Can FCRs be mounted on straight manifolds on a Commando engine?

Fast Eddie

Fast Eddie

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I was looking at the FCRs on the Seeley and pondering the fact that if I used straight manifolds in place of the curved ones, it may improve flow and increase the down draft effect.

Does anyone know if FCRs can be mounted ok at that angle?
 
You got me wonderin'
Downdraught is downdraught - it's all in the head.
How can a straight manifold imitate that?
 
robs ss said:
You got me wonderin'
Downdraught is downdraught - it's all in the head.
How can a straight manifold imitate that?
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I guess what I really mean is we’re eliminating a bend, so the charge has an uninterrupted dead straight path right up to the valve throat.

In my minds eye at least, that looks like a good thing.

Utterly irrelevant / impossible with a Commando frame of course, but a relatively easy thing to play with on a Seeley or Featherbed.
 
Fast Eddie said:
I guess what I really mean is we’re eliminating a bend, so the charge has an uninterrupted dead straight path right up to the valve throat.

In my minds eye at least, that looks like a good thing.

Utterly irrelevant / impossible with a Commando frame of course, but a relatively easy thing to play with on a Seeley or Featherbed.
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....or a Rickman....with a vertical motor!

However, my stainless steel fabricated long Mikuni inlet manifold does have a 15 degree kink at the head mounting plate. (of course they also splay outward)I have to make sure I fit it the right way up, it isn't that obvious without carbs hanging on it! Any less and the throttle cables would be hammering the tank bottom..... With the increased inlet length, the bellmouth ends are the other side of the frame tube and close to the top cross tube.

Without the cabs on, you can at least look at the valve and guide!

I can't see you getting it done on a Seeley Commando (leant forward motor) considering the Amal installations I have seen! But worth a go with your FCRs.
 
I wonder what effect a 15% angle would have on the float level, and float valve operation?
 
The 650ss and Atlas have tipped carbs clamped almost directly onto the downdraft head. The engine is vertical so the tip might be less than with a Commando setup that way. I'll guess that the 650ss carbs are tipped forward about 10 degrees?
Neither the close mounting nor the tip seems to be a problem with the Concentrics on the 650ss.
Doug Hele must have thought it was important to line the carb up with the flow of the downdraft head as it would have been easy to machine the port face such that the carb mounted level.

Glen
 
You can buy a version of the FCR that is designed for a steep angle. They made them for inline 4's that had downdraft heads much steeper than the Norton Commando angle. I had a set on an FZR400. The 35mm FCRs I have probably would not work that well at that angle. That said, didn't Greer put FCRs on straight intakes on the 880? Ask GP what he thinks. Not a Seeley frame though.
 
Schwany said:
You can buy a version of the FCR that is designed for a steep angle. They made them for inline 4's that had downdraft heads much steeper than the Norton Commando angle. I had a set on an FZR400. The 35mm FCRs I have probably would not work that well at that angle. That said, didn't Greer put FCRs on straight intakes on the 880? Ask GP what he thinks. Not a Seeley frame though.
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Good call, yes Kenny did do that. And looking at that set up, I think it answers my question that it’ll also be fine on an old Commando motor…

Can FCRs be mounted on straight manifolds on a Commando engine?
 
Perhaps it's more like 20-25 degrees tip on the 650 ss. With the inclined Commando engine that number would be higher.
Screenshot_20240616_084045_Google.jpg
 
Fast Eddie said:
Good call, yes Kenny did do that. And looking at that set up, I think it answers my question that it’ll also be fine on an old Commando motor…

View attachment 114876
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If only that steep, the FCRs you have would definitely work. So would mine, but I'm not about to build a Seeley to find out.

If I were to do it, I'd make a couple, maybe three sets of intake manifolds to test different lengths. They work better with the throat of the carburetor almost touching the port matched intake manifold material. If length is added with the rubber coupling the bottom end is not as good with air and fuel going over the dropped wider diameter gap. Well, that's what I found out. I'm not sure what a more intelligent person using all kinds of math would find out. I'm just a simple practical use kind of guy. :)
 
Schwany said:
If only that steep, the FCRs you have would definitely work. So would mine, but I'm not about to build a Seeley to find out.

If I were to do it, I'd make a couple, maybe three sets of intake manifolds to test different lengths. They work better with the throat of the carburetor almost touching the port matched intake manifold material. If length is added with the rubber coupling the bottom end is not as good with air and fuel going over the dropped wider diameter gap. Well, that's what I found out. I'm not sure what a more intelligent person using all kinds of math would find out. I'm just a simple practical use kind of guy. :)
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Can FCRs be mounted on straight manifolds on a Commando engine?
 
Maybe make a set of carb manifolds that are angled near where they bolt onto the head so the carbs sit out to the sides and rubber long mounts to the desired lengths, I have seen pics set up on Commando race bikes.
I did this when I first built my 850 Featherbed back in 1982 running Deletos pumper carbs but I cut up 2 Amal and 2 Deletos manifolds and welded them both together so the carbs sat flat as the high up angle interfered with the slide cables under the tank, it worked a treat and bike ran well but was a bastard to start, too much fuel getting pump into the motor on start up, I could have spent more time tuning the carbs but I wanted to ride my build and went back to the Amals and I wasn't very experience with carb tuning way back then.
 
BrianK said:
K&N RC1820 pod filters (as supplied by CNW with their FCRs) will work. They're tight to be sure: Tight enough that I just replaced my original set as I'd managed to mangle them getting them on and off a few times (patience, moi?)
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I didn't have the luxury of those manifolds back in '09.
 
I got mine from CNW in 2008. Apparently Matt Rