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  1. #1
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    Close, but no [CARB] cigar....

    Hey folks. Based on help received here on the forum and articles/how-to's from the Wiki, we were able to get the bike in the best running condition so far. For those who helped on the last thread - thank you! Unfortunately, there is still a gremlin(s) effecting a very specific area of the throttle range.

    Despite initially cleaning with ultrasonic cleaner, carb dip and what seemed like gallons of carb cleaner spray, it turned out that the very tiny holes near the butterfly were still clogged, causing some issues with hesitation and bog/stumble just off-idle. After several more ultrasonic sessions, and heavy hits with a steam cleaner (may be the new secret weapon for stubborn clogs), finally got the holes clear.

    The results were positive - but while much better, we still have a bog when quickly cracking the throttle (think pulling away from stop sign or merging into moving traffic when you really need acceleration). RPMs pull nicely if you roll on the throttle, but any quick movement causes this bog. The air/fuel mixture screw allowed us to dial it out a bit, but we hit diminishing returns and the bog was never fully eliminated. The best results were shown while running 90/120 jets (stock exhaust, pods) with mixture screw somewhere between 2-3 out. As a test to determine whether it's rich/lean (starved/drowned) condition, taking the 90 down to 85 proved to make it much worse, so we are assuming jets are within range - or damn close?

    My questions:

    1. Do you think this condition is caused by jet sizes?

    2. Could the needle be the issue? The needle appears to be non-adjustable (like the CB circlip style), and needs to be shimmed???

    3. After doing all the electrical tests from the Wiki, the only issue/bad reading was on the #9 pin, Source Coil Low Speed. The measurement was 301 (instead of the 387-473 spec). Could this be coming back to haunt us?

    4. Could someone please clarify when/where/what jets handle which position of the throttle range? I have searched for an illustration that shows this - to make it easier to hone in on an answer, but have not found anything.

    Thank you so much for all your past and future help.

    Scott

  2. #2
    Super Moderator CXPHREAK's Avatar
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    1 Maybe.

    2 Don't shim the needle.

    3 Maybe. It is likely your spark is not the strongest. It can be checked with a spark stretcher and/or check the voltage coming from pin 9 while cranking the motor over. Tell us what you have.

    4 You'll run on the idle jet through idle, choke and off idle. These are the three holes you found blocked under the butterfly. They may not still be entirely clear. They are .5 mm and best cleaned with the plain end of that size welding tip cleaner bent 90 degrees at the end. You may have these clear, but not clear enough.

    5 What is your air filtration?

    6 Are the springs present on top of your piston slides?
    Last edited by CXPHREAK; 12-12-2016 at 06:50 AM.
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  3. #3
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    CHPHREAK, you are saving me here!

    1 Figures! I think we are at the end of the line for jets that I ordered already (80, 82, 85, 88, 90 - 118, 120, 122).

    2 Don't shim the needle. LOVE THAT ANSWER!

    3 The resistance is still at 301. The voltage jumped a bit - but the highest it got was about 7.x volts. Not sure I did this correct. I measured voltage across the #9 pin and the )#5 pin.

    4 I was able to get the welding cleaner (I had read .023 which is a bit bigger than .5mm) fully through the hole closest to the outside. The 2 behind the butterfly only went in a small amount. Should these be able to have the cleaner pushed down far??? The how-to only stated "not very far."

    5 Well.... fairly cheap pods. I did modify them though - to allow the air passages clearance inside the throat of the carb.

    6 The springs are definitely present on top of piston slides And I polished the slides, they seem to travel unencumbered when moved with a finger on the bike.

    Thanks again for all the help.

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  5. #4
    Super Moderator CXPHREAK's Avatar
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    3 What scale did you do the voltage test on? Run it on 200 volts.

    4 You only need to go into those a few mm. The tube below them isn't large.

    5 Are you sure the pods aren't obstructing the vacuum ports in the mouth of the carbs? These are where the vacuum chamber gets the vacuum signal to lift the slides. If obstructed at all the slides don't lift properly.

    6 Cool.
    Rebuilding Handlebar Switches

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  6. #5
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    3 I was on 20v scale....Just switched to 200 volts and came up with around 1.6. Make more sense???

    4 If they only go in a few millimeters, I am pretty confident these are clean/clear.

    5 I cut the internal diameter as far as I could (pic below). It measures around 52mm, and appears not to block the passage (as best as I can tell).


