New member, new bike, and some questions


XS400 Member
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New Haven
Hello, first post on the forums and was looking for some advice.

Last fall I obtained my first street bike, 1982 xs400 heritage special. It was my boss's, she rode it a little bit a few years ago, had a kid, and quit riding it. It sat in the garage for 4 years and her husband recently took the carbs off and sent them to a friend for cleaning to get the bike running again.

They got a divorce, she said if I could haul the bike away it was mine, and the carbs were never seen again and never will be :p

So the weather here in Michigan is just starting to break and I am getting the urge to get this bike running and take my very first ride down the road on my first bike. But I've run into some problems with my original plan, "buy carbs off eBay, rebuild, grease and inspect everything, ride."

My vin number and title shows the bike is a 1982 xs400. But the stamp on the engine says 360cc. I do not know much about Yamahas (Honda ATV guy), could this be a swapped in engine?

Distinguishing factors I know about my bike:
-Spoked wheels
-Manual drum brakes front and back
-Electric start, glass fuses (will be upgraded to modern fuse block)
-Six speed, 1-N-2-3-4-5-6

My questions for the experts:

-Were the 400's only bored to 360cc? I thought there was a separate bike, the xs360, is that bored smaller or do I have an xs360 engine in my xs400?

-Consequently, should I order carbs for the xs360 or xs400 for this bike?

-Mike's XS has a "performance" new carb kit that includes intake manifold, throttle cable, and nice filters for a price cheaper than used carbs and rebuild kits... would it be foolish to toss a non-stock setup onto a non-running bike? It would be so much easier as I need intake manifolds and a cable anyways, and it's all in one neat kit for a decent price.

Thank you for all your help, this is my first street bike and first Yamaha and I am super excited to learn the ropes on it. I am relatively mechanically inclined with engines from cars and bikes, but these decisions stump me a little bit since google doesn't offer much good information on these bikes and their differences.

Attached are a few pictures of the dusty bike when I brought it home. If engine numbers or close up photos are needed I'll grab them right away! Apologies for my girlfriend's judgemental face, she wasn't the happiest to be woken from a nap to unload a dirty motorcycle I brought home.
Welcome to the forum! Nice score on the bike, but I think you are about to find out that free bikes aren't always cheap.

The bike is indeed an SOHC Heritage Special that looks pretty complete. The engine, however is not the original. I can see from the pictures that it has squared off fins on the cylinder block and head that the specials don't have. If the casting on the cylinders says 360cc, then it is probably an engine from an XS360 - can you post the engine number that is stamped on the crankcase right side near the kickstart crank? We can use that as additional evidence as to what carbs you need.

If you are going to have to get carbs anyway, I would probably consider the Mikuni VM series round slide carbs. I don't have any knowledge of the MikesXS stuff, but the Mikuni VMs might be easier in the long run with tuning advice and jetting, and they work well without the stock intake setup. One source that sells complete kits for either the XS360 or XS400 is at
Thank you for all the information. I know this bike will cost me much more than what it takes to get it running, I've got a 1982 Honda ATC 185s, and have obtained a few old machines to fix and get attached too I mean sell. I have known my boss for years and trust that the bike was running when parked, and all it needs to get it running is carbs, but there will be many things to find a long the way broken, rotted, leaking, etc. on a vintage machine like this. Still doesn't steal my love for old bikes!

I don't recall the exact number, but I think this bike (or at least the odometer on it, but the general condition seems to back it up) has only 14k miles. Everything is in great condition but I have been re-greasing and inspecting everything for good measure. Not to mention replacing all the crusty old electronics I don't want to trust. Tires are in great condition and were new right before storage, and the bike was stored off the ground too.

I will have the engine number posted tomorrow afternoon after work. I will check out speedmotoco for carbs and supplies in the meantime.
Engine #1T6-005349

Yup, it's an XS360 engine. Specifically the "1T6" is the model code and the numbers following it are the serial number. 1T6 is the code for a 1977 XS360-2D. Your bike VIN should start with "14V" which is the code for a 1982 XS400SJ.

One thing to check for is if the person doing the engine swap removed the TCI box (electronic ignition) from the bike. The 1980-1982 SOHC 400s used this instead of a points ignition. It is mounted to the underside of the battery box and looks like this:

If it is there, remove it and store it off of the bike. You can sell this on the marketplace here to some needy owner with a fried box and offset some of the cost of buying the new carbs.
Holy Frankenbike Batman! I just relooked at the first picture that was posted. It is hard to tell, but it looks like the engine swapper retrofitted the electronic ignition to the XS360 motor. It looks like the bike is using the late model cam rotor cover and not the points cover and there appears to be the wires from the pickup coil coming out of that cover leading up under the tank to plug into the wiring harness. If this is the case, the TCI box will definitely be mounted under the battery box, and you should leave it right there because you need it.

