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Author Topic: 1982 CB750F Resto-mod. At least that's the current plan.  (Read 1375 times)

Offline advCo

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"He broke the mirrors off his Cadillac, 'cause he doesn't like it looking like he looks back."

74 CB360 - Luna - http://www.dotheton.com/forum/index.php?topic=63294.0 - Sold
82 GS550L - Tracker-ish - http://www.dotheton.com/forum/index.php?topic=67229.0 - Sold
74 XL350 - The Turd - http://www.dotheton.com/forum/index.php?topic=70252.0 - Sold
Suzuki FA50 "No-Ped" - http://www.dotheton.com/forum/index.php?topic=71189.0
73 Suzuki RV125 -http://www.dotheton.com/forum/index.php?topic=73875.0
'97 BMW F650st - http://www.dotheton.com/forum/index.php?topic=75732.0

Offline The Jimbonaut

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #31 on: Aug 06, 2018, 13:44:07 »
So thatís what that thingís called. Learn something new every day 🧐


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"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline advCo

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #32 on: Aug 06, 2018, 13:45:30 »
So thatís what that thingís called. Learn something new every day 🧐


Sent from my iPhone using DO THE TON

I only know the name from looking it up for popping dents on a motorcycle tank  ;D
"He broke the mirrors off his Cadillac, 'cause he doesn't like it looking like he looks back."

74 CB360 - Luna - http://www.dotheton.com/forum/index.php?topic=63294.0 - Sold
82 GS550L - Tracker-ish - http://www.dotheton.com/forum/index.php?topic=67229.0 - Sold
74 XL350 - The Turd - http://www.dotheton.com/forum/index.php?topic=70252.0 - Sold
Suzuki FA50 "No-Ped" - http://www.dotheton.com/forum/index.php?topic=71189.0
73 Suzuki RV125 -http://www.dotheton.com/forum/index.php?topic=73875.0
'97 BMW F650st - http://www.dotheton.com/forum/index.php?topic=75732.0

Offline The Jimbonaut

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #33 on: Aug 06, 2018, 13:59:29 »
I only know the name from looking it up for popping dents on a motorcycle tank  ;D
Better that than for spiking blood pressure


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"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline irk miller

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #34 on: Aug 06, 2018, 14:24:34 »
Cheers Irk. Any idea what the differences between the carbs are?


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Hard to say.  I've never see anything about your particular E carbs.  They might be Euro spec or something, but all the VB42 carbs (in the US) are jetted the same and share common specs on paper:

3 Jet Vacuum Slide:

EPA Spec (US), Hidden Emulsion Type Idle Mixture Screw, Non-Replaceable Slow Speed Jet (Some Models) Non-Adjustable Jet Needle (All Models) Air Cut Valves (All Models), Twin Sequentially Functioning Main Jets (68/102), Slow Speed/Pilot Jet (35), Accelerator Pump (All Models)

Offline The Jimbonaut

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #35 on: Aug 06, 2018, 14:30:48 »
Cheers man - from what I've read the number after VB (in this case 42) refers to the size of the venturi.  Jets-wise, these carbs have been fitted with 68 primary and 100 secondary.  But the Clymers indicates the F should have 102 I think.

"Dabbled with" definitely applies to this bike.
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline irk miller

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #36 on: Aug 06, 2018, 14:36:38 »
Cheers man - from what I've read the number after VB (in this case 42) refers to the size of the venturi.  Jets-wise, these carbs have been fitted with 68 primary and 100 secondary.  But the Clymers indicates the F should have 102 I think.

"Dabbled with" definitely applies to this bike.
That's correct.  It's always Venturi size at the slide.  And definitely should have a 68/102 in stock form.

Offline The Jimbonaut

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #37 on: Aug 06, 2018, 14:48:42 »
The bike has a 4 into 1 Kerker exhaust - may that be why the jetting has been adjusted?
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline The Jimbonaut

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #38 on: Aug 06, 2018, 23:21:29 »
Carb hose question - when I pulled the carbs, both hose A and hose B were connected to the carb body at one end but not the other -



here's another shot -



But on my other CB750 there's only one hose that's connected to both ports on the carb.  So I did the same with this, ditched one tube and looped the other -



Is that correct?

Hooked up the carbs, tank, airbox again, fired it up - seems to idle ok but as soon as I crack the throttle the revs stay high.  I checked all the boots to see if there was a vacuum leak but they seem ok, and the throttle cable isn't binding.  Any ideas what could be causing this?
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline irk miller

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Re: 1982 CB750F Resto-mod. At least that's the current plan.
« Reply #39 on: Aug 06, 2018, 23:44:30 »
That's your automatic fuel valve.



The tube in your fingers is an air line.  The tube in your thumb is a vacuum line.  Your high idle sounds like maybe the carb is running out of fuel and going lean.