79 Magnum XK, Round intake port?

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79 Magnum XK, Round intake port?

Ben S /

Sep 26, 2020 01:52PM

Howdy,

I recently picked up my dream bike, a 79 Magnum Xk with around 400 miles on it. Originally a PrettyBombers build I believe!

I'm gonna keep it pretty stock, but I wanted to put on a 15 bing to get a little more power out of it here at altitude (CO) - when I went to take the carb off I noticed it wasn't the stock carb, its a 1/14/157 with a round intake, and the cylinder seems to have been modded to also have a round port? (pictures attached) Any ideas what the deal is here? I assume I cant just put a rectangular 15bing intake one it... The bike has great low end but tops out around 27 and i'd like to get it to 30-35. Any suggestions on mods that will keep it fairly stock but help me with top end a bit?

Cheers!

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Re: 79 Magnum XK, Round intake port?

Overpriced Parts /

roffman

Sep 26, 2020 01:55PM

Stock Magnum cylinders and maxi hi torque cylinders all have round port,

Use a stock puch round port 14mm intake

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Re: 79 Magnum XK, Round intake port?

Ben S /

sheuxmlin

Sep 26, 2020 01:58PM

Nice! Good to know. It does have a 14mm intake. Any recs then for a little more tope end?

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Re: 79 Magnum XK, Round intake port?

Jeff Parr /

bigbadbrother

Sep 26, 2020 05:59PM

My experience with round port motors is bad, no matter what I did the manifold would not seal and it would bend even with light torque it would still bend (really cheap metal) so I dumped it for a square port.

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Re: 79 Magnum XK, Round intake port?

Overpriced Parts /

roffman

Sep 26, 2020 06:45PM

> Ben S Wrote:

> -------------------------------------------------------

> Nice! Good to know. It does have a 14mm intake. Any recs then for a

> little more tope end?

I made many posts about metal mesh 1/4-5/16 in hole in magnum chamber and end cap

Time around 18° Btdc Then Jet around 68-70 jet with 222 atomizer then tune the clutch with thick clutch springs and you will get this:

I also sand or mill puch heads flat and sometimes add a squish band, but on a piston that little it seems to make very little difference, Just flat works fine for more compression and power