The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: clouseau on July 15, 2009, 09:35:44 AM
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This is a valid question, I think, since these bikes were designed for leaded fuel.
I live in California, so we refine our own fuels here. I put in 91 octane.
I have also been playing with the timing advance. If I advance it just a bit, I get better power all through the power band but experience pinging between 4-5k rpm. When I set the timing back to normal, I still get pinging in that range only less. So I am wondering if a certain amount of pinging is just normal given today's fuels.
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Pinging, rattling, and any other terms you may have heard are synonyms for pre-detonation... the destroyer of engines.
Hot spots within the cylinder head are igniting the fuel prior to the firing of the spark plug/s. At 4-5K revs, there's little time for accumulated bits of carbon on top of the piston crown, or other hot spots, to cool. Cool being a relative term for the tremendous explosions occurring in the cylinders.
Retard the ignition a bit more and try again. Also, might be time to peek inside the cylinder heads. A shop with a glass fiber video viewing system can scan valves, pistons, cylinder walls, etc.
[smiley=2cents.gif] Monte
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I have to retarded the ignition by approx 2 Deg. to avoid pinging on 95 Ron unleaded (90-91 AKI) and even then some tanks of fuel will cause a little pinging until the engine warms. I can feel the slight roughness that pinging causes as a vibration in the tank at 2500 to 3000 rpm. 98 RON unleaded (93-94 AKI) is OK but around 7% more expensive at £4.95 a gallon.
Compression is 9.2 : 1
What ignition timing/compression are you using?
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Just a hint of intermittent pinging under heavy load (lugging up a hill in high gear/low revs) is usually OK and probably indicates your optimal ignition timing point. Pinging/constant rattle every time you give even a bit of throttle will eventually hole a piston, or worse...
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The Inspector is, "...experience pinging between 4-5k rpm."
That ain't lugging. That's some serious rattlin'. Pull some advance out of the ignition, pronto. R65s never were known as hi-perf motors.
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OK, will do on the timing. I will retard a bit.
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I was trying to give some general guidelines that would apply to everybody...
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Mine is timed right to the mark and doesn't ping on regular octane fuel (tho if I had to ride in Bob's 115 degree weather it might. So might I.)
I'm trying to imagine how I could get it to ping at 4K rpms; maybe going up a hill in top gear and try to accelerate hard? I don't do that, I would shift down. 5 speed trannies are nice.
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I backed it (the advance) off just a tad and the pinging/rattle is gone and no loss of power. The idle went to crap, tho. So instead of bumping up the idle adjust screws, I played with the air/fuel mixture screws and sure enough they needed a bit of leaning and the idle was straight.
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I was reading an article the other day about pinging and fuel and the bottom line was - Use the highest octane fuel available, it doesn't burn hotter, it is designed to minimise pinging problems. Especially good for our 80's low tech engines. I always run premium unleaded, it's 95 octane here is Oz, and I dont have any pinging issues.
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I'm running 87 oct with good power but I have the Omega Ignition set on curve 4. It runs a little bit less advance than stock. (I think stock is 32 degrees?)
TTFN,
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I ran plain old 87 octane in my 82 LS (stock carbs and pipes) on the 2100 mile round trip to the BMWMOA rally and experienced no pinging.
The temps didn't get above ~90F though I did do plenty of mountain climbing and high speed interstate runs -> all without a hint of pinging.
I think that I've got the carbs dialed in just right and don't dare take them apart right now!
:)