Spark plugs are burning

I have the opposite problem of plugs that burn white, almost melting the electrodes within a 100 miles on my XJ 550. My main jet size is 211 which is HUGE for my bike (spec. is 112.5), so it should be burning rich. Any ideas ?

 

um... Stop riding NOW!

Need a TON of info here. What bike, what mods?

 

Massive vacuum leak, valves way out of spec, or carbs WAY not set up correctly. One or more of these are possibilities.

All we know is that it's a 550.

History, your history with the bike, mileage on it, MODS to intake and/or exhaust?

What plugs are you running?

And I agree you need to stop riding it before you hole a piston.

 

There haven't been any MODS, it only has 7500 miles, i just recently bought it. The oil was really dirty, so the previous owner didn't care about maintenance. All the intake valves and exhaust valve have ZERO clearance, but why would that cause the plugs to burn ? I hope I didn't buy a lemon

 

What you bought is a motor on the verge of self-destructing.

Get the valves in spec, PRONTO! You're burning more than plugs, you're about to burn up the motor.

Get the valves in spec; then do a compression test and let's hope it's not too late. If you know the valves have zero clearance you shouldn't be running the motor.

 

Running tight valves is a bad thing.

Make sure you have the correct spark plug too. The wrong plug may run way too hot.

 

STOP EVERYTHING!

Now start here: New bike checklist:http://xjbikes.com/Forums/viewtopic/t=43470.html

You got a choice to make right now... get her 100% right, or start sourcing a new engine. NO WAY AROUND IT, hopefully you haven't burnt a valve

 

I replaced all the valve shims which was no easy feat. I'm just a backyard mechanic. Took it for a spin and it takes off like a rocket at 7000 rpm. runs great, even idles now, but the plugs are still too hot. I'm using NKG D8EA plugs. and my bike is a 1981 XJ 550. What would be a colder Plug ? Thanks for the Info. so far, there might be hope in salvaging this buyer beware nightmare

 

It's only a "buyer beware nightmare" if you don't quickly come to the realization that it's like any other maintenance-neglected 30+ year old bike; and you have a lot of work to do.

If you thought that you could just jump on and start riding it, then you were horribly mistaken. It's not an old car; this is a vastly different situation.

Those are the correct plugs for the 550. It's probably running way lean. Now that the valves are in spec you need to do a basic carb service, wet-set the float levels and do a running vacuum sync, with YICS blocked.

Then get after rebuilding the brakes (completely.) READ: http://xjbikes.com/Forums/viewtopic/t=15874.html

 

Search for "The whole nine yards" and "in the church of clean" for carb cleaning info. NO SHORTCUTS. You won't be pleased with the results if you cut corners.

EDITED POST - Sorry Fitz!

 

No, what Fitz meant was indeed start with a "basic carb service." Mikuni throttle shaft seals seem to hold up better than in "those other" carbs.

With only 7500 miles on it, he may very well be able to get by with a basic "field strip, clean and service" as outlined in the Clymer and factory service manuals. But that much, at the very least, needs to be done. And it will entail replacing some parts for sure; like the pilot screw o-rings and the o-rings on the outside of the float valve seats.

Wet-setting floats is critical on the Mik's with only a +/- 1mm spec.

The need to tear into them further (breaking the rack) has yet to be determined.

 

Thanks for the info. The bike was in a garage for 20 years and still looks like new, so I assumed the internal parts were also "like new". I bought it for $1750 and come to find out no valve clearance ! I woulda, coulda, shoulda done a compression check but it looked so new and i'm a couch potato. I'll check her out from top to bottom, especially the brakes. Thanks again

 

Hey there! I like my Hitachis.

Sorry, off topic.

 

You should still do a compression test to be sure nothing's been damaged.

You said all the valves were dead tight; what shim-size jumps did you have to make to get them in spec?

What are the clearances now? (Cylinders are numbered 1-4 L-R as you sit on the bike.)

With the valves in spec, the next step would be a compression test to ensure you're not fighting a losing battle, then dig into the carbs.

YOU NEED A SERVICE MANUAL if you don't already have one; the Clymer is good, factory book better, and the best is to have both (plus this site of course.) There is a lot of work you'll need the book for; you didn't buy a "lemon" you bought a 30-year old motorcycle.

How successful you are going to be in resurrecting it will depend entirely upon you. We're here to help.