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No whining allowed!
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A few years back, I started this monster of a thread: https://www.xr1200ownersgroup.com/site/showthread.php?t=13330

Dris in the Netherlands did some research about creating a kit to retrofit an improved shaft, but concluded it was beyond a do-it-yourself project and this fix never progressed further.

In another more recent thread a rider in Australia had a similar problem and reportedly got the last OEM throttle body on the planet, with reference to HD not supplying any more - which is likely because they only have to keep parts around for so long.

Is it time perhaps to revisit an aftermarket fix, but maybe from the perspective of an exchange type service? Is there a shop (maybe Dris') who can develop a fix and turn these around on an exchange service basis with an improved shaft? He has certainly done a lot of R&D on the matter and perhaps is in the best position to speculate on the feasibility of this.

If the throttle bodies are or are about to be NLA, then the economics of such a proposal may just start making sense.

Comment is certainly invited!
 

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Michael i totally agree with you, everyone out there is riding a ticking time bomb just waiting for these things to fail . They are too good a bike to be scrapped! Maybe if we can create enough interest we might get some one of a higher intelligence level to take up the challenge. Les.
 

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Everyone runs the same risk except those with a carb!

Seriously, I've never heard of a carb butterfly going the same way. I guess it's just under engineered.
 

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GreaseMonkeyWithMBA
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78 Posts
my son is mechanical design engineer and works at a machine shop - he has the skills and tools available - I would prefer not to take my throttle body apart - does anyone have a throttle shaft that I could get my hands on to investigate reverse engineering and a better design?
 

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GreaseMonkeyWithMBA
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78 Posts
let me throw this out there also..... would our bikes benefit from larger bore throttle body?

background is this - I run a Jeep with the 4.0L - high-flow intake - header & straight exhaust - with 2mm larger throttle body (from 58 to 60mm) the combination gives me about 30hp more than stock (190 improved to 220 - it's not much - but the torque of this motor is legendary) - mind you this is at WOT. Likely because of having no muffler, I did lose about 1mpg (from 15 down to 14mpg). What we have done on our Jeeps is just have the stock throttle body bored out and new butterfly - and we are able to modify the existing throttle shaft. While my Jeep was my daily driver in AZ - I spent a lot of time in the Imperial Sand Dunes - running at WOT - which is where I needed the power. www.DuneToyz.com is where I have some pictures of many years ago fun in the dunes. I could go on and on about Jeeps - but that is not what we are here for..... the XR is my new favorite toy (although I can say I have never fallen off my Jeep (or my XR) - but I did have the Jeep standing on it's front bumper twice)

Since many of our bikes have a better flowing air filter & some exhaust modification - if we want to look into re-engineering the throttle shaft - would we benefit from 0.5 - 1mm larger throttle body? I assume we would need to get the bike tuned again so it isn't leaned out further and the benefit would likely only be at WOT. I have a recent dyno at 88-89hp with just a K&N and Bassani.
 

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GreaseMonkeyWithMBA
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thomgoo - thank you for the references - I am not surprised at the results they observed - bigger isn't always better - on the Jeep with it being 4.0L - the throttle body alone is only worth maybe 4-5hp - taking that down to our 1.2L bikes - yes - 1-2HP might be plausible. However on the Jeep we still needed to work with an engine shop out of Alabama - HESCO - to get a throttle body spacer that would increase the intake volume correctly.... lots of testing and engineering on their part - some of you guys in the southern US may know the HESCO guys (http://www.hesco.us/) - they built NASCAR engines for a few guys back in the day and were kind of a skunkworks for some

In the end - assumption at this time is bigger won't necessarily be better for our XR's - but we can still work on that throttle shaft - if anyone has even a broken one - that can be reverse engineered, we will take a shot at it.
 

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XRated
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Can still have too big carb, same principle of dropping air velocity too much reducing fuel atomisation.
The math is easy to determine max TB bore for what cuin, max RPM and considering street riding rideability. A bike doing only 1/4 mile can use different bore compared to riding on street.
There are formula for determing intake length also but one length does not suit all RPM and why they make variable intake runner lengths for other gear and high, mid and low intake plenum heights for V8s etc.
 

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A few years back, I started this monster of a thread: Throttle plate screw/shaft "fix" ideas??

Dris in the Netherlands did some research about creating a kit to retrofit an improved shaft, but concluded it was beyond a do-it-yourself project and this fix never progressed further.

In another more recent thread a rider in Australia had a similar problem and reportedly got the last OEM throttle body on the planet, with reference to HD not supplying any more - which is likely because they only have to keep parts around for so long.

Is it time perhaps to revisit an aftermarket fix, but maybe from the perspective of an exchange type service? Is there a shop (maybe Dris') who can develop a fix and turn these around on an exchange service basis with an improved shaft? He has certainly done a lot of R&D on the matter and perhaps is in the best position to speculate on the feasibility of this.

If the throttle bodies are or are about to be NLA, then the economics of such a proposal may just start making sense.

Comment is certainly invited!
I watched the video of a guy on youtube making one with a lathe. Can we just pull a similar shaft from another model of harley and somehow use it?
 
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