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High rpms in lower gears

Discussion in 'The Garage' started by Robert Dell Aquila, Apr 16, 2019.

  1. Hi everyone, hope all is well. I finally got my 650 running somewhat decent. I can finally ride her around. Only problem is when Im riding I noticed the rpms are really high in the lower gears. Rpms will shoot up to 4k in 1st and continue around that range up until 3rd gear. When I shift gears the rpms drop slightly. Shift point is usually around 4k-5k. Also the bike makes a really noticeable rattling noise when riding (probably from the high rpms) almost sounds like loose valves. My first reaction was maybe the carbs weren't tuned properly. I can guarantee I have no air leaks, carbs are sync'd, mix screws are set. Running 2-1 exhaust with uni-pods, have 78' bs38 carbs: 1 up on pilots, 2 up on mains and 2nd slot on needle clip. Also read that a slipping clutch could cause this? I had some clutch issues before but lately its been pretty good. Any insight on my issue would be greatly appreciated. Thanks!
     
  2. Signal

    Signal XS650 Junkie

    I don't know what others think but I don't consider 5k RPM a high shift point for these bikes.
    The symptom of a slipping clutch is the rpms rise and you do not accelerate. I find it hard to describe but you know when you have it.
    Is the RPM increasing without speed increasing when you open the throttle again after shifting up a gear?
    If so that's clutch slip.
    So far as the rattle goes I have no clue.
     
    TwoManyXS1Bs likes this.
  3. Bushyeyed1

    Bushyeyed1 XS650 Addict XS650.com Supporter

    Sounds wierd rpm just shoots up while riding. My thoughts would be a leak in carb area causing a lean condition, but rattling does also lead me to check valves. You can't just set to top dead center and adjust both sides on the valves if you weren't tracking. Carbs and valves is what I'd be looking too for your issue IMO.
     
    Moabite likes this.
  4. 650Skull

    650Skull Dinosaur Lives Top Contributor

    If the clutch was slipping when changing gears the revs would drop considerably.........As signal says it the bike doesn't pick up sped and the revs climb it's slipping..........
     
  5. kshansen

    kshansen XS650 Junkie Top Contributor

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    Or is the tach sticking and not dropping back when you let off throttle? I know the 1978 I have that has been parked since 2008 or longer the tach is very sluggish to move. Sometimes it stays down low or then it moves up and does not come back fast even is engine is shut off.

    This is one time being there would be very helpful as some people describe things in different terms that can cause all kinds of confusion!
     
  6. Thanks everyone for the replies. I don't believe my clutch is slipping from reading everyones description of it. I guess I just dont know what the rpms are suppose to be while in different gears. It just seems to always be around 4k-5k range. I do have my idle speed a little high. Have it set around 1500 at idle right now. I'll try more tuning with the carbs to get it to idle smoothly at 1200. Also will adjust valve clearance again and see if that helps the rattle. Thanks yall
     
  7. kshansen

    kshansen XS650 Junkie Top Contributor

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    Maybe it just we are having a problem with understanding what is being said, at least I am!

    If I'm not saying the following correct someone please correct me!

    RPM in any gear is a direct relation to road speed. If you double the RPM in a gear you double the road speed in that gear.

    So if you are in first gear riding 5 MPH and motor is running at 1,000 RPM then you increase Road speed to 10 MPH your RPMs should be 2,000. Then if you raise RPMs to 4,000 your road speed should be 20 miles an hour.

    I'm having a hard time understanding what is meant by: "RPMs will shoot up to 4k in 1st and continue around that range up until 3rd gear."
    Unless you are saying the motor won't rev past that point in the higher gears.
     
    Robert Dell Aquila likes this.
  8. xjwmx

    xjwmx XS650 Guru Top Contributor

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    I agree with kshansen. If it revs up and it's in gear and you don't go faster the only reasonable explanation is the clutch is slipping.

    Another kind of possibility is it revs when the clutch is pulled. That will happen for example if you leave the choke on after the engine warms up. If it involves pulling the clutch then it could fuel related, air leak, and so on.
     
  9. Yea sorry for the confusing explanation. From what you just said about RPM's and road speed makes sense. When I increase rpm I do increase road speed. It's just that it seems real high for the gear that I'm in. For instance: if I'm in 2nd riding at lets say 25-30mph, the rpms will be around 5k, then when i shift to 3rd it will stay around 4k until I shift to 4th. I guess what I'm asking is, Is this a normal range of RPM?
     
  10. kshansen

    kshansen XS650 Junkie Top Contributor

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    Ok, anyone here have a chart or spec showing relationship of rpm to road speed.?

