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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. Thanks Chris, I'll give that a try. While I don't have a center stand I do have a triple tree stand and spool stand so I can lift the bike up to do the test as it says in the manual you pictured.

    A thought I just had was to turn the petcock off while riding. If it improves as I keep riding (with no more gas coming in and the engine running the floats will start to drop) then that could very well be it.
  2. Is the 22mm taking into account the needle being depressed the extra bit? Or am I supposed to hold the float up so that the needle just shuts completely but doesn't compress the needle?

    I know normally you do not compress the needle but I'm not sure if the 22mm already has that considered.
  3. xschris

    xschris XS400 Guru Top Contributor

    Measure with the float resting on the needle as it lies after turning it over. Measure both sides of the float and make sure the gasket is removed. There are a bunch of threads on this in the forum.
  4. That didn't do it either. Still won't go.
  5. I took the valve cover off to check cam timing. It seemed that when the crank lined up to LT the cam and sprocket seemed a little to far toward the front of the motor rather than parallel with the head like is indicated in the manual.

    I removed the sprocket bolts, removed tensioner, moved the sprocket and cam so it was closer to parallel with the head but it was a little closer to the rear of the engine now.

    I bolted it back together, checked valve clearances again and now I have to rotate the pick up all the way the other way to what I had it and it is now firing late. It is firing after the LF mark now and I can't rotate the pick up anymore. The exhaust got very hot very quick for the minute i had it running. I'm afraid to do any sort of ride to see how it works because it just doesn't seem right.

    I can't seem to find a middle ground. With the cam-crank timing I had before I could only get it to fire at the second mark before LF on the crank and still wouldn't rev up. Now I've got the pickup turned all the other way and it fires way after LF and seems quite lean.

    I also noticed that the right intake valve hisses air when I rotate it by hand even though I have 180 psi compression. I'd hate to have to take the head off again.
    Last edited: Aug 7, 2015
  6. xschris

    xschris XS400 Guru Top Contributor

    If the crank was set to LT and the cam pin is at 12 o'clock, if the hole pip on the sprocket don't line up with the cam then your off a tooth on the chain and sprocket. That is all that I can think of. Also 180 psi compression sounds a bit high. A new broken in motor should be around 150-160psi. Did you shave the head when you had it off?
  7. Nope, only work I did to the head was lapping the valves because the seats were not the best looking and one seat had a little rust.

    I'm setting the crank to LT, the pip on the cam is pointing straight up relative to the head. The cam sprocket has the arrow pointing up same as the pip and the line across the sprocket is parallel with the head.

    I'll take the cover off again today and try again.

    I'm wondering if my leaky valve on that side could be causing this. I'm hesitant to take the head off since i don't have another headgasket.
  8. xschris

    xschris XS400 Guru Top Contributor

    If the valve seats where that bad a re-grind will need to be done it fix it. The valve won't cause the timing issue.
  9. I know I probably should have had them cut at a shop but they came out well when I hand lapped them.

    You're right it wouldn't cause the timing issue, I was referring to it possibly being the culprit of it not revving.

    However I just took it for a quick ride since changing the cam timing yesterday and it revved up higher. Didn't take it too high because the tach cable fell out but it revved higher and didn't sputter down low. Thinking its lean at this point since I have smaller jets in it and the exhaust gets hot quick.

    I'm going to see if I can find the middle ground in the cam timing when I get a chance but I think I'm making progress.
  10. Tried about 5 times resetting the cam chain but couldn't get it perfectly parallel after releasing the tensioner. Pulls it back, must be a little stretched but I think that's the best it's going to get.

    Double checked the firing mark just after LF on the rotor and the pick up after bolting it back together and they line up finally so I think this is sorted out and was just a slightly off cam-crank timing....

    Will find out later today and hopefully be able to get on to carb tuning finally.
  11. Finally!!! Cam-crank timing was slightly off. Fixed and it now drives great. Now to fix the headlight popping fuses and carb tuning and oil leaks and it'll be done!
  12. Chad

    Chad 81 yam

    rshutchinson (and others) - Just did a head rebuild/valve replacement (81 XS foo special), and having the same issue as you describe - RPM limits (and throttle delay/clear lack of HP vs. what I had the day before I took the head off) - and went thru many of the same things you described. Of course everyone on the site suggests I just need to clean/adjust the carb - while this may be appropriate in some cases, it was fine the day before disassembly, and I would likely do more damage than good!. Also with similar symptoms as you mention, you did all the carb work - only to find it was something else...I have synced them and played with the mix some, but not too much - it idles great, but wont get up to speed or does so very slowly - again - it sounds a lot like what you went thru - and solved. I also don't wanna take the head off again!

