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Thread: 1974 R90/6 issue(s)

  1. #1

    1974 R90/6 issue(s)

    Issue with 1974 R90/6

    I’ve recently started experiencing what I would term as “slight hesitations” when riding my bike,,,,by “hesitations” I mean it feels like there’s a momentary loss of power and by “slight” I mean that it’s a very light, (not noticeable via the tach) hesitation,,,similar to what one might call a misfire?.
    These hesitations are occasional and not limited to one range of RPMs or gear….it really feels like the engine is starved momentarily for fuel. The hesitations can happen under acceleration and just cruising along at stable throttle setting.

    Initially, I thought it might be some crappy fuel, so I discarded the remaining two gallons and purchased fresh gas from a station that is very reputable and popular (thinking their gas has a high turnover,,,) Changing the gas didn’t improve the situation.

    I double checked the carb fuel level in the float bowls and both were at 23 mm as measured from the center of the bowl to the top of fuel.

    I verified the floats still floated, removed the carbs and thoroughly cleaned the body and the jets and the passage ways. I checked the timing at idle and at 3500 rpms and it was spot on,,,,I verified the valve clearances were within spec then I doubled checked the balance of the carbs and only had to make some very minor tweaks to the throttle cable locking barrel,,,,issue still exists.

    Some additional info: the bike has an electronic ignition (Motorrad Elektric Alpha Classic), a Dynatek dual tower 3.0 ohm ignition coil, enduralast III charging system with heavy duty diode board, new starter relay, new voltage regulator, new battery, new battery cables, new engine wiring harness (not the main harness). The contacts/connectors for the grounds and other electrical connections were cleaned and given a slight coating of no-ox-id when I was putting the bike back together earlier this past summer.

    Also, after I got the bike back together and timed and carb balanced it ran really, really well for about 300 miles,,,this occasional “hesitation” issue has just recently cropped up.

    So now I’m leaning away from carbs/fuel delivery but am not sure where to look next.

    Any ideas/thoughts/guidance would be appreciated.

  2. #2
    Registered User m_stock10506's Avatar
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    Wow. I will be watching this thread. I have a 1974 R60/6, and I have been fighting with this same issue for a long time. Runs great, then suddenly misfires/stumbles/hesitates (pick one), then returns to normal running. Just yesterday, it really gave indication like it was fuel starved. I checked both sides and I'm getting over 10 ounces of gas thru each carb in less than a minute.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  3. #3
    Registered User barryg's Avatar
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    A Possibility

    Gas cap? The tank vents through the cap. Could be stopped up. Had it happen to me on my ‘74 R90. Slight miss, a little stumble, misfire, finally just engine shut down. Good luck with your diagnosis.

  4. #4
    Registered User STEVENRANKIN's Avatar
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    My two cents

    Okay, I will chime in with my two cents and maybe or maybe not it might help. I don't have the bikes you guys talk about, my problem was with an 84 R80RT. LOL, I spent almost a year and a half chasing a slight hesitation while riding that became a complete shutdown of the bike while riding only to turn the ignition key off back on and everything would work fine.

    Before you start thinking about swapping out parts and such, I can tell you, over the period I was looking for a clue, I swapped out the ignition switch, no joy, same problem put the old switch back in. The electronic ignition module and bean can, again no fix, old stuff went back in.

    Somewhere down the long long road, the problem finally was determined to be a ground issue. LOL, don't ask me what particular ground wire, I had all of them apart, cleaned and tightened, just like all the hot wires.

    I NEVER found a smoking gun that I could point directly at all I can say is clean terminals, check the grounds, do the cheap easy stuff first, don't get sucked into thinking it is an expensive item failing, it may not be. Good luck.

    Intermittent crap is the WORST problem to chase down. When you want it to fail, it won't and when it does, it is at the worst possible time. St.

  5. #5
    Curmudgeon nrpetersen's Avatar
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    Grasping at carb-induced stumble threads - Make sure the carbs are level about a longitudinal axis when the bike is on its center stand. Probably not it but it is easy to do.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  6. #6

    so far,,,,,

    Thank you all for the feedback/advice. This morning I checked and cleaned all the ground wires attach points and the connections at the starter relay, voltage regulator, diode board, stator, electronic ignition, coils and connections inside the headlight shell (those I just verified were on and snug,,,to take all those connections off and clean the connectors is a nightmare for another life, for me, anyways). I had an older gas cap on the tank when this issue first arose but I swapped that gas cap out for a new one just a week or so ago, so I'm doubtful it's a venting issue.

    I'll take it out for a ride a bit later after it warms up a bit. BTW, it started right up and idled great right from the start when I tested it the garage after this mornings efforts (that's been the norm for this bike since I got it back together)

  7. #7
    Liaison 20774's Avatar
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    Just crack the gas cap when out for the ride...or when you first feel the miss. Easiest way to rule the cap breathing out.
    Kurt -- Forum Liaison ---> 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!

  8. #8
    Registered User STEVENRANKIN's Avatar
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    Rs

    My RS had a gas cap venting problem, no matter how much I tried to clean the vent, it would hiccup from time to time. St.

