« previous next »
Pages: [1]   Go Down

Author Topic: Big bore-big cam--high altitude carb help!  (Read 1345 times)

0 Members and 1 Guest are viewing this topic.

Offline andrewharris182

  • Full Member
  • *
  • Posts: 4
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.

Logged

Offline dragracer

  • Really Old Timer ...
  • *******
  • Posts: 5,101
  • CB750F Dragbike
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.
Logged

Offline Medyo Bastos

  • Master
  • *****
  • Posts: 1,579
  • Gusto mo titi ko?
    • project
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 »
Logged

Offline andrewharris182

  • Full Member
  • *
  • Posts: 4
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.
Logged

Offline Bill/BentON Racing

  • Really Old Timer ...
  • *******
  • Posts: 6,725
  • Ex Honda Service Manager, Cert. Honda Tech - Racer
    • BentON Racing
Re: Big bore-big cam--high altitude carb help!
« Reply #4 on: May 17, 2016, 02:05:44 PM »
29mm-31 max.
Logged
BentON Racing Website
OEM Parts | Service | Custom Builds
BentON Racing Facebook
Over 35 years of experience working on vintage motorcycles, with a speciality in Honda SOHC/4 with a focus on the CB750 and other models as well from 1966 - 1985.
______________________________________
1993 HRC RS125 | 1984 NS400R | 1974 Honda CB750/836cc (Calendar Girl) | 1972 CB 500/550 Yoshi Kitted 590cc | 1965 Honda CB450 Black Bomber | 1972 Suzuki T350 | 1973 88cc | Z50/Falcons Pit Bike | 1967 CA100| 1974 CB350 (400F motor)...and more.
______________________________________
See our latest build 'Captain Marvel' CLICK HERE

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,902
  • Bought her new 4/75
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 »
Logged
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

  • Full Member
  • *
  • Posts: 4
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.
Logged

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,902
  • Bought her new 4/75
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 »
Logged
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

  • Full Member
  • *
  • Posts: 4
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!
Logged

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,902
  • Bought her new 4/75
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.
Logged
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)
Pages: [1]   Go Up
« previous next »