    So my question is this - after all you did, i am trying to translate what finally solved the issue?
    - You mention the fuel mix screw - what should I do to ensure adjusted properly - or look for on my plugs to check this?
    - Best way to check compression - you mention full open throttle (I want to double check it)
    - 2 posts back you were messing with the cam chain and tensioner to get it parallel - was there an issue here I should check that could be a cause or helped you?
    - Finally - all my chats have led me to the fact that the ATU may need adjustment - not sure how to. Your last comment mentions cam-crank timing being off which solved it - are you referring to adjusting the ATU? If so - how did you do it - light? Matching its position to the LF mark (see http://www.xs400.com/threads/ignition-timing-on-a-1981-special.11608/)?

    Appreciate any ideas here!
  13. My issue was the cam-crank timing was off due to the timing chain. I believe I was off a tooth on the cam timing. However, also double check after you've released the tensioner by spinning the crank and checking the positions. When you release the tensioner and it takes the slack out of the chain it also rolls the cam with it. If the chain is really stretched it exacerbates the problem. It took me a few tries of resetting the tensioner and chain to finally get it in a position that after turning the crank a few times the lines on the crank and cam were still in the correct position.

    To set the 'ignition timing' with electronic ignition you'll need a timing light. Clamp the pick up around the plug wire and using the strobe light you can check the timing. You 'set' the timing by slightly moving the plate (where the points would normally be on the head) so that the strobe light strobes at the LF mark. The TCI boxes are not adjustable, your timing is what it is. You can only advance or retard it slightly with the plate on the engine but the timing ramping is already set.

    As for the fuel mix screw, start at 2-1/2 turns out. It really only adjusts the mix at idle so don't worry about that too much if you're not able to get the engine to higher RPM's.

    When checking compression you need to have the throttle wide open or the carbs off. If it's low it could be a few things so I'd check it first and come back and we can go from there. If it's not then don't worry about it.
  14. Chad

    Chad 81 yam

    Great info - couple follow ups before I roll up my sleeves - I am as frustrated as you were! This clarifies - because originally I thought you were saying you messed with the chain, but it was ATU adjustment that did the job.

    Going in order of what I need to do:

    1) So how do I know the right position for the timing chain (and is it possible to be 180 degrees off as was suggested)? I followed the manual carefully, and I just put the cam and oil seal in as I slid the chain on, dropped in the tensioners - and adjusted the valves after. I had no idea (and still don't) if there is a specific chain position you need to have the cam on when you put the chain on. If I recall it just had to have the sprocket bolt hole directly up 90 degrees or something like that, which I believ i was - but could be a link off like you said - is this it?. I figured the notch in the end of the cam where the ATU slips on would ensure it was in the right place, and from there it was just valve adjustment (done), and then rotating the ATU housing front or back to adjust timing (which is what I have been doing) - which could make up for - say - being off by one link. Not sure what I am missing with ensuring the proper chain positioning means - you say: "lines on the crank and cam were still in the correct position" - appreciate any elaboration here.

    2) If I get this right, even without a timing light, i should be able to do some minor adjustment up and back of the ATU and know if I am in the ballpark - did you notice a difference right away?

    3) I will follow instructions on fuel mix screw. Did you mess with the other idle screws also? Do you need a special driver (mine are brass and recessed)?

    4) Finally, on compression, I disconnect fuel and plug lines, put in the tester and leave the other plug I am not testing in, open the throttle, and do a few cranks, yes? If I am having issues with the valves (dont think I am), or issues with timing (above), would these affect my readings?

    Thanks Man! This forum is priceless. Wanna get back on the road!
  15. To set the timing chain correctly you put the crank at the LT mark. The cam sprocket has 2 lines on it, they should be parallel with the head and I believe there is also an arrow that should point up. So look at it from the side and the lines on the cam sprocket should follow the mating surface of the head and valve cover. Understand what I mean? I will try to find a picture if you don't.

    Now, when you go to do the tensioner, try to keep the cam and crank from turning when you release the tensioner. You want the tensioner to take up the slack but you also want to keep them in the same positions relative to one another when it does. This may require a few tries of resetting the tensioner and messing with it. Once you've released the tensioner, turn the crank a few times and get it back to the LT mark. When it is there, check the position of the two lines on the cam. If they aren't parallel enough with the mating surface of the valve cover to head then try again. If it's way off then your chain is off a tooth. Fix that, then try again. It may take some time but it's important, obviously. Once you've reset the tensioner, check again. To sum that up, every two turns of the crank will do one turn of the cam, so starting crank at LT mark, rotate twice and the cam should still have the lines parallel with the head.

    2) If you have the cam-crank timing correct on the timing chain side of things then your engine should still run regardless of the timing pickup position on the end of the camshaft. I say that only because there is only a finite amount of adjustment on that thing which will not allow you to get the engine timing so far out that it won't run. My engine idled great even with the timing chain off a tooth and the timing way out because of that. So you can't just guess it, know what I mean? You need to use a strobe light. A dead give away if your timing chain is off a tooth is by using the strobe timing light. If you hook it up and you're timing is way off on the flywheel (inspection cover where you can see the LF marks) and you can't adjust the pick up sensor enough to get it spot on then it's off. You'll know as soon as you test it.

