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Discussion Starter · #1 ·
Hey Ladies and Gents!

Long time forum stalker, first time poster…
First off, this community is great and has been extremely helpful in providing context and insight as I dive into a project I’m working on.
I recently acquired a 1978 XS750 with the objective of bringing it back to life and going full cafe racer. It’s been a project I’ve wanted to take on for a while and I’ve finally made the leap. I have a background in motorcycles as I’ve grown up around them my whole life, and I have a background in maintenance as a crew chief in the USAF. I know helicopters and motorcycles don’t directly translate but it’s better than nothing.

I am aiming to diagnose a few things before I invest too much time and money, ie that electricals are good, and then engine, carbs, etc are in good order. Currently there is no sign of life from the bike from an electrics perspective and I’m wondering if I’m missing something. I’ve installed a new battery, checked fuses, and ground wire and from what I can see, everything looks good. However there is one wire that I’m not sure what purpose it serves or where it should be connected. I’ve included photos in this post. It’s a wire that goes to one of the ignition coils and then has a disconnected end by the battery.
Any thoughts as to what this might be? And any general words of wisdom as to what might be preventing the bike from sparking?

thanks again in advance for the help and I’m looking forward to being a part of this forum.
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Step one clean thoroughly.
How do you work on anything that cruddy?
Never a good sign to have a bike that dirty with no airbox or filters. I always wonder what other than water moved inside.
Was that thing in a flood or mud puddle its looks worse than the bikes I saves from the chickens in a chicken coop.
Did you just look to see the ground straps were on the bike or did you clean them?
Fuse box? Mud box?
Funny shit really.
Start with cleaning all listed above.
 

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Discussion Starter · #4 ·
Step one clean thoroughly.
How do you work on anything that cruddy?
Never a good sign to have a bike that dirty with no airbox or filters. I always wonder what other than water moved inside.
Was that thing in a flood or mud puddle its looks worse than the bikes I saves from the chickens in a chicken coop.
Did you just look to see the ground straps were on the bike or did you clean them?
Fuse box? Mud box?
Funny shit really.
Start with cleaning all listed above.
Hahahah ahhh thanks for the warm welcome! Yeah the bike has been sitting in a yard for a while and has seen some things it looks like….definitly need to do a thorough clean/rebuild of the carbs and engine. I only looked to see the ground straps and fuse box (all present and accounted for). Ill give them a thorough clean and see where we go from there.
Still strange about the cable though right?

thanks again for the speedy response, thoughts, and warm forum welcome ;)
 

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FYI: Make a big cup of coffee and pull out the multi-meter. Trace the ground from the battery to the frame/engine. Go through and disconnect and reconnect all the connectors you can find including the fuses. You would be surprised how often this fixes incurable electrical problems. Check ignition and switches for proper continuity and disconnect. Crimp connectors like the one shown often corrode and fail unless soldered.
 

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Multi-meter is great if you know how to operate them (y) from here it looks like the wiring is one of the smaller service problems. Agree with classic250 the purple shielded wire does not look original, much love and many parts this one needs to be nice again.
 

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Multi-meter is great if you know how to operate them (y) from here it looks like the wiring is one of the smaller service problems. Agree with classic250 the purple shielded wire does not look original, much love and many parts this one needs to be nice again.
Some just cost more to repair than they are worth in the end. A lot of them to be true.
 

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Discussion Starter · #10 ·
Alright boys! I’ve taken the advice given, gave the bike a shower, said bye bye cobwebs, and brought out the ol multimeter. Sure enough, we have progress!! I’ve been tracking the battery current wire by wire, and have managed to get the headlight, tail light, and horn on line and lighting up. Progress!! It’s going to be a journey getting this thing all the way to rideable but I’m committed and determined at this point. I’ll keep you all posted and I’ve started an Instagram for the build “diybikebuild” if anyone is interested.
Looks like next steps are ensuring power is going to the spark plugs, and then I’ll need to take apart, clean and rebuild the carbs and engine. Turns out….the bike was stored (and by “stored” I mean parked in a backyard for 20 years) with the spark plugs out. So gunk and god knows what has made its way into the engine…

the journey continues….
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Hello

I'd suggest a generous shot of WD40 down those sparkplug holes for now.
Go on with the sorting and sifting and fantasizing about the day it's done . Then,
A few days before cracking open the motor, split a 1 liter bottle of coke between the cylinders. Your rings should be rusted to the cylinder wall.
Coke eats everything.
If that doesn't do it, hydrologic pressure will.
Use a small pokey thing to identify the piston closest to tdc. Make a fitting to screw into the sparkplug hole with a grease fitting on top.

40 years and a hundred motorcycles ago I heard about an Kawasaki H3 in a guys back yard, in about the same shape as your new life partner there.
I convinced the cat that I would would take on his pain and suffering for free & dragged it home.
A crabby old guy named Sonny Angel, of all things, in San Diego passed this on to me.
Enjoy the adventure, it takes a certain kind to start bringing something to life that's been dead a decade.
The odyssey begins !
Cheers
 

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Discussion Starter · #13 ·
Thanks for the info guys and Cricket that advice on getting into the cylinders was gold thank you! I’m heading to the store to get myself some coke, A bottle for the bike and a bottle for me, and a pokey thing.
In the meantime while the WD40 is loosing up the deposit build ups, I’ve taken apart the carbs, going to rebuild those, they look alright and I was going to drain all fluids but ran into a little problem. Somehow it seems that the engine is misaligned witb the bike frame. Unless I’m completely losing my mind and have had too many beers before going at the bolts. But both drain plugs under the engine are hitting the frame before they can be completely pulled out. Crazy right?? I’m thinking that can’t be a good sign…some sort of misalignment here. I guess instead of pulling the engine (or smashing in the frame with a hammer) I can drain the oil by removing the side covers (probably not the correct technical term) on the engine?

anyways, appreciate the insight so thank you and when this is running, everyone that’s helped me out here is getting a beer, a coke or a pokey thing. Your choice.
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Discussion Starter · #15 ·
I don't know much about your bike, but I'm pretty sure you are mistaking crankcase bolts for your sump plug. I'm guessing the bolt highlighted in the pic is your sump plug. Most bikes (not all) only have one sump plug.

View attachment 107155
Ha! You’re 100% right. I just realized that and was coming back in to update my post before I got wrecked For being an idiot. Your right, mistook those bolts for the drain plugs. Phew!! Thanks for catching that.
 

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Seems like you are just winging it, download and save the shop service manual for free from the carl salter site, you can't possibly service what you need to without it. Read and understand the whole manual first, if there is anything you don't understand in it, ask :geek:

Save up your old tooth brushes for cleaning things, they work great.
 

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Do you have the original intake parts?
Whatever you do don't just stick some tiny pod filters directly on those CV carbs, the bike came fitted with intake stacks and it needs them.
 

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If that sat for 20 years without spark plugs and was outside, you will need a re-bore and oversize pistons. May be easier and cheaper to get hold of XS850 block and pistons in good condition instead of boring what you have as it will probably be $500+ for pistons and bore vs <$200 for block/pistons
 
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