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Author Topic: Big bore-big cam--high altitude carb help!  (Read 1254 times)

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Offline andrewharris182

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Big bore-big cam--high altitude carb help!
« on: May 16, 2016, 10:30:52 pm »
Hey Guys,
       Long time listener first time caller... So I have looked for carb sizing high and low to no avail. I have a '74 750 with a 836 wiesco kit, kenny harmon f--grind, kerker 4-1, and a ported head. Right now I'm running on stock keihin 657b carbs with k&n pod filters. I live in Colorado at 6500 ft. So my my bike used to be fast as a bean burrito through a middle aged white man (that's me) down in houston. Now I'm up here and my bike can't beat a vtec civic. Basicly I am trying to find the optimal carbs to tune. I don't want to do this twice/8 times. Any help would be greatly appriciated.

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Offline dragracer

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Re: Big bore-big cam--high altitude carb help!
« Reply #1 on: May 17, 2016, 09:32:00 am »
Quote from: andrewharris182 on May 16, 2016, 10:30:52 pm
Hey Guys,
       Long time listener first time caller... So I have looked for carb sizing high and low to no avail. I have a '74 750 with a 836 wiesco kit, kenny harmon f--grind, kerker 4-1, and a ported head. Right now I'm running on stock keihin 657b carbs with k&n pod filters. I live in Colorado at 6500 ft. So my my bike used to be fast as a bean burrito through a middle aged white man (that's me) down in houston. Now I'm up here and my bike can't beat a vtec civic. Basicly I am trying to find the optimal carbs to tune. I don't want to do this twice/8 times. Any help would be greatly appriciated.



Check with Jerry RxMan  on the jetting. He's in Colorado also and has likely gone through the jetting issue already.
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Offline Medyo Bastos

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Big bore-big cam--high altitude carb help!
« Reply #2 on: May 17, 2016, 10:28:08 am »
125 main 41 pilot clip 1 notch down grom center 1 turn out on screws where i ran in denver


...Save a tree, eat a beaver...
« Last Edit: May 17, 2016, 05:44:53 pm by Medyo Bastos »
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Offline andrewharris182

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Re: Big bore-big cam--high altitude carb help!
« Reply #3 on: May 17, 2016, 01:37:53 pm »
Sorry guys, I should have been a little more clear. I guess my question is what throat size would be recommended for my setup? I want to get good flow without over carbing.
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Offline Bill/BentON Racing

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Re: Big bore-big cam--high altitude carb help!
« Reply #4 on: May 17, 2016, 02:05:44 pm »
29mm-31 max.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Big bore-big cam--high altitude carb help!
« Reply #5 on: May 17, 2016, 05:43:29 pm »
Quote from: Medyo Bastos on May 17, 2016, 10:28:08 am
125 main 40 pilot clip 1 notch down 1 turn out on screws where i ran in denver


...Save a tree, eat a beaver...

Good start. You don't necessarily need larger carbs. I'm gonna try my stock carbs on my 1000 hot rod at 6900' in the Springs pretty much starting at these numbers with a stock air box and K & N filter.

+1 with what Bill says too if you just have to spend another $800 and still experiment with jetting. And with this in mind I have a set of CR31's on my higher tech 900.
« Last Edit: May 17, 2016, 05:47:59 pm by Jerry Rxman Griffin aka MuthaF'er »
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline andrewharris182

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Re: Big bore-big cam--high altitude carb help!
« Reply #6 on: May 17, 2016, 07:29:26 pm »
Thanks for the replies! Yeah, I'm in the springs too. I'll tinker with the jets for now. Hopefully that will work for the summer.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Big bore-big cam--high altitude carb help!
« Reply #7 on: May 17, 2016, 07:53:44 pm »
When I had the 812 in it with stock head and big cam with Kerker and stock air box I ran 115's which were slightly rich. How are you jetted now? I'd start by dropping 1 size main.

Drop by for a garage day sometime. Briargate area.
« Last Edit: May 17, 2016, 07:56:08 pm by Jerry Rxman Griffin aka MuthaF'er »
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline andrewharris182

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Re: Big bore-big cam--high altitude carb help!
« Reply #8 on: May 20, 2016, 04:25:17 pm »
Definately man. I'm over by palmer park.Yeah I dropped by that classic bike night at the principals office last night. Good time!
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Big bore-big cam--high altitude carb help!
« Reply #9 on: May 20, 2016, 06:20:05 pm »
I gotta start wrenching again SOON so I can ride. You're welcome to watch/help.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)
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