Valve or injector noise?

  • My engine has been rough. There was some clattering noise around number 3 cylinder so I decided to check the valve clearances. Six of them were very good but number 3 in and ex were slightly loose.

    I fixed them and now the engine is a little more quiet and smooth but there is still a noise around number 3. It is just a single metallic tapping noise now instead of the clattering.

    I think it might be the injector but it is hard to tell. I just had them all rebuilt 6 months ago by a reputable injector service centre.

    Is it possible that the electrical signals may be weak on one injector, or would it just be dirt? Should I swap number 1 and 3 to see if the noise moves?

  • It could be the injector, but it could also be a small vacuum leak. With the engine on and fully warmed, try spraying a little non-flammable brake cleaner or contact cleaner around the intake and where the injector fits into the cylinder head. If the idle varies when sprayed, you have found a vacuum leak. I have found over the years that some vacuum leaks can sound an awful lot like a mechanical tick. Oh, make sure the rubber cover over the little vacuum spigots on each throttle body are not cracked or leaking. Those ten to go pretty regularly on older bikes.

  • I replaced the vacuum caps and checked for leaks. All OK. I also ran some injector cleaner and went for a blast. The idle has changed slightly. Will re-tune and re-listen when I can.

  • I've had a chance to use the carbsticks. I can balance the throttles but one of the screws is in almost all the way, and one is out enough to be loose.

    I have also noticed something I didn't notice before. If I rev to 1500 or 2000 the vacuum goes out of balance. The cylinder with the tight airscrew goes high and the one with the loose screw stays low. (EDIT: turning the screws when I have the engine revved like this has much less effect and makes me think the throttle butterflies are out of sync)

    I tried the spray, and even used carb cleaner but I can't notice anything. I pulled the throttle bodies off earlier this year looking for leaks , found nothing, and noticed nothing when I put them back on.

  • Keep your hands off the Throttle Flap Screws. This is a case for one who knows how to do it, and it's only "well done" with the right equipment. But you're right if you guess they are our of balance.

    If you have another chance to use any equipments and you have a spare throttle system if you fail ;) :

    machine warm
    every false air problem solved BEFORE balancing

    clean vacuum screws ;)
    close vacuum screws
    keep revs about 1400
    balance with the throttle screws, the THIRD cylinder is fixed, here is your reference!!
    if you are balanced, fix screws with loctite

    open vacuum screws each ONE and a half turn
    start engine, its about 800 revs.
    now balance your engine up to 950 revs with the screws.

    If there is a great difference in the position of the screws there is a problem with the axis of the single throttles. Try to find another throttle system with less mileage, or send it to "Bing" to overhaul it - save money before :o

    This is a short info, if you like to do this try to download the english text of VAC-Diag I : <!-- m --><a class="postlink" href="" onclick=";return false;"> ... 64</a><!-- m -->

    Schöne Grüsse, Ralf CH

  • Thank you. I might try this, it cannot be worse (I think :( )

    I found out more. I fully closed the screws, only 1 at a time. Each cylinder produced full vacuum except the rear cylinder, only partial vacuum. I think there is either a leak or the butterfly is open more.

    But I cannot find a leak. Anyway, if there was a leak and I compensated with the air screw, it is like fixing the leak, isn't it? Why should the vacuum change when I apply throttle?

    So, I think it is a butterfly problem. The butterfly is open too far and when I apply the throttle, the airscrew cannot help anymore.

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