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| Satanic Mechanic |
 Posted: Sat Sep 24, 2005 6:22 pm |
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Moderator
Joined: 04 Sep 2005
Posts: 309
Location: Munich, Germany
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| Mats has problems getting the Webers running well under 3000 RPM. Maybe you could help him out? |
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| Ron |
| Posted: Mon Sep 26, 2005 12:22 am |
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Member
Joined: 15 Sep 2005
Posts: 30
Location: Indianapolis
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Satanic Mechanic wrote: Mats has problems getting the Webers running well under 3000 RPM. Maybe you could help him out?
I'd be happy to, its been nearly 25 years but i remember the basics. Have him sign in.
IIRC, there are 2 emulsion tubes under a common cap. One for each throat. they carry the main jet and the tube itself control the midrange. Seems there were separate tubes for the low range, below 3k in this case, under the same cap, parallel to the main emulsion tubes. Should just be an issue of getting holt of a selection and trial and error. I don't remember any adjustable air bleed screws or anything like that, common on a mikuni or keihin.
The main thing was to get the right size venturis for the dispacement, though i can't rememebr how much bearing those had on low speed performance. My head was ported by Yosh, with the valve seats tripple cut and the carb manifolds ported to the head, and a high flow pipe, and I could only use 32mm venturis. If his engine can't flow high volumes, he'll need smaller, say 30mm or 28mm venturis or the air flow will just collapse and he won't get any venturi effect to suck gas thru the low speed tubes.
What's his engine like?
Ron |
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| mats_58 |
| Posted: Fri Sep 30, 2005 9:09 am |
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Rookie
Joined: 30 Sep 2005
Posts: 1
Location: Sweden
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Hi Ron!
My engine has an orginal head and 915cc, mild camshaft (regrind for app. 1,5-2 mm higher lift) the carbs has 32mm venturis, 130 main, 150 air, F16 emul. , 45F9 lowjets, short stacks otherwise they hit the frame. I have spoken to people that race with Weber carbs mostly they have mounted Mikuni instead. But I think the Weber looks nice on a streetbike as mine, and its more classic.
I am building another engine with 73,5 bore (1069cc, Powroll pistons) and Megacycle 125-05, ported head, maybe the Weber fit this engine better.
Bye from Sweden!
Ron wrote: Satanic Mechanic wrote: Mats has problems getting the Webers running well under 3000 RPM. Maybe you could help him out?
I'd be happy to, its been nearly 25 years but i remember the basics. Have him sign in.
IIRC, there are 2 emulsion tubes under a common cap. One for each throat. they carry the main jet and the tube itself control the midrange. Seems there were separate tubes for the low range, below 3k in this case, under the same cap, parallel to the main emulsion tubes. Should just be an issue of getting holt of a selection and trial and error. I don't remember any adjustable air bleed screws or anything like that, common on a mikuni or keihin.
The main thing was to get the right size venturis for the dispacement, though i can't rememebr how much bearing those had on low speed performance. My head was ported by Yosh, with the valve seats tripple cut and the carb manifolds ported to the head, and a high flow pipe, and I could only use 32mm venturis. If his engine can't flow high volumes, he'll need smaller, say 30mm or 28mm venturis or the air flow will just collapse and he won't get any venturi effect to suck gas thru the low speed tubes.
What's his engine like?
Ron |
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| Ron |
| Posted: Fri Sep 30, 2005 1:33 pm |
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Joined: 15 Sep 2005
Posts: 30
Location: Indianapolis
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Here is an article from the time:
http://members.tripod.com/cb750k2/Technical/porting/Porting_the_Honda_Head.htm
Once I got my first ported head, I realized that was the key. As the article states, the stock head does not allow benefit from higher lift cam. My engine was a 750cc with a ported head. The article estimates the head alone is worth 15% horsepower. I think it make for cleaner running also.
You'll like it on your new 1069cc engine.
Ron |
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| Satanic Mechanic |
| Posted: Fri Sep 30, 2005 7:49 pm |
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Moderator
Joined: 04 Sep 2005
Posts: 309
Location: Munich, Germany
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mats_58 wrote: My engine has an orginal head
Nonetheless, a few basics: The intake port should match your header's inner diameter where both connect, then get constantly narrower to speed up the gas velocity.
The narrowest point should be shortly (1-1.5 cm or 1/2") before the valve so that the gas flow at the valve stays laminar (no turbulence). Porting the intake port is much more important than the exhaust port - the gas pressure in the exhaust is much higher that flow resistance is much less of a factor. |
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| pedro750 |
| Posted: Wed Jan 18, 2006 1:10 pm |
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Member
Joined: 16 Jan 2006
Posts: 48
Location: Italy
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Satanic Mechanic wrote: mats_58 wrote: My engine has an orginal head Ooops - are you saying the head is not ported to adapt the bigger carbs? That won't work, at least not well. Now, porting is a science of it's own (which is why I haven't put together a page on the subject yet). Don't get me wrong, it is not becaus I would not like to share the information I have, it's rather that the subjct is a bit controversial.
Nonetheless, a few basics: The intake port should match your header's inner diameter where both connect, then get constantly narrower to speed up the gas velocity.
The narrowest point should be shortly (1-1.5 cm or 1/2") before the valve so that the gas flow at the valve stays laminar (no turbulence). Porting the intake port is much more important than the exhaust port - the gas pressure in the exhaust is much higher that flow resistance is much less of a factor.
Ok, so what I've to do on my original head to have a good head with 900cc pistons, CMC camshaft and dellrto PHBE 36mm?
Where I can find this:
Where I can find most info about this work? |
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| Ron |
| Posted: Wed Jan 18, 2006 2:18 pm |
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Member
Joined: 15 Sep 2005
Posts: 30
Location: Indianapolis
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Here's a good start: http://www.aperaceparts.com/headwork.html
Scroll down to HW-4-8 for $189. Good price, basic work.
Larger intake valve would be nice, not necessary. I had Stainless Steel valves, tri-angle valve job, porting work etc, for about $450 incl parts from another source, not APE.
Head work absolute best thing to do IMO. I once had a complete stocker made out of salvaged parts. Got a discarded head from a drag racer that had been ported but had broken fins. I put that on the stocker and it was amazingly faster.
You should send your carb manifold so they can match the ports. Exhaust side not so necessary to match. |
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| pedro750 |
| Posted: Wed Jan 18, 2006 2:41 pm |
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Member
Joined: 16 Jan 2006
Posts: 48
Location: Italy
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Ron wrote: I once had a complete stocker made out of salvaged parts. Got a discarded head from a drag racer that had been ported but had broken fins. I put that on the stocker and it was amazingly faster.
Thanks for your suggest, but other question, now where's your old discarded head??? 
We can organize about it? |
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| Ron |
| Posted: Wed Jan 18, 2006 6:05 pm |
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Member
Joined: 15 Sep 2005
Posts: 30
Location: Indianapolis
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That motorcycle episode was way back in 1973. Being built from scratch there was no original head to discard. I loaned the bike to a "friend" who proceeded to total it (crashed beyond salvage) I sold that head to another drag racer who didn't mind about the fins.
I currently own 2 heads both ported and ready for project bikes. No spares on hand. However, used heads are a dime a dozen here in the States in salvage yards. "CycleReCycle" in Indianapolis I'm sure has some.
http://www.crc2onlinecatalog.com/ You won't find the salvage parts in his online catalogue, you'll have to email him. He knows the CB750SOHC quite well. |
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