  7. #6
    Super Moderator LRCXed's Avatar
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    Scott,
    You mention sonic cleaning and spraying the carbs out, you don't say if you've cleaned the low jet manually or not. If that jet is still even partially restricted with old hard deposit build up in it, you won't get the proper fuel delivery at the low end no matter what jets you put in it. Being an 81, you should have the pressed in low jets. If you don't want to pull them out, you can clean them by gluing a .018" micro bit to a straighten out large paper clip I use JBWeld for mine. This will allow you to clean the small hole in the low jet. But, since there were plugged delivery holes in the venturi, the emulsion side of the low jet may still be plugged as well. It's best to pull them out to ensure they are well cleared. The pictures below show the low end circuit as well as the optional cleaning method.






    This is an example of a clogged and clear low jet on the emulsion tube side of it. With the emulsion side being clogged, the vacuum will not be able to pull the fuel up into the low end circuit.
    Note that these carbs had been dipped in carb cleaner and sprayed out. This was also before I started using a sonic cleaner. But it still wouldn't clean them properly even if I had. Food for thought.
    "If you're going to do something, "Do It Right" don't do it half assed"

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  8. #7
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    Thanks so much for the reply LCR and detailed info. We were looking at those cross-sections the whole cleaning process! Great pics!!!

    I should have mentioned that I did in fact remove the pressed in jets to clean them thoroughly. One was a little chewed up - so I replaced it with one from a donor set of carbs (cleaned well before putting it in). I also ran a small Drill through the passage that ports into the side of the idle jet passage - so I know that's clean. I'm pretty sure all 3 holes from the carb throat - but obviously the 2 behind the butterfly are a bit of a mystery with their twists and turns. The welder cleaner did decend a couple/few mm though. And pressurized steam and carb cleaner were sprayed down the idle jet passage as well after the multiple soaks etc.

    I'm now trying to determine whether this issue in having is carb or electrical related. I now see that I could infinitely clean these carbs. But at this point it seems we have addressed all the pitfalls thoroughly. At least the ones that can be seen . But the low reading on the electrical test - and it being specific to low speed coil has me concerned and a bit confused. I'd hate to spend a ton more time chasing a carb-demon that turns out to be the CDI/electrics.

    Just having a real hard time diagnosing...separating real from imagined.

  9. #8
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    is that stumble fuel or electrical? Have you checked the condition of your plug caps , or done the brass rod mod to the resistor caps ? That might be worth a try too.
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  10. #9
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    Quote Originally Posted by muzza View Post
    is that stumble fuel or electrical? Have you checked the condition of your plug caps , or done the brass rod mod to the resistor caps ? That might be worth a try too.
    Muzza, thanks so much for the response.

    We had already trimmed back the plug wires to make sure we got good connection, and have tested the resistance of the caps themselves (measured 4.91). The spark to the engine block looks decent (not super-blue, but it's there for sure) on both cylinders. So I am not sure that part of the electrical chain is the culprit.

    Have you had issues like the stumble from not having the brass rod mod done? I can see why that might offer a more stable setup, but could it be the cause of these symptoms? Is there a test we can do to see if this is in fact something we should change?

    I feel myself wanting to throw everything against the wall to see what sticks But so far we have been methodically going through each potential issue that could cause the problems encountered on this bike - so I'm doing my best to resist that temptation, to try to stay on track and make sure that our efforts (and money) are targeted at the specific symptoms.

    I'd hate to have my friend spend a bunch of money on a new CDI if in fact this bog/stumble is electrical. But if these symptoms are now pointing to electrical, and not the carbs - we will put the order in today!

    Thanks again for all the help folks. Great forum.

    Scott

  11. #10
    Super Moderator CXPHREAK's Avatar
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    The voltage output test on the stator are meaningless. If that was all the voltage the ignition had available it wouldn't start.

    Maybe your meter won't read this on DC. Try AC .... but my 2 meters read this on DC.

    What do the plugs look like?
    Rebuilding Handlebar Switches

    http://s1085.photobucket.com/user/CXPHREAK/library/Switchgear%20rebuild?sort=6&page=1

    Rider 81 500C, Thingy Born a 78Z. Ozdeluxe born an 80 shadow.

    GET A MULTIMETER RTFM I am a CX500. If you maintain me I will run forever.

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