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Won't rev over 5000 rpm and how to test solid state reg

Discussion in 'The Garage' started by rshutchinson, Jul 22, 2015.

  1. The TCI does it all.

    I'm going to take the side cover off and see if the timing is way off with the strobe light.

    I just have a hard time seeing it being weak valve springs due to the double spring and having also never heard of an xs with that being a problem.

    I did measure the springs before install and they were within specs.

    I can double check the ground on the harness going to the TCI but I would think it would rear it's head all the time, not specifically at 5000 rpm.
  2. BBS360

    BBS360 XS400 Guru Top Contributor

    As the rpm rises the frequency of coil charging increases, more power is required by the tci to charge the primary coils and more demand is placed on the ground connection for that power. Electronics can act pretty funny with bad connections.

    I'm totally guessing though. Seems like you've eliminated all the solutions from every other "no power over Xrpm" thread that I can find.
  3. Makes sense.

    I'll have a look at it but I really don't think that is the problem. I have one ground wire that every ground connection on the bike is soldered to so I would imagine it show issues elsewhere as well.

    I'm contemplating pulling the motor and putting it in the other xs I have here to see if it's something to do with my wiring or components or the motor itself.
  4. First off I set the timing with the timing light. At 1200 it was firing way before any of the 3 lines before the LF mark. Should I set it for the middle line? After setting the timing to the middle mark it still wouldn't go above 5k and didn't seem any different than before. When revved at all it advances to well before any of the lines.

    I pulled the UNI filters off and it revs up to 8-9k RPM but still does not go to redline. Could that just be because I don't have any type of runner on the carb mouth? However, I don't see why the UNI's are really causing it not to rev up and break up at lower RPM's? I thought they were much better than the other type of pod's like the Emgo's and K&N's?

    There is a lip inside the UNI's but it is about 1/4" or more from the carb mouth so they are not covering the air jets that I know of.

    I built this bike around the UNI's so I'll be really disappointed if they can't work.

    Perhaps it is just a carb issue after all. More testing tomorrow.
    Last edited: Aug 4, 2015
  5. bcware

    bcware Well-read Top Contributor

    I just set mine via static timing and it runs great. The lip might cause an issue, but you'd have to test another filter to know for sure. Not many people opt for Uni filters because they are relatively expensive (which means less knowledge on the board here). I will say that the Mikesxs K&N knock-off pod filters work great straight on the carbs.
  6. Changed the main jets to 137.5's and no change. Tried just barely attaching the filters incase they were somewhat blocking the ports (though they are barely even shadowing them) and no change either. It's definitely missing when this happens with the filters on and it also misses at some throttle and RPM's.

    I'd hate to buy the other filters after getting what everyone says are superior (UNI foams) filters and have it not work.

    I'll look at other filters or using a boot (I can't fit the factory crossover piece with my wiring routing unfortunately) to space the filters away from the carbs.
  7. xschris

    xschris XS400 Guru Top Contributor

    With oiled uni's the bike will tend to run rich. If your plugs are getting black or dark brown I would say the bike is rich. But I thought you said it was smoking and you used old oil rings in the rebuild. Also I would not try to red line a rebuilt motor for at least a few hundred miles or more of riding.
  8. Smoking has gone away, must have been condensation or fuel.

    I did use old oil rings yes with new compression rings.

    I've tried:

    145 mains, 45 pilots
    137.5 mains, 45 pilots

    On a second set of carbs I've tried:

    135 mains, 42.5 pilots.

    All the same result. Both sets of carbs had the float height set using clear tube to ~2mm below bowl mating surface.

    I took the filters off and the bike will reach 8500-9000 with the 145 mains and 45 pilots. This is tested while riding and a quick blip in neutral.

