Finally riding my XS400, but still not ready for the road?!?

[markjs]

So I got the tires on, everything back together and all that is keeping me from licensing it is that it seems to lose the right cylinder around 3K to 4K RPMs. I've tried it with and without the air filter (dirty but still functional till I get her on the road), and it seems worse with the air filter out, but not much, almost the same. Now I do know there have been some issues with the forward motion switch and she almost stranded me a ways from home but it seemed to work itself out. Gonna just jumper that thing.

In any case, I know the carbs should not be the issue. I fully disassembled them, cleaned the jets in carb cleaner, boiled them in vinegar (some very nasty stuff came out), inspected the diaphragms, all that is fine. I'm gonna compression test tomorrow but it sounds very smooth and I suspect it isn't sparking great. The thing sat in the weather for like 12 years. Any particular trouble spots I should look into? Got a can of power lube and tomorrow I aim to start checking electrical, but any pointers would be helpful!

 

[bcware]

Forward motion switch?

What is the year? Do you have points ignition?

 

[markjs]

It's an 83, so I'd guess it's electronic. There has been a lot of places water has gotten in, I guess it's possible the advance is sticking if it has one of the centrifugal kind. Another thing that makes me suspect electrical is that when I started the headlight did not work but after just a bit of running and a small squirt of power lube it now works.

 

[bcware]

Test the coils and plug caps for resistance to see if they are out of spec.

Even if the springs on the centrifugal advance are worn out I would think the bike would still fire; it might run poorly, but I doubt you'd lose a side entirely. And anyway, wouldn't the advancer affect both sides? Why aren't you losing both?

What plugs are you using? Are they new? Did you check the gap? How do the plugs look in terms of color?

Does the problem cylinder run at high rpms (say, above 6k) or only below 3 or 4k?

 

[markjs]

OK, I noticed some things...

I think it may be the plugs; everything seems to work fine at low RPM but dies out actually around 3K. You can't get it to the upper RPMs at all. I swapped the spark plug though and it seemes like the opposite cylinder is doing this, so I suspect the plugs and am off to get some new ones, though if it is the plugs it's the first time I've seen a plug partially work like this. In my experience they've worked or not.

The coils are actually tucked up into the backbone and the shop manual assumes you know how to take them out (there is very little in it about how anything on the bike comes apart), and I am clueless on the coils thus far. I may be able to test them by wire, but gonna pop some new plugs in first since that's a cheap fix and needs done anyway.

Lastly, there was a lot of water in the oil. Not sure how it got there but there was enough that the oil came out foamy, but the new oil also is foamy so it's gonna have to be changed again. I imagine that water could interfere with the ignition units on the end of the crank, producing a somewhat weakened spark? I was unable to get an oil filter locally, that's gonna have to be ordered, so for now I am just gonna have to keep running oil though it.

 

[bcware]

The water in the oil probably won't affect your electrics, just your lubricity. Are you sure you're not over-filling the oil? If the oil level is too high the crank will start making espresso foam out of the oil; foamy oil won't flow to the top end and probably won't allow for good compression.

Definitely get that oil situation sorted before trying to run the bike again. If you have to, let it drain for a few days.

 

[markjs]

No it was water, condensation. remember the bike sat for 12 years. I put new plugs in it and still seems to be missing a cylinder. Tried to borrow a compression tester but the guy wasn't home. I guess I'm starting to despair this might need more work than just the carbs. If the head has to come off, the project gets shitcanned and I part it out to you guys I guess. If I can't get a cheap bike out of it easily it's not worth it to me to get deeper into a project I am not prepared to tackle.

 

[markjs]

One more possible thing I'd forgotten though...

Can it be that I'm using a gravity feed tank? The bike's tank had holes and leaked and the only tank I have is a gravity feed one from an old Honda. I am patching the tank with Marine Tex epoxy but I want to let that cure well before I pot gas in it.