  9. #9
    'Intermittent' reeks of electrical issues, a ground sitting high on the list.
    '13 690 Duke, '19 Ninja 400 (track bike), '21 Duke 890R, '22 Street Triple RS, '22 S1000XR (gone but not forgotten: '61 Clubman's Gold Star, '76 R75/6, '84 R100, '76 R90S, '20 R1250R)

  10. #10

    so far,,,,hesitation still present

    after yesterday's efforts of checking grounds and cleaning contacts and so forth I went for a ride,,,,issue still present. I tried to be more observant on this ride,,,what I noticed is it took about 5 miles of riding at moderate speed to have the hesitation(s) appear, but once they started (still occasional and very fleeting) they were prevalent for the rest of the ride (a total of about 15 miles or so). The bike still idles well at stop signs and sitting still in the garage,,so now I'm wondering if it's something "mechanical"? as opposed to electrical or carburation? I did try the open-the-gas-tank-cap on the ride but that didn't prevent the hesitations.

  11. #11
    Registered User Guenther's Avatar
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    When it happens during a ride I would pull the clutch immediately and rev the motor up-and-down to ~5,000 RPM.

    If the motor runs 'clean' at that point I would then look at fuel supply.

    I put one of the early versions of the Alpha Omega ignition system on my '89 R100GS. It wasn't working perfectly. Motor started well but riding the motor 'stuttered'.

    At that time I put the old ignition module and 'bean can' in and no problems.

    I reported the problem to the seller and a few weeks later I got an email from someone in Taiwan who claimed to be the engineer on the Alpha system. I got two more sets of the Alpha Omega systems to try out and the last one worked correctly.

    And my point...it could be the ignition system.
    Last edited by Guenther; 11-13-2022 at 09:58 PM.
    2017 F700GS

  12. #12
    Quote Originally Posted by Guenther View Post
    When it happens during a ride I would pull the clutch immediately and rev the motor up-and-down to ~5,000 RPM.

    If the motor runs 'clean' at that point I would then look at fuel supply.

    I put one of the early versions of the Alpha ignition system on my '89 R100GS. It wasn't working perfectly. Motor started well but riding the motor 'stuttered'.

    At that time I put the old ignition module and 'bean can' in and no problems.

    I reported the problem to the seller and a few weeks later I got an email from someone in Taiwan who claimed to be the engineer on the Alpha system. I got two more sets of the Alpha to try out and the last one worked correctly.

    And my point...I could be the ignition system.

    thank you for the input, I am tempted to put the points back in just to see what happens. The first time the engine hesitated it was after about 20 miles into a ride,,,,it happened only a couple more times that ride (total ride about 60 miles), then it started to happen with more frequency and much earlier into a ride such that now within just a few miles it starts and will repeat it quite a few times in just the first 10-11 miles

  13. #13
    Registered User STEVENRANKIN's Avatar
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    It won't hurt

    To be honest, it wouldn't hurt to put the points back in and give it a try.

    I have to admit, I have an Alpha system on my 84 R80RT and have never had a problem with it. LOL, I fell for the hype about improved performance and found I could have kept the stock electronic ignition and saved money. I can't see any advantage of the Alpha over stock.

    And as I said, the intermittent problem I was having didn't go away with swapping out parts. I disappeared after a lot of contact and ground cleaning.

    Over the winter, I installed a Wedgetail system on my 78 R100RS, now I could see performance gains with that system and I was very happy with spending the money on it. It was far better than the Dyna system I had in place. Sadly, I only put 1000 miles on it when Monday, I rear ended a stopped car because I took my eyes off the path to wave at a group of bikers on the side of the road.

    The RS is pretty badly damaged, not sure if the frame is bent but I know I won't be rebuilding it. So I guess I won't be able to give long time report of the Wedgetail system performance. St.

  14. #14
    Quote Originally Posted by STEVENRANKIN View Post
    To be honest, it wouldn't hurt to put the points back in and give it a try.

    I have to admit, I have an Alpha system on my 84 R80RT and have never had a problem with it. LOL, I fell for the hype about improved performance and found I could have kept the stock electronic ignition and saved money. I can't see any advantage of the Alpha over stock.

    And as I said, the intermittent problem I was having didn't go away with swapping out parts. I disappeared after a lot of contact and ground cleaning.

    Over the winter, I installed a Wedgetail system on my 78 R100RS, now I could see performance gains with that system and I was very happy with spending the money on it. It was far better than the Dyna system I had in place. Sadly, I only put 1000 miles on it when Monday, I rear ended a stopped car because I took my eyes off the path to wave at a group of bikers on the side of the road.

    The RS is pretty badly damaged, not sure if the frame is bent but I know I won't be rebuilding it. So I guess I won't be able to give long time report of the Wedgetail system performance. St.
    Holy smokes ! I hope you're ok, and that your bike can be fixed! What a bummer. Dang

  15. #15
    Registered User STEVENRANKIN's Avatar
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    Walking an talking

    Oh I am walking and talking thank God, cracked a vertebra in my neck, lots of pulled muscles and bruising. Not bad for a 35ft flight at 6ft 45mph hard landing. Thank goodness I had a great helmet and gear. It could have been much worse. St.

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