    I've got about 70 miles on it now. I'm not trying to redline it necessarily as the bike will never reach that when my wife rides. I'm only doing this so I can figure out what is wrong so I can find the correct jetting and get it rideable.
  9. xschris

    xschris XS400 Guru Top Contributor

    If you have the same results with large and small jets and your confident with your float height, ( I measure them with a ruler with the bowl off) then it has to be mechanical or electrical. Does it do it more under a load.
  10. xschris

    xschris XS400 Guru Top Contributor

    Have you done anything with the needles in the slides? If they are assembled wrong this can cause poor running.
  11. The one tang had to be really bent to get that float height. It sits lower than the other float when it is right side up but I don't think that has any affect as they never hang that low when in operation. I'll measure them next time I have them off.

    last night I took the air filters off and the bike rode much better and would reach 9k when I rode it.

    It does it the same under load or when in neutral. I can feel it miss at times when accelerating.

    The needles are in the middle clip position and assembled correctly as well.

    I did notice that when I had the filters off and I blipped the throttle, the slides would bounce up and down quickly. Is that normal or are they supposed to go up and down smoothly?
  12. BBS360

    BBS360 XS400 Guru Top Contributor

    Just more speculation here but even if the unis don't completely cover the air passages they might be preventing direct air flow into the air passages.

    Before I suggest cutting up the unis, do you still have the stock h-pipe intake? Some pod filter users have seen better performance with the stock intake runners between the filters & carbs.
  13. I do but unfortunately due to my wiring and cable routing the breather pipe to the crankcase doesn't fit. I've taped off the holes in those tubes and ran the bike like that. Would only go to about 4500 when riding but I still had the 137.5 jets in there.

    I'm going to put the 145's back in as that's sort of my baseline right now and stick the UNI's on the end of the pipes to see how that goes tomorrow.
  14. xschris

    xschris XS400 Guru Top Contributor

    On almost all of the floats I have set, they all where pretty much level with the float. If you have to bend the tang way far then something is wrong or off. The plastic ones are the same. If you are using the 77-79 needles make sure you install than as 80-82 needles in the slides. The one on the left is the setup on the 77-79 carbs and the one on the right is 80-82. They use a different spacer, spring and configuration.

    Attached Files:

  15. I have the 80-82 style and assembled correctly.

    Also have plastic floats. The left carb has the tang flat, the other side is bent more but that is what the carb says it needs when I set it with the clear tubing. I just took everything apart in the carbs again yesterday and it's all assembled correctly and nothing blocked.

    I really feel this is an electrical issue somehow rather than a carb issue though.

    I have swapped coils before with no better results. However, I just went and swapped the harness connectors and plug wires over to the other cylinder and I feel it is missing on that cylinder now. It may just be the wiring from the TCI to the pick up and coils. It's the only part of the factory harness that I used. I resistance tested the wiring and it all checked out but I will replace it anyway to try it out.

    I tried another coil, no go.

    I removed the carbs and their is lots of gas between the carbs and head. It pools in the rubber carb boots on the head and when I pull the carbs off it lets off a poof of fuel vapor. I've set the floats with the plastic tube and a level to make sure they're level. I'm losing my mind lol.
    Last edited: Aug 6, 2015
  16. xschris

    xschris XS400 Guru Top Contributor

    If fuel is pooling up in the intake your float valves are not closing or set too high.
  17. I shouldn't say 'lots' of gas in the intake, it's really only some in the carb boots but there shouldn't be any. The thing is they don't leak out of the air filters or anywhere.

    I'm going to lower the float levels a little and replace that section of the TCI wiring next.
  18. xschris

    xschris XS400 Guru Top Contributor

    Are you doing them with the bike on it's center stand and the carbs leveled. There is a full procedure for this in the manual. I would try to set the manually to 22mm with the carbs off and turned over.
  19. No center stand on the bike. I am doing them off the bike, in a vice, with a level on top and using clear tube on the bowl.

    When I first did them the right side carb was really low so that's why I had to bend the tang out.

    I'll try the other way.
  20. xschris

    xschris XS400 Guru Top Contributor

    It's worth a shot. The tube method requires them to be on the bike and starting the motor. When you do them with a ruler make sure to do both sides of the float and remove the gasket from the carb surface when measuring.

    Attached Files:

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