from stator before I took off the bike.

To answer you question on haywire, I was driving along fine and then bam it dies. I came to a slow stop on the side of the road and accessed the issue. I didn't have any power. Battery was showing 4 volts. Looked it over and realized I was dead in the water so I started pushing her home. When I got back and charged battery my aftermarket dash was a Christmas tree of lights and my headlight was toast. All fuses were ok though, which was weird. So I unhooked dash and replaced headlight bulb and all came back ok but it will not charge.

I am assuming I got some sort of spike in voltage but not amps? That is the only way I can determine causing the issue without blowing the fuses.

So stator is ok? I just don't understand how they are all good independently but when in the bike I was getting nada.

CM

[Bodi]

Connect the field coil so it's getting full power - between "black" switched 12V and ground (I don't know if you kept the Honda color code). Then switch on and confirm you have field current - easiest is to hold a steel tool at the alternator cover, the field from a working coil will pull at it. Then start. This puts the alternator at 100% power, so you should get a charge current. You can measure charge/discharge with an amp meter between the battery and bike if you have a single harness connection to the battery. If you have a separate connection from rectifier to battery, that will be alternator output current only - reasonably useful - but not overall charge/discharge to/from the battery.
Do not try electric start if you have a meter between battery + and the entire bike including starter motor...

[CarmOgden]

Connect the field coil so it's getting full power - between "black" switched 12V and ground (I don't know if you kept the Honda color code). Then switch on and confirm you have field current - easiest is to hold a steel tool at the alternator cover, the field from a working coil will pull at it. Then start. This puts the alternator at 100% power, so you should get a charge current. You can measure charge/discharge with an amp meter between the battery and bike if you have a single harness connection to the battery. If you have a separate connection from rectifier to battery, that will be alternator output current only - reasonably useful - but not overall charge/discharge to/from the battery.
Do not try electric start if you have a meter between battery + and the entire bike including starter motor...

Ok, so I did keep the color code on the charging system. On the field coil I have the green and white. Assuming white is the hot, so in place of your black switched but I get the overall idea there.

Thanks again and if I missed your point let me know, I will run this down in the am as I have the day off.

[CarmOgden]

Ok Bodi

Ran down what you said and got 15 ac volts at idle and around 40 at 4000 rpm on all three lines. I went ahead and cut out stock connections and ran new wires all the way up to new harness, to eliminate any concerns there. So when I energize the coil I get what I need to.

So I worked my way up to the rec/reg and hooked everything back up. According to the schematic the white wire to the coil should energize the coil but I am getting nada. I ran down all other connections and all is well just nothing from the white power wire to field coil. So I retested the reg/rec and it shows good but something is off.

Any thoughts on that one? Other than replacement, would the coil not energize right away? Does the rec/reg only energize coil when voltage is at a certain level? I'm thinking that is the case based on the schematic I found.

Next step to test that is pull down battery voltage? Thanks again for the help!

CM

[CarmOgden]

Ok Bodi

Ran down what you said and got 15 ac volts at idle and around 40 at 4000 rpm on all three lines. I went ahead and cut out stock connections and ran new wires all the way up to new harness, to eliminate any concerns there. So when I energize the coil I get what I need to.

So I worked my way up to the rec/reg and hooked everything back up. According to the schematic the white wire to the coil should energize the coil but I am getting nada. I ran down all other connections and all is well just nothing from the white power wire to field coil. So I retested the reg/rec and it shows good but something is off.

Any thoughts on that one? Other than replacement, would the coil not energize right away? Does the rec/reg only energize coil when voltage is at a certain level? I'm thinking that is the case based on the schematic I found.

Next step to test that is pull down battery voltage? Thanks again for the help!

CM

Went ahead and bench tested the reg portion of the reg/rec and so far I’m down to 9 volts with no clear +pos from the field coil side. Now I’m trying to determine what controls the reg in the rec. if that worked I’d be good to go.

I’m thinking I just need a new one unless you guys know something I don’t




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[MRieck]

What does going haywire look like?

A bipolar women long off her meds with 4 Gimlets in her. That's my personal experience. Sorry....I couldn't resist.

[CarmOgden]

What does going haywire look like?

A bipolar women long off her meds with 4 Gimlets in her. That's my personal experience. Sorry....I couldn't resist.

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[dave500]

where did you get the rec/reg?

[CarmOgden]

where did you get the rec/reg?

Got it on amazon from 4in1

I’m hoping it’s better quality than the Chinese junk I got last time


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[CarmOgden]

Ok well I have a clutch now but running into other issues.

