Title: Help with diagnosis s.v.p.
Description: 83 XJ650 "missing"
Description: 83 XJ650 "missing"
Jim W - July 9, 2005 03:09 PM (GMT)
The bike seems like it's missing up to around 6000 rpm, when suddenly everything becomes wonderful and it pulls away smartly and sounds great. Below that, it feels like it's running on three cylinders, perhaps. Not smooth.
Got the bike recently so don't know its previous history except that it did run well when I test drove it just before buying.
Since I've had it:
1. I inadvertently doubled the amount of oil, and then drained it and refilled with new and changed the filter. It has not run well since.
2. I had it tipped over far enough to weld a new kickstand bracket to the frame i.e. a little bit "belly-up", and wonder if this could have caused oil or gas to end up where it shouldn't have.
3. I took off the carbs for cleaning, but did not go too deep into them. One air jet was blocked (pilot if I remember well; it was a #42), and one main fuel jet snapped when I went to reinstall it. This led to my replacing all four main fuel jets while I was at it (with size 112.5).
4. I put some Marvel Mystery oil in the gas hoping it might clean up the carbs but no noticable change so far, albeit I have only driven about 80 kms since doing so.
5. The other day after it was running rough I took out the plugs and while three of them looked just about right, a nice tan-grey colour, the #1 plug was noticably blacker, and a bit oily around the bottom of the threaded part. Wondering if it was as simple as just a bad plug, I reinstalled them but swapped plugs 1 and 4 to see if the problem would follow the plug, or stay in cylinder #1. I have since looked at them twice after a drive, and now all four plugs look great, which confounds me. It could be that both times I had it revving over 6K not long before shutdown, which might have cleaned them up. The plugs are NGK BPR8ES.
6. While pursuing the ignition idea, I checked the resistance of the secondaries of the coils, where I got 20K ohms for the 2&3 coil and 30K ohms for the 1&4 coil. This seems to line up with Haynes.
So now I am going to go out and put the plugs back in , and just let it idle for a bit, and check them again to see whether plug #1 looks like it was burning colder.
But, I am leaning back toward carburetor problems. I was really hoping not to have to do a major teardown.
Ideas? I'm beginning to go around in circles and getting frustrated......
Thanks,
Jim
Got the bike recently so don't know its previous history except that it did run well when I test drove it just before buying.
Since I've had it:
1. I inadvertently doubled the amount of oil, and then drained it and refilled with new and changed the filter. It has not run well since.
2. I had it tipped over far enough to weld a new kickstand bracket to the frame i.e. a little bit "belly-up", and wonder if this could have caused oil or gas to end up where it shouldn't have.
3. I took off the carbs for cleaning, but did not go too deep into them. One air jet was blocked (pilot if I remember well; it was a #42), and one main fuel jet snapped when I went to reinstall it. This led to my replacing all four main fuel jets while I was at it (with size 112.5).
4. I put some Marvel Mystery oil in the gas hoping it might clean up the carbs but no noticable change so far, albeit I have only driven about 80 kms since doing so.
5. The other day after it was running rough I took out the plugs and while three of them looked just about right, a nice tan-grey colour, the #1 plug was noticably blacker, and a bit oily around the bottom of the threaded part. Wondering if it was as simple as just a bad plug, I reinstalled them but swapped plugs 1 and 4 to see if the problem would follow the plug, or stay in cylinder #1. I have since looked at them twice after a drive, and now all four plugs look great, which confounds me. It could be that both times I had it revving over 6K not long before shutdown, which might have cleaned them up. The plugs are NGK BPR8ES.
6. While pursuing the ignition idea, I checked the resistance of the secondaries of the coils, where I got 20K ohms for the 2&3 coil and 30K ohms for the 1&4 coil. This seems to line up with Haynes.
So now I am going to go out and put the plugs back in , and just let it idle for a bit, and check them again to see whether plug #1 looks like it was burning colder.
But, I am leaning back toward carburetor problems. I was really hoping not to have to do a major teardown.
Ideas? I'm beginning to go around in circles and getting frustrated......
Thanks,
Jim
TaZMaNiaK - July 9, 2005 05:21 PM (GMT)
You may have a cracked intake boot on the #1 cylinder. If they've never been replaced, they probably look like this:
These are my plugs... Guess which one is #1?
As you can see, there's a lot of crap in the cylinder from the mixture being screwed up:
Mine always idled like crap.. I could get it to even out with the choke, but as it heated up, especially sitting in traffic, there was no taming it. It would either want to stall, or it would idle at 3,000.
A word of caution: If the boots have never been replaced, the bolts holding them on are more than likely corroded in place because of galvanic reaction. It is unlikely that you'll be able to get them all out without breaking at least one. If you do, you will have to take the head off and have them drilled out. That's what I had to do. The shop is drilling out all 8 holes, putting in stainless steel helicoils, and using stainless bolts so that never happens again.
Good luck,
Matt
These are my plugs... Guess which one is #1?
As you can see, there's a lot of crap in the cylinder from the mixture being screwed up:
Mine always idled like crap.. I could get it to even out with the choke, but as it heated up, especially sitting in traffic, there was no taming it. It would either want to stall, or it would idle at 3,000.
A word of caution: If the boots have never been replaced, the bolts holding them on are more than likely corroded in place because of galvanic reaction. It is unlikely that you'll be able to get them all out without breaking at least one. If you do, you will have to take the head off and have them drilled out. That's what I had to do. The shop is drilling out all 8 holes, putting in stainless steel helicoils, and using stainless bolts so that never happens again.
Good luck,
Matt
Jim W - July 10, 2005 06:08 AM (GMT)
Replaced all four plugs with NGK BP7ES as specified by Haynes and the difference is amazing. Not sure if the other plugs were the wroing heat range, or if some were defective, but the bike is much more rideable now.
Jim
Jim
RocketRider - July 21, 2005 07:10 PM (GMT)
My Maxim was running a little rough at first. It would backfire.
It turned out to be one of the sparkplugs. I changed all four and like you wrote. The difference was amazing.
It turned out to be one of the sparkplugs. I changed all four and like you wrote. The difference was amazing.
laskey - August 9, 2005 04:11 AM (GMT)
My 81 XJ650H did this. I guessed the problem right... My ingniter module had some components go out of spec (from sheer age), and half my spark plugs didn't fire until the system voltage came up far enough and heated things up in the module. It was like an un-reliable turbo boost. Rather than spend forever with my desoldering iron, and a meter. I just bought a used module off e-bay. It works great now. No problems now.