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Thread: Help, '75 R90/6 stalling out.

  1. #1
    kade010101
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    Help, '75 R90/6 stalling out.

    I'm stuck with this '75 R90/6.
    This is what's wrong:

    It starts fine, and when I have the rear wheel jacked up the bike goes through its gears smooth and easy. When I get on it for a ride it will stall unless I give it near full throttle but when I get into 2nd and 3rd the 'stalling' becomes slightly less at each gear.

    This is what I've done so far:

    Checked the timing and it seems to be fine. The only problem is that the bike is dual plugged and has a DYNA 3 ignition on it, so trying to find the correct information on where to set it is frustrating. I've been through 'Snowbums' explanation and many others and I'm pretty sure that I have it set correctly.

    Checked the valve clearances and they were within .001 inch of what they should be.

    Checked the compression and both sides are near 120 PSI (within 2-3 PSI of 120)
    This is where I think the problem is:

    I went to check the balance on the carbs (32mm Bing CV's) with the "$4.00 carb balancer" and the right carb damn near pulled the oil into it (glad that I'm quick with the kill switch).

    Ultimately I put a vacuum gauge on the carbs (It's a dial gauge and it bounces all over the place) and on the right side I got about 15 PSI of vacuum on the high end and 10 PSI on the low end, but on the left side I was getting 15 PSI of vacuum on the high end but on the low end the gauge was showing a positive pressure of 5 PSI.

    The carbs were rebuilt 2 years ago and I figured that everything was still ok in it, but I tore into them anyways. The diaphragm is in good shape and all of the O rings are good (I didn't go into the throttle body because I figured that if the other O rings are good they are good too).

    I replaced the carbs and tried spraying starter fluid on left one while the bike was running but I didn't get any increase in RPM.

    Sorry for the book above but right now I'm at a complete loss, so any insight will be greatly appreciated.

  2. #2
    Administrator 20774's Avatar
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    Setting the Dyna III timing is really not that much different than a stock ignition. You want the S-mark in the window at idle and you want to see the F-mark (full advance) appear in the window at around 3K RPM. Have you used a timing light to confirm that? The Dyna gives you the ability to adjust the firing of individual cylinders. If set perfectly, you'll see a single S or F-mark. If the sensors are off a bit, you'll see a double image or a ghost image.

    Choke is off, right?

    If you're getting those kinds of differences on the carb, that seems like a likely area to dig into.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    #4869 DennisDarrow's Avatar
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    The carbs could be out of sync someway due to cable problems; but actually you dont give enough of a description in your lengthy entry to actually diagnose what is going on with the carbs................You would have to be WAYYYYYY out of time to cause the machine to stall out when engaging the clutch.........

    Is your clutch adjusted properly.....is it by chance slipping and thus causing a stall??????

    What actually do you mean by stalling?.........How do you get it up to the shift point in 2nd and 3rd if it stalls out in 1st?????

    A bit more info please........God bless........Dennis

  4. #4
    Registered User lmo1131's Avatar
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    The diaphragm is in good shape and all of the O rings are good (I didn't go into the throttle body because I figured that if the other O rings are good they are good too).
    Tear them completely down, soak the carb bodies and parts for an hour or so, blow them out with compressed air, and reassemble with new o-rings. Are the diaphragms "supple"; as opposed to a bit stiff?

    I'd even go so far as to pull the throttle shaft out and check that o-ring. It's a pain because you have to re-center the butterfly and peen (or Loctite) the two little screws... but then you will KNOW that everything is in good order rather than, "I figured that if the other O rings are good they are good too."

    Have you checked float levels? If one side is low, and not providing sufficient fuel, you might get a response like this.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  5. #5
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    Mine had something like that

    After fixing everything that wasn't the problem I pulled the carbs off, took them down to the bodies and a pile of parts and found that the last person who had installed the "atomizer' above the main jet must have done it with the card still on the bike (Right side carb) and got it out of kilter. It was flat, the jet was damaged but even worse a chunk of the carb body had broken off and I assume got chewed up in the combustion chamber. Never looked for the chunk and had no compression or valve issue with the bike but did have to think fast on a fix. Well its keeper and the JB Weld was in my tool box so its been two years and its still running fine. Check your cables first and then go through the carbs completely.

  6. #6
    kade010101
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    Quote Originally Posted by 20774 View Post
    Setting the Dyna III timing is really not that much different than a stock ignition. You want the S-mark in the window at idle and you want to see the F-mark (full advance) appear in the window at around 3K RPM. Have you used a timing light to confirm that? The Dyna gives you the ability to adjust the firing of individual cylinders. If set perfectly, you'll see a single S or F-mark. If the sensors are off a bit, you'll see a double image or a ghost image.

