Cafe Racer Forum banner

Frankenstein Build

3585 Views 59 Replies 10 Participants Last post by  TrialsRider
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.
Automotive tire Motor vehicle Wood Gas Automotive exterior

Automotive tire Motor vehicle Bumper Tread Wood

Tire Wheel Automotive lighting Motor vehicle Motorcycle

Electrical wiring Cable Electric blue Wire Electrical supply
See less See more
1 - 12 of 60 Posts
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 ;)
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….
Automotive tire Wood Gesture Grey Tread

Wheel Tire Sky Fuel tank Vehicle

Tire Wheel Land vehicle Automotive parking light Car

Wheel Tire Sky Fuel tank Vehicle
See less See more
  • Like
Reactions: 1
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.
Bottle Metalworking hand tool Wood Electrical wiring Circuit component

Automotive tire Hood Motor vehicle Automotive exterior Bumper

Tire Hood Automotive tire Light Motor vehicle

Black Personal protective equipment Font Bag Auto part

Motor vehicle Automotive tire Automotive wheel system Engineering Gas
See less See more
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.
Alright the journey continues ladies and gents and “operation ressurection” has hit a bit of a corroded snag. Might need to emphasize the “ressurection” part of the title.

as the bike was stored in a backyard with no spark plugs in it I figured that there may be some debris in the cylinders that should be inspected before I start her up. Well… turns out there was a bit of “debris” and it looks pretty intense. Lots of build up in the 2nd cylinder and will need a significant amount of cleaning it the bike is to live again. Pictures provided and all suggestions are welcome. Of which I’m sure atleast 1/3 will be “get a new bike”. Thanks for going on the journey with me

Automotive tire Motor vehicle Gas Machine Automotive wheel system

Automotive tire Motor vehicle Bumper Automotive engine gasket Automotive exterior

Motor vehicle Automotive tire Hood Automotive design Automotive exterior

Tire Wheel Automotive tire Automotive lighting Motor vehicle
See less See more
  • Like
Reactions: 1
I have a confession to make…..and I may end up regretting this….if so I’ll admit it on this thread….I’m determined to bring this bike back to life. I know I know, it’s in rough condition (ie a rusted out heart) but I think there’s hope and also my wife said there’s no way I could get it running so…:there’s that challenge too. But I’m pressing on! I was able to source a rust/corrosion free engine block, I removed the old block (it was beyond any sort of salvaging) and it’s only appropriate that I update the title of this thread to Frankenstein Build. This bike will eventually be a compilation of donor parts from other bikes (hence the name “Frankenstein”), oh and it’s green which I’ll incorporate into the final paint job as well but here we go….again I might regret it but hey it’s about the journey along the way too as I try and bring this back to life bit by bit. Let the Frankenstein Build commence!
Tire Wheel Fuel tank Vehicle Automotive tire

Wheel Tire Vehicle Automotive tire Automotive lighting
See less See more
  • Like
  • Wow
Reactions: 2
Is this an engine that should run when it has fuel and spark? It will be a learning process.

I got started on street bikes by purchasing GSXR 750 wrecks rebuilding and than street racing them. The first one I got still had the crusted blood all over the frame. My friends thought I was nutz. No one else that knew the bikes story would touch the thing. .
Wow that’s gnarly and thankfully I can skip the blood scrub step. Word on the “here’s an engine, good luck street” is that the engine should run with some fuel and spark. So let’s all keep our forum typing fingers crossed.
  • Helpful
Reactions: 1
Thanks for the guidance and the optimism! I know it’s going to be a journey but I’m looking forward to going through it all. Thanks for the insight YT Zombie. I’m planning to do all of that.
Quick question for the gurus on here….these lines are on my “new engine” but my original engine didn’t have these. Are these the vacuum lines and do they hook up to the petcocks? Do I even need them? It seems like most people just have these lines capped essentially….
Motor vehicle Automotive tire Automotive exterior Gas Automotive wheel system

Reflex camera Camera lens Digital camera Camera Mirrorless interchangeable-lens camera
See less See more
Started installing the “new” engine onto the bike and found that the piston rings on the piston that was rusted have completely seized and essentially become one with the piston. Made my way onto eBay (thank god for people parting out bikes) and found a “new” one with rings. It’s a few weeks out and then the journey continues. Why didn’t anyone tell me this would be a time and money pit?! ;)
Hey everyone! Alright soooo the bike isn’t running quite yet but I’ve rebuilt the engine with new engine blocks, put it all back together, checked compression and it’s looking good. One of the engine mount posts snapped off in the process….so had to take apart everything and reinstall it all over again with a new post. Now I’m starting to see why maybe buying a bike that’s been dormant for 20 years is a bit of a large project….anyway. Now it’s onto electrical and I can’t seem to get any spark to the plugs. I have a wiring diagram, a multimeter, lots of beer and im trying to figure out the issue. I’ve bypassed the kill switch and ensured the new battery is charged. Lights turn on when the ignition key is turned, and the horn works so there are some signs of life! But when I go to kickstart the bike, there’s no spark. I have the plugs out of the engine and grounded when im testing this.
Any thoughts on where to begin or what the issue might be? It seems like power is going through all four fuses but I’ve definitly reached a point where im stuck.
Any thoughts or suggestions on what to check or where to begin to get spark to the plugs?

thanks everyone!!
See less See more
Hello ladies and gents!! Yup still here and still crankin away at the Frankenstein build. Making some progress though! Installed a starter button because the last one was bogus, rewired the wiring to the starter motor, got the starter motor working and now got 2 of 3 spark plugs sparking. I’m getting closer and closer to yelling “it’s alive!!” (Frankenstein pun intended).
I’m running into a problem though and that’s with the third spark plug. There’s no spark at the plug and no visible spark at the points ignition. I replaced the condenser and tested both the condenser that I took off and the new one I put on and both checked out but still no spark. I swapped out ignition coils and those are all working fine as well. Swapped out plugs and those are all in working order as well. So I’m 99% sure I’ve narrowed it down to the actual contact point. There were a couple times we’re an initial spark did occur on the plug but then no sparks following that. I cleaned the ignition contact points and took a little sand paper to them. It seems like something is shorting out? I’m not sure what the problem is….does any one have any thoughts on this? Should I just buy a new contact point?

I’ve included a video and photo too incase that helps!
Thanks everyone!! Turns out taking on a non-running Craigslist bike was more work than I thought…why didn’t you guys tell me?? ;)

Automotive tire Automotive lighting Motor vehicle Vehicle brake Bicycle part

Oh maybe I can’t post a video?? It’s the point that the gray wire goes to
See less See more
1 - 12 of 60 Posts