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  • XJ Timing Advance

    Hi, guys...
    I'm having a real issue with the idle speed on my XJ. It refuses to remain @ 1100 rpm... it will for a few minutes, then soars to 3000, you can barely move the idle speed adjustment and blip the throttle, and it'll come back down... too low... set it back to 1100, it'll stay for a few, then soars again.
    It's been a pain like this since I got the bike back in Jan.

    Been through the carbs, checked, cleaned, and blew air through every orifice, been through all the levels, adjustments, synch procedures more than once... still the problem persists. I have 4 new float valve assemblies on order, which should be here in a few days... but doubting now that the issue is really "carb" related.

    I'm trying to figure out how the '82 XJ1100's electronic timing advance system works. I have located the Vacuum Boost Sendor, located under the tank, (which has a vacuum hose that goes to the carbs.) I have also found the page that shows how to check it, which initially has passed the check.
    But, it appears to be a replacement item... and I need a source! Anyone ever have an XJ issue like this, and replace one of these to fix?
    (Knowing how electronic parts act when they get hot...)

    I'm also trying to get the circuit in my head... does the TCI on the XJ control timing advance, by changing signals sent to the coils? Thinking it gets it's base timing signals from the pickup coils (which are on a fixed plate) and the other from this Vacuum Boost Sendor based off of engine vacuum, sends those voltages to the TCI, which controls the coils. Is this correct?

    It's seeming more like a timing advancement issue... it has always taken a few seconds to let the rpm's fall before it goes back to idle... now it not only sticks and doesn't want to come down, but it will be idling ok sometimes, then soar by itself like it's possessed! LOL

    Thanks "in advance".
    Bob
    '82 XJ1100J Maxim (has been sold.)

    '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

    2011 Kaw Concours 14 ABS

    In the warden's words from Cool Hand Luke;
    "What we have here is a failure to communicate."

  • #2
    Pure advance won't make the idle jump that high. Sounds like a fuel delivery problem to me. I know you wrote that you went through the carbs, synched, etc, but if fuel delivery was erratic during the synch, well.... it ain't synched.

    Comment


    • #3
      Hey, Randy...
      Cody's helping me with it... and you know how many times he's done carb work... we've been through them to the point he's even stumped...

      He's thinking this 10M is one of the ones you rebuilt for him here a while back.

      We can unplug the vacuum hose off the boost sendor, and idle will instantly drop.

      That's what made us think it could be faulty... but voltages check good when we test it.

      No way advancement could cause it, huh?

      In every other way... bike runs great.
      '82 XJ1100J Maxim (has been sold.)

      '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

      2011 Kaw Concours 14 ABS

      In the warden's words from Cool Hand Luke;
      "What we have here is a failure to communicate."

      Comment


      • #4
        Too much advance will cause SOME change in idle but it can't go that high without the help of the carb. When you unplug the boost line have you plugged the end?

        Comment


        • #5
          Just spoke w/ Cody... he's there now working on it. With the bike running @ 1100 rpm, hose disconnected, (not sure if he plugged it yet...) He can apply vacuum to the sendor with a hand pump, and it will go clear to 3500 rpm.

          I'm thinking this sendor's fubared. Any sources known to get another one?
          '82 XJ1100J Maxim (has been sold.)

          '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

          2011 Kaw Concours 14 ABS

          In the warden's words from Cool Hand Luke;
          "What we have here is a failure to communicate."

          Comment


          • #6
            Interesting. Well, I know that won't work on a car engine

            Is it possible that #2 carb butterfly is open too far, allowing too much vacuum at idle??

            Comment


            • #7
              Physically looking at the butterflies they're just about closed...synch always looks good...on all 4. Vacuum readings appear good.

              We sprayed carb cleaner through the number 2 carb vacuum port as well yesterday...

              Where we're at... we can unplug the boost sendor, idle's perfect. Plug it back up, goes to 3000! Now, is it too much vacuum, or a defective sendor?
              If it's a sendor, I need another one...

              Can't be plugged to wrong port... there's only one.

              Only other thought would be to leave it unplugged, ride it, and see if it run's right...(Probably not...)

              Might could drill the timing plate and manually set the advance...
              '82 XJ1100J Maxim (has been sold.)

              '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

              2011 Kaw Concours 14 ABS

              In the warden's words from Cool Hand Luke;
              "What we have here is a failure to communicate."

              Comment


              • #8
                What kind of signal does the boos sensor send? Is it a 5v or a 12v sensor? There is a possibility, if we can figure out the correct signal, we could match up a MAP sensor (same thing really) from a car.
                Ich habe dich nicht gefragt.

                Comment


                • #9
                  Originally posted by XJOK2PLAY View Post
                  Physically looking at the butterflies they're just about closed...synch always looks good...on all 4. Vacuum readings appear good.

                  We sprayed carb cleaner through the number 2 carb vacuum port as well yesterday...

                  Where we're at... we can unplug the boost sendor, idle's perfect. Plug it back up, goes to 3000! Now, is it too much vacuum, or a defective sendor?
                  If it's a sendor, I need another one...

                  Can't be plugged to wrong port... there's only one.

                  Only other thought would be to leave it unplugged, ride it, and see if it run's right...(Probably not...)