Charging is good too

So here is my dilemma. I tore off the carbs because it was running pretty piss poor before the clutch setup. Found a good deal of junk in there. Assuming it’s ethanol gas as I just tore this down last year. Found a non ethanol place just recently. Also found one float that was way off.

Then I put them back in, bench synced first off bike and hooked up my vacuum gauges. Set them all to about 10 and thought it looked great, throttle was snappy and smoking stopped almost completely. So I button it all back up and push her out of the garage. As soon as I sit on it and start it the throttle races up to 3k rpm for no reason. Pull on the throttle and let it snap back and no change.

So I pulled it all back apart and check for binding etc, nothing. Try again and it does the exact same thing. Wth!

Anyone seen this before? Did a screw up the sync or what?




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[70CB750]

Did you replace needles? 

I did get a kit to rebuild carbs and needles from the kit were too thick to let slides all the way down.  So I reused old needles and all was well.

[dave500]

the aftermarket kits are only good for paper gaskets,the brass parts are all hit and miss,clean up and reuse any and all factory brass where you can,the bowl gasket rubbers are never shaped,i think their mostly poor value for money!some have luck with them or maybe they don't know any better?might be why all the carb problem threads appear?,add pods and other mods and its all out the window?the stock needle taper is very important and would be very hard to copy,for example ive had a keyster #100 main jet that a brand new 1mm drill shank wouldn't fit through but it was like a precision bush in a genuine Honda jet,it would be lean by two numbers,cheap jets can go either way rich or lean and add plug chops performed by learners and its all #$%*,if a simple jet hole can be so wrong a complex compound needle taper just has to be.

[CarmOgden]

Did you replace needles? 

I did get a kit to rebuild carbs and needles from the kit were too thick to let slides all the way down.  So I reused old needles and all was well.

Nope all stock needles. I just cleaned them up and set floats


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[CarmOgden]

Did you replace needles? 

I did get a kit to rebuild carbs and needles from the kit were too thick to let slides all the way down.  So I reused old needles and all was well.

Nope all stock needles. I just cleaned them up and set floats


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I’m going to try and bench sync them again and see if maybe I overdid it with vacuum syncing

Should I be using one carb as the constant or can I adjust all 4 to the best vacuum. Any idea what vacuum should be?



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[dave500]

forget the vacuum reading just get them all the same,a bench sync gets you in the ball park enough to run the engine then the vacuum sync finishes it off,ya cant over do a vac sync man!bench sync is akin to setting points gap by eye,itll run but needs that fine tuning.

[CarmOgden]

forget the vacuum reading just get them all the same,a bench sync gets you in the ball park enough to run the engine then the vacuum sync finishes it off,ya cant over do a vac sync man!bench sync is akin to setting points gap by eye,itll run but needs that fine tuning.

Ok so once I have my gauges on how much adjusting should I be doing? Just getting them all close or shooting for a number?

I think that’s where I may have screwed up. I was trying to get them to a high vacuum.


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[Gordo]

forget the vacuum reading just get them all the same,a bench sync gets you in the ball park enough to run the engine then the vacuum sync finishes it off,ya cant over do a vac sync man!bench sync is akin to setting points gap by eye,itll run but needs that fine tuning.

Ok so once I have my gauges on how much adjusting should I be doing? Just getting them all close or shooting for a number?

I think that’s where I may have screwed up. I was trying to get them to a high vacuum.


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Bench synch the carbs, Chuck them on the bike and get the bike warm. Select one carb as master and leave that one alone, adjust the other three carbs to the master.

[CarmOgden]

10-4 I’m sure that’s where I messed up


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[CarmOgden]

ok guys

Finally figured out what was up. Resynced and put the tank back on and it did it again. So I stared taking things off and checking all I could. Turns out my tank had pinched my pull throttle cable. So after putting that back on the frame rail, no idea where my zip ties went.

So took her for a drive right at twilight and wrapped her up through my hilly neighborhood. At first it was stuttering, when I gunned it I would get a stall and then a delay and boom power. After about 20 minutes it started to clear up but not perfect. Hit 9 and watched as a few of my neighbors called the cops. Thought I would call it a day. I know they are n't happy with me but I got into the garage right at the wire. haha.

Taking her on a long drive tomorrow.

So far the good is; got a great clutch, got charging, and got a running bike. Not perfect yet but far far better! Plus I pissed off a few neighbors. Not too bad for a full workday and then two hours in the garage.