Spark issues

Maintenance, repair, troubleshooting, etc.
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Magnus
New to XJR
New to XJR
Posts: 9
Joined: Fri Aug 18, 2017 10:40 am
Region or State: Sweden
Motorcycles Owned Currently: 1984 Yamaha XJ 600 51J
Sweden

Thu Sep 07, 2017 11:28 am

Hello!

This relates to my 1984 XJ 600.

This morning it was finally decent weather again so i thought i'd ride into work. However, when i started up the bike it ran very rough and it didn't want to run off the choke and it wouldn't rev more than 4-5k. So i abandoned and took the car (bleh).

Now after work i did some trouble shooting and realised that #4 wasn't firing at all. I took out the spark plug and it was fairly black. Cleaned it and put it back in. Now it started to fire again but on a short test run it didn't want to rev more than 6k.

Since it's been raining for quite a few days i figured maybe the problem really is the hi voltage leads getting moist. The bike is parked in cover but outside. So I took of the cap from the wire and on a hunch I cut off 5-6mm from the end of the lead and screwed the cap back on. This helped and it started running pretty well again. Now it runs perfect at high and mid revs but i get a very intermittent missfire on the right side (probably #4) on low revs, like below 4k. It's hardly noticable when riding but i can clearly hear it if i listen close to the muffler.

So since i know very little about motorcycle electrics i wanted to ask you guys what you think. My plan atm is to change the spark plugs since i have no idea how old they are and also change out the hi voltage leads from the caps to the coils. I figure if trimming off a bit of the lead to the cap seemed to fix most of the problem maybe the leads are really old and needs replacing? It's difficult to tell or know if they are still the original 33 year old leads the came with the bike, if so the rubber covering could be crap by now?

I hope this made sense, english isn't my first language so finding the correct technical words isn't that easy. :)

Now i'm gonna get a beer!

Cheers,
Magnus

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kiwi5000
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Posts: 10
Joined: Sat Jul 01, 2017 8:21 pm
Region or State: TN
Motorcycles Owned Currently: 1986 Yamaha Radian FJ
United States of America

Fri Sep 08, 2017 7:00 am

Magnus - Totally made sense. Once you get the new plugs in let us know how it idles. Is number four plug wet or dry? Try swapping the lead wires from one and four to see if it makes a difference.
It's been a rough day. I got up this morning put on a shirt the button fell off. Picked up my briefcase the handle came off. I'm afraid to go the bathroom.

User avatar
Magnus
New to XJR
New to XJR
Posts: 9
Joined: Fri Aug 18, 2017 10:40 am
Region or State: Sweden
Motorcycles Owned Currently: 1984 Yamaha XJ 600 51J
Sweden

Sat Sep 09, 2017 6:52 am

Hi again, thanks for the reply kiwi5000. :)

I've now changed the plugs. The bike is running pretty good at the moment but it is a bit rough on lower revs. I'm suspecting that the intake manifolds might be the reason for this. They are old and have some visible cracks.

The old plugs revealed an interesting pattern. The two plugs to the left in the image is number 1 and 2 and on the right 3 and 4. 3 and 4 both are very black with soot. Is this an indication that they might be getting a bit too rich fuel mix compared to 1 and 2, that's my guess at least.

Image

Cheers,
Magnus

User avatar
Magnus
New to XJR
New to XJR
Posts: 9
Joined: Fri Aug 18, 2017 10:40 am
Region or State: Sweden
Motorcycles Owned Currently: 1984 Yamaha XJ 600 51J
Sweden

Wed Sep 13, 2017 5:45 am

An update.

So after riding for a few days in horrible rain conditions and giving it a proper wash as well, I conclude that my XJ has no problem with moisture. I now think that the spark plug was the problem. The reason the spark plug developed a problem i'm guessing is due to #3 and #4 getting too much fuel. On the list of things to fix with the bike during the winter I've got cleaning the carbs, fixing the intake manifolds and balancing the carbs. That should fix it i hope. :)

Cheers,
Magnus

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kiwi5000
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Posts: 10
Joined: Sat Jul 01, 2017 8:21 pm
Region or State: TN
Motorcycles Owned Currently: 1986 Yamaha Radian FJ
United States of America

Wed Sep 13, 2017 11:12 am

Awesome to hear! A little advice on the carbs. Take them completely apart if you can or take them somewhere that can. I assume you have a repair manual. Take it from me, you want every little thing inspected and in spec with every jet and orifice clean. Good luck!
It's been a rough day. I got up this morning put on a shirt the button fell off. Picked up my briefcase the handle came off. I'm afraid to go the bathroom.

User avatar
Magnus
New to XJR
New to XJR
Posts: 9
Joined: Fri Aug 18, 2017 10:40 am
Region or State: Sweden
Motorcycles Owned Currently: 1984 Yamaha XJ 600 51J
Sweden

Wed Sep 13, 2017 12:56 pm

Thanks will do. I'm going to try it myself with help from the service manual and youtube i think. What could possibly go wrong. :)

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