    Not sure if this will help but found this chart for some other bike but even if the spec's are off for an XS650 the idea is the same:
    speed to rpm001.jpg
    Number to the right would indicate the gear you are in.

    As you can see in this example if you are running at say 6,000 rpm in 1st and shift to 2nd but maintain the same road speed the rpms would drop to about 4,500. Then if you were to next shift to 3rd and maintain the same road speed of 40 mph your rpms would drop to around 3,200.

    Now if we change the way we look at this and instead of maintaining a steady road speed we keep engine rpms the same at 4,000 rpms. In first that would give a road speed of about 25 mph, shift to 2nd and now the 4,000 rpms would have you going about 36 mph and 3rd at 4,000 would have your road speed right at 50 mph.

    Like I said the rpms to road speed are not correct for an XS650 but the relationship between the two are the same. Just guessing that for an XS650 you could add maybe 1,500 to 2,000 to the rpm numbers across the bottom. Also note that the spacing of the gear ratios up the line may also be off. But again the basics are the same, Change rpm for any one gear and speed changes. Change gear for set road speed and rpms have to change
     
    Robert Dell Aquila likes this.
  11. Moabite

    Moabite XS650 Enthusiast Top Contributor

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    Or is he saying rpm not drop when he let off gas before shifting?
     
  12. xjwmx

    xjwmx XS650 Guru Top Contributor

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    ^ could be the throttle cable is sticking then. Or the grip is dragging on the handle bar.

    Anyway, for reference I've noticed in 5th at 55 I'm at 3500, all stock. Could be you have the wrong size rear sprocket. Or wrong tachometer. Somebody somewhere has the final gear ratios for each gear on a stock bike...
     
    peanut likes this.
  13. kshansen

    kshansen XS650 Junkie Top Contributor

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    I've read this through a few times and still not sure exactly what the problem being reported is.

    Trying to figure out if the rpms are dropping off when throttle is released and clutch pulled in or are the rpms staying the same irrespective of the gear or throttle position.

    Not trying to fault the original poster but just trying to be clear about what is not clear in this thread.

    These are the kind of things that can be hard to trouble shoot via text messages alone. I see this a lot on a heavy equipment form I'm on. Someone will use a term that makes sense to themselves but maybe because of slightly different regional differences in terms things get muddy fast. One example is when some one says in relation to a starting problem for a machine that they had put in a new battery but it won't crank. Now to me and from what I understand saying "It won't crank" means turning the key to try to start the starter does not turn the motor over to start. However once in a while there will be someone who says "It won't crank" means the starter spins the engine over but it won't "Crank-up" . They are using "crank" to mean "start and run"
     
    peanut and Moabite like this.
  14. 650Skull

    650Skull Dinosaur Lives Top Contributor

    Terminology is poor.......need to think about the answers and how they relate to the problem

    .

    Another way to test for a slipping clutch........when the revs climb, (and the bike doesn'r seem to gather speed), hold the throttle steady at a set of revs, 3500, 4000 whatever.........if the bike slowly speeds up and then steadies at the revs, (when they have been kept at a steady pace), then the clutch is slipping...........if the bike doesn't speed up there could be something wrong with the rev counter.................
     
  15. You're chart has probably been the most useful. Sorry to everyone reading this forum if I have conveyed my problem poorly. The chart you posted shows the RPM's relative to the gear and MPH which is pretty much what I wanted to know (even though its not for our bike). I wanted to know if the high RPM's were "too" high for the gear I was in. I don't believe I have a slipping clutch. From what I have been reading some say that 4k-5k RPM's are not a high shift point for these bikes. I want to know what others think. Thanks to all for the help.
     
  16. xjwmx

    xjwmx XS650 Guru Top Contributor

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    I shift when acceleration isn't going up as fast as rpms anymore. Probably around 4k most of the time. If you keep revving past the optimal shift point and it feels like you're accelerating less it might be completely normal. I think modern bikes will keep revving and keep pulling in lower gears, if they're what you're used to.
     
  17. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Here's the old "256" performance chart.
    In 5th gear, expect about 15mph per 1,000 rpms.
    4,000 rpms in 5th should be about 60mph...
    256-Performance02.jpg
     
  18. xjwmx

    xjwmx XS650 Guru Top Contributor

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    To clarify, the straight lines are speed for rpm, for each gear. I'm curious what the curved lines are though.
     
  19. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Looks like the horsepower (or maybe torque) curve above each gears RPM, you can see it stretches out as the gearing gets taller and the RPM angle decreases.
     
    peanut likes this.
  20. I going to stick my speedometer back on my bike and try and see if my numbers match the chart. Thanks yall, you guys always go into tremendous detail (which I love).
     
    Last edited: Apr 18, 2019

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