1978 750F electrical inquiry

[Krenisky]

Hey all!

Just picked up my first old school motorcycle and I'm really pumped to get started. When I bought the bike, the guy was able to start it instantly with the electric starter but we had to jump it off of a car battery. We let it run for about 15 minutes but as soon as we disconnected the jumper cables it shut off. I was guessing the battery is probably fried but before I just start replacing stuff I thought I'd ask everyone on here.

I wouldn't mind just having a kick start honestly but I'm not sure what the smallest battery I could get away with would be. I'm seeing 12V batteries with various amp hour ratings, I think the stock battery had 12 amp hours but I'm not sure if that is completely necessary.

On to my final big question: Has anyone replaced all of the old electrical components with modern ones? I'd really like to hide all of the electrical system that is under the side cover and it seems that it would be easier to just remake the whole system with updated components. Thoughts?

Thanks in advance!

 

[dirtdigger]

More then likely the battery is bad and wont hold a charge.

Yes you can replace the the voltage regulator and rectifier with a newer modern electronic unit. Has been done many times and work well.

Lot of people want to kick their bikes...dont know why but to each their own. Things to think about...the kickstarter on the 750 was not meant to be a primary source of starting, it was only designed as a back up system. The shafts can bend over time with a lot of heavy kicking, which gets much worse with bigger bore high compression motors. It might be cool to kick it once in a while but it will get old and the electric start is so nice and easy.

 

[Krenisky]

Thanks dirtdigger, I'll definitely keep the electrical start as the primary starting method then. I have a handful of 1999 Yamaha R6 voltage rectifiers/regulators, would it be possible to hook one of these up? I'm just unsure how they differ from bike to bike, it seems that with a couple resistors I could make any regulator work on any bike?

Also, does anyone have experience with putting say two small 6v batteries in series?

 

[dirtdigger]

I have no idea on other brands of regulators, there are already regulators on the market that are sold to be used for conversions. I use the regulator off of the dohc 750 bikes and works fine.

As far as batteries just go with a smaller battery out of late model bikes that are sealed. Nomally they are more compact and have more power then the old vented batteries that are sold as a replacement for the 750. I dont see how you would gain anything by using two 6v batteries, you can get very small sealed 12v batteries. Just gotta look at some different battery manufacturers and look at the dimensions. Or look for a sealed battery that you can mount in any position.

 

[amc49]

X2 on the 6 volt battery idea, no need.

You CANNOT swap regulators willy-nilly even though some will, there is more than one way of making power and permag vs. not being the big difference. Wrong regulator and you won't charge at all. One type feeds power to make power, the other type simply makes too much and bleeds off the extra through ground, they are NOT interchangeable. WAY more difference than just resistors, the entire electric schematic changes there.

I had no idea the DOHC would work on SOHC but it makes sense, both are external field exciters and both have an alt fairly close to the same output. The alts are almost the same but one spins the field and the other doesn't.