If this is true, then whomever did the swap, I salute them!
That's funny, in my learning journey about this bike I was reading somewhere that they made the change from points ignition to electronic ignition somewhere down the model line. When I start tearing into the electronics in the next few weeks I will survey what kind of system one of the previous owners fitted to this bike. I know my boss sure didn't lol. Good thing you brought it up, I would have just overlooked it!
I think you are going to find that the ignition components you now have on that engine are stock XS400 ones that were removed from the original engine and "transplanted" onto the donor engine. A transplant was also done with the starter motor and associated bits as it sure looks like there is a power wire going to the housing where the motor is. XS360-2D bikes did not have a starter, they were kick only. If you have electric start, that was added to the donor engine as well.
Back with some updates and questions!

Carburators came in the mail yesterday. I had the day off and worked to de-rust the gas tank and start the project. First off, the bike decided to seize up over the winter. My heart sank, but after an hour with PB blaster in the cylinders it freed up readily. I feel the crank was probably at the very top or bottom of its rotation and there was just a little gunk in the cylinder.

The front tire decided to develop a small crack over the winter so that's a bit sad. But it is what it is, it will get a new one before any real riding.

Carbs were an easy install. Came with all new intakes, and all other rubber parts associated. A few hours of rust remover brought the inside of the tank from brown to a nice shine. Rinsed it a few times and dried it out. I like how easy this gas tank is to remove, it's just like my old Honda.

The metal elbow at the handlebars on the new cable doesn't fit the old hole, but I'll get creative with mounting it properly. Currently rigged up for testing.

Bike took a bit after priming to start, but it did start. Strong spark on both cylinders, but the bike will only run manageably (even when warm) when the left cylinder's choke (well, enrichener on these VM30's) is just barely engaged. Still idles at 1900rpm, and is only idling on the right cylinder. Confirmed by pulling left plug boot with no change in idle. As soon as you get in the throttle, both cylinders fire properly and the bikes seems to run smooth-ish.

Leaving the choke completely off and the bike will idle at 3500rpm... more of a dash than an idle.

BUT in defense of the bike, I have yet to sync or balance anything. That is today's project, if it stops raining. I'm just happy to hear it fire.

I do not yet have a battery for this bike and have heard they like a lot of available amperage, so I am not going to mess with the carbs and firing issues until it gets a battery of its own and isn't being run off jumpers.


-Could badly out of sinc carburators cause the left cylinder to refuse firing at idle, and cause the wacky idle when messing with choke? Or does this sound like vacuum problems?

-Should I be using any sealant where the carbs clamp into the rubber intake boots?

-Since these cylinders fire in sync, can I swap the plug boots to confirm it's not an electrical issue?

-Since I do not have stock carburators with that nifty single adjustment screw, how should I go about syncing these carbs? Adjusting idle as low as possible still running smooth, then hook up the DIY manometer and make fine adjustments?

-Crankcase breather is missing. Is it the kind that just drains under the bike, or the kind that is routed to vacuum?

Still have to pop the side cover off and see if the ignition points have been swapped for a contactless retrofit. I didn't do much with the electronics yesterday and maybe a dirty ignition point (if they are still there) could cause the firing issues? This is the first engine I've ever had that has (or had) ignition points.

I will post updates as progress is made, dependant on weather. If these symptoms scream any particular issue to anyone before I figure them out myself, I'm looking forward to hearing ideas on what to look for.

I've been working on the bike for a while and think I fixed most all of my problems.

The high idle and hesitation to start was because the vacuum petcock apparently doesn't work any more and was causing a direct vacuum leak. If I can't find a cheap replacement, I'll just cap it off and use the prime setting, watching my fuel level on trips. Disconnected and capped the bike starts right up.

The firing issue at idle was because the idle adjustment for that cylinder came from the factory (or whatever hands in between) almost bottomed out, while the other was a almost all the way out. I never bothered to look at them since I was racing the sunlight yesterday and just wanted to hear the bike fire lol.

I have got them both about the same amount of turns out to hold an idle around 1200 rpm. Still have to break out some clear tubing (or ask around and see if any friends have a manometer) and properly sync them but it's as good as it gets doing it by ear and feel.

No clue about the revving up with choke issue, that's gone now after messing with other stuff.

Scouring google images, I finally found a decent photo showing the crank vent going to the bottom of a stock intake. So I ran it to one of the vacuum ports on the intake manifolds. I've seen what kind of goo builds up in those on an old dirt bike, so I ran a filter in between. It's odd to me how many old machines (and maybe modern) have no crank vent filters or fuel filters from the factory.

Battery should arrive tomorrow so I can take her for a spin around the block without stalling every time I use the brake light at idle. It does seem to love amps, doesn't stall when connected to a car battery.

Pictures to come on a sunny day and after a good engine degreasing .
I don't think running the crank vent to the vacport is a good idea. When connected to the air filter side, it only sees minimal vacuum, enough to scavenge out some crank vapors. On the vacuum port, it will have full vacuum at idle. Not at all what it was designed for. Many people just put a mini pod filter on it and let it vent to atmosphere.
It did cross my mind that that negative pressure is a lot stronger on the engine side of the carbs vs the filter side. But I have also read a few articles about the benefits of pulling a vacuum on the crankcase, like reducing the risk of blowing a gasket out and subsequent oil leaks.