    3) There is only the idle mix screw which are the recessed ones on the top of the carbs. Those are the screws I'm referring to when I said start at 2-1/2 turns out. The other 'screw' in the middle of the rack of carbs just opens or closes the plates to raise or lower the idle, it doesn't affect fuel mixture at all. Just turn that to whatever position is needed to get about 1200 rpm at idle.

    4) Anything to do with the valves or piston/rings can affect compression. If a valve is sticking open then pressure can escape which will lower your reading, however it's not likely. After confirming that your timing chain is correct, re do your valves to ensure they're at the proper clearances. But yes, to check the compression, disconnect plug wires, remove both plugs and keep the throttle wide open. Then put in your tester and crank it for a few seconds. You want atleast 5 rotations to get a good reading. If it's not low, stop fretting.

    I'd rent/borrow/buy a strobe timing light and check your ignition timing first. If it's way off then adjust the pick up on the cam to set it so the strobe flashes right on the correct firing mark on the flywheel. If you can't adjust the pick up to get the ignition timing right then you know for sure you're off a tooth on the timing chain or that at least it needs looking at and what you need to do to get it correctly set. Once the ignition timing is set, then I'd move on to checking and setting the valve clearances. Once that's done check compression again and then you can fine tune the carbs to get the engine dialled in just right.

    All good?
  16. Chad

    Chad 81 yam

    Wow thanks for the detail. Can't wait to try - will keep ya posted! Thx! Hope to do this soon!

    Last edited: Oct 18, 2016
  17. Chad

    Chad 81 yam

    OK had a nice day and thought I'd dive back in. Before pulling the exhaust, engine, and so on to get at the chain, and before looking at the timing, I figured I would do a compression test. Remember that I completely tore down the head and valves and reassembled everything after finding the the broken valve (see the story here - http://www.xs400.com/threads/low-hp-and-slow-throttle-response.15942/#post-162747). Once again, the engine got hot and a valve broke (pistons looked fantastic) and had head and valves totally redone.

    Here are the plugs - very black and oily.

    So I then did the compression test and found:
    Dry: L - 75, R - 95 and Wet - :L -160, R - 175?

    So now I am worried about the rings - whereas I thought I just needed to maybe fix the timing chain. Wondering if the symptoms (slow throttle response, lower power) are due to the potential timing mentioned above - or the rings or something.

    Any thoughts/ways to rule this out? I am starting to get to the end of my rope looking at pulling the engine out again after total reassembly - thinking timing issues - and now it seems like I need to get all new gaskets and a complete tear apart. Anyone have any thoughts as to what I can do to verify my issues before I open the patient up?

    Last edited: Oct 25, 2016
  18. Chad

    Chad 81 yam

    OK so I have an update! Thanks RS Hutchinson...

    I finally found a guy in town that works on older asian bikes - and he was going to pick the bike up and do some testing for me yesterday. However the day before, I went back and:
    - re-checked valve clearance (not much adjustment needed)
    - adjusted the timing (this is where I gave up)
    - reset my idle - dialed it back down

    If you remember - I had slow throttle response and was chasing down timing, until I got the very low compression readings. I have 100+ hours into my disassembly and reassembly + a few bills $$ into the head reman/valves replacement and tank repaint...

    The last 2 things I did were key - and I cannot stress this enough:
    - put a lot of fresh gas in
    - new, solid charge on the battery

    HFS if the bike didn't start right up and GOOOOO! Just like before - all the HP was working for me and had immediate throttle response! Yahoo! I drove it to my kids school for a band show that night - it was 74 degrees in Cleveland. Just too bad the Indians didn't have the same luck!


    So - I was surprisingly baffled. here is what I think happened - please learn from my errors (Remember - I was about to tear into the timing chain, carbs, and potentially the lower unit to replace the rings and so on):

    1) Doing my compression test, I believe that the combination of some worn threads on the nearly new compression tester, some slight valve mis-adjustment, a weak battery, and lack of lube in the cylinders/valves (until i did the wet test) gave me the low compression readings
    2) While adjusting the timing, I was so focused on the idle and timing, that I really was not aware that with all the stops and starts my battery was really low (and a no-start made me think I needed to re-adjust, but sometimes it would catch), and also with low to no gas in it, I would get fooled when it stalled or wouldn't throttle up, thinking the idle or timing was bad - leading to more adjustment and more use of gas and electricity

    In the end, the issue WAS my timing, and the advancement of the ATU (by rotating the unit slightly) made the difference - but I couldn't see it because of low gas and battery power used during the adjustment - and a bad compression test mis-lead me down another path. Stupid? Yes! Happy? Very! The way it came about was like magic - Thanks to everyone for their help.

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