only running on two cylinders

i have a 1981 xj650 it is only firing on the right side 2 cylinders when sitin on the bike. and the other to are not geting spark. yesterday it was running just fine. theres a little rectangle rubber box in my head light that got melted. could that be the cause? i think its called a diode box

 

That's odd- - do both running cylinder plug wires go to the same coil??
because they should not, and if each coil is firing, it should be firing on all 4.
Have you put all 4 reasonably clean plugs up on the valve cover (to ground them) and crank the motor, to see all 4 spark at the same time??
Do you have a fully charged battery?
Have you checked and cleaned your basic ignition connections for corrosion?

 

yeah im not geting any spark out of that side of the bike got all new plugs and that didnt change it either. i have to new batterys one outa my other bike and thats not the prob. i might have to do some cleanin. the po didnt take very good care of this bike. who know it might only be firing on one cylinder. im just confused. i hate electrical

 

sitting on the bike, from left to right, the cylinders are 1,2,3,4

1 and 4 should run off one coil, 2 and 3 off the other.

you should get ~11kOhms between the spark plug wires between 1&4 and 2&3.

might wanna try swapping the wires between 1&4 and or 2&3 to see if the problem migrates or stays put. that'll tell you if it's ignition related or not. . .

i don't know much about the diode box, but if it's running on 3 and 4, then i would assume that's not the problem.

how did the old plugs look?

 

ill try swapping wires. im just confused on how im geting fire on 3 qnd 4 but not one and two. cause of how the coils run.

 

i was thinking maybe the wires for 1 and 2 are bad - it's probly not that easy, but it would be nice if it was . . .

 

im hoping its gonna be something simple like that.

 

That is kinda my problem. I am getting fouled up on 1 and 2. Very dark, rich looking plugs and runs really funky. My wires are in the right spots though. One coil for 1 and 4 and the other for 2 and 3. I can't see it being a timing issue or a valve or exhaust issue. There is something really wierd about that. I had read briefly somewhere on this sit that the carbs share some kind of vent with eachother. 1 and 2 then 3 and 4. I talked to a bike mechanic today who said a blocked vent can cause the symptoms I am having and they sound very similar to yours. Kinda wierd.

 

yeah i am very confused cause i just got my carbs bak from cleaning. so im very stumped cause just 2 days ago it was running great and now this mind boggling deal

 

Yeah mine are clean as a whistle. But there are mechanics that look at you like you are retarded when you ask them about the YICS eliminator tool. So if mine is nothing but a carb sync issue, i'll post the results here right away and pm you. I am hoping that is what it is. Then you might have the same problem where one side isn't synced with the other and you are getting flooded on one side. I mean, my bike will be fine in the morning, run fine for a few minutes on the road, then I get the 2 cylinder thing happening.
With mine, though, if I open it up a couple of time til I get a clean rev, it'll run normal again for a bit then go back to the funkiness. And when I get out and really open the throttle up, I am running smooth again.
#1 and #2 plugs are showing just horribly rich condition. So there is way too much fuel to air on that side. The other side is showing rich, but more of a typical black on the plugs. Running rich is common. But new plugs shouldn't have an almost measurable coat of black soot on them in just a few minutes.
Keep digging and I'll do the same. I'll bet our problems are either exactly the same or very similar. I am taking mine back to redline friday so I may have a definite answer then.

 

what is this "vent" you speak of between carb 1&2 and 3&4?

 

I found out that the "vents" as they were referred to are actually the YICS chamber ports. Disregard the vent thing. Didn't really make sense to me either because i went through I don't know how many carb diagrams and didn't see anything about vents.
I am wondering this... I have weaker spark than I should on my bike. Its still blue but not a nice fat solid blue. I just balanced the carbs. They were just a tad off balance from the 1 +2 pair and the 3 and 4 pair. With weaker spark I am thinking (hoping I am right) that the slight but noticeable unbalance between the two sides shows up more. I am running richer than spec and don't often ride like a psycho so I balanced the carbs as perfect as the merc sticks would show and switched to a hotter plug (NGK D7ES instead of D8ES) and so far the bike is running really good again with my low/mid range throttle response back to normal, low end and idle perfect. I am affraid to really get into the top end for now with the hotter plugs but so far so good. It is too cold right now but i am going to do some higher end plug chops later on and see where I am at. I am hitting on all 4 right now with what I have but still rich. But now I am rich across the board which is better than an uneven thing like before.
So far the rings are doing good and I don't seem to have any blow-by. The hotter plugs are burning off the deposites way better and the plugs aren't fouling up. Just a slight blackness but otherwise a light brown or tan. The black is only around the edge og the threaded part but they seem to be good.
If when I go romp on it for a bit and check the plugs and everything is looking good, i am going to keep using the hotter plugs and keep it rich. If I ping AT ALL then I am going back to colder and will be here to ask wild carb tuning questions if I can't find the answers in a search.
My carbs are modded now so it might be harder to tune them right.

 

Oops... posted this on a different thread by accident. But these are my results and, for now, my solution to my wierd problem similar to the original post on this thread. After regapping to .25 (was .28 which is max gap according to the manual) I am getting a nice color on the plugs. Very clean with a light tan shade on the electrodes. Base and insulator are clean as new still after the plug tests and checks and about 20 miles riding.

Total success. I am running the hotter plugs. I tried a .28 gap which was too much so went to 25/26, ran the bike in the power band mostly, plug chop, tan color. The vacuum is in tact and operating again. Did a couple more chops to be sure and we have tan. I think that is the first tan plugs I have ever seen on that bike! haha. Throttle response was excellent, power was perfect, running at idle VERY smooth. Actually smoother than ever. I think i found the solution, at least to my problem. And I let the plugs get hot enough to where if I was going to ping it probably would have. So I am happy.