I have been thinking about it and am debating about leaving it there in contrast to getting a mini pod filter with no vacuum like you said.

I replaced the fuse box and fixed up a few not-so-trustworthy looking wires. I used the same generic fuse block from Amazon I've seen posted on here a few times, it fits nicely and uses the same mounts as the old one.

A past owner soldered a fuse into a broken holder on the old one...

Excuse the terrible photo, again working into the night and it was raining.


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These old engines didn't have a pcv system like cars did from the 70's on up. You'll probably run leaner on that side too since it'll be unmetered air. Just watch you don't start sucking oil into that cylinder when letting off the throttle.
I'll keep an eye on it and may remove the breather, I haven't been on the bike yet due to weather and not going out to sync the carbs yet. But it is a good point that any tiny entrance into the crankcase would be a source of air entry into the vacuum system, and there isn't any real pressing reason to have it connected as is.
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The advice from @tstidham is good stuff. I have also replaced my petcock with a manual one as it removes one more source of vacuum leaks.

Since these cylinders fire in sync, can I swap the plug boots to confirm it's not an electrical issue?

I just want to point out that the cylinders do not fire at the same time (I assume that is what "sync" means here - correct me if I am wrong). So, do not swap the leads on the plugs.

Synching the carbs will not be as easy as the one screw method for the stock carb manifold. You will probably have to adjust the throttle pull at one of the carbs and go from there depending what your gage or manometer does.
You can also do what's known as a bench sync for the initial setup. Use some sort of "gauge" (could be a paper clip, small drill bit, brake cleaner plastic straw) and set both carb throttles to the gauge where there is slight drag when moving it between the throttle blade and the carb body. Then make sure to do your idle speed adjustments 1/4 or 1/8 turn to each carb screw to keep them very close to one another. This is how I set my 78 up, and it's been running great since. I don't own any sort of sync tool. For setting the idle mixture and idle. Start off the idle mixture screws at something like 2 turns out and adjust the idle speed down as far as possible to avoid the carb transitioning on to the main jet circuit. Then start turning out the mixture screws evenly until you get the highest idle speed. During this process, you may need to lower the idle speed screws if the idle gets too high from the mixture screws.
Thanks for the link on the petcock, I'll probably pick one up. Though mine "works fine", I don't need the annoyance of having no viable shut off when a carb needle decides to not seat and leak all over.

About the cylinders firing at the same time, it was a friend who used to have an xs650 who told me the parallel twin acted like a big single cylinder together and I wasn't sure. It's obviously ruled out now, but if I did pursue a possible electrical issue I would have confirmed firing order first before switching the leads.

As of the carbs, what I did was bottom out the idle adjustments then bring them out a few turns, keeping them even with each other the whole time during idle adjustment. I've got the bike running pretty nice, but will probably use the diy clear tube manometer trick just because it makes me feel a little better to actually see equilibrium. I'll mess with the fuel/air screws after I get to take the bike for a little ride and see how the plugs look.

Thank you for all the help! This is my first time dealing with more than one carburator, everything I've ever had was either fuel injected or a thumper.
I've got the bike running pretty nice, but will probably use the diy clear tube manometer trick just because it makes me feel a little better to actually see equilibrium. I'll mess with the fuel/air screws after I get to take the bike for a little ride and see how the plugs look.
Good call! The manometer and plug color show you the facts of how the cylinders are performing.
Just a point on the XS650 and XS400 parallel twin engines. They are different in that the stock XS650 engine is a 360 degree engine where the pistons are both going up and down together, but one cylinder is on the power stroke when the other is on the intake stroke and will not fire until the crank rotates another 360 degrees. The XS400 engine is a 180 degree engine, so when left cylinder is at TDC and fires, the right cylinder is at BDC and starting its compression stroke. The right cylinder will not fire until the crank rotates 180 degrees.
Sorry for such a long gap on updates, it's either been raining, hot as hell outside, or I've been stuck at work, so progress has been relatively slow.

The bike has been tuned and runs very well at this time. I have yet to finish adding a cycle endorsement to my license (everywhere is booked up here, but I'm getting close to the final road test) so I haven't had the bike past 30 yet. I'm limited to my neighborhood currently.

Everything has been cleaned and shined up, fuel/air mixture has been dialed into a good mix for performance without being too lean, and I got the oil drip to stop with a little bit of the oil leak stop that works by expanding old gaskets.

I did remove the vacuum on the crank breather, it was accumulating water somehow. Fresh oil, so no clue where that was coming from but it would accumulate in the little filter and drip back into the crank. So it's gone for just the little filter to atmosphere.

Brighter than stock LED taillights for extra visibility, and a sleek LED headlights to come soon. I left the turn signals incandescent, as I like the self canceling feature. LEDs for all the gauges that were mostly burnt out, and the little dash indicators.

I can confirm that newer LEDs that include a bridge rectifier (so they work either way you put them into the socket) will work in the turn signal indicator since they will conduct either way.

Once my headlight and bag for the rear rack arrive, I'll do a nice photoshoot of the bike.