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XS650 Ignition timing revisited - Are we too advanced?

Discussion in 'The Garage' started by TwoManyXS1Bs, Mar 19, 2016.

  1. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Several years ago, I set my XS1B ignition timing a bit retarded to improve my idle stability, reduce vibrations, and give a smoother and more docile power output to match my sedate 'old man' riding style. Then, after building my LED Ignition Timing Light, I reset my retarded ignition timing back to the factory spec of 40° BTDC full advance.

    This new performance of the engine was awful. The idle became unstable again, but more importantly, the highway performance was alarming. To maintain 60-70 mph required much more throttle, power was down, vibration was way up, and my typical hot oil temps rose from 230°F to around 250°F.

    Whut's goin' on?

    Warning: *Ramble mode engaged*

    The XS1 was developed in the late '60s, and held a respectable position in the early '70s. Fuels, oils, and sparkplugs of that time have changed, and we've had to adapt. I'm still catching up on this new world of low-octane gasohol, and its effects on vintage engines. Back in the late '60s - early '70s, gasoline was easily available in 98-108 octane, enhanced with tetra-ethyl-lead. My primitive 'oldschool' understanding of octane ratings was that the higher octanes had a higher flash temperature and a slower, controlled burn, a requirement of the high-compression muscle cars of that time. Folks thought that higher octane gave you more power, but the reverse was true. To get more power, you increased the compression ratio (C/R), which then required the higher octane rating. On a lower C/R engine, more power was realized on the lower octane (faster burning) fuels.

    Fast forward to our modern gasohols, with octane ratings of 87-91. Which makes me think that these modern fuels burn faster, and need LESS spark advance.

    A Google search of "ignition timing curve" and "spark advance curve" shows numerous charts where the vast majority of modern engines limit max spark advance to around 30° BTDC, with very few going to 35° BTDC, and rarely to 40° BTDC (for vintage engines).

    Thanks to advancements in engine design technology, and associated analysis tools, a new perspective exists that may be applied to our vintage engine. For example, this pictorial of combustion chamber designs shows associated max spark advance values. Note the vintage side-plug hemi-chamber value of 40°-42°, versus the newer pentroof at 30° and less. Our combustion chamber is somewhat between the two, with its higher mounted plug position. This would seem to support reducing our full advance timing.


    I'm not having much luck finding good comparisons of fuel burn rates, fuels of 45 years ago versus modern gasohols.

    But, this somewhat summarizes my thinking of what's going on:
    Energy density of gasohol is about 3% less than gasoline, requiring more throttle.
    More throttle requires less spark advance.
    Faster burn rate of lower octane rated fuels requires less spark advance.

    A search thru this forum found recommendations from XSJohn (rip) of retarding timing about 5°, from this thread:
    View attachment 2243

    And, I found a post from grizld1 of his running a max of 38° BTDC. There may be more, like the recommended ignition timing setups for the track, but those would probably apply to the old days and vintage fuels.

    For now, until I can do more exhaustive testing, these are the ignition timing positions I'm running:
    IgnitionIdle.jpg IgnitionAdvanced.jpg

    This represents my modified current ignition timing curve:

    So, I'm thinking that if you're experiencing poor highway performance, excessive vibration, hot engine, poor gas mileage, an ignition timing 'retard' of about 5° may help your condition.

    Comments, guys...?
    Jim, Rasputin, gggGary and 1 other person like this.
  2. jussumguy

    jussumguy XS650 Addict

  3. jussumguy

    jussumguy XS650 Addict

    ( non-rambling mode)
  4. barncat

    barncat XS650 Addict

    helpful observations 2M. even though some dislike burning corn I think we can all agree that getting the lead out of gas was a good idea healthwise at least... I ingested more than my share indirectly through 2 decades of hard core road cycling (as in bicycle) from passing car and truck exhaust.

    I've sensed that my current two XS's run a bit smoother on 93 octane. must have to do with the slightly slower burn you suggest.

    have to confess I just set timing experimentally. there's a limited points plate travel range and the correct setting is usually near the center. you know in a hurry if it's off, and biasing a bit toward retard does smooth things out some.

    I was unable to successfully drill out an old spark plug to make a piston stop. some people say it's easy...I disagree. gotta buy one some time. once you switch to PMA all the marks are gone anyway.

    motor vibration also seems pretty affected by carb sync and tuning of course. noticeable difference when you get 'em dialed in. I've been using VM34's exclusively... am going to try a single TM flatslide next time for comparison, but I digress.
  5. 5twins

    5twins XS650 Guru Top Contributor

    I've been aware of the different timing specs for the early XS1s and the later models for quite some time. In fact, Yamaha issued a Tech or Service Bulletin about the change or "upgrade" in early '71 .....


    When I first installed my Pamco, I set it to the later timing spec, which was correct for my '78. I was getting some minor pinging in the really hot weather so I retarded it a little. A few years later, I retarded yet a little more. I run my full advance about like this now, probably very near the early 38°BTDC full advance spec .....


    I think the bike runs very well like this. In fact, I think the performance is better at higher RPMs and higher speeds. This puts my idle setting over at the right slash mark next to the "F". Yes, my idle speed did drop off slightly and the idle did sound a bit lumpier, but that was easily compensated for by turning the idle speed back up a little.

    So, I'm probably running about 37° or 38° advance and 12° or 13° idle timing, 2° or 3° less than the later timing specs. I don't know if I'd go as much as 5°. I did this, as I mentioned, to cure some pinging, which it has, but I got a free performance boost as well. I've mentioned this timing thing in the past a few times, and recommended the slightly more retarded settings. Hey, you can always change it back if you don't like (or get) these good results, but I know I never will on mine. In fact, when I tune these for other guys, this is how I set their timing now.
    Last edited: Apr 4, 2018
    Grimly and Paul Sutton like this.
  6. dps650rider

    dps650rider XS650 Addict

    I too have found that my bike runs better on today's fuel with the timing retarded. I think I now have it retarded between 3 and 5 degrees from stock. As an added safety measure I almost always run 93 octane in it which helps a lot especially when the humidity is low and riding double in the hilly terrain in my area.

    Back in the day I found that it ran the best with the timing on the high side of the marks using leaded premium, preferably Sunoco 260.
  7. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    I've had my suspicions that Yamaha (or their American counterpart) may have been trying to solve some 'field' issues by applying some quick tricks. I recall they were chasing that insidious idling *pop*, *spit*, *stop* issue. Shortly after that service bulletin, came out the next concerning the idle discharge port position. So, something going on there.

    My '71 BS38 carbs have a slightly non-round, tilted ovalish throttle bore. Shown here:


    With timing set to factory spec, my idle stops are almost all the way closed, which exaggerates the imprecise fit of butterfly valve to throttle bore, which I believe causes my unstable idle, like that pop-spit-stop. Retarding the timing requires that the idle stops be turned-up 1/8-1/4 turn, reducing the relative influence of the butterfly/bore misfit, and the idle is much more stable.

    I'm thinking that others may also have non-round throttle bores, accompanied with idle problems, that could be solved with the retarded timing.

    Yes, I've found those now, and I agree. Hence, this 'revisit' of the ignition timing.
    gggGary likes this.
  8. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Thanx for the confirmation, dps650rider. The list grows.

    We now have 'ethanol-free' 93 octane out here, which I run exclusively now. The federally mandated renewable fuels regs require something instead, so this fuel is blended with 10% isobutanol. It has several features superior to ethanol, like non water absorbing, which eliminated my carb gunk problems. But, it still runs better with the retarded timing.

    Ditto. And that's most of what I remember, the old-days fuels...
    Paul Sutton and gggGary like this.
  9. 5twins

    5twins XS650 Guru Top Contributor

    I'm afraid I never had the pleasure of getting to use leaded high test. It was long gone by the time I got my 650. I did my timing change to cure some pinging, as mentioned, but I also didn't consider it running "out of spec" because of the earlier setting. Something else to think about is how many new models are introduced in a higher state of tune and with more power/performance for their first year or two. Then the manufacturer starts de-tuning them and mellowing them out a bit. I imagine it's a sales ploy to establish the model and generate more sales. The early 650s had a few more horsepower than the later models and I figured maybe this difference in timing specs had something to do with that.

    Another thought that comes to mind is that by retarding the firing point, we are actually igniting the fuel/air charge closer to TDC than before, probably under slightly more compression. A higher compression motor is usually more powerful and we may be giving ourselves that. And for free, lol.
  10. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Haha, yes, I've experienced 'new' restaurants like that. Great food, for the first month or two, then lookout.

    The ideal ignition timing point is to have the combustion pressures (up to 800psi) peak at about 15° ATDC. Some folks prefer a little earlier, around 8°-9°, but that's for modern designs. My engine simulator uses vintage fuel burn models, and prefers the more advanced position, which is why I've been looking for modern fuel specs and algorythms.

    Never ran hi-test 'ethyl' in your XS650, and never an early model?
    Oh, those were the days.

    Good point about the slightly elevated compression pressure at spark event. This higher pressure puts a little more demand on the ignition system, while also improving combustion initiation and propagation...
    Paul Sutton, gggGary and Musick76 like this.
  11. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    Have "thought of" a vacuum advance mod a time or two. Even better a modern mapped advance.........
    Paul Sutton and TwoManyXS1Bs like this.
  12. 59Tebo

    59Tebo 59Tebo Top Contributor

    Yup.... we've become too advanced. I've been told before, there's no such thing as a 'perfect' machine. I mentioned in someone else's thread, you're trying to build a 'perfect' engine. Perhaps we just have to accept "close enough" is close enough. Measure it by eye, time it by ear, adjust it by feel, and if you're happy with it, lock it down and ride it into the sunset... :bike:
  13. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Reading some other articles on critical squish geometries, got to thinking about carboned-up pistons and combustion chambers. This would affect compression ratio, and the induced turbulence from our annular ring squish zone. The combustion chamber pics in post #1 show significant differences in ignition timing with subtle changes in the squish geometries.

    I know I've got a bit of carbon coating in mine. Maybe it's affecting the squish.

    I can see a possible influence of different head gasket thicknesses on the squish zone.

    Overall, convinces me that tuning to the engine, not specifically to book specs, is important...
    grizld1 likes this.
  14. grizld1

    grizld1 Grumpy old man Top Contributor

    Good stuff as always, 2M! In Gordon Jennings' classic article on spark plugs and plug reading, he noted that recommended factory settings for most Japanese motorcycles were farther advanced than optimal. He recommended reading the electrode tip to guide ignition timing. Ignoring the bit of the tip that might be flushed clean by turbulence, look for the clean burn line toward the end. If it's thicker than a whisker, ignition is too far advanced. M. "Jacques Strappe" has done us a great service by making Jennings' article available at www.strappe.com . Click on Tech, then click on the spark plug icon.
    mrtwowheel, gggGary and TwoManyXS1Bs like this.
  15. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Excellent article, Grizld1.


    I suspect that was for the benefit of gas mileage at cruise throttle positions, when manifold vacuum is high. As applied in automotive distributors with vacuum advance plumbed to a carb's "timed port". The high-revving Jap bikes could get away with that since they were normally operated beyond what GM called the "detonation prone zone" of 2,700-3,000 rpm. But, our slower revving XS650s should be excluded from that practice, especially with these new fuels...
    Paul Sutton, grizld1 and gggGary like this.
  16. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    taken right after peoria ride. So a few hundred road miles and 200' up the driveway before shutdown.
    plugs and a borescope shot of the squish area.

    madness plugs 8-2018.jpg 2018-08-21-10-28-11.jpeg

    Not sure what if anything this shows :whistle: :wink2: maybe that the squish is too thin to let carbon build up?

    Madness, 750, high compression or so I've been told. It does get 175/195 compression readings. Same gauge typically shows 150-155 on a healthy 650.
    TwoManyXS1Bs and grizld1 like this.
  17. grizld1

    grizld1 Grumpy old man Top Contributor

    Hmmmmm.....Electrode tips look good to me, but if the little lumps on the plug on the right in the photo are aluminum, you know what to do (for those who don't-- aluminum lumps or flecks on a plug are material that used to live in the piston crown and has been blown onto the plug by detonation). I like to see deposits going halfway down the horizontal segment of the ground strap; try 1 step colder plugs? Porcelain is darker than I wind up with after a highway run.
    TwoManyXS1Bs and gggGary like this.
  18. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Nice borescope pic, gggGary.

    The 80mm bore and piston present a "dual character" squish zone. On the 75mm bore, it's defined by the slanted annular ring of the combustion chamber. The 80mm adds another 2.5mm wide ring that's flat.

    "Squish" is what you get on the piston's upstroke, as the relative volume reduction in the squish zone occurs faster than the volume reduction in the central combustion chamber, and "squishes" the mix into the main area, creating turbulence, improving combustion.

    "Quench" is what you get after combustion, due to (2) things.
    - The relatively large surface-area to volume in the quench zone absorbs heat.
    - The piston's downstroke, as the relative volume increase in the quench zone occurs faster than the volume increase in the central combustion chamber.

    These (2) reduce combustion propagation and pressures in that area, reducing the chance of detonation.

    It looks like your flat/outer ring shows no signs of combustion residue, a severely quenched area. A good safety margin for detonation.

    I smoothed the combustion chamber edges of the dragon's head to reduce this "dual personality" of the 80mm squish area.

    Thought of the day:

    Don't sweat the petty things,
    and don't pet the sweaty things.
  19. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    In spite of quite few miles on Madness it needs some more sleuthing, tuning. Gotta start out by installing a tacho I can trust. My current thought is that it's running well on the needles but the mains are too small. :umm:
    Last edited: Aug 31, 2018
    grizld1 likes this.
  20. Goldenboy

    Goldenboy . Top Contributor

    Another problem in a parallel universe. You've all reminded me of something. That my bike really didn't start to breath before 70 mph, and I would always use American high test, a clear, high octane, lead free fuel, no longer available. Lake George vacation, Gold Cup Races 509.JPG Lake George vacation, Gold Cup Races 509.JPG Lake George vacation, Gold Cup Races 140.JPG The manual says retard the timing for city driving. No, I always wanted to hit that speed and take off, but it would load up and heat up at a traffic light. Hot enough to melt a cheap set of points. And, yes, I was really surprised to see how much carbon has built up in the engine after taking the pipes off last week to rebuild the system. But, this is not my only old motor. I also own a 1970 Johnson Seahorse. There are problems facing the boating industry as well. The marine engines which sit in basements and get used 3 or 4 times a year in fresh water last longer than their owners and get passed to the next generation, are also being damaged by the fuels now available as govt. mandate. If you gas your boat up on the highway it is advised to use an additive. The fuels available, today are detrimental to our engines. The article I read in The Fisherman, an east coast magazine, said the marine engine builders are also faced with the fact that newly designed engines made for the fuels available at the time they were designed are now using levels of ethanol they weren't designed for. Compared to all the farmers who grow corn and the auto industry, the marine boat builder's lobby in Washington is whale s#!t at the bottom of the ocean. And, besides, who feels sorry for rich people who own boats? My bike is a time machine. I started it for the first time in 27 years a few weeks ago ( I thought it was only 20 years 'til I found the last reg, renewal form from 1990) The mufflers were off, so it sounded like a "B" altered dragster with open dumps. Now, I see that I'm faced with fuels which this bike has never seen.
    . After gleaning your advice as a general consensus, I will start by replacing the exhaust washers, spacers, and bushings to eliminate back pressure issues. Then try a fuel additive which is generally called "lead substitute" and back off the timing in five degree increments and adjust the idle if necessary. And if it becomes sluggish at high speed, then find a middle ground with the advance where it will idle and run. Tests were recently done to check engine life of old marine engines with and without additives which demonstrated significant differences in longevity by using them.This is Lake George, in the Adirondak Mountains of New York. Check out Bike Week and the Americade event held there each year..

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