Budget City Bike Build

I was lucky enough to recently pick up a very cheap 78 Yamaha XS750 special. The previous owner had just spent $300 putting new tires on it, and I picked it up for $350, somehow managing to tow it home on a uhaul trailer behind a 1990s corolla for about $50 including gas, tolls and the trailer rental, for a total of $400 into this bike. For comparison, local craigslist has two clean, running XS750 standards priced at $3,500 each: one a cafe racer mod and one bone stock.

According to the seller, the electrics were "all broken", he couldn't get the motor to turn, and the wiring harness was "totally melted". All of this turned out to be wrong.

It was cheap because the #3 carb spit flames and lit the airbox and fuel lines (and a couple of wires) on fire, which spooked the previous owner. I'm pretty sure he didn't even try to put it out, and just let it burn until it burn until the tank ran out of gas.

Carnage!

After I got it on the trailer, I put the key in the ignition and the starter turned the motor without issue. Score! Also, all the electrics worked save for the lights and the turn signals seem to have a stuck switch or relay.

My plan, at least initially, is to get this thing running and riding for as little money as possible, as a personal challenge, and also because my RX-7 build is bleeding me dry. First, I want to get it to start and run for $0 spent, just using junk from my garage. Then, I want to get it running well enough to use in my city as a fair-weather daily. Finally, I want to swap out the cruiser tank for a standard tank, mount clip on bars and make it look like a mad max-esque cafe. I might even break out my new welder to make a rear frame hoop.

This past weekend, I was able to extract the melted air box, open the carbs, and solder the #1 plug wire back together. Carb #3 has a melted needle seat in the piston and a stuck float bowl valve causing it to overflow fuel everywhere, both potentially a result of the fire. The piston needle is still firmly attached, and somewhat aligned, so I'm hopeful I can get the bike running (probably poorly) after addressing the pissing fuel problem. I was also able to fix the not working lights - the circuit was just missing its fuse.

I welcome any suggestions, criticism or direction for this build.

I had a '78 XS750 standard. Be careful of the thing backfiring or stumbling under starting. It's a petcock problem that had a recall, IIRC. Otherwise, mine ran strong. Too much driveshaft jacking but if you don't invest a pile of money it should make a decent commuter.

I trackerized a Radian using an old school XV tank and some other bits a while ago:

If you want it to be fun in the city, I'd recommend lowering the front/raising the rear to get it to steer nicely, and running wide-ish bars rather than clip-ons for both leverage and a non-E36 M3ty riding position.

The old aircooled Yamaha 4 cylinders are pretty bulletproof, but I don't envy you having to work on those carbs. If the bike has a vacuum petcock, just cap the vacuum ports and use it manually, it's one less thing to have to troubleshoot around.

curious to see where this goes.

So I met the first goal of the project and got the bike running with $0.00 spent on it, just by using spare fuel line to replace what was burned, and soldering shut the brass float in carburetor 3. It even ran with a 10amp fuse in place of what should be a 20amp main fuse. It drove (very, very slowly) around the block. The next goal is to turn this into a daily-able city bike for as little money as possible. First purchase was a universal turn signal relay for $15 to replace the crusty OEM one.

In the mail:

$3.00 in fuses, $6.00 in carb bits, and $28 for the cheapest (US-shipped) eBay pod filters, which, I am hoping through some combination of electrical tape choking and adjustment of the carbs' needle heights, can fix my super-lean condition.

Total cost (roughly):

350 for the bike, 15 for the trailer rental, 35 for gas and tolls, 15 for a relay, 28 for pod filters, 3 for fuses and 6 for carb plastic. Total: $452.

stroker wrote: I had a '78 XS750 standard. Be careful of the thing backfiring or stumbling under starting. It's a petcock problem that had a recall, IIRC. Otherwise, mine ran strong. Too much driveshaft jacking but if you don't invest a pile of money it should make a decent commuter.

Thanks, I didn't know the petcock was responsible here. Now I know what to research. It did spit flames a few times when starting up, but that might have more to do with the starter fluid used. Also, the petcock vacuum lines were totally destroyed in the fire, so out of laziness I just got the bike running on the prime setting, and with no air box or filters, and rode it around the block with all of 5 horsepower and 2,000RPM. Pod filters are in the mail along with pieces to replace the melted needle mount in carb 3.

¯\\\_(ツ)_/¯ wrote: If you want it to be fun in the city, I'd recommend lowering the front/raising the rear to get it to steer nicely, and running wide-ish bars rather than clip-ons for both leverage and a non-E36 M3ty riding position. The old aircooled Yamaha 4 cylinders are pretty bulletproof, but I don't envy you having to work on those carbs. If the bike has a vacuum petcock, just cap the vacuum ports and use it manually, it's one less thing to have to troubleshoot around.