 

[markjs]

OK, here's a weird one; I got the new plugs and I left them in and I fired it up on one cylinder with the right side spark plug wire with the old plug in it up against the block. Just what I suspected for some reason, the spark is fine till you rev the engine then the spark disappears entirely until it's back around 2500RPM or less. This is on the right cylinder. Has anyone seen this? Does it mean my spark unit is faulty?

 

[16VGTIDave]

Could be a bad coil. Have you tested the caps on the ends of the sparkplug wires? The TCI modules are known to be problematic, and they are a PITA to take apart, but usually they just fail. Time to do some electrical testing...

 

[markjs]

How do you test caps? I suspect you may be right, that it's a coil issue but they are way up in there and it's a project for tomorrow I suppose.

No way to test the spark box itself is there? I'm suspecting coil since it's just one side though, plus a quick look inside the spark box showed no discoloration or corrosion inside it.

 

[16VGTIDave]

You need to unscrew the cap from the plug wire and measure the resistance with an Ohm meter or Multi-meter. The specs and instructions should be in the manual. You could also just try swapping them from one side to the other and see if the problem follows the cap.

You should be able to disconnect the coil wiring without removing the coils, and test them in the bike. That said, it may be faster to just remove them.

 

[bcware]

Yes, you may as well unscrew both spark plug caps and clip off a bit of the coil wire for a fresh connection.

I am pretty sure the stock cap should be about 5,000 ohms of resistance. I replaced my old ones with new 5k ohm caps and it works great. Other members have used a lower resistance cap with a 5k ohm spark plug.

 

[markjs]

OK, I am new to using a multimeter for resistance anyway, so I hope I'm doing it right, but one reads 10.x on the 20K setting the other never registers anything (just reads "1"), so that can't be good?!?

 

[16VGTIDave]

Time to get new caps! Most motorcycle shops have them, or order online and wait.

 

[markjs]

Sure beats new coils if that fixes it! I am so broke today I will be cannibalizing a friend's dead Honda, but I know his should be fine (will test of course), until I can get a couple new ones.

 

[markjs]

Well the project is all for naught, a complete waste of my time, energy and money on a total waste of a POS bike. Really sucks for me because I desperately needed cheaper transportation and now I'm SOL, with no hope or prospects.

Turns out it's the spark box, which puts the project financially out of reach for me. Even if I could afford one, there's no waty to test them and since I can't afford it even if you could, it's a waste of time trying. Sucks because I really needed this bad and was so excited,and now I am completely screwed.

So anyone wants a junker Maxim or parts, it's all on the chopping block. Sooner this POS is out of my life the sooner I can start looking for another derelict to try and get running. Hopefully this time a Honda because at least I can get parts for those and it's a bit more affordable. In fact I'd rather trade it for a mid sized Honda project if anyone has one The way things are going I'll probably have to pay to get this thing hauled.

 

[markjs]

Just looked you can't even get one new, and an aftermarket would cost me more than another project bike. Man this is a very bad day for me!

 

[markjs]

I mean I am assuming it is the spark box; what else could it be? I actually removed and replaced the coils and they both tested identically, so I swapped them and I still have the same problem, at 2500RPM spark completely drops on the right side, so I ccan't figure what else it could be, but then maybe there is something I am unaware of?!?

I guess I am wondering about the kickstand relay and starter cutout relay, plus the last owner did some weird wiring of some lights. Man am I frustrated, maybe I will be thinking clearer tomorrow, and hopefully one of you has some good advice...

 

[16VGTIDave]

Wow. Way to blame the bike for your short comings. You admit to jumping to the conclusion that it is the TCI module that has failed, and you have the nerve to call the bike a POS?

I understand your frustration, a bit. What I don't understand is why you are insulting us and your bike.

It appears that you now have 2 options. You can give up, cut your losses and sell the bike. Or you can take a deep breath, lift your chin, and decide that you will get the bike running and that it will be what you need it to be. And probably more.

Your choice.