1981 Yamaha XJ650 Maxim

[Brandon12V]

Hey fellas. Trying to finish up the first stage of my build. I converted it from a bobber to a cafe/streetfighter. Still has a long way to go cosmetically but Im in need of fixing a tuning issue at the moment. Before I started the build the bike ran lean due to drag pipes and pods on stock jets(PO was an idiot). I had the carbs cleaned, and went up a couple of sizes on the pilots and mains. added reverse cone mufflers for back pressure and replaced the carb joints with new OEM. My buddy sync'd as close as possible but there's an issue with fueling that seems more intense than just the carbs being out of tune. Cylinder 1 started to misfire. after doing a continuity check, there was none post plug cap. i replaced all the caps with rajah ends. after that, cyl 2 started to misfire and is currently spitting unburnt fuel out of the header pipe. I replaced the plugs as the old ones were washed out. the issue remains even with open headers and baffles tack welded in right after the h-pipe collector. Could the be an valve adjustment issue? too rich? cyl 2 was firing prior when cyl 1 was misfiring. coil output low? I have not checked resistance on the coil. any direction is appreciated. I don't want to start throwing parts at it. Thanks in advance.

-Brandon

 

[Brandon12V]

bike in question

 

[Bozz]

more info would be helpful, like a compression check to rule out valve issues.

Are you sure you have spark where and when you should?

I know those use paired coils/wasted spark, so a truly failed coil should result in 2 cylinders loosing spark.

Check plug wires/caps/plugs.

What you currently describe sounds like electrical issues, but your description of "wet plugs" sounds like you may have gone too rich in your jets as well.

These can be tricky to diagnose long distance, as you have 3 systems converging, carbs, ignition and compression.

More info will yield much more helpful information!

 

[RoadRash]

Finally, another Maxim cafe owner, here.

If you go to xjbikes.com forums, they can be of great assistance to you, there, since it is a Maxim/SECA-specific site. First thing they are gonna ask you is "Did you check your valve clearances?", I guarantee it. If you haven't, then they are gonna advise you go off and do that, first. Second, if you haven't already done away with the pods, many there are gonna tell you to dump them on a CV carb'd bike like ours. Even though I am a fellow XJ owner, your issue is not one that I have personally run into.

Please keep us posted on your progress. I'm very interested on how you fair.

 

[Brandon12V]

thanks for the advice guys. first thing I'll do is change the oil to see if theres is excessive gas from wash out on cyl 1 and/or 2. then ill check resistance on the coils and check compression. if the oil smells potent of of gas then I'll do a leak down but I have a feeling dry test is all that's necessary. what I don't understand is why they would go out in that order unless both coils are indeed "bad". I would assume 1&4 to go out since they are the in the same bank or the same with 2&3.
Roadrash, do you have specs(cold) on lash/clearance for the valves?

 

[Brandon12V]

I'm happy to join the site btw! There are some very impressive builders here that deserve more recognition. Hope to soak up all I can as this certainly won't be my last build. Although, I would rather not fuck with 4 cylinders on the next few. Cheers

 

[Bozz]

fwiw, I have seen float/needle valve issues show up as fowled plugs in 1 and/or 2.

With the bike on the side stand the fuel can potentially flow into the cylinder and flood the system.

Like I said, it is hard to know for sure.

Be systematic and logical. Check compression, then check spark, then double check your carbs.

If you have questions as you go, just ask.

Cheers!

 

[RoadRash]

Yup. Here ya go, Brandon:

 

[Brandon12V]

thank ya sir

 

[RoadRash]

My pleasure to help out a fellow XJ'er!

 

[Brandon12V]

Just an update(a year later,lol).. The bike is running pretty optimal now. I put the air box back on and had my buddy sync the carbs on vacuum. Went up a size on pilots and mains. It still leans out a little up top so I may go up one more size. It can't keep idle for shit and I can track down a vacuum leak of any kind. Compression is STRONG tho! Numbers were solid after a leak down. Seat is being upholstered, changing out the pipes for Lossa's. Just received new pegs and putting in a new starter button. More to come.