I'll have to take a closer look this weekend, but the ape hangers on the bike are mounted with some sort of flexible rubber vibration damper, and I hate it. When you push on the handlebars to walk the bike, they move. I will have to see how I can rigidly mount the handlebars.

I'm used to CV carbs, my first bike was an XJ550. What I'm not used to, and am coming to really dislike is the dual petcock system on the XS750. My only concern with eliminating the vacuum is not being able to use the reserve function and running out of fuel.

In reply to WatanabeWannabe:

A lot of the time those rubber dampers are big grommets in the upper triple- if that's the case some washers should do the trick. If it's dual petcock, eliminate the vacuum junk and use one side as your main and the other as reserve- or just get cheap universal petcocks for it.

clip-ons without rearsets looks stupid when you are riding. drag bars or superbike bend bars will be a lot better.

I have two Yamaha XS400's - one is a parts bike and the rubbers in the triple clamp are done and move like yours do. the other bike has good rubbers and you wouldn't know that they are not solid mounted.

they are $20 a set for the XS650 - probably the same for your bike.

https://www.mikesxs.net/parts/yamaha-xs650-handlebar-damper-rubbers-set-4-oem-1t4-23434-00-00-1j7-23434-00

https://www.mikesxs.net/parts/yamaha-xs650-handlebar-damper-rubbers-set-4-oem-1t4-23434-00-00-1j7-23434-00

plus, if you go from those mini-apes to clip-ons, you will need all new cables. throttle, brake and clutch. you may be able to get by with-out having to switch with a superbike bar.

This weekend I replaced the melted needle mount on carb #3. (I felt like a heroin addict because I had to heat up the piston with a Bic lighter to re-melt the melted needle mount in order to remove the piston return spring.)

I also: installed the Chinese pod filters, fuses, and patched up and rewrapped a melted section of wiring harness.

These Mikunis have 5-way adjustable needle mounts. They come stock in the middle position, and you can adjust them two positions richer or leaner than stock. I set all 3 to the richest position to account for the pod filters. In this position, the bike runs WAY better- it has (more or less) full power, rather than what felt like 2hp when I ran it without air filters.

It isn't idling yet, (granted, I haven't run it for more than 1-2 minutes at a time because it's not plated yet) so I've been holding the choke open halfway with a bit of cardboard. It's a shame the choke on this bike snaps shut. On my XJ550 you could leave it half-open.

Also, after riding it around a few times, the starter decided to stop working through the button. It works fine if you jump it from the battery, but the starter button does nothing. In hindsight, I did have the kickstand down, but I don't think this bike has a kickstand kill switch. Will troubleshoot later, or just delete the starter.

Also, this is cool- I kept hearing a loud "crack" from the starter intermittently, which I assumed was the starter not being shimmed correctly, or the gears being ground. It turns out, the sound is the starter arcing from the starter body to the engine block! I have no idea how the starter body is getting a positive charge.

When I got the bike, it was very hard to roll- I couldn't sit on it and move it without help from a friend. The front tire is a little low on air, but I think this is mostly the weight of the bike and corrosion on the brake discs, as it seems to be getting better. In any case, I would like to remove weight from this bike as, stock, it's 500lbs dry.

Plans for the near-future are: Buy a superbike handlebar and the new steering bushings Rusnak linked (making it rigid with washers would be great, but replacing the rubber requires no brainpower or risks), buy a kickstart lever (somehow missing on this bike), delete the starter motor, run a smaller, lighter battery, and possibly re-jet the main jets and/or pilot jets as needed. Oh, also I need to fix the turn signals and install the tail lights. I might need to look for more melted wiring.

After taking the battery box out in the picture above, I really, really like the open triangle look coupled with the pod filters. I want to make a little tray to hold the electronics tight up under the seat, and then find some small battery I can tuck away somewhere. Maybe there's space next to the rear brake fluid reservoir for a tiny battery. Otherwise, I saw someone on the internet mount the battery behind the license plate and use the plate itself as the battery tie down strap.

It's been a while since I got to work on the bike, but I finally found out why the kick starter was slipping: half of the teeth on the innermost kick start gear were sheared off: I ordered a new assembly off of eBay for about $50 shipped. Hopefully I can piece the clutch assembly back together using my poorly-scanned service manual. I am planning to delete the electric starter because it throws blue arcs to the transmission when it works, and often doesn't work at all because the relay is bad. I bought a rubber freeze-plug type thing sized to fill the hole.

Because it cost nothing, I decided to fix my pod filters the sleazy way: by putting cut up cans inside to choke the airflow and richen the mixture. This is just a stop-gap until I have time to re-jet correctly. Also on the agenda is fixing the turn signal and taillight wiring (right now, the left turn signal makes the brake light flash). Hoping to get it riding very soon- just in time to put it away for the winter.

