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Author Topic: An Update on Jetting  (Read 1436 times)

PaulF

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An Update on Jetting
« on: June 20, 2008, 12:29:37 PM »
For those wishing to add an aftermarket exhaust or air filter, (or both), I wanted to provide an update on my efforts to dial in my AVL. Airflow to these engines in stock form is very restricted to meet the Euro emissions. Its been my experience thus far, that given the (relatively), large piston and long stroke, these engines yearn to breathe and the richer they run, the happier they seem to be.

The addition of the K&N filter and Dunstall muffler, without any jetting mods, revealed a bike that would barely run. My dealer was kind enough to make a house call and install a pilot jet one size up, a 120 main jet, (110 is stock), and move the needle setting one click down. For most motorcycles, this would be adequate. Not so the AVL, which showed little improvement in driveability, a high idle and an ash-grey spark plug, revealing a still lean condition.

The next step was to order three jets from our host, a 125, 127.5 and 130. The installation of the 125 was a noticable improvement, providing quicker throttle response and driveability, (I no longer have to crack the throttle every 10 seconds to maintain a given speed, it stays where you put it). After the test ride however, it still had a high idle, (no cracked or broken hoses and pulse valve hose is stell-braided), and the plug was ash-grey again - no dice. The AVL wants more still.

I bumped up to the 127.5 main last night after dark and haven't yet test drove. Each step up has been an improvement. Low-range torque has been phenominally improved and this motor has yet to be broken in so I ride it with kid gloves. All indications point to an impressive little torque monster at this point. Gas mileage be damned, I'm impressed with the power that can be released in these engines when you let them breathe.

I'll keep you posted. ;D




REpozer

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Re: An Update on Jetting
« Reply #1 on: June 20, 2008, 03:29:06 PM »
Sounds fun ,I wouldn't mind reclaiming the right tool box back, currently has an air cleaner in it. The torque is good in stock form, I guess I don't know what I'm missing.
2008 AVL Classic Bullet in British Racing Green
REA # 84 ( the first time)

Thumper

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Re: An Update on Jetting
« Reply #2 on: June 20, 2008, 05:50:11 PM »
Paul,

Sounds like its going to be a runner!

Will you make any changes to the idle jet or idle mixture?

Matt

PaulF

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Re: An Update on Jetting
« Reply #3 on: June 20, 2008, 06:12:31 PM »
Thats a major item I neglected to put in my original post. Throughout the whole process and even now, the mixture screw has been only 1/2 to 3/4 turn out from seated!! So the motor is now gulping so much air, I'm having difficulty feeding it an adequate, corresponding fuel supply.

I won't be a bit surprised if the 127.5 is not adequate and if the 130 is barely adequate, (I know it's a Lean-Burn, but Geez).

That raises a question for the RE gurus out there: Since too lean is bad, cylinder head runs hotter, etc, was the Lean-Burn designed with these extra stresses in mind? Or, does it just shed heat far more efficiently than the iron lung since it is an all alloy design, (and did I just answer my own question)? ;D

PhilJ

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Re: An Update on Jetting
« Reply #4 on: June 20, 2008, 09:52:59 PM »
Probably!

PaulF

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Re: An Update on Jetting
« Reply #5 on: June 23, 2008, 11:51:43 AM »
Final report: The 127.5 main jet turned out to be "OK". Translation: A steady, loping 500 (+/-) RPM idle, (when very warm), good throttle response and pop-back kept to an absolute minimum with the mixture screw a reasonable 1, 3/4 - 2 turns out.

Anyone wishing these upgrades and using any non-factory silencer WITH a baffle should be able to get away with a 125 main jet.

 ;D