Topic: Which webers?

[afkrejci90]

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.

[BPellerine]

most people run the 40s ,with the right chokes and jets would be more than enough carb I think.bill

[scottly]

1+ for 40's. You can fit chokes as large as 36mm, if you think the motor needs that much air.

[754]

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

[ivanhoew]

[Tintop]

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.

[754]

That is the beauty of the Webers, just change it around to suit your needs.

[ivanhoew]

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.

[afkrejci90]

OK, I'm going with the 40's then.  Thank you for the help everyone.

[MidnightLamp]

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.

[Lostboy Steve]

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?

[MidnightLamp]

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.

[jaguar]

What style manifold are you going to be making?
cost?

[MidnightLamp]

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.

[Tintop]

I'd be interested in one.

[afkrejci90]

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.

[scottly]

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?

[seanbarney41]

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.

subscribed

[Jerry Rxman Griffin aka MuthaF'er]

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.

[MidnightLamp]

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.

[ivanhoew]

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.