It looks like a nuclear reaction happening in there.... glad to hear you're bringing this old girl back to life

If you need help emptying those Miller cans, I'm available.

You might not need new cables. Try some creative re-routing. I managed to eat up 3 extra inches on my TwinStar going from buckhorns to clubmans.

Long time since my last post, but I am getting more and more sick of the NYC subway/public transportation system and really want this thing riding for springtime commuting.

@jfryjfry- My apologies but the lighting in my buddy's garage isn't great. I'm trying to convince him to invest in overhead fluorescents

@minimac- Much appreciated

@Appleseed- Everything appears to work, though I hate that the clutch cable comes straight out at your face and can partially block the view of the gauges. I guess I need to learn how to trim cables to length.

This weekend I got it running with a new float, fixed the electricals, a broken plug wire, installed new turn signals, converted the fuel petcocks to manual, and fixed the clutch adjustment. Main issues now are a bad starter clutch and dragging front brakes.

I spent a lot of time last session fixing the kickstarter. I had been hoping to delete the starter motor as its clutch is bad and I think stays engaged while the engine runs (I can hear the sound of the starter winding down when I shut the bike off).

I removed the starter and tried kickstarting it from cold (around 20 degrees F) for 30-45 minutes with no luck, so I guess I will just need to fix the starter clutch. It will kick start when warm.

It won't idle without choke, so I think I need larger idle jets, and probably also larger main jets to go with the pod filters. Sunday I couldn't start it and it backfired like gunshots out the exhaust pipes- I may need to check the timing.

I do have some questions for the pros:

1. When setting float height, do you measure to the top of the float barrel or the top of the bracket it's soldered to? On mine, the bracket comes up 1-2mm higher than the barrels.

2. How can I make sure this thing starts well every time? Should I set the timing to a specific range? Get new plugs? New battery? The plugs all put out bright blue spark, and when I pulled them after cranking they were lightly covered in fuel, so I'm thinking my issue is with timing or AFR. IIRC the "choke" on these mikunis is somehow not like a traditional choke, I'm not sure how it works yet.

3. Why does the bike sometimes puff smoke backwards out the carbs when starting? I think this issue is what caused the engine fire that the PO had. Seems to me like improper valve timing.

Pictures: New turn signal on left (has an orange lens, not pictured)

Petcock mod - "Prime" is now "Off"

The pig as it sits. That's a new seat cover waiting to be installed (to replace the burnt up one).

Finally got it running and riding.

Fixed the starter clutch with dremel sandpaper discs, and discovered that I had a dead spark plug, which I'd never seen before (they must have been the OEM plugs from 1978).

Idles and revs pretty well when warmed up, but has no power above 3krpm under load, so I have ordered bigger main jets. It sometimes jumps to a high idle around 4krpm, probably due to bad butterfly shaft seals on the carbs.

Next steps: rebuild the dragging brakes, rejet the carbs, and insuring and registering it.

6 months and (less than) $600 later, I finally have a working bike.

I'd be more done with the bike but this glorious hardtop NA miata came into my life:

Just visited the bike to rebuild and paint the front calipers, and decided to try and kick start it for fun.

3rd kick it fired right up, and that's just because my shoe was wet and slipped the first two kicks.

There is something so undeniably manly and cool about kickstarting a bike, especially as big as this one, and especially when it starts right up. All the hours spent tearing open the gearbox to fix the sheared kickstarter gear were well worth it.

I used to only use the kickstart on my '74 CB-750 even though the starter worked flawlessly.

It just felt right.

My GS-850 has no kickstart capability and I'm sad about that.

Same here on the TwinStar. Feel like a bad ass when I do it.

Got the bike registered and fixed the bogging carbs under load. Turns out the beer can mod doesn't work, the vacuum just crumples the cans and totally disrupts all laminar flow. Removed those and it runs great, even with the Chinese pod filters.

Rebuilt and painted the front calipers and saw that the pads don't wear evenly- like the caliper is not parallel with the rotor. Strange. Also, the front brake still drags a little.

Bled the brakes after putting them back together and went for a test ride and found that there's no braking pressure the first 1 or 2 times you pull the lever, which is terrifying. Thinking it's just air somewhere in the system.

The bike also leaks so badly from the left side cover that it leaves an oil trail for the first 20 feet or so after starting. Will need to address that.

All in all I'm happy with the bike. It handles great with superbike bars (tried a friend's ninja 600 with clip ons this weekend and realized they make for a E36 M3 riding position. Thanks for the suggestion!) It has plenty of power and the air cooled 3 sounds awesome. Looking forward to dailying this 40 year old machine soon.

After a once-in-a-lifetime, bone-chilling, below-freezing ride out to my apartment, it's """""done""""". It's too cold to daily this thing, so for the near future, riding will consist of moving it to the opposite side of the street for street cleaning.

