83 Xs400k Maxim troubles

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JackWolf

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Hey, all. I've been going through and fixing up an 83 maxim for the last month or so. And although I've gotten through some of it, I still have a couple kinks to work out that I'm not quite sure how to solve. So here goes.

As of a few nights ago I was out riding the bike around when I had a sudden loss of power. When I pulled over to the curb to start it up again the engine just wouldn't turn over. I called in a friend who brought over new spark plugs (he had the exact ones I needed) and after a swap I was good as new. However, this morning when I was getting ready to go for a ride, I put it in gear, got about halfway down the street and the same thing happened, I couldn't get the bike to turn back on. I checked the plugs and they're still clean, I parked it for an hour or two, came back and it started up fine! I let it warm up for twice as long and it still happened again. I'm kind of at a loss as to what the issue is. I have no idea if it's electrical or air/carb related. I've got no header or vacuum leaks and I still have a solid spark. The bike will turn on if I let it sit for a bit but as soon as I start riding it around it dies and doesn't want to start back up. Any ideas?
 
sounds to me like possible coil problem once the coils start to warm up from the heat of the engine rising the coils shit the bed if i was u i would ohm read both coils well cold then ohm read both coils when the bike warms up and shuts off that should tell u if it is a coil problem u could allso try bringing an extra spark plug and just use that to check for spark when the bike dies let us know what ya find
 
In addition to what @danalpatt suggested, the TCI Module could be failing. Or the gas cap not venting and starving the engine for fuel.

Be very careful when working with the ignition system! The 30+ year old TCI modules can be fragile, both physically and electrically. Getting shocked by the ignition is nothing compared to finding and buying a good replacement TCI module. DAMHIK.
 
Where would I find a good replacement TCI module? I've been looking around and so far I've got nothing. As far as coils go, I still have spark even after the bike dies. I rode it around for all of five minutes after letting it warm up and it still dies and won't turn back on. Slowly starting to hate myself for buying a bike I knew nothing about lol
 
I pull the plugs out, plug them back into the wire, hold them against the cylinder head and crank it. I have spark on both sides yet the bike still refuses to turn on after its been warmed up. Any other potential causes, here?
 
It takes 4 things to get an engine to run: Air, Fuel, Compression, and Ignition. Air is a given and you appear to have ignition. So that leaves fuel and compression. Since you can get it to run cold, compression is probably ok, though if the valves are too tight they may cause issues once warmed up. So, how is the fuel supply? Have you checked the gas cap? The fuel filters?
 
I have experienced the same sort of problem on 1982 XS400RJ Seca (same engine?). Root cause was bad floats in carburetor + still open petcock. Symptoms: run fine for a while then while riding loss of power, more throttle bogs the engine, eventually stops. Try to restart... nothing, cranks, spark, but no go. Wait awhile - starts. Sometimes after prolonged cranking then when runs stumbles and if given throttle dies. After a minute or so of stumbling along runs better then rideable again. Other times the hour or two wait clears things up. Excess fuel in intake system... If this has happened a few times can even see/smell the gas when you drain the oil. I blamed the electrical first but after watching good spark knew I had to look elsewhere. good luck
 
Holy wow, that sounds like my issue exactly, I'll yank the carbs and check the floats tonight and see if I can grab some new ones online, awesome!!
 
I hope this solves your problem. I don't know how the Maxim is laid out, but "yanking the carbs" on the Seca is a pain. The best technique I've come up with is removing the top motor mounts and letting the engine pivot forward. Its a struggle to get the carbs in and out (if you use the boots) from the side. I wouldn't doubt its one of the big reasons people go to pods. Again, good luck.
 
MAG-XS400RJ said:
I hope this solves your problem. I don't know how the Maxim is laid out, but "yanking the carbs" on the Seca is a pain. The best technique I've come up with is removing the top motor mounts and letting the engine pivot forward. Its a struggle to get the carbs in and out (if you use the boots) from the side. I wouldn't doubt its one of the big reasons people go to pods. Again, good luck.
Click to expand...
ya my 84 maxim carbs r a huge pain to pull
 
I haven't gotten to taking the carbs off yet but I'll definitely give that method a shot, for sure. If anything I should have them off the bike at least by tomorrow. Ordering new floats regardless of the condition of the old ones, might as well. In the meantime I'll give them a good cleaning and try bending the tabs on the old floats to see if I can get less fuel through the system.
 
I take masochistic pleasure in doing the same task over and over again, so, yes? Also I don't even know if a manual exists for the Xs400k, can't find it anywhere. If I can find it, I'll check for proper float heights and adjust accordingly.
 
It turns out I'm an idiot and I didn't check my airbox and this was the problem all along. That's what I get for buying a bike I knew nothing about at all. Always check your airbox!
received_10205652373827313.jpeg
 
Looked like a mouse made its home in my airbox I think. Couldn't tell, I just cleaned out as much as I could at the time. I'll give it a proper cleaning tomorrow.
 

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