The details.
Bike - 1978 SOHC xs400.
Me - Handy with a wrench and reader of instructions.
New Parts:
Carburetor to cylinder boots
Brass Floats
Exhaust gaskets
Emulsion tubes
42.5 pilots
142.5 mains
Float pin valve and seat
Emulsion washers
Battery
Uni foam pods
Chain
Countless spark plugs
Oil
Oil filter
Light bulbs all around
Petcock to vacuum tubing
Vacuum barbs
Couple new lengths of wiring
Spark plug wires and boots
NOS 1979 ish H pipe exhaust
in-line filter
Condenser
Points
Rigged up a new seat
H-Pipe for carburetors!!! Found a great condition one on ebay
Throttle cable
and the smiles i have riding it.
Intro
Hi folks thought i would post a proper introduction. The names Dillon and i've been scooting around on a xs400 for about 10 months now. My obsession with 2 wheels goes back rather far and I always new i would be sitting on top of one that weighed 4-6 times heavier then me. What kind of 2 wheel'ers? Bicycles! everyone's got one and there is nothing easier right? Any who i literally get paid to work on bicycles and fallow instructions to the letter. My College days brought me a few courses of Automotive technology and at one point after about 5 years of regular practice i thought i was going to do something with my welding experience, but who would've thought around that same time i would land the "dream" job. Pedal bikes baby, lots of them and some of the latest technology. These days though I could not want to pedal a bike less, suit me up for a day on the motorcycle and i'll see you in 5 hours. So here i am, as i find the time to update this thread i'll be certain to include in depth trial and error, reasoning behind plans of attack and ultimately what the fix was. The engine is finally running very well and as i compile my notes i'll be sure to post pictures soon. Thanks for any future insight!
Petcock
Post 9-23-2017
What I've learned.
Petcock rebuild kits are about 8-11 dollars less then a manual petcock. There is little reason to attempt the rebuild. The time spent ordering, waiting, cleaning, and reassembling, for what i consider a 50% chance at success and a 50% chance of a gas filled crankcase make the decision for a manual petcock a no brain-er. I have to wait another month till i get mine and guess what, i carry a plastic bag around with a small rubber stopper that reeks of gas, get gas on my hands undoing my fuel delivery tubing and plug it up. My rebuild didn't take.
Update. 09/27/2017.
So i had to jump back into the petcock, i was refusing to believe that it all went well. All looked good till i took off my petcock selector plate and switch to get into the large circular gasket with the 5 holes in it. 4 in a circle and 1 in the center. So i had installed everything dry since i thought grease and gas wouldn't be ideal. The problem was that i installed dry and let it sit for about a month. I assume the 1st time i turned the selector the dry gasket attempted to pull with it and lodged part of it into places it was not supposed to go. Tried to clean the gasket up, greased it and reinstalled with the least amount of damage connecting the reserve to my outlet tube. This almost worked, sometimes it drips about 1 drip every 2 minutes and other times it doesn't drip at all. Replacement ordered as the circular gasket was 6 bucks with shipping. Long story short, a rebuild done slowly in a clean environment and greased may very well be a sure bet. That's your call though as the kit is really just a couple bucks less then a manual replacement. I will probably keep the vacuum petcock once zero leaking is observed, or if it seems mine is 100% operational.
09/30/2017
Zero leaking has been observed once my large circular gasket was replaced after ruining the first one to a dry install and letting it sit for a few weeks. BUT, vacuum petcocks connect to many places and require all those connections to be in good condition. Carb boot to petcock vacuum inlet must be in good shape as well as the gas tank flip cap O-ring.
Don't jet yet unless you a vet.
You've got the new to you xs400, your convinced you can make it go faster by cracking open your carbs and screwing in 4 brass thingies with little holes. Enjoy your bike for a few months double checking the easy things, or you can do it my way and attempt jetting on a 99% operational fuel and air system and a 45% or less ignition system. Get your ignition in order. Inlet and exhaust valve clearances, gap points and time. Then once the expected base operations are solidified, you can try and jet. To make it more confusing i would suspect that the majority of us have yet to develop the subtle detection skills to really dial this aspect of our bikes but what i'm starting to pick up is, that these bikes will run a multitude of pilot and main combinations as long as there relatively similar to what you took out. Fine tuning requires detailed notation and observation. There is a website i'm having trouble finding again that if i can remember correctly had a pink background? or pink writing, i fallowed a link from another thread on this forum there and it was hands down the best jetting guide. I'm still trying to nail down my main jet and the guide says that is absolutely step number 1, there is no pilot and needle tuning without figuring out your main jet. If you know this site please link it again in this thread. Finally freaking found it!!!!!!!
Here it is
http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html
You Might need new points and or a condenser.
A new condenser would only be appropriate if you observe or notice evidence of the points sparking excessively. Double check point gap before getting too far in. I had also noticed a light coating of dust on and around the effected area, it would easily wipe away and was brown greenish yellow dust, you know, the weird "thats an electrical fire" type stuff. A bad condenser will ruin points until replaced. Pitted or poor condition points can be dressed flat again with good results. I suspect though, as you dress your points multiple times the removal of material will eventually effect the point at which the lobe would normally contact the points lever. Potentially making timing the bike gradually harder.
Gap Tip.
Rotate the engine and test the corresponding point you are gaping at all the spots it appears to be the "most" open with your feeler gauge. You will find at least 2 positions that will be more open or closed then other positions. The trick is to find the largest gap throughout. Identify the deviations in gap width and make sure the "most" open is set according to the manual. Keeping the lower point plate bolt slightly tighter then the top will allow you to utilize the small raised dots on the timing plates to help slowly and accurately move the points plate with an appropriately sized flat head screwdriver. I set any feeler gauges to a loose target size, tight next size up. Keep in mind that gaping the left and right cylinders must be done together starting with the left, immediately fallowed by the right. There is no one or the other and frankly in my mind there is no gaping without timing although the manual dosn't quite say this and the inspection intervals pertaining to each adjustment are different but I've already got my crankcase cover off i might as well triple check timing.
Time it.
If your going to statically time your machine I would recommend making the light the manual suggests. It is also of the utmost importance to triple check your gap before attempting timing. As of writing this i don't know how to pull off a dynamic time and i would have to watch someone do it, the manual says oil will issue from case, no thanks. sounds scary. I made a light out of a turn signal i had lying around and some alligator clips. Connect the positive and negative leads to the alligator clips and i'll put a clip on the point spring ribbon and the other on a cooling fin on the engine. Key set to on, with the spark plugs removed, and as your points separate the circuit will open illuminating the turn signal or other small light. Set this to the exact moment your LF/RF line crosses the timing point on your engine and you've statically timed your engine. Triple check and button up.
Helpful corner -
http://www.randakksblog.com/lean-vs-rich/
http://www.amckayltd.com/carbguide.pdf
Last edited:
