R100 Sputtering At Speed

Discussion in 'Airheads' started by senatorperkins, Aug 23, 2012.

  1. senatorperkins

    senatorperkins Adventurer

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    Mmm I've never heard of a dual point setup doing what you're describing Disston, but I do know that most Japanese bikes have this exact setup (Honda CB350 has two sets of points, independently adjustable on the valve cam). I guess a longer dwell time is a bonus, as there would then be no wasted spark.

    Anyway.. I swapped my old advance in, tried indexing the advance to the left or right of the minimal slop caused by the flat on the cam, and no changes.


    I'm doing it.. I'm getting a Sachse alternator-mounted electronic ignition. I like that it uses photo gates as opposed to Hall sensors, and I can keep my points in place to save headaches if it quits. Not as expensive as SH, easier to get than Omega. Just hope it's not my coils or timing chain causing the issues.. apparently there's no easy way to tell if the timing chain is worn on pre-canister models.
    #41
  2. disston

    disston ShadeTreeExpert

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    Off the beaten path, that's all. Should be my middle name maybe.

    Yes many bikes use a separate set points for the other cylinder and therefore it can be independently timed. Great idea. I do not know why somebody has not made an after market system like that for our bikes. Maybe it's just a mater of not enough space? It's the only reason I can think of that I've never heard of this being done.

    Dual point distributors in V8 cars do work the way I described but it doesn't have anything to do with what you were asking. File this in the round file.
    #42
  3. Chobro

    Chobro spinning the wheel

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    Well, it turned out to be my float heights. I adjusted for 23mm and it runs like a champ once again. Ran up to 90 and held it there for a while and no more stumble. It stuck me as strange. I rescued this bike and did a whole bunch of work on it before getting it on the road in 2010.

    Question is: What would cause this problem to come on so suddenly?

    Thanks for the thread, we're all in this together.

    Off to the Sipapu, NM Beemer Rally ! (in the nick of time)
    :clap
    #43
  4. senatorperkins

    senatorperkins Adventurer

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    chobro, thanks for getting back to us!

    Possibly a weather-related issue? Hotter days, less humidity brought the lean condition over the edge? My issue was (way) worse on certain days.
    #44
  5. Chobro

    Chobro spinning the wheel

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    No problem senator.

    Made it up to the rally and back with no issues, the bike ran especially well since the air was a bit cooler. I won oldest bike ridden to the rally ('76, it was a tie with one other rider), which is just sad. :lol3

    I'll order some new floats this week. Apparently they get heavy with age and the tabs need adjusting to maintain the correct height. At the parallel position, my level was at 17mm.

    Hope you get yours figured out soon.
    #45
  6. disston

    disston ShadeTreeExpert

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    The Alcohol in the Gasoline, now to be called Gasohol, is more corrosive to the Styrofoam float material. Eventually the floats have to be replaced.

    Several riders have talked about sealing the floats with some kind of spray shellac or something but I never heard of any successful experiments. Maybe somebody tried it but I never heard it actually worked. I guess you have to start with new floats before spraying and if the material doesn't work it might make them not work from the beginning. I guess this could get expensive.

    My idea is to use the metal bracket for the Styrofoam floats and construct small brass float chambers by hand from thin brass. I've never done anything like this before but I think it can be done. I just don't have enough time to play with it. I'm too busy trying to survive and writing diatribes all day long on the Web. :freaky
    #46
  7. supershaft

    supershaft because I can

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    We already have a lot of years experience with alcohol in most all the gas here in Ca. I have seen no change in how long the floats last. I see floats lasting decades in bikes all the time. Some people say they replace them every year? I see some of these bikes. My advise is that there are plenty of things that really need replacing.
    #47
  8. senatorperkins

    senatorperkins Adventurer

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    Chobro, wouldn't heavier floats be less buoyant thus requiring a larger displaced volume, resulting in a higher float level? My level is 17mm as well when they're parallel. I wonder if there were different float replacements sold with different geometry or buoyancy. Or could the floats be getting lighter/more buoyant with age?

    Okay, I think I was lean for this trip as well, seeing as my floats were set parallel, and the stutter only showed up on certain days (come to think of it, the weather was on average 15-20 degrees colder during those two weeks than the rest of the time I've had the bike this summer, so this makes sense because colder air causes leaner running. Also, when it rained it stuttered less, which checks out as well.)

    What bugs me is that my plugs look like they do on page one (specifically the photos after I took it for a ride, not after idling) - half of the insulator looks white, which would indicate lean to me, but the other half is black. Could my exhaust valve guides be worn and leaking oil which is burning only on that side of the plug, which happens to be facing the exhaust port? I'll mention again that my consumption is high at 1500miles/liter.

    Glad I'm fixing the timing too, but maybe that wasn't the cause of my issue.
    #48
  9. ME 109

    ME 109 Long timer

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    Thumbs up for Aussie premium and 31 year old carby floats.
    Miss that super tho'
    #49
  10. MickeyDee

    MickeyDee Adventurer

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    I experienced some of the problems you are having. It took two years to figure it out,and talking to everybody I could to now avail. I stumbled across a photo of the Bing carb and thought something looked different. I checked it out and discovered the linkage for the enrichment (choke) was upside down. I didn't notice when I rebuilt the carbs, it still had spring tension which leads you to think that all is right with the install. The bike ran fairly good at first but after a couple of hundred miles it started exhibiting some of the same problems as yours. It ends up fouling your heads allowing your valves to stay open with subsequent loss of power and the sputtering. My linkage had a bend to it, that bend should look down. If yours are the straight variety you might have the enricheners on the wrong sides. They are right and left sided. Good luck with your project. Have thought about joining the Airheads? There is a lot of good info on all the old warheads.
    #50
  11. Chobro

    Chobro spinning the wheel

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    I reckon that's right, mind boggling. . .:lol3 That two tone spark plug is really interesting. Would a leak down test confirm valve/valve guide condition?
    #51
  12. disston

    disston ShadeTreeExpert

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    A lot of good ideas. But. Gasohol soaked floats will cause too high a fuel level. Problems would more likely be at idle. I set the float levels one time to cause the gas level to run really, really low. At 80 mph I would run the carbs completely out of gas, the bike would stall but because I was moving at 80 mph it just slowed down. I backed off the throttle, the carb bowls filled and I cranked them open till it did it again, till I used all the fuel. It was not a stuttering situation. The carbs were either on or off. That's my point. Not something I would call stuttering.

    I forget which bike this is? Does it have ignition points? Too little Dwell, which is too wide a gap, will cause a stutter at higher rpm.

    I've seen the two tone plugs a lot. I think it's a result of Gasohol. It may be that a proper plug reading on Gasohol will be more white than anything else. We are not seeing brown very much, I think. We did a thread on this subject several months ago. Sorry I couldn't find it.
    #52
  13. senatorperkins

    senatorperkins Adventurer

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    Oh, I'm glad these 2-tone plugs aren't totally alien, I've never seen them before and they were freaking me out.

    Yes, points, I always set at 0.016 with slight drag on the feeler gauge. We'll see how the Sachse ignition does when it comes. Planning a trip at some point in the fall, I'll report back.

    Chobro, a leakdown test won't tell anything about the valve guides.. the valve guides are only exposed to the combustion chamber when the valves are open.
    #53
  14. senatorperkins

    senatorperkins Adventurer

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    Okay, so here's a coda to this thread as I don't like to leave things hanging.

    While waiting for my Sachse ignition to arrive from Germany I did a whole laundry list of maintenance items including some that were suggested to me on this thread. I flushed the tank, cleaned the petcocks, inspected and cleaned the crankcase breather, changed all the fluids, oil filter, new oil pan gasket, cleaned and rebuilt the carbs with new gaskets and o-rings, installed with new plastic elbows and fuel hose, new cables, did the pushrod seals, sealed the cylinder base, new head gaskets, set the float height to 24mm, set the valve clearances, installed the ignition, timed it, and synced the carbs. Obviously not everything here could be related to the issue, but they were things I was planning on doing anyway once I had the time.

    Here's a photo of the Sachse. On my model I had to relieve a section of the front cover with a dremel to make room for unit. The wiring was easy, I mounted the control box behind the battery, and I just need to switch a wire terminal at the right coil to swap back to points. No modifications to the harness necessary.

    [​IMG]
    A word of caution to anyone thinking of installing a Sachse - see the wire heading down from the Y terminal on the alternator in this photo? It looks like it's insulated, but the insulation did nothing, and it shorted through the aluminum base of the sensor (you can actually see it touching in this photo), which shorted out my whole charging system. Luckily it came back to life when I bent the wire out of the way and added some shrink wrap.

    I went for a 70 mile ride yesterday and there was not a single issue. I didn't have the time to isolate the problem by doing an item then testing, then proceeding, but I believe it was either fuel starvation from a low float height or misfiring from my screwed up points.

    So thank everyone for your help, I'll see you on the road and around the forums!
    #54
  15. ozmoses

    ozmoses Ride On

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    How do your plugs look now?
    #55
  16. senatorperkins

    senatorperkins Adventurer

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    They look pretty good - perhaps a little lean, but then I realized I left the vacuum port plugs out for the whole ride after my carb sync :D. I'll do a plug chop at the end of my next ride.
    #56
  17. chasbmw

    chasbmw Long timer

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    The Sachse set up is really nice, the timing on mine was absolutely spot on for a dual plugged engine. Setting the timing initially was also very easy. Much easier than the Silent Hektick ignition on my other bike.

    I feel that the misfire was most likely caused by the float height being too low. It seems that it is too easy to change it when doing a carb refurb?
    #57
  18. Beemerboff

    Beemerboff Long timer

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    http://www.gremlinracetech.com/product/BBMP

    These systems fit your bike, and include coils, leads and plug caps , so the price of around $200- is more than reasonable , and if you can convince them not to charge the 18 ? % UK sales tax it is a positive bargain.

    I have had the basic system on my 75/7 for 15 years / 150,000 trouble free km, fit and forget, so it has probably been cheaper than replacing points , etc over the same distance, and the the Micropower system on my twin plug 1000cc G/S has been the the same over 100,000 km, and it has a curve which suits my bike very well.
    #58