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Author Topic: Which webers?  (Read 1601 times)

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Offline afkrejci90

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Which webers?
« on: November 27, 2014, 03:55:42 pm »
Looking to purchase a set of webers dcoe, 40 or 45?  What's the difference between them and will I see any benefit from one over the other?  Stage 3 head, hi comp, 1000cc.
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR

Offline BPellerine

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Re: Which webers?
« Reply #1 on: November 27, 2014, 04:45:03 pm »
most people run the 40s ,with the right chokes and jets would be more than enough carb I think.bill
1978 CB 750K ard and webers
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Online scottly

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Re: Which webers?
« Reply #2 on: November 27, 2014, 06:24:46 pm »
1+ for 40's. You can fit chokes as large as 36mm, if you think the motor needs that much air. ;)
Don't fix it if it ain't broke!
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Offline 754

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Re: Which webers?
« Reply #3 on: November 27, 2014, 08:18:50 pm »
Pretty sure 45 bodies are bigger, won't fit in there..
Maker of the WELDLESS 750 Frame Kit
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Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline ivanhoew

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Re: Which webers?
« Reply #4 on: November 28, 2014, 12:09:28 am »



« Last Edit: November 28, 2014, 12:14:24 am by ivanhoew »
just do it .

Offline Tintop

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Re: Which webers?
« Reply #5 on: November 28, 2014, 06:03:01 am »
Pretty sure 45 bodies are bigger, won't fit in there..

45's are definitely bigger, you will have problems with frame / tank clearance.  Finding a manifold will be an issue as well, unlike with the 40's.






That chart is in various Weber books, take it with a grain of salt as it represents the absolute perfect set-up.  From what has been posted on the Forum, 80 CFM would appear to be a 'wish list' upper limit for the best CB 750 head.  As for choke size, I run a 40DCOE with 34's on my 750 twin sidecar engine.  The chart says I could / should be using 36mm or 38.  If I did I would have no mid-range at all.  Actually thinking of going to 32's to improve overall tractability, and throttle response.
1977 CB550/4 Cafe - Speed Warrior / BOTM 03/11
1980 CB750F (project)
Whittaker GBF Vintage Racing Sidecar (XS750 power) - ITG / 151's / CMR Racing Products (SOLD)
1976 CB400 SS - stock / BOTM 04/11 (SOLD)
1973 CB750 K - basket case (SOLD)
77 CB550 Cafe build
550/750 Filter Thread
Sidecar Rebuild Thread

Offline 754

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Re: Which webers?
« Reply #6 on: November 28, 2014, 07:56:42 am »
That is the beauty of the Webers, just change it around to suit your needs.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline ivanhoew

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Re: Which webers?
« Reply #7 on: November 29, 2014, 01:35:07 am »
i agree tintop ,

i think something to bear in mind is pk bhp rpm , not what will it rev to rpm .

eg if a bike has a 10k rpm, its pk powr may still be at 8700 rpm , so thats the place on the weber chart to refer to .

also , a 10k rpm  r1 engine is going to flow a lot more than a 10k rpm honda 1000 sohc .

it would be better if they did a bhp line on the x axis .


Pretty sure 45 bodies are bigger, won't fit in there..

45's are definitely bigger, you will have problems with frame / tank clearance.  Finding a manifold will be an issue as well, unlike with the 40's.






That chart is in various Weber books, take it with a grain of salt as it represents the absolute perfect set-up.  From what has been posted on the Forum, 80 CFM would appear to be a 'wish list' upper limit for the best CB 750 head.  As for choke size, I run a 40DCOE with 34's on my 750 twin sidecar engine.  The chart says I could / should be using 36mm or 38.  If I did I would have no mid-range at all.  Actually thinking of going to 32's to improve overall tractability, and throttle response.
just do it .

Offline afkrejci90

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Re: Which webers?
« Reply #8 on: November 29, 2014, 03:22:41 pm »
OK, I'm going with the 40's then.  Thank you for the help everyone.
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR

Offline MidnightLamp

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Re: Which webers?
« Reply #9 on: November 30, 2014, 11:52:30 am »
If you need manifolds, I'll be fabbing up a set sometime soon. I have measurements for early K carb adapters and late K carb adapters.
'75 CB750 - Racer
'69 CB350 - Racer
'68 Enfield 350/440(flat top) - Steet
'54 Enfield 350 - Resto
'74 Commando 850 - Restomod
'67 Enfield 750 (TT7) - Resto

Offline Lostboy Steve

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Re: Which webers?
« Reply #10 on: November 30, 2014, 12:45:17 pm »
If you need manifolds, I'll be fabbing up a set sometime soon. I have measurements for early K carb adapters and late K carb adapters.

