Author Topic: One for the 250cc folk  (Read 101334 times)

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Offline stay`tee

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Re: One for the 250cc folk
« Reply #120 on: September 17, 2014, 06:27:50 AM »
im seeing to much timing advance, needs a cuppla degrees less,,
« Last Edit: September 17, 2014, 06:34:01 AM by stay`tee »
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #121 on: September 17, 2014, 06:52:03 AM »
im seeing to much timing advance, needs a cuppla degrees less,,


Not an easy task Ronnie, 12 degrees static,ramping to and fixed at 47 btdc @ max hp, (15,000 rpm) dropping to 37 after.(not much info out there, took 3 yrs to find that info  :-o
To change, I need some more cubic dollars, and minisquirt, plus another lifetime to learn efi
Tiny
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #122 on: September 19, 2014, 11:36:49 PM »
It might save a lot of time to set the jetting on a dyno and get traces of HP, torque, and mixture.  Advice I got this summer is to jet the engine to produce maximum torque.  Then, jet it to produce maximum power.  Then adjust the air jetting, emulsion tubes, etc so the same jets produce maximum torque and max HP.  His advice is to let the engine tell you the mixture it wants.

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #123 on: September 20, 2014, 12:33:08 AM »
Thanks Bo, unfortunately, I don't have access to a dyno , the closest is over 300 miles away, but I hear what you are saying mate.
I'm getting close, I just need to make the WOT a little safer, and get rid of the midrange miss (new plugs should do that), then I should be ready for a 3 mile run down the salt  :?
Tiny
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #124 on: September 20, 2014, 11:27:28 AM »
Chapter 3 in David Vizard's "How to Build Horsepower" might have the info you need to get started on a fix.  The setup you are running now might be a good one after some adjustments.  This book is in print and reasonably priced.

 

Offline RansomT

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Re: One for the 250cc folk
« Reply #125 on: September 20, 2014, 09:11:48 PM »
You know that is a "ton" of timing.  I don't know of any of the "modern" sport bikes that come close to 47 degrees... heck, a Gen 2 Busa is set to 34 BTDC from the factory.

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #126 on: September 20, 2014, 10:01:39 PM »


Remember these little engines have a miniscule 32mm stroke, and spin like hair driers.
I cannot verify the chart is an accurate representation ?
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline maj

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Re: One for the 250cc folk
« Reply #127 on: September 20, 2014, 10:36:23 PM »
Tiny you need something like the Dyna  ARC2 that has a timing retard feature and much better spark
I am surprised your not killing the spark even now with that much cyl density

Offline stay`tee

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Re: One for the 250cc folk
« Reply #128 on: September 20, 2014, 11:07:38 PM »
i run a Dyna ARC2 on the 12 and have been told that its good for 6-8 extra horsepower at peak,, on Methanol, with the spark restrike activated it cleans up the 1-4k range noticably,,

the retard function is 10* user activated,, had a button on the bars, on a pass at Bonneville i tried it at about 10k, the motor nosed right over, never used it anymore,,,
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #129 on: September 22, 2014, 12:50:22 AM »
Maj & Stay'tee, thanks for the tip(s)
I had a GREAT run today, NO MISS !, took it out to 17,000 in 1st thru 4th (remembered the button too)then short shifted into 6th and held it flat for 1/4 mile, did a plug chop & coasted to a stop collecting flies in my teeth.




http://youtu.be/5xLWzshRkwY      (MP3 sound file only)

Bo, Iv'e ordered that book, thanks mate

Remember, the ign timing this bike uses is unchanged from what it was sold with new, they usually burn ULP (gas), and NEVER ping
Considering methanol burns slower than gas, retarding the ign timing might make the time available for a burn ?
A once champion speedway outfit rider, Spotty Burke told me, ( despite his age his memory with his Triumph setup in 1956 remains as clear ), he ran 47 degrees btdc with methanol & beat a Vincent to gain the championship that year
« Last Edit: September 22, 2014, 02:14:17 AM by generatorshovel »
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline maj

