78 GS1000 low voltage at coils while cranking

[gs11ezrydr]

I,m working on a 1978 GS1000 I removed the separate regulator and separate rectifier, bypassed the stator wire that runs to the left hand switch and installed a newer aftermarket combined unit since it was over charging at approx. 16 vdc and even a little higher and could smell it cooking the battery. The customer kept it full and it test ok with my Yuasa battery tester. It is charging at 13.8-14vdc now with headlight etc. on. The problem I am having is that I have battery voltage 12.6-12.8 at the orange/white ignition coil leads but when cranking it drops to 8.5 to 9.5 vdc. I did a voltage drop test between the O/W wire at the fuse box plug to the coils and loose 1.2-1.6 volts just in the wiring harness which I know is too high therefore makes the bike hard to start. I have cleaned every connection in the ignition system that feeds the coils which I found quite a bit of corrosion in places but still did not increase my voltage when cranking. I have not tried the coil relay mod at this time, I was going to run a fused hot wire directly to the coils from the battery for test purposes at this time and see if that helps any. I have a Dyna S that I was going to install to get rid of the points but I wanted to correct my overcharging and my low coil voltage first as to not damage the Dyna S unit by either high or low voltages. I have not done a starter draw test yet either. I was also just wondering if anyone had any ideas on amperage and voltage that a normal starter draws. And am I heading in the right direction with feeding battery voltage to the coils to eliminate the old wiring system, switches and connections,. Any input or help is appreciated in advance.

[hillsy]

Starter motors draw a fair amount of current. Especially on a system / battery as small as a motorcycle.

I can't quote you figures but to give you an idea I currently have a digital voltmeter on my VL1500 and I can see the reading drop to around 8-9v when the motor is cranking over (just before it fires). And that's with a 16 series / sized AGM battery.

In other words, I think what you are seeing is normal.

[hillsy]

BTW - doing the relay mod to get power to the coils isn't a bad idea. It won't make anything worse.

[tom203]

"...I was going to run a fused hot wire directly to the coils from the battery for test purposes at this time "

sure try this, it will give you an idea of what the coil relay mod will do.
But I think this battery is weak from the prior overcharging stuff. Try a booster battery from a non running vehicle to see if that helps.
Lots of stuff contributes to hard starting, misadjusted valves ,dirty carbs , so if you haven't check other stuff be suspicious and don't blame it all on electricals yet.

[OldVet66]

Did you include switches, fuse box and grounds in your cleanup and check the charging health per "posplayr's" signature links. The coil relay mod will most definitely help, but your voltage drops are excessive and I suspect a weak charging system.

[posplayr]

Did you include switches, fuse box and grounds in your cleanup and check the charging health per "posplayr's" signature links. The coil relay mod will most definitely help, but your voltage drops are excessive and I suspect a weak charging system.

Yes this is low and symptomatic of worse things to come unless corrected.

It is charging at 13.8-14vdc now with headlight etc. on.

[gs11ezrydr]

Yes this is low and symptomatic of worse things to come unless corrected.

Did you include switches, fuse box and grounds in your cleanup and check the charging health per "posplayr's" signature links. The coil relay mod will most definitely help, but your voltage drops are excessive and I suspect a weak charging system.

Yes I did clean the ignition switch in he R.H. switch all the connections inside the head light, I did by-pass 2 wires that went into and out of the ignition switch that were melted and corroded The Red going in and the Orange going to the fuse box. I was surprised that the fuse box connections were so clean so I just sandpapered them and replaced the glass fuses, All the grounds were part of the first round of cleaning, even at the engine I removed the large wire and cleaned the block and cable ends, Ran a new ground from the rubber mounted mounting plate on the L hand side to the battery,Grounded the new Reg/Rect directly to the battery. And yes it charges at 13.8- 14 vdc at idle but seems to drop to 13.6 or so when revved up.(weird ) Still believe I have high resistance in the harness causing my voltage drop or is that normal consumption within the machine? The bike is now starting instantly when cold and choked, Oil smokes some at first then cleans out. Told the customer we need to do a valve adj. as soon as he can afford it. Rings and valve seals also if he wants to spend the cash on such a bike of that age that needs some other repairs also.. It has pods and a header I installed 130 mains out of the air as a guess and the bike puffs a little black at first but runs strong. I set the air screws at 1 3/4 and the fuel screws at 2 3/4 Seems to run best there. I also timed the Dyna S at full advance as per instructions Is that right because you are to set the points at the F position without turning the advance as far as I remember. I Might be wrong so long since I worked on points. Figured the Dyna S would time the same but did not so I timed it at full advance. Thanks for the input guys.

[posplayr]

Ran a new ground from the rubber mounted mounting plate on the L hand side to the battery,Grounded the new Reg/Rect directly to the battery. And yes it charges at 13.8- 14 vdc at idle but seems to drop to 13.6 or so when revved up.(weird )


This is not weird, it is conclusive evidence you have dirty connections. This is a known feature of the charging system. Dirty connections and your voltage drops with RPM. Did you clean out the fuse box? You need to focus on every contact and connection between the R/R and the battery to correct the problem.

"to clean" means to d a chemical clean not "sand paper"........ Sand paper does very little for corrosion in the crimps.

Do you have DeOxit?

