CR Corsa Head Inlet Ports/Flanged rubbers

hooksey

hooksey

Hero member
Location
Vic , Australia
Fellas,

I have a factory delivered Corsa to Aus, with a known history.
Im replacing perished.......dare i say it, 'Inlet manifolds' or flanged inlet rubbers.
These haven't been replaced to date so are factory fitted........

As we know cr heads have 36mm Inlet Ports......ke ??
Why would said flanged inlet rubbers measure 32mm?
I would of thought transition from rubber to port would be same same.....?

Has anybody come across this before with CR head? Or has Luigi reached into the wrong
parts bin after a long lunch......

Thanks in advance, Hooksey.
 
From memory when the late Jeremy Bowdler ( 2 wheels editor ) purchased his SFC 1000 from the factory he insisted on having the 36mm carbs and that is what the factory supplied. However on getting the bike back to Aus it was noted that the bike had indeed 36mm carbs but the ports on the head were for a 32mm carb. Martin Shields of Forecycle fame spent many an hour reshaping the head to accommodate the 36mm carbs.
My SFC also has 32mm carbs.
 
hooksey said:
Why would said flanged inlet rubbers measure 32mm?
I would of thought transition from rubber to port would be same same.....?
Click to expand...
You need to remember the factory were struggling financially at the time the Corsa was produced. Suspect there was a fine balance between what was planned and what could be delivered.
 
That may be true Rob……but Has anybody come across this before with CR head? Or has Luigi reached into the wrong
parts bin after a long lunch......

What size inlet Ports on the SFC Thou Chris?
 
Rob said:
You need to remember the factory were struggling financially at the time the Corsa was produced. Suspect there was a fine balance between what was planned and what could be delivered.
Click to expand...
Did not have to do with financial issues as far as I know. They simply beliefed that 32mm is enough for street use and would give more torque rather than power.
What I did on mine (when it still had 32mm Dell'Ortos and influenced by the exhaust headers design at the exhaust ports) is to tapper the alloy part from 32 (carb side) to 36mm (head side). My feeling (!!!) was, that this milded a bit the drop in torque around midrange. I can not proof it with a dyno chart though, it was just my personal feeling, maybe influenced by the hope it brings something... ;-)

Completely removed the drop though only by changing the whole exhaust to a completely "tailored to the bike" one.
 
My 1984 Corsa came with 32mm rubber inlet manifolds and carbs which I believe was standard spec. And GRP sidepanels 😭 which weren't.
 
As far as I can remember my ex-Motodd/Moto Vecchia Corsarised RGS had 32mm carbs and inlets, as did both my SFC1000s, but Ray Peacock’s Corsa I rode in 1985 had 36mm carbs, but I have no idea what size inlets.
 
Just checked my SFC1000, it had 36mm inlet on the head & 32mm carbs & manifolds which I replaced with the ally stubs taper bored 32 - 36mm when the rubber flanged stubs started to look past it. Not sure if they make a difference but in my imagination it will, same as when you polish the bike it always seems to run smoother & faster ⚡️
 
stivesvelo said:
Just checked my SFC1000, it had 36mm inlet on the head & 32mm carbs & manifolds which I replaced with the ally stubs taper bored 32 - 36mm when the rubber flanged stubs started to look past it. Not sure if they make a difference but in my imagination it will, same as when you polish the bike it always seems to run smoother & faster ⚡️
Click to expand...
Cheers for that info, can you remember where you purchased you tapered inlet flanges?
 
I bought them off eBay, a guy in UK who made them to order (not expensive). They weren't taper bored but I think he would have done that if I had asked, (did it later), they were smooth on the outside & when I fitted them it didn't matter how tight I made the jubilee clips they 'drooped' so I machined grooves to match the ribs inside the rubber tubes which solved the problem.

It's a few years ago that I bought them, I'll see if I can find out where they are from (something like Milton Keynes) & let you know.
 
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