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Re: One for the 250cc folk
« Reply #130 on: September 22, 2014, 04:18:49 AM »
The only real positive way of figuring spark advance suitability to your setup is to retard it and see if power goes up or down
you could slot the crank pickup and maybe pickup a few degrees adjustment , but without a dyno or datalogging its a guessing game as the timing line on the sparkplug only gives you an basic indication

What plug gap are you running , looks like .035 (.8mm) or so , i would aim at much less

In 09 i tried methanol on the 750 and had to run what i considered a bit lean to get it to run clean throughout the range on a stock ign system, needless to say i burnt valves and head as the leaner mixtures gave me too much cyl temp
This Aussie season i hope to run it again if i can get everything together in time , and the first thing on the shopping list was a CDI ignition , that gave great spark energy for little power cost (counting my amps left for fuel pumps etc ) , before the Feb setback i had run high boost pressures cleanly at a very rich mixture , very promising , but its so rich the wideband is not reliable and will be backing it up with EGT when i get tuning again

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #131 on: September 22, 2014, 05:14:10 AM »

you could slot the crank pickup and maybe pickup a few degrees adjustment ,
Not really


What plug gap are you running , looks like .035 (.8mm) or so , i would aim at much less
Yep. out of the box 35 thou
 i had run high boost pressures cleanly at a very rich mixture , very promising , but its so rich the wideband is not reliable and will be backing it up with EGT when i get tuning again
On the previous run, A/F , although wrong ? was indicating 5.9 to 6.5
This run, it was hi sevens before the gauge freaked out and error coded, I'd gone from #620 main, to # 640, egt's were previously 1150, this run, 1050


I realize there are a zillion improvements that should / could be done to maximize the tune, but as this builds main purpose has been to keep me sane, and hasn't always been the case,,,,one slip will make it all worthwhile, especially if it's around 125, Iv'e been running since '96 & never gotten my 125 licence (Postie bikes tend to do that, Dave Plecas might have a chance on his though ?)

I'll fatten up the top end until it drowns, then work my way back from there (.22 thou plug gap next was the plan Greg)

Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #132 on: September 22, 2014, 11:58:43 PM »
In a few years when I retire I am going to drive ti A2 wind tunnel with the bike and rent a space at the local KOA for several days.  The bike will go into the tunnel, I will make some mods, and it will go back in until I get the aero sorted.  The I drive back home.  Maybe you could do this at the dyno shop?

Offline Peter Jack

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Re: One for the 250cc folk
« Reply #133 on: September 23, 2014, 01:24:51 AM »
Why not go to the new tunnel in Salt Lake City? It's way closer and very similar.

Peter

Offline TheBaron

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Re: One for the 250cc folk
« Reply #134 on: September 23, 2014, 11:59:33 AM »
I understand the trouble you are having tuning with methanol and the supercharger... It is not for the faint of heart, but you can do it if you understand most of the major issues....

Methanol burn rate is slower than gasoline (18% to 22%), so all else being equal, you need more spark advance so peak cylinder pressure occurs at the sweet spot of the power stroke (10 to 15 degrees atdc or so).

Boost pressurized fuel mix burns at a faster rate than normally aspired mixtures so you need less spark advance to get the cylinder pressure at the power stroke sweet spot....retard about 1 to 2 degrees per 5 psi boost is a good starting point

Yes, they tend to offset somewhat with the methanol burn rate being the major effect .

Boost mixtures become harder and harder to ignite due to the insulation effect of nitrogen gas, so spark plug gaps have to  go down.... .016" to .018" at very high boost or with a weak ignition system.....

Methanol will detonate when pushed to it thermal stability limit... It is about the equal of 116 octane gas when it is good ,,, a lot less when lean...

A/F GAUGES usually don't read accurately when methanol is rich,,, use the EGT instead.

Timing should be set for  "best continuous  torque" in the power band of the engine... Setting for the peak output using an inertia type dynamometer or short sprint runs has killed more endurance type racing engines than saints in heaven .... When one is WFO for more than a few seconds at a time,,, the tune must be turned down else killer detonation will occur...

A "Knock-Sensor" system would be your best friend in finalizing your tune....

Good luck and I'll continue following your efforts with interest....I have a air-cooled blown 350 pushrod motor that is also very tricky to tune....

Robert in California