Need help from all the xs400 maxim owners out there.

I have been trying to resurrect an 82 xs400 maxim dohc now for a few months, had been treated terribly by previous owner and I felt bad for it, not run in years, guy told me he tried to start it and a friend tore apart the carbs, ran better and they parked it again. I do not trust him or his friend so I bought another set of carbs that appeared unmolested, cleaned and blew out everything ( I thought) put it together and it runs like crap. Pipes were glowing red so I think it is running lean and the problem may still be in the carbs, I am also feeding the carbs with a small tube and a funnel to pour gas in since the tank is off. Runs at idle and revs up but often it kind of sticks in a high rpm and does not come down quickly. I have not done anything else to engine except a lot of cleaning and changed the oil. Could it be valves, timing or carbs ? (Wouldn't be the first time a had redo the carbs, second or third time is a charm) Does not feel like it is running at full power, revs up very high and will idle just doesn't sound or smell right?

Are these twin cylinders running together (firing at the the same time) or are they alternating ?

 

The symptom you are describing is most likely carburetors.

Timing is fixed unless you have a wiring rproblem that is most likely not the cause.

If I remember correctly, the "XJ" XS's use Mikuni carbs like the 550s. Syncronization is important, as is CLEANLINESS. The slides have to go "clunk." Search this site for "clunk test." Check and adjust float levels, and do a "bench sync." (Much easier than the fours but the same principle.)

Valves very well could (and probably do) need attention. They are adjusted via shims on top of the cam follower buckets, directly below the camshafts. While most likely NOT at heart of the problem you are having right now, you won't be able to EFFECTIVELY fine-tune the carbs if you have a couple of seriously tight valves.

The pistons in your motor don't rise and fall together, they are on a "true" crank (one up/one down) and they fire alternately as well.

 

Thank You, that is what I thought, If the cylinders are alternately firing, would it make sense in the rough state it is in now that It would feel at the exhaust pipes that they were firing at the same time (Is there a cross tie in the cylinders or in the exhaust itself that would cause it to feel like they were firing together) in other words if the one cylinder was not getting gas at all or the timing was off would both mufflers be "putting" in sync ? It runs like it is only hitting on 1 cylinder but the exhaust pipes were both putting out exhaust gas at the same time ?

 

There is a cross member for the exhaust just behind the engine, so you will feel every exhaust stroke out of both mufflers.

 

Your timing isn't off. You may have a misfire however. Your problem sounds like carburetors, these bikes have CV carbs and they are the most sensitive part of the whole equation. Second most common cause of problems is electrical CONNECTIONS, at the battery, the starter relay, everywhere. They like to turn green; your fusebox likes to disintegrate for NO apparent reason.

Actually, I lied. Those are the second and third most common causes of problems; first place goes to all the neglectful PREVIOUS OWNERS.

You are going to have to be methodical if you want to get this bike running right again. Pull the plugs, let's have a look and see what you have; you can't guess by putting your hand over the exhaust pipe. Check for fuel; check for spark. Make sure your air filter isn't plugged. Put the petcock on "PRI." Be sure the battery is fully charged. Lots of things to check.

You really ought to find a manual too.

 

Sounds like carbs, but don't ignore the wiring either....
A loose ground can also cause issues, and fry your reg/rect unit
(ask me how I know)
Replace that fuse panel as well, they can also cause grief....

I cleaned my carbs a few times after I got it to get it running, it had sat in a basement for 7 years with gas in the tank and carbs, so don't give up on her.. they are a fun bike ...

Click the www button under my sig for my rebuild page

 

Thanks for all the help, I will definitely start with the carbs again and go from there. I did just by a manual that is very helpful, but does not have the typical symptoms and cure section, the help from these forums is unbeatable. I have had many Yamaha's and currently have a 79 xs1100 special my dad bought brand new, I bought the 400 so I don't have to ride the monster every day. I hope it is a fun bike.

I have checked that both cylinders were getting spark, and that appeared good, I think one exhaust pipe was glowing but both were hot , Should I pay more attention to the side that was glowing or the other ? Would this condition having run for a few minutes have damaged anything in the cylinders or valves ?

Does anyone have a set of upper fork tubes for this thing, are any other tubes from another bike interchangeable ??

If the fork tubes are already out of the tree, how do you hold onto the top to keep it from spinning to remove the cylinder securing bolt (20) ?

 

I put mine back in the tree and secure it at the top . worked great on both tubes. I also used a small diameter wrench and a screw from the fender put it in the fender bolt hole and used the wrench as leverage to break loose the hex head at the bottom of the tubes.

BTW the tubes will take aprox 9.5 oz of 10 w 30 for each fork . according to the service manual