Missing on steady throttle

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Atoyot

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G'Day all,

I've been reading a lot of the great material on this forum for a while now, but this is my first post. I hope I'll be forgiven for this first one being a quesiton, but I just need some help to get started.

I've got an XS650C that I've hardly had to touch since buying it some time ago, as I've mainly ridden it around town at low speeds, but recently, on a trip out of town, I found that on a steady throttle at 40 - 60mph (and faster), it misses and stutters badly. It accelerates nicely with no problems, idles beautifully, and does everything as it should other than missing on a steady throttle. Using full choke at speed seems to stop the missing, so it's telling me that it's running lean on 1/4 to 1/2 throttle, so the first thing I should check is the needle?

The bike is standard, and apart from this issue, it starts easilly, warms up well and otherwise runs great. My mechanic hasn't looked at it, and won't until I've upgraded the ignition and charging system, but I think that this problem is with the carbs, as using the choke seems to fix, or more accurately, mask the issue.

I haven't checked anything yet, but am I on the right track to start troubleshooting this issue? I think I'm on top of all things to check, but is that the most likely place to start?

regards

Andrew
 
Last edited:
whats wrong with your ignition and charging?
Raise the needle a half notch, and see what happens. Its possible something may be up with the charging system, not charging the battery fully, so as you cruise, it kinda stutters, then when you whack it open, rpms shoot up, throwing a bunch of energy thru thr system.
What volts are your-
Battery-running and not running, volts at idle and 4k?
 
Long time lurker, huh?
I'll go with the carbs. Like you said, clears when using the choke.

Thinking in terms of air leakage at cruise throttle position, do the slide diaphragm leakdown/drop tests.

Thinking in terms of fuel restriction at cruise throttle position, I'd check the pilot jets. A quick test for this would be to do a reverse flush of the pilot circuit. Then, if it runs differently, suspect the pilots.

http://www.xs650.com/forum/showthread.php?t=42002
 
Thanks Angus67 and TwoManyXS1Bs! I'll take your advice as offered, as I haven't had an XS on the road since about 1983, and I wasn't that interesting in doing my own mechanical stuff then. I've done a fair bit of my own work since then, but not so much on carbies on any other bikes I've had. I've got another 4 XS's (well 2 are TXA's), but only one in one peice and the rest in boxes, including the TXA I had in the 80's, so plenty of spares on hand!

I will also check the voltages, as I hadn't considered it a potential electrical issue, but doesn't hurt to check. The charging system seems ok, but I spose until I've check the rates, I don't really know, particularly with the shorter runs I tend to do. I also keep it hooked up to a battery tender, so it could be masking a problem. There isn't anything wrong with the ignition system, as I know of, so until or if I do have problems, I'll leave it as is and just checked the system every 6 months or so.

I'm from Australia, and although I live in a relatively cold area here, we do tend to ride 12 months of the year, so plenty of scope for things going out of tune, as I do more miles.

I'll let you know what I find when I get the chance to check it out, hopefully later in the week,

Andrew
 
TwoManyXS1Bs said:
Long time lurker, huh?
I'll go with the carbs. Like you said, clears when using the choke.

Thinking in terms of air leakage at cruise throttle position, do the slide diaphragm leakdown/drop tests.

Thinking in terms of fuel restriction at cruise throttle position, I'd check the pilot jets. A quick test for this would be to do a reverse flush of the pilot circuit. Then, if it runs differently, suspect the pilots.

http://www.xs650.com/forum/showthread.php?t=42002
Click to expand...

Hey TwoManyXS1Bs, just looking through the above link, and that's a great idea, specially when you're just starting to troubleshoot a problem and don't want to pull everything apart to check likely culprits!

The more I think about it, the more I think you might be right about the pilot jets, but I'll force myself to check one thing at a time and then test it. Great article!
 
TwoManyXS1Bs said:
Thinking in terms of fuel restriction at cruise throttle position, I'd check the pilot jets. A quick test for this would be to do a reverse flush of the pilot circuit. Then, if it runs differently, suspect the pilots.

http://www.xs650.com/forum/showthread.php?t=42002
Click to expand...

Interesting. The focus of the link was on early BS38's.

Assuming one creates a custom nozzle suitable for the dimensions of late ('79) carbs, is this still a viable procedure? Looks like something I'd be willing to do as a winter project on my bike. It runs pretty clean, but I never have had the reaction I expected to idle adjustments. Pretty much none, actually...
 
Downeaster said:
Interesting. The focus of the link was on early BS38's.

Assuming one creates a custom nozzle suitable for the dimensions of late ('79) carbs, is this still a viable procedure? Looks like something I'd be willing to do as a winter project on my bike....
Click to expand...

Hey, Downeaster! Now THAT'S a good idea. Run with it, post it up. Add it to that thread if you like.

BTW, I found another "paint shaker" video, by "fawteen" and wuz wonderin' if it was yours.
 
any miss brings up ignition as well as carb issues. a strong ignition will fire a mixture a weak one won't. Once both sides have a strong blue spark firing at the proper time both at idle and advanced then start carb futzing. Check that all the brass is correct for your year BS38s, many "kits" have the wrong parts in them.
 
Yep, "Fawteen" is my alter-ego on a number of forums.

Just used my paint shaker today, painting up a freshly-sandblasted battery box for the Zook.
 

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