intro/build cafe/brat style 78'

Euros4life · Jun 20, 2016

I've been lurking for a bit now, figured it's time to introduce myself. Names Mike. I'm 30 with 4 small boys under 6. I've been riding sport bikes most of my adult life up until about 3 years ago. Life just got the best of me. I've missed it every day since.

So about a month ago I scored a 1978 xs400 for $300. Running (like poo) and driving, but no title.

It pretty much sat for a month while I dealt with title drama. Got that squared away and this last Monday I started tearing into it. Every night after work for a few hours. Ending the week with a very much ridable bike. Just missing air filters.

the very first thing I did.

Still tons left to do but now I can ride it while I tinker. Drag bars are in the mail along with UNI filters. I actually dig the stock seat, may attempt shaving the foam down a bit, but otherwise the tail will stay relatively stock for now.
Most newbs tend to have at least one question in there post so heres mine. I've seen in multiply post the mention of a "tech" section. Now I've searched for this infamous place with no luck and am seriously doubting its existence.

BBS360 · Jun 20, 2016

Looks good! Welcome to the forum! Glad you're going to keep some of the stock appearance.

The forum was recently upgrade to a new platform, "xenforo." Prior to the upgrade The Garage had multiple subcategories including restoration, electrical, mechanical, etc, which could all be read through the main Garage section, AND a "Tech" section on the main xs400.com website.

The Garage subcategories are gone and so is the Tech section, but here it is!

Yamaha XS400 Technical References
Updated 11/21/2011
Listed below are quick-reference links to threads in the forum on specific XS400 technical topics. Not all of the links below are to completed articles, but all contain at least some useful information on the topic. The list is a work in progress so if you can't find what you are looking for, try the Forum Search feature or browsing the main forum by Topic. If you're knowledgeable on a specific topic that is not well represented below, consider starting your own XS400 technical thread in the forum and it will most likely be included in the list below. A big thank you to everyone who has contributed so far!

Engine and Transmission
How To: split your engine crankcase
How to check the oil level in your XS400 *

Carburetors, Fuel, Intake, and Air Filters

XS400 2 into 1 carburetor
Mikuni BS34 air intake jets/passages
Carb Adjustment
Jetting Guide
Jetting tip

Exhaust

MAC 2 into 1 Exhaust Install

Electrical

XS400 wiring diagrams
How To: rewire an XS400 *
Charging system upgrade - Permanent magnet alternator *

Suspension
Removing fork caps
Lowering forks

Brakes

How To: XS400 twin disc conversion (dual disc brakes)

Controls

Making cables

Maintenance and General Troubleshooting

XS400 Manuals

Miscellaneous
History of the Yamaha XS400
Polishing made easy

Tools
How To: make a bottle style manometer *

Fabricating
How To: Make your own Knee Dent Tank

Yamaha XS400 Technical Article Suggestions
Listed below are some XS400 technical topics that would make great technical articles. Some of these topics are briefly covered by threads in the list above. The threads could use improvement or a new comprehensive article could be created on the topic. Consider helping the XS400 community by creating a How-To or technical article on any of the topics below.

Fitting a hardtail
Caliper service/rebuild
Dismantling rear shocks
Steering head taper bearing swap
Swingarm bronze bushes swap
2-1 Carb manifold
Shortening cables
Wheel bearing replacement
Carb cleaning and rebuild
Engine rebuild
Timing
Cleaning a rusting tank
Torque specs and torque patterns
How to remove the starter

General Motorcycle Technical References from XS650.com

Euros4life · Jun 20, 2016

good to know. I stumbled across this post a while back. Great stuff here.

Euros4life · Jun 21, 2016

So filters showed up today right before I had to leave for work, decided to ride in. This is only the second time I've rode this bike, and pulling into work parking lot it stales out............ heart dropped WTF moment.

Fuel filters dry, I ran out of gas. :doh:

Switched to prime then reserve and fired right back up. :bike:

Euros4life · Jun 23, 2016

Small update. Filters and bars are here. Threw the filters on and the bike starts and idles great, but under heavy throttle it bogs bad. Turned the mix screws 1/2 turn out with little difference. Plugs were black. It has 142.5 mains in and 40 pilot. I plan to drop the main down to a 140 tonight. Hopfully get it dialed in better.

Side note about my carbs, my needles have no adjustments what so ever and both my mix screws clearly had a cap that was drilled out. My understanding is the 78' should have adjustments on the needle and no caps. someone swapped carbs at some point I guess. Hopfully wont hinder tuning much. Not to clear on shimming the needles.

And the drag bars, look great but are ridiculously wide. Is it pretty common to have to cut these down? I'm thinking 1.5-2" on each side.

Euros4life · Jun 28, 2016

Been into the carbs 3 times since my last post. 140 main is dead on for the top end. Bike pulls hard and continuous from 5k up. Still struggles at anything below that. Typo above, I actually have 45 pilots and went to swap them but discovered my float pin seat was stuck open.

perfect that's my problem. clean and re assemble. Still way off.