Want to do a 550 while youre at it?
1968 Honda Z50
1977 Honda CB550K
1982 Honda GL1100i
2005 Yamaha Raptor 50
2009 Honda FourTrax Foreman Rubicon
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For my projects/activities: http://www.atomicgarage.net

Offline MidnightLamp

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Re: Which webers?
« Reply #11 on: November 30, 2014, 01:05:32 pm »
I could probably be persuaded to do so. Have measurements from the carbs? Would want the C-C distance (spacing) of the outer set, the OD of the carb outlet, and the ID of the carb outlet as well.

I saw the post on the single weber though, that'd be out of the question for the way these manifolds work.
'75 CB750 - Racer
'69 CB350 - Racer
'68 Enfield 350/440(flat top) - Steet
'54 Enfield 350 - Resto
'74 Commando 850 - Restomod
'67 Enfield 750 (TT7) - Resto

Offline jaguar

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Re: Which webers?
« Reply #12 on: December 01, 2014, 07:15:37 am »
What style manifold are you going to be making?
cost?

Offline MidnightLamp

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Re: Which webers?
« Reply #13 on: December 01, 2014, 10:52:43 am »
They're a new style adapter manifold, bolts onto the weber, accepts a CB750 carb rubber and is CNC ported to match both. My proto set is off getting anodized, will post up pics when they're back.
'75 CB750 - Racer
'69 CB350 - Racer
'68 Enfield 350/440(flat top) - Steet
'54 Enfield 350 - Resto
'74 Commando 850 - Restomod
'67 Enfield 750 (TT7) - Resto

Offline Tintop

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Re: Which webers?
« Reply #14 on: December 01, 2014, 02:07:53 pm »
I'd be interested in one.
1977 CB550/4 Cafe - Speed Warrior / BOTM 03/11
1980 CB750F (project)
Whittaker GBF Vintage Racing Sidecar (XS750 power) - ITG / 151's / CMR Racing Products (SOLD)
1976 CB400 SS - stock / BOTM 04/11 (SOLD)
1973 CB750 K - basket case (SOLD)
77 CB550 Cafe build
550/750 Filter Thread
Sidecar Rebuild Thread

Offline afkrejci90

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Re: Which webers?
« Reply #15 on: December 01, 2014, 03:24:17 pm »
They're a new style adapter manifold, bolts onto the weber, accepts a CB750 carb rubber and is CNC ported to match both. My proto set is off getting anodized, will post up pics when they're back.

I was thinking of doing the same, I'd like to see how yours turn out.
'78 CB750K http://forums.sohc4.net/index.php?topic=105327.0
'80 CB750C - Sold
'06 CBR600RR

Online scottly

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Re: Which webers?
« Reply #16 on: December 01, 2014, 06:39:28 pm »




Ivan, I've never seen that airflow chart. According to it, the max flow doesn't change much from the smaller chokes to the larger ones?
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline seanbarney41

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Re: Which webers?
« Reply #17 on: December 01, 2014, 06:44:22 pm »
They're a new style adapter manifold, bolts onto the weber, accepts a CB750 carb rubber and is CNC ported to match both. My proto set is off getting anodized, will post up pics when they're back.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Which webers?
« Reply #18 on: December 01, 2014, 07:39:32 pm »
Sounds like a great project. Hopefully there will be a few sets made while you're at it. Economy of scale. I have a RC set off the bike if you need any measurements, etc.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline MidnightLamp

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Re: Which webers?
« Reply #19 on: December 01, 2014, 09:56:47 pm »
I'll see what I can do, lets hope it works out first! I actually started this project because I didn't like the RC Carbs adapters because mine had cracks and were all welded up in places.
'75 CB750 - Racer
'69 CB350 - Racer
'68 Enfield 350/440(flat top) - Steet
'54 Enfield 350 - Resto
'74 Commando 850 - Restomod
'67 Enfield 750 (TT7) - Resto

Offline ivanhoew

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Re: Which webers?
« Reply #20 on: December 02, 2014, 10:45:30 am »




Ivan, I've never seen that airflow chart. According to it, the max flow doesn't change much from the smaller chokes to the larger ones?


yes  i agree scott , its a bit odd that there would be on benefit from 36 to 40 on the 45 too.

regards
robert.
just do it .

 

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