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Old 03-28-2011, 03:22 PM   #1
Smallwheelsgood OP
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Single Carb Airhead

Hello all, newbie to this site, I have lurked for a while and have found a wealth of information and experience, plus some cracking pictures.
I have 2 no. R100RS's, 1 x 1978 in bits, 1 x 1983 running reasonably well. I have long wondered about converting to a single carb setup, does anyone know of this ever having being done? If not, what would be the pros and cons of such a setup. I have heard that carb icing may occur with such long inlet tracts, other than that I envisage that it would offer less complication and maintenance, and perfect balance with only a small reduction in top end performance. Any help would be much appreciated.

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Old 03-28-2011, 03:32 PM   #2
Houseoffubar
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It will work, if you are OK with harder starting, and about 27HP, but it will "work" I would recommend avoiding such thoughts
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Old 03-28-2011, 05:37 PM   #3
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"small reduction in top end performance"

If you are talented enough to pull off this mod you have to be talented enough to balance your carbs every 5-10,000 miles.
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Old 03-28-2011, 06:16 PM   #4
Tosh Togo
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Quote:
Originally Posted by Houseoffubar View Post
It will work, if you are OK with harder starting, and about 27HP, but it will "work" I would recommend avoiding such thoughts
Quote:
Originally Posted by kadesean View Post
"small reduction in top end performance"

If you are talented enough to pull off this mod you have to be talented enough to balance your carbs every 5-10,000 miles.
What they both said, and you WILL need carb & manifold heat, unless you want it to chug to a stop on rainy days. If you'd like to see how to do it, take a peek at any 1970 or older stock VW beetle for a simple carb-heat setup. Even enclosed under the rear lid, Bugs had to have heat unless it was a nice dry day. As an added bonus, the intake pulsations from that looooong path to each intake valve will make jetting a real treat, and throttle response will be soggy at best.


If you wanna go slow that bad, buy a Harley.
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Old 03-28-2011, 08:11 PM   #5
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Hmmm....

The last time I saw one of those conversions was back around 1990 at the MOA National Rally. A guy had converted an R65 using what looked like a Ford single pot sitting where the airbox used to be, with long intake tubes going to the heads. The install was very simple IIRC.

The bike ran quite well. I don't remember seeing any provisions for carb heating, so I can't comment on that aspect of things but I have held that conversion in the back of my mind, thinking that the info might be useful one day.

search around the net. Someone has to know something concrete because it has been done and more than once.
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Old 03-28-2011, 08:33 PM   #6
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First, I love the creative out of the box thinking. I'll never scoff at an idea that is different if only that it helps us learn and play.

Buy, please explain this to my like I'm the village idiot (I know, I know...), why would we want to do this? Is it simplicity of operations? Available materials? Efficiencies?

Thanks.
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Old 03-31-2011, 07:20 AM   #7
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If you are talented enough to pull off this mod you have to be talented enough to balance your carbs every 5-10,000 miles.
Very true ... but if you convert to the one-into-two throttle cables, that will be the last time the carbs need balancing until they're removed for rebuilding.
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Old 03-31-2011, 04:57 PM   #8
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Very true ... but if you convert to the one-into-two throttle cables, that will be the last time the carbs need balancing until they're removed for rebuilding.
That hasn't been my experience.... this is with five airheads and 20-ish years. BUT, I could be doing something wrong
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Old 03-31-2011, 05:06 PM   #9
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That hasn't been my experience.... this is with five airheads and 20-ish years. BUT, I could be doing something wrong
Yeah, I was kind of wondering if he had a line on magic throttle cables.




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Old 03-29-2011, 01:20 PM   #10
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Originally Posted by Smallwheelsgood View Post
I have heard that carb icing may occur with such long inlet tracts, other than that I envisage that it would offer less complication and maintenance, and perfect balance with only a small reduction in top end performance. Any help would be much appreciated.


I'd say to look to history. When Ducati installed a single Weber (I think) on their late 1980's/early 1990's SS series the results were not good, and many owners went back to two carbs.

Setting up seperate carbs to work well can take a few minutes, but holds well between valve adjustements or longer. If you are concerned about the time it takes to keep a bike running well, perhaps an airhead is not the bike for you.
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your bike is suitably dirty. Well done.
R65LazaruS
So I sold my GS and went shopping for a G/S!
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Old 03-30-2011, 01:38 PM   #11
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Ok, thanks to all. What about supercharging then? I know about the factory racer, but has it been achieved by anybody else since?
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Old 03-30-2011, 01:53 PM   #12
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Originally Posted by Smallwheelsgood View Post
Ok, thanks to all. What about supercharging then? I know about the factory racer, but has it been achieved by anybody else since?
Seriously why not consider mechanical fuel injection if complexity is the goal. BTW what is the goal?
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Old 03-30-2011, 02:05 PM   #13
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Seriously why not consider mechanical fuel injection if complexity is the goal. BTW what is the goal?
The goal concerning the single carb was simplicity. As far as the above is concerned, just curiosity.
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Old 03-30-2011, 02:43 PM   #14
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The goal concerning the single carb was simplicity. As far as the above is concerned, just curiosity.
OK gotcha, well the stock cv carb is pretty simple but I see where you are going. I had a Judson Super Charger on my VW for a while, did not gain much power but it looked cool.
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Old 03-30-2011, 02:07 PM   #15
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Seriously why not consider mechanical fuel injection if complexity is the goal. BTW what is the goal?
Thats another item that has been successfully applied to Airheads. Once again, there were several people who transplanted VW injector systems into Airheads in the late 80's/early 90's.

I would think that it would be much easier today but that stuff is over my head. I'm doing well to take care of what I have!
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