                  Might could drill the timing plate and manually set the advance...
                  At idle there shouldn't be any vacuum at the port. You ARE hooking it to the port on the carb right? Not the one on the boot? (I'm pretty sure you are but had to ask anyways). But if your getting vacuum at the port at idle something is wrong.
                  Cy

                  1980 XS1100G (Brutus) w/81H Engine
                  Duplicolor Mirage Paint Job (Purple/Green)
                  Vetter Windjammer IV
                  Vetter hard bags & Trunk
                  OEM Luggage Rack
                  Jardine Spaghetti 4-2 exhaust system
                  Spade Fuse Box
                  Turn Signal Auto Cancel Mod
                  750 FD Mod
                  TC Spin on Oil Filter Adapter (temp removed)
                  XJ1100 Front Footpegs
                  XJ1100 Shocks

                  I was always taught to respect my elders, but it keeps getting harder to find one.

                  Comment


                  • #10
                    sorry to jump on post

                    i am going through the same XSact thing on my XJ right now. just got bike the other day. po had rpm up to 2500. i cleaned carbs,reinstalled 2500rpm. the idle screw is 1/4 in. away from touching the arm! have not had a chance to sync yet. i pulled the cap on vaccum of number one intake boot and got it to idle at 1500. sorry for jumping on ur post bro i will slide back into the woodwork now and read on ...lol
                    1982 XJ 1100
                    going strong after 60,000 miles

                    The new and not yet improved TRIXY
                    now in the stable. 1982 xj11, 18,000miles

                    Comment


                    • #11
                      Had the same issue on a 2000 gs500. Turned out the vacuum operated petcock had a small hole in the diaphram allowing one cyclinder to pickup more fuel then the other. After it was replaced the idle went back to being to holding steady.

                      Comment


                      • #12
                        Here's the latest as of this A.M.-

                        After doing a more intensive and critical adjustment of the pilot air screws, we saw a MAJOR change in vacuum readings. Then we performed a very critical synch, and got all 4 just as close as we could get them.

                        Throttle response is now great, and idle returns now to 1100 rpm instantly... (with the boost sendor unplugged from it's vacuum source... which is on the carb, and not the boot by the way.)

                        We have not had time yet to plug the boost sendor back in and see if idle starts acting up again or not since we did this.

                        I expected it to run like a dog with it unplugged...but could tell no difference at all! In fact, we rode it yesterday for 150 miles, and it's never ran better!
                        Gas mileage also has increased from 32 to 38! WooHoo!
                        Runs and even starts like a new bike! (Saying this as I knock on my wooden head, of course...)

                        If you'll remember, I just installed a new Dynojet kit. (But I had these issues before the kit, and was hoping it would solve some of these issues...)

                        New float valve assemblies should be here in the next couple of days... so we plan to pull the carbs once more for that, and possibly drop the needles one notch, just to see if that will enable it to get in the 40's, and still run good.

                        Ivan... this boost sendor GENERATES a voltage... (like an O2 sensor does on a car) of between 2.0- 2.6 with no vac, and 1.2- 1.6 with vac.

                        It sends that to the TCI, which electronically alters timing.
                        I've always noticed how when I'd release the throttle when riding and pull in the clutch, it would drop RPM in increments, not instantly return to 1100.
                        Now I know why... cause with it unplugged, it returns immediately!
                        Wild how I don't notice any effect of timing loss... it pulls like a Banshee on fire!

                        We also may have found my source of "oil consumption"... looks like the crank seal on the timing plate side has been leaking... not a lot, but enough to lose about a 1/2 qt. every 600 miles or so. New seal's also on the way.
                        Guess it hangs out far enough, and leaks slow enough that it all hit the road, and not the bike. I could never see any visable leaks... and the cover contained most of it, so it wouldn't leave a puddle in the floor.

                        Sure was great to ride 150 miles last night w/o trouble, and then be rewarded w/ an increase in mileage of +6!

                        Talimena, here I come!

                        I'll post back when we go farther... thanks for all the responses...

                        I would still like to find a source for this Boost Sendor to replace it, but glad the thing runs good w/o it!
                        Last edited by XJOK2PLAY; 09-23-2009, 06:56 AM.
                        '82 XJ1100J Maxim (has been sold.)

                        '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

                        2011 Kaw Concours 14 ABS

                        In the warden's words from Cool Hand Luke;
                        "What we have here is a failure to communicate."

                        Comment


                        • #13
                          Confused...seems like we've got two threads going here about the same issue...or is it me?

                          Comment


                          • #14
                            Randy,

                            Yes... there are 2 threads...
                            I posted here this am...
                            then was reading DBeardslee's problems... and he had mentioned how the one they're dealing with was having a low vacuum issue.

                            I had mentioned to him what we found last night on mine, and how we saw an increase in vacuum readings after more pilot screw adjustments and synching as something he might want to take another look at on his.
                            Sorry for the confusion.
                            '82 XJ1100J Maxim (has been sold.)

                            '79 F "Time Machine"... oh yeah, Baby.... (Sold back to Maximan)

                            2011 Kaw Concours 14 ABS

                            In the warden's words from Cool Hand Luke;
                            "What we have here is a failure to communicate."

                            Comment


                            • #15
                              Here is one from an ebay store. Bike it came off of only had 5900 miles on it.

                              http://cgi.ebay.com/ebaymotors/YAMAH...Q5fAccessories

                              Hope the link works, if not search XJ1100J Pressure Sensor

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