Lackluster low end power

[hyaall]

I've got a 79 XS11 I've recently restored, however, I am still sorting out one problem with what I think is poor low end power (off idle to about 3500 rpm). The bike starts and idles well, and has good power over 3500, although it will surge a bit over 6000. Below that it tends to hesitate and bog down somewhat when the throttle is opened unless I'm in the lower gears. It has been timed, compression is good, plug color seems ok, carbs have been rebuilt twice now, with speck mk jets, and synchronized and appear at this point to be in excellent condition (I'm running 4 into 1 with glasspack muffler). From what I've read, these bikes should pull well across the band. I'm wondering if anyone has experienced a similar problem or has any ideas for me. All I can think of now is to try jetting up a size or two and to finish the job of replacing the plug wires (one coil is completed as per instructions on this site - the other is quite frayed exiting the coil).
Any thoughts?


Wes G

[sixtysix]

Main jets won't help under 4000K rpm, basically you are running of the pilot circuit (at low throttle like 1/8 turn or so) goto tje links section and go to the factory pro tuning page. They tell you to mark the trhottle in like 1/8 turn increments or something then just follow the procedure and the problem should be found. I used it on my Baandit to tune the pilots for low rpm response. If you are talking about gunning it at low RPMS, forget it on an XS til you get to 3000-3500 then it wakes up.

[MartyA]

Hi Wes!

How's the battery? Gotta have a good charge, or the spark may be weak. How's the plug gap?

The first year I owned mine, I experienced a great surge at 3500 RPM. Below that it pulled just OK, and at the time I thought it was normal. While playing around one day, I manually moved the spark advance system and found the centrifugal advance was quite gummed up. I took it apart and cleaned it, put a light coat of lithium on vacuum advance post After assembling I lost that great 3500 RPM surge, it just pulled fine throughout the RPM band. I didn't have any stumbling below 3500, but it goes much better now at the lower RPM. I think the advance was delaying itself until the RPMs' went up.

[hyaall]

Thanks to both Marty and 66 for the replies.

Marty, your question about the battery is interesting and I think I'll take it in for testing. Recently after I had presumably run the battery down a bit after checking compression, I experienced a loss of power generally and the turn signals weren't working. This seemed to resolve after I ran the bike for a half hour or so. It would be a simple solution, just the kind I like.

To the more difficult, 66 are you suggesting that the bike is running off the pilot circiut under 4000 rpm generally, or would that be just at low throttle (under 1/8 turn or so)? Im not so much talking about gunning it at low RPM. In higher gears at lower rpms it seems to actually loose torque when I pull the throttle slightly (I suppose to about 1/8) and accelerate rather sluggishly up to about 3500 when I open the throttle more. Doesn't seem to make any difference how much I open the throttle and I'm not sure it should be this way. If my problem was the pilot circuit what would I do? Change jets? Without the low rpms it a real Jekyl or Hyde kinda ride.

Wes

[sixtysix]

Pilot affects both idle and up to about 4000RPM. To check I think you ride in second gear and slowly acceleate to like 3K-4K with steady throttle. If it surges-too lean. If it bogs with a throttle blip from idle - too rich. Check out the Factory Pro link for more complete diagnostics.

[Jeff]

Mine reacted that way before I did a REALLY thorough cleaning..... especially the emulsion tubes. At first.... all I did was pull all the jets and spray carb cleaner thru the tube since I was unsure about how to get them out. What I found was a nasty layer of varnish plugging all of the holes in 2 of the 4 tubes. In 2 of the carbs... the passage between the main jet bore and the pilot jet was plugged up a bit. The bike did fine for the first quarter turn of the throttle.... after that... it bogged bad until I got the rpms up around 4k or 5k and then took off again.