    Choke is off, right?

    If you're getting those kinds of differences on the carb, that seems like a likely area to dig into.
    Since the bike is also dual plugged it is my understanding that the standard timing method no longer aplies. The reason that it becomes confusing is because on Snowbum's site his description goes into adjusting the points mechanism; which I don't have.

    As for the choke, yes it is off.

  7. #7
    kade010101
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    Quote Originally Posted by DennisDarrow View Post
    The carbs could be out of sync someway due to cable problems; but actually you dont give enough of a description in your lengthy entry to actually diagnose what is going on with the carbs................You would have to be WAYYYYYY out of time to cause the machine to stall out when engaging the clutch.........

    Is your clutch adjusted properly.....is it by chance slipping and thus causing a stall??????

    What actually do you mean by stalling?.........How do you get it up to the shift point in 2nd and 3rd if it stalls out in 1st?????

    A bit more info please........God bless........Dennis
    The best way to describe it is that as I let the clutch out and twist the throttle the bike begins to pull away at its regular pace but once I get to about 3500 RPM it lurches and dies on the spot; similar to poping the clutch.

    The way that I am able to keep the bike going is by twisting hard on the throttle, damn near to full. The bike stuggles for a couple seconds but makes it through and pulls the way it regularly would. When I change gears I don't have to give it as much throttle to keep it going.

    So for first I have to open the throttle close to full to keep it going, second gear I maybe have to give it 50% of full, third gear I have to give slightly more on the throttle than normal. I haven't been over third gear yet so I don't know what happens beyond third.

    I haven't gone into checking the clutch itself but I have adjusted the cable.

  8. #8
    kade010101
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    Quote Originally Posted by 69zeff65 View Post
    After fixing everything that wasn't the problem I pulled the carbs off, took them down to the bodies and a pile of parts and found that the last person who had installed the "atomizer' above the main jet must have done it with the card still on the bike (Right side carb) and got it out of kilter. It was flat, the jet was damaged but even worse a chunk of the carb body had broken off and I assume got chewed up in the combustion chamber. Never looked for the chunk and had no compression or valve issue with the bike but did have to think fast on a fix. Well its keeper and the JB Weld was in my tool box so its been two years and its still running fine. Check your cables first and then go through the carbs completely.
    I was hoping that I wouldn't have to tear the carbs apart again, but when it's 70 degrees outside and I can't ride something has to be done.

  9. #9
    Administrator 20774's Avatar
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    Quote Originally Posted by kade010101 View Post
    Since the bike is also dual plugged it is my understanding that the standard timing method no longer aplies. The reason that it becomes confusing is because on Snowbum's site his description goes into adjusting the points mechanism; which I don't have.
    Sorry...missed that...but his reference to points is somewhat related to timing. The points gap on our bikes has little true meaning, other than the fact that the points much actually open and close. If not, then the coils never get charged or have a chance to dissipate. But points gap and the ability to rotate the whole timing plate are definitely related...many have run into the problem of not being able to rotate the plate enought to adjust the timing. Changing the points gap solves that problem.

    The Dyna III is nothing more than an electronic switch as opposed to the mechanical switch that is points. The Dyna has more adjustability to it which makes it useful.

    But yes, with dual plugging, you want to retard the timing to get full advance maybe around 27 degrees TDC. A simple way to do that is to simply retard the timing such that at idle you see the S-mark in the window...probably at the top of the window IIRC which would put idle timing around 2-3 degrees
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  10. #10
    Bluenoser
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    If it runs OK at idle & up to about 3500 rpm, then if it is fuel related it has to be something with the needle jet/ main jet. It in fact could be an over rich condition which is causing the low power on accleration.

    Carbs have basically 3 types of circuits, an idle/low speed circuit, the needle controls from about 1/4 throttle to 3/4 and the main jet from 3/4 to full throttle.

    Again if it is carb related you might want to recheck the main jet/needle to see if they are correct. The stock main jet is a 150 & the needle is a 2.68 for a 90/6.

    You should also make sure the advance is working properly. If you have a timing light you should be able to see the timing marks on the flywheel to see that the advance is working.

    To do a carb sync you have to start with some kind of proper sync gauge, loosen the cables off & set them at the stock setting and then progress through the rest of the carb syncing. You'll be totally frustrated with just a vacuum gauge as you have no way to dampen the pulses of the engine vacuum.
    1971 R50/5 SWB with R75/6 drivetrain
    2013 DL650

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