[OldVet66]

You can discount any appreciable resistance in the wire loom unless it is damaged. Electrical contact points is where you get your high contact resistances as you have seen in the wires that were melted going to the ignition switch. I'll bet that if you feel the main plugs connecting the various parts of the wiring harness together when the bike is running you will find that some are warm or hot. That's your high contact resistance. Add them all up and you have your problem. All the wire strands that you can't see down in the crimp need cleaning or replacing if necessary. Your start up smoking sounds like valve seals. You can tell by downshifting from speed, it will certainly show itself under those conditions and then clear up.

[Sandy]

Yes I did clean the ignition switch in he R.H. switch all the connections insid.........

Did you actually disassemble and clean the contacts in the bottom of the main ignition switch, the one the key goes in? There are 2 sets of contacts in there that all the power goes through. If they're dirty as they usually are you'll be chasing electrical gremlins forever until you clean them.

[posplayr]

Did you actually disassemble and clean the contacts in the bottom of the main ignition switch, the one the key goes in? There are 2 sets of contacts in there that all the power goes through. If they're dirty as they usually are you'll be chasing electrical gremlins forever until you clean them.

I should clarify that we now have at least two different issues here. The original problem is the low coil voltage ; the primary culprit is the ignition switch (as Sandy mentions), fuse box , right hand kill switch and a litany of connectors that go in between.


The new problem identified is a decreasing voltage during revving. That is dirty contacts between R/R and Battery. Primary culprits are power and ground paths between R/R and Battery. These are the Fuse box and how your grounds run. The GS Charging health outlines a Single point Grounding scheme that tends to minimize ground sensitivities.

As Old Vet mentioned it is usually not and issue with the wire itself, but rather dirty connections and corrosion inside the crimps. This can only be cleaned chemically. An products like DeOxit beyond cleaning also leave a protective layer to prevent re-oxidations which is what you will get real clean if you chemically clean brass and leave it exposed bare to the elements.

[JTGS850GL]

I might add that none of this information is completely relevant until we know what the voltage is at the battery terminals when cranking. If the voltage at the battery drops to below 11V when cranking then the battery is very suspect. If the voltage at the battery remains around 12V and the voltage at the coils goes to 8-9V then have issues as stated above.

[posplayr]

I might add that none of this information is completely relevant until we know what the voltage is at the battery terminals when cranking. If the voltage at the battery drops to below 11V when cranking then the battery is very suspect. If the voltage at the battery remains around 12V and the voltage at the coils goes to 8-9V then have issues as stated above.

In the first post the OP seems to be directly measuring battery voltage as well as voltage drop between battery and O/W. He is concerned about the Voltage drop to O/W and has now discovered a dropping voltage when revving.

It is charging at 13.8-14vdc now with headlight etc. on. The problem I am having is that I have battery voltage 12.6-12.8 at the orange/white ignition coil leads but when cranking it drops to 8.5 to 9.5 vdc. I did a voltage drop test between the O/W wire at the fuse box plug to the coils and loose 1.2-1.6 volts just in the wiring harness which I know is too high therefore makes the bike hard to start.

The only thing unstated are the results of a battery test, but he apparently did that.

The customer kept it full and it test ok with my Yuasa battery tester.

While we do not know everything (e.g. exact state of the battery) what we do know is:

1.) Too high of a voltage drop to O/W
2.) Too high of resistance between R/R and Battery.

[JTGS850GL]

Wasn't sure if the aforementioned voltages were all conducted while cranking. Just wanted clarification that the previously stated battery voltage was indeed while cranking and not static.

[gs11ezrydr]

Yes this is low and symptomatic of worse things to come unless corrected.

Ran a new ground from the rubber mounted mounting plate on the L hand side to the battery,Grounded the new Reg/Rect directly to the battery. And yes it charges at 13.8- 14 vdc at idle but seems to drop to 13.6 or so when revved up.(weird )


This is not weird, it is conclusive evidence you have dirty connections. This is a known feature of the charging system. Dirty connections and your voltage drops with RPM. Did you clean out the fuse box? You need to focus on every contact and connection between the R/R and the battery to correct the problem.

"to clean" means to d a chemical clean not "sand paper"........ Sand paper does very little for corrosion in the crimps.

Do you have DeOxit?

No I do not have DeOxit and have not heard of it until now. Where can this miracle solution be purchased? Battery voltage drops to about 12 or so seems to just loose voltage going to the coils. The only spray cleaner I have been using is Maxima contact cleaner after my fine grit sanding of the connections. I also have a set of what looks like tweezers but have diamond grit filing ends on them for cleaning flat terminals and are in 3 sizes. And I understand that I am not fully cleaning my connections especially when it comes to where they are crimped to the wires. I am confident that my red wire from the R/R has high resistance inside the harness along with every other bullet connector since I have only cleaned the contacting surface arrears. The customer picked up the bike today and was tickled. It starts right up after pulling the chokes and hitting the starter button. Not over charging anymore and I explained to him on a bike this old a 1978 we have high resistance within the whole system and nothing short of rewiring or replacing the harness with a known good one will truly correct our problems. He was just glad it is running the best it has since he purchased the bike. But we know ourselves impending doom is obviously in the future. But at our shop rate of $75 an hour we do what we can do (the best we can within an allotted time frame) since most owners are on a budget. Perfection can be obtained with the proper amount of money that is. Thanks for the input I am still learning even after 35 years even if it is (slowly).Again where does one obtain this DeOxit for future repairs and cleaning? I'm dying to try some. I live in the sticks and no one seems to have heard of it here. I have used Oxiguard paste in my breaker box connections here at home.