1978 Yamaha XS400 full tune up

Then the problem is in either your tci box or the pickup coil on the end of the camshaft. By switching the wires, you proved your original coil was still good and probably didn't need to be replaced.
Nah that coil pack was for sure done, had burn marks on the under side of it and was spitting out this wax like material, not sure if it was hot glue from the previous owner or some sort of insulation.

The TCI box and pickup coil, would you happen to have a picture for them and how I can begin diagnosing this further?
 
I think you have the coils wired up wrong. that 2-prong connector is from your ignition and is supposed to connect to a coil. Based on the wire colors, that loose connector looks like it should be connected to the right-hand coil. You need to trace the wires from your ignition to the coils to make sure they are correct. Here is what the factory coils and connectors looked like.
Coils.jpg


From your ignition, you should have Red/White and Gray wires leading to the left coil and Red/White and Orange wires leading to the right coil. From your picture, the yellow wires on the coils connect to factory Orange or Gray wires and the black coil wires go to the Red/White factory wires in the harness.
 
this looks like from the model after 1779, he has the older one with a mix up with the coils

only the newer bikes with the cdi have this connectors, the older ones have round ones
 
I was under the impression it was an 1980 or newer. I see now you have a 1978, so it should have points. Pull the points cover off the left side of the engine and inspect them. Check the points gap is correct. They can get arc carboned up if their really old so they may need to be replaced. There is also a condenser wired inline that can go bad. Sometimes you can restore functionality with some fine sand paper to clean up the contacts.
 
only the newer bikes with the cdi have this connectors, the older ones have round ones
Ah, yes my photo is of a 1981 bike. I didn't know the pre-1980 bikes had different connectors. Also, I zoomed in on @arm's "loose" connector and it looks like an orange and gray wire installed in a newish connector.

So I was wrong on both accounts! This typically happens when I discuss anything with my wife, or so I am told....
 
I was under the impression it was an 1980 or newer. I see now you have a 1978, so it should have points. Pull the points cover off the left side of the engine and inspect them. Check the points gap is correct. They can get arc carboned up if their really old so they may need to be replaced. There is also a condenser wired inline that can go bad. Sometimes you can restore functionality with some fine sand paper to clean up the contacts.
I think i opened up the right part of the bike, here's a video on it
Link

It looks to be clean and new, nothing wrong with any of the contacts so I'm really scratching my head as to what it could be, maybe cable is broken? maybe its something near the battery since that's where the orange cable leads to
 
Ah, someone removed your points and installed the mikes xs electronic ignition kit. I also bought the same kit, but haven't installed it yet. There is a warning on the install instructions to not leave the ignition turned on for too long without running or it can be damaged. Not sure why or how that should damage anything as I'd think running would be more heat or power then just turned on. You can download the install sheet to see the wiring details, hopefully something is just wired wrong.
 
Update on the XS, I found this amazing video for exactly the same points-based system by Brick House Builds. I been keeping up with his xs400 build and when I was debugging this issue I came across this video


In his video I noticed this
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You can see the plate with the PCBs has a notch at 12 O'clock where as mine (right side) is more at 9-11 so i think that plate needs to be reinstalled because the video explained that there are magnets in the process that help control timing and spark, im not sure if this is for sure the reason why the left sidde dosent spark but im willing to give it a try.

Also his rotar has a small indicator thats at 12 O'clock aswell with the 2 silver dots facing the right. in bike i noticed that my rotars silver dots are facing downwards, Im pretty sure this isnt to alarming though since (if im not mistaken) the rotar spins and maybe mine landed at that position from the last time i rode the bike but just to be safe i think the safest thing would be to reinstall the points based kit according to the manual


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I also managed to strip the screw in the top right position so any tips on how to get that out would be cool :)
I tried using a really long flat head but no luck, im thinking of using a even longer flat head perhaps
 
Update:

So the previous owner routed the wires from the ignition system to some wire that then went into the coil, I thought that was weird so I unplugged them and wired the ignition straight into the coils. Still, no luck, only one spark plug is firing and the other isn't. So now I'm thinking either that little plate is off from 12 o clock and that's the issue. After that I'm pooped

I guess I would just contact mikes xs customer service for a replacement cause the unit looks to be perfectly fine but isn't really preforming as it should
 
Hey all!

I'm finally done my exams and back to wrenching at this bike. I wanted to reinstall the points based system all the way from the start so I tore it all down and the first instruction was to get the engine into the "LT" position.

After doing that the camshaft locating pin has a small bump on it that *should* be at 12 o'clock but for me it's a 6 o'clock

Any ideas of how to fix this? All the instructions say it should be at 12 but don't mention what to do if it's not.
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In this video at the 49 minute mark I noticed how he can rotate the cam gear. Im guessing I need to take off the upper motor mount and the top part of the motor to get to that?

 
Yes, you pull the rocker cover. There are two cam gear bolts you can remove and then rotate the cam 180 and reattach.
If the cam is 180 deg out of time, that will certainly give you trouble running. Did the bike run before you bought it? I would make sure you are on the compression stroke of the left cylinder first though and not at TDC of the exhaust stroke. With the plugs out, put your finger over the left spark plug hole and rotate the crank again one full turn. You should feel suction of the intake stroke, then compression and realign the LT mark.
 
