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Old 02-08-2011, 11:20 AM   #16
El Hombre
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I think at $9.20 a gallon, I'd be trying to lean it out; with acceptable drive ability. It's only!! $3.50 a gallon for the 91 octane stuff around here.
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Old 02-10-2011, 06:39 AM   #17
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Had a chat with Richie Moore today. Lots of pointers from him. It an absolute pleasure to talk with someone who's so clued up and open with his knowledge.

Nice guy
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Old 02-10-2011, 08:22 AM   #18
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Had a chat with Richie Moore today. Lots of pointers from him. It an absolute pleasure to talk with someone who's so clued up and open with his knowledge.

Nice guy
So what did he say?

I was looking at my dyno chart and thinking back and I might have been stretching 13.5 a bit. My bike is probably around 13.25 the most and it is probably below that more than above it. Still, from my experience around more than a couple of dyno's. I would call 12.5 good for power but slightly rich. Slightly rich is never best for power on top. It can really help you get off bottom and through the lower midrange but other than that IMO rich and best power almost never go together. One thing is sure. More than just slightly rich is a power killer anywhere you look at it. I would call 11.5 too rich and costing you power and efficiency. Remember that between two and three HP on our bikes is a 5% difference in power! It all adds up!

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Old 02-10-2011, 08:58 AM   #19
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You could drill out smaller jets to get the exact size you need. Since you want what BMW doesn't sell.

There are precise drill bits to do the job.
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Old 02-10-2011, 11:01 AM   #20
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You could drill out smaller jets to get the exact size you need. Since you want what BMW doesn't sell.

There are precise drill bits to do the job.
This.

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Old 02-10-2011, 11:17 AM   #21
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In a previous life I worked with testing natural and LP gas construction heaters and used precise numbered injector drills to tweak combustion. You should be able to purchase the exact size drill bit you need, but will need access to pin gauges to get measurements of what you have. I'm not sure how BMW measures the jets. I would expect a GOOD motorcycle shop would have these.

Also obviously, if you do drill out a jet, remove the markings, scribe on the "new" jet the size. Not sure if it's large enough to dot hat though.
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Old 02-10-2011, 01:37 PM   #22
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Just for your info on drilling out jets.
I needed a 190 dellorto main jet but couldn't find one in the shops, so I bought a 180 and took it to a good machine shop and asked them to drill it to 1.9mm .....the 1.9 mm drill fell straight through the hole 0f the 180 even though the size on the jet is supposed to be its internal diameter on dells.
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Old 02-10-2011, 02:27 PM   #23
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That's why I recommended checking checking w/ pin gauges, to determine the CORRECT size! Don't take anything for granted. Best to drill one size smaller than what you think then go up one size from there.

BTW- it isn't necessary to HAVE it drilled. Good numbered bits have a little brass hex end to grab onto which allows you to drill w/ your fingers. Unless enlarging the hole quite a bit. Heck jets are only brass.
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Old 02-10-2011, 03:36 PM   #24
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14.7

I believe you'll find that 14.7:1 is the ideal mixture ratio in terms of the best combustion, the best and most complete burn of the fuel. Any gasoline engine. The ability to keep the ratio close to this number is a major reason that electronic fuel control has resulted in better mileage and lower CO (incompletely burned fuel) and HC (unburned fuel) emissions.
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Old 02-10-2011, 07:01 PM   #25
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I believe you'll find that 14.7:1 is the ideal mixture ratio in terms of the best combustion, the best and most complete burn of the fuel. Any gasoline engine. The ability to keep the ratio close to this number is a major reason that electronic fuel control has resulted in better mileage and lower CO (incompletely burned fuel) and HC (unburned fuel) emissions.

That's what fuel injection will use for idle and constant speed highway driving.
I'm pretty sure it will be richer for acceleration and full throttle operation.
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Old 02-10-2011, 07:37 PM   #26
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I used to run a chassis dyno tuning service and I did a few Airheads built up by San Jose BMW. You will make peak power with about 11.5 to 1 air fuel ratio. The air cooled engines need some extra gas to keep cool and prevent any detonation. The famous 14.7 air fuel ratio is for keeping the catalytic converter at the correct stoichiometric ratio and is much too lean for peak power. A water cooled engine will make peak power at about 12.5 to 1. A turbocharged car will post its best power numbers with about 11 to 1.
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Old 02-10-2011, 07:59 PM   #27
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Oh my, this thread is actually tending toward science instead of internet bull shite. Kinda like when Farmer Rob posted dyno charts showing the difference between a GS y-pipe and original collector box.

Thanks for the breath of fresh air.
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Old 02-10-2011, 10:44 PM   #28
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I spent some time yesterday tinkering and now have the needle on the top notch. This has me around the 12.8:1 area on the mid range crossing through to 13.2:1 at the top end. Seat of the pants riding though suggests it feels happier and produces more torque with the mixture slightly richer. The 11.8:1 on the chart I posted at the start of the thread is a Wide open throttle (WOT) run up a long, steep hill where the air/fuel drops like a stone to it's base level. Running the same jetting and doing a similar WOT run on a flat road has the mixture in the mid to high 12's so if I jet to 13 (ish) on the hill climb I'm actually going to be running lean and not making max power for normal riding conditions. I'd normally be taking that hill at 70/80 mph gently opening the throttle to maintain speed with the richer jetting I'd be bang on 13/13.5:1.

After talking to Richie yesterday we have some doubts about the cam that's in there. Before I bought bike the original engine had suffered from the $2,000 O ring problem taking out the bottom end, another bottom end had been fitted that was supposed to be from an early 80's RS. The cam has nothing stamped on the end to identify it, Richie suggested that it may be a 296 Cam. The plan is to fit the original 308 Cam (the bike came with the original wrecked bottom end) and effectively get the bike back to point 0. The standard needle position is on the 3rd notch from the top, dropping the needle 2 positions is a big change to the jetting and is a cause for concern.

Reading the above may give the impression that the bikes a jalopy, the reality is it's a lovely quick thing to ride and has virtually no vibration from 5k up to the red line. The last dyno run had the power in the low 50's

I'll get some air/fuel charts once the standard cams fitted. Once it's running as well as it can be I'll be fitting a set of Richie's pistons and few of his other goodies.

Just dug out my air/fuel charts for my fuel injected Guzzi. It had had the Airbox mod and was running a decatted H Pipe, A very fast bike.

The spikes in the air/fuel read out are reversion (air gets drawn back up the exhaust) when changing gear. the double spike at 45 seconds was me missing gear between 5th and 6th. The black line is the RPM - believe me at those revs on a Guzzi you are really moving.


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Old 02-10-2011, 11:42 PM   #29
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Originally Posted by Rob Farmer View Post
I spent some time tinkering yesterday and now have the needle on the top notch. This has me around the 12.8:1 area on the mid range crossing through to 13.2:1 at the top end. Seat of the pants riding though suggests it feels happier and produces more torque with the mixture slightly richer.
If it was 11.5 before, and now it's 12.8, it's leaner. Or are you saying it felt better before at 11.5:1?
Id be interested to see dyno results of the rich/lean tests.
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Old 02-11-2011, 12:05 AM   #30
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Oh my, this thread is actually tending toward science instead of internet bull...
Yes, and lapping onto the art of tuning.

Good read.
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