So checked and adjusted valves, points, clutch and floats. Valves, points and clutch were pretty good, only slight adjustment. Floats were WAY rich. Set to suggested 26mm with only marginal improvement. Actually have a crazy flat spot at 8.5k.

no clue what that's about.

Plan now is to check the plugs verify still a rich condition and adjust floats a little more. then throw stock pilot and see where I'm at. Any better suggestions or ideas are welcome. Love to be able to just ride this thing

Im running UNI pods with the stock H pipe. Stock exhaust, little rotted but no holes.

xschris · Jun 29, 2016

Sync carbs with manometer? Bike reds around 9k.

Euros4life · Jun 29, 2016

I did sync with the initial clean and rebuild. I've been in there so many times since im sure its off. Plugs kinda confirm that. Ones dry with a light tan others black and wet.

Bike falls on its face at 8.5k then picks up again and pulls to 9k.

I did shim the needles slightly with pretty much no change. Still trying to find stock pilots locally.

xschris · Jun 29, 2016

Also are you floats brass or foam. The brass ones are set to 26 and the foam are 22mm.

Euros4life · Jun 29, 2016

brass floats. set at 26mm. Also tried the 32mm with no improvement.

Euros4life · Jul 13, 2016

Slight update, been a busy month with the holiday and tons of overtime. Didn't lave much time for the bike. I have gotten it running at a state I can live with. :thumbsup:

ended up lowering the needles some and the plugs are pretty brown. Pulls great threw first few gears, still kinda sluggish if I hammer it around 4-5k in 4th or 5th. I just ride around that.

My headlight was cracked and during inspection I found it was soldered on, no plug to be had. I have plans to eventually replace the headlight and bucket completely as mines rather trashed, so I resoldered a stock light I had laying around. :redface:

Boy does the light output suck.

I got a universal build your own clutch cable for my front brake. Pretty straightforward but as it was my first solder cable I measured 3-4 times before cutting and soldering. Turned out good and now have working front brakes. Of course my first pull of the lever and the front end dives, I was only rolling out of the garage. :doh:

So looks like fork rebuild is in my near future. For now I plan to throw some fresh oil and hope for the best.

On a side note I've noticed some pretty bad head shake when cruising around town. Could this be from the super soft forks? Or maybe the lack of front fender? (read it acts as a fork brace) I plan to cut it down and paint it, just wasn't a priority. Maybe I need t make it one.
:cheers:

Euros4life · Aug 6, 2016

So new fork oil only helped marginally, as both seals leak. Rebuild will have to happen sooner then later.

Been riding the bike more then working on it and its been slowly running worse and worse. Todays stroll to work left me with a 3000k idle. First start was fine but after a short spurt to the stop sign down the road it wouldn't idle down. Even with clutch release, it would go to 1200 or so then slowly crawl right back up. Sticky float? Or maybe lean condition? Another carb overhaul is in order I guess.

Also had my battery die last week. Now I don't drive far to work, and its all city so my thoughts are I'm not charging the battery up enough before shutting the bike back off. Its a small gel battery. 12v 3amp. Kick start only so its been more then enough. I got a push start and made it home, threw the charger on and left it over night. Batterys held a full charge ever since.

Euros4life · Aug 7, 2016

Any one know how crucial are the rubber plugs on the idle jets? Mine are dry and fall out every time.

levdir · Aug 7, 2016

I'm sure someone knows better than I do, but I've always heard that they're critical to smooth running. If they're dry and loose, try soaking them in mineral oil overnight.

Euros4life · Aug 7, 2016

That's a good idea. Tried brake clean in the hopes they would swell. No luck. Ended up wrapping them in Teflon tape.

Euros4life · Aug 8, 2016

Swapped in a good float. Idles great and runs good.

I am still having a more then comfortable amount of whitish smoke coming from the left exhaust under decell. I didn't mention it as I figured it was from the float needle being stuck open. (excess gas burning up) But it didn't change at all. Any guesses or ideas on how to figure the cause of this? Valves were checked and adjusted less then 50 miles ago.

Euros4life · Aug 8, 2016

http://www.xs400.com/threads/one-of-exhaust-pipe-smokes-more.7137/#post-75040

I'm gonna go with this for now. Bike sat for 10+ years. I have owned it for roughly 3 months and only managed ~50miles

Every time I ride another gremlin would rear its ugly head. So anyways just going to put some miles on and watch the smoke dwindle away. :thumbsup:

xschris · Aug 8, 2016

If you have the 80-82 sohc carbs that take the rubber pilot jet plugs get some new ones!! The 77-79 bikes took a screw in metal plug. Make sure you have the right ones. The best thing for a bike that has sat is to ride it for as long as you can at highway speeds. It will get things loose and clean.

Euros4life · Aug 8, 2016

Carbs are not the originals. They have the rubber plug. Mixture screws had caps that were drilled out. And the needles are not adjustable. Also came with 135 main jet and 42.5 pilot. From what I have read here that is all incorrect for a 78.

Mikes xs has the plugs I will order them along with some other goodies.

Euros4life · Aug 16, 2016

Radiator on the truck cracked today so the bikes my main mode of transportation. Of course its gonna rain. :laugh:

Fingers crossed she starts after work.

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