Flatback carb conversion

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ted johnson
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Flatback carb conversion

Post by ted johnson » Sun Jul 22, 2012 3:43 pm

Do we have a real guru in the ranks with all the drill numbers for converting the old flatback Mac aluminum carbs to alcohol? I have two of them on my 101/Mc20 clone. I was going back to gas, but after one try, I'll return to alky. These have been rebuilt with fresh diaphragms and screens, and are in good condition for conversion. Who do we have that's done a good number of them with success? Prices? Thanks! Ted Johnson

Glenn Duvall
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Re: Flatback carb conversion

Post by Glenn Duvall » Wed Jul 25, 2012 9:05 pm

Well, I don't know about being a "guru"....but I can forward scans from the July 1964 issue of "Karting World" that provide the drill sizes for opening the passges for methanol fuel.
(I can't post either page due to the 2.0 Mb files size limit.)
Also, on McBob's website (http://macbobaust.com/mac_karts.html) there is an article on 1962 fuel mix data (the Vernon Ray Johnson letter) that also contains the data.

Rob Voska
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Re: Flatback carb conversion

Post by Rob Voska » Wed Jul 25, 2012 9:57 pm

Just my .02 worth. Carb is similar in operation to a tillotson. Why not use a tillitson drill pattern?

ted johnson
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Re: Flatback carb conversion

Post by ted johnson » Thu Jul 26, 2012 9:05 am

Glenn, thanks. I have the McCulloch fuel document from Jeff Campbell. I had a copy of it fifty years ago, but had forgotten it existed. My Bud has the old KW magazines, I can get him to dig it out for me.
Rob, I figured it would be about the same as the Tilly.
I hate to do it myself because my hands aren't steady, and the old eyes aren't worth a darn up close.
Paul Booth has kindly said that he will do them for me. All I need do now is tear myself away from the disaster that is Charlie's 101D, and get the flatbacks off the Swoopster and send them to Paul. It's worth paying Paul, as I know his workmanship! Ted

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Kurt Bogerman
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Vintage Karting items owned: 1964(?) Rupp Grand Prix, MC 90, Safari Gearbox.
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Re: Flatback carb conversion

Post by Kurt Bogerman » Sat Aug 18, 2018 10:36 pm

As the original question was never fully addressed, I would like to resurrect this old topic:

Does anyone have a copy of the July 1964 issue of "Karting World" article that descibes the carb modification, or another resource that covers this topic? I have a small flatback that I need to... uh... verify whether or not it's in stock configuration🙄

Thanks,

Kurt

ted johnson
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Re: Flatback carb conversion

Post by ted johnson » Sun Aug 19, 2018 9:23 am

Kurt, the best trick is to PM Paul Booth and establish communication with him. His flatbacks work great, so he knows what's what. TJ

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Kurt Bogerman
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Re: Flatback carb conversion

Post by Kurt Bogerman » Mon Aug 20, 2018 1:28 am

Thanks, Ted.

While I'm absolutely confident that Paul is the sure thing, I'd really like to have the experience of getting into the carb and doing any modifications myself. Maybe he would share some knowledge? I've emailed with him before: He supplied me with my Margay clutch drum. It can't hurt to ask.

I have two small flatbacks. One is on my MC90. That one I overhauled and put away several years ago until I restored the Grand Prix last winter. It meters gasoline flawlessly. The other is one I purchased via eBay about a year ago. I thoroughly cleaned and rebuilt it, in the meantime, but I haven't used it yet, and I don't know if it's been tinkered with previously. I'd like to find and put into my binder that Karting News article or some other documentation like that for possible future projects.

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Re: Flatback carb conversion

Post by Paul Hunter » Mon Aug 20, 2018 2:31 pm

Small Mac Flatback Carb Drillings.jpg
Small Mac Flatback Carb Drillings.jpg (50.85 KiB) Viewed 588 times
Lets see if you can open this and if it helps.
Paul

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Kurt Bogerman
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Re: Flatback carb conversion

Post by Kurt Bogerman » Tue Aug 21, 2018 12:56 am

Thanks, Paul. As you know, I love collecting this kind of data.

Now.... I still wonder if that Karting News article or some other documentation of the process is out there?

Rob Voska
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Re: Flatback carb conversion

Post by Rob Voska » Tue Aug 21, 2018 4:16 pm

Interesting they run the pop off that high. Wonder if it was because of direct drive / low RPM clutches to help keep it clean.

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