Though I just rebuilt the stupid friction-activated starter clutch (after buying a defective replacement from ebay), it's almost totally broken again after minor use. I guess I'll just need a strong right leg for kick start duty.

And though I thoroughly polished the left side case cover and all mating surfaces on the engine, it still leaks a small puddle from the left side after running. Funny thing is I swear the ebay replacement left side cover gasket I was shipped was a cleaned up take-off off of another 40 year old bike. When it arrived, it was inside a manila envelope sandwiched between two pages of a 30 year old newspaper. Who sells used gaskets???

Probably the biggest problem with the bike is that despite a friend and I flushing 2 full (small) bottles worth of brake fluid through the system, the front brakes still have enough air in them that you need to pump them twice to build the pressure to stop. My guess is that my friend let the master cylinder aspirate air a few times on accident, so now I'll need to find an 8mm wrench and fix that in the city.

I hear the forum at yamaha-triples.org is a great resource for these bikes, but whichever admin is in charge of registrations is not doing their job as I've tried to register 3 times without success. Until then, I'll continue to make GRM this bike's home.

On the left side leak- can you just use RTV in place of the gasket?

On the front brake- is it possible that one of the pistons is hanging up? That would explain both the odd pad wear and the need to pump the lever to get the pads to bite.

¯\_(ツ)_/¯ wrote: On the left side leak- can you just use RTV in place of the gasket? On the front brake- is it possible that one of the pistons is hanging up? That would explain both the odd pad wear and the need to pump the lever to get the pads to bite.

RTV is the plan next time I drain the oil. Removing the left side cover is really annoying so I'm putting it off.

The brake I'm sure is air in the top of the system; I just polished the front brake pistons and cylinder walls and installed a rebuild kit. Hoping to bleed it tonight.

Aside from the not-so-good front brake, the bike has been OK. The clutch cable snapped when I went to get groceries recently, but fortunately I was able to ride the 10 blocks home without a clutch, starting off in neutral on a downhill. And I found a NEW replacement on eBay.

I've been pretty much unable to start it in the mornings, but it seems to fire right up first or third kick in the afternoon. The temperature recently is 10-20F at night and 30F during the day. I wonder if it's just the cold, but wish there was some way to make this thing more reliable on cold starts. Possibly a lighter oil?

Spent all day yesterday working curbside in Manhattan trying to get the bike to start.

First I replaced the battery with a charged AGM one, still no start. Fired on one or two cylinders rarely.

Cleaned off the plugs. Still no start.

Took off the carbs and soaked the jets with the only solvent I had, starter fluid. Couldn't remove the idle Jets because I didn't have a narrow enough screwdriver. Put it all back together, still wouldn't start. By this point the new battery is low.

Rode my bicycle into the Bronx to the world's worst AutoZone to get carb cleaner and screwdrivers. Came back and disassembled the carbs again, cleaning the idle Jets and passages well. Put it back together and it started after about 2 minutes of kicking. Charged the battery by running it and it starts OK now.

Rode around to charge the battery and get gas, and the rear brake was dragging. By the time I got home, it was near impossible to back it into a parallel parking space because the rear disc was heat seized.

This morning, I pulled apart the rear caliper and scraped off some melted junk and forced the piston open some. Noticed the rear MC leaks, ordered rebuild kit.

Stripped a front MC reservoir screw while attempting to bleed the 10% air front lines, so I couldn't bleed them.

Rode it anyway for 20 miles to meet a girl, the second >1mi trip this bike has had, following very far back. Almost rear ended someone at 1mph. Would not repeat that insane journey.

Vintage motorcycling is a wild ride.

Up next: brake bleeding, rear MC rebuild, rear caliper rebuild, new carb seals, carb rebuild kits. Time to make this old machine safe again.

Thought I should update this, but I put in a bit more work into refreshing the brakes. I rebuilt the front master cylinder, and found the rear master cylinder was cracked and only attached with one of its mounting bolts, so when you pushed the rear brake, it moved the cylinder around the bike's frame rather than driving the plunger. I decided I was done with it, having already bought a BMW K75 (fuel injection and ABS ftw) as a New York daily ride, so I listed it for sale and quickly got interest. I rode the XS750 to the new buyer's house a few miles away, but it wasn't quick, and would bog with medium or heavy throttle. I ordered UNI pods for the guy to improve airflow to the carbs, but imagine it would have needed some upjetting.

Anyway, this build was a failure in some ways. I spent a lot of time, but I made a couple bucks and at least saved it from the scrapper. I have heard that the buyer is getting a lot of work done professionally to get it all finished.

Here's how I last saw it:

Just an FYI- pods are about the worst thing you can do with a set of factory CV carbs.