Yes, you pull the rocker cover. There are two cam gear bolts you can remove and then rotate the cam 180 and reattach.
If the cam is 180 deg out of time, that will certainly give you trouble running. Did the bike run before you bought it? I would make sure you are on the compression stroke of the left cylinder first though and not at TDC of the exhaust stroke. With the plugs out, put your finger over the left spark plug hole and rotate the crank again one full turn. You should feel suction of the intake stroke, then compression and realign the LT mark.
Thanks for the tip! Yes I been setting it to LT whenever I do any work but I'll make sure that it's on its compression stroke using your method.

And yes the bike did run when I bought it, I actually drove it home. I've been riding it around here and there but to my suprise, only on one cylinder. Maybe this is why the second cylinder wasn't sparking at all?
 
If the cam timing is off, you may need to also remove the caps for the valve adjustment for the left side and observe the valve opening/ closing actions for intake and exhaust. You should start by observing the intake opening then closing and as you continue to rotate the crank, this will be compression so align the LT mark. As you continue rotating, you'll see the exhaust open then before the exhaust fully closes, the intake should start opening again (overlap). Intake closes again and again we are one compression stroke so align the LT. Here you can confirm the cam gear mark.
 
Just to make sure i understand correctly
If the cam timing is off,
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This is the cam? and yes i think it is off since at LT its at the bottom rather then the top
you may need to also remove the caps for the valve adjustment for the left side and observe the valve opening/ closing actions for intake and exhaust. You should start by observing the intake opening then closing and as you continue to rotate the crank, this will be compression so align the LT mark. As you continue rotating, you'll see the exhaust open then before the exhaust fully closes, the intake should start opening again (overlap). Intake closes again and again we are one compression stroke so align the LT. Here you can confirm the cam gear mark.
This part confused me a fair bit, is there any video or picture that points out the caps for the valve adjustment? Is this similar to your last response where i need to make sure that im on the compression stroke and THEN manually fix the cam? (if that's the right word for it)

:umm:
 
Yes, you'll see big round caps on the rocker cover for doing the valve lash adjustments, I think a 17mm hex head. Intake on the carb side and exhaust on the front. I'd suggest searching a YouTube video of a four stroke engine animation to see how the valves open and close during the firing cycle to better understand what you'll be watching for.
 
Hey guys, I'm back after a month or so as I was on vacation in pakistan!

out there my uncle introduced me to a buddy of his who helped honda solve an issue on the Asian models of their 125cc bikes where they would randomly shutoff, point being, the dude knew his stuff.

I showed him my bike and explained to him the endless fires ive been putting out and how im currently working on the camshaft and figuring out why its 180 degree out of place and he explained to me that thats most likely not the issue. He said that if 1 plug is sparking and the bike is running and able to start then your engine is fine, its the electrical that needs to be investigated.

He mentioned a TCI box which @tstidham also mentioned earlier on this thread.

My question is, where/what does this box look like and how can i begin debugging?

cheers!
 
Hey friend, glad you're back at it!

I'm betting you don't have a TCI module--if you do, it's a black box mounted on the underside of your battery box.
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CDI (capacitor-discharge ignition) is what your bike came with, not TCI (transistor-controlled ignition). These were introduced in the 80s, so your bike probably doesn't have one to find.

The XS-Charge module you have IS the TCI in your case--you can see the transistors mounted on the round plate. It's just a different shape.

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Instead of running the wires to a separate box for processing, it does it all in-house. The Yamaha TCIs have chunky old 80's electronics inside; the XS-Charge has neat, small, modern components and connects directly to the coil wires.

As far as troubleshooting, make sure that you're wired up correctly. The Install Guide says your black wires should go to ground, and each board is responsible for one cylinder. Red wires to coil power, and a green each goes bottom board-LH coil, top board-RH coil.

Have you done a continuity test between each end of the reds and greens? It's possible there's a problem with the wire itself, or only one of the boards has gone bad, or something similar.
 
Well, you do want the petcock to be able to shut off. My original vacuum petcock also went bad, but to be expected for 40+ year old seals. I tried a rebuild kit on it but it didn't work as there was some pitting in the metal inside thus I changed to a full manual petcock with off/on/reserve switching.
You also need the floats to be able to close off fuel entering the carbs or you could be running rich at the lower rpms and idle as fuel overfills the bowls. I bought new needles and seats and very carefully set the float levels to 26mm measured from the bowl gasket surface to the top most part of the float while holding the carbs upside down. You gently bend the needle tang on the float to adjust height. I also made sure each side of the float was 26mm by twisting them gently. I know it sucks to pull them back off, but dumping that much fuel is no good for the engine as it can wash the oil from the cylinders leading to excess ring wear or make it's way into the oil via the crankcase vent tube in the air filter boot, diluting the oil and then causing main and rod bearing wear.
hi fella just been reading your notes,welcome to the xs forum.captain chrome was my guide when I started dabbling with the carbs and helped me lots.ive sent u a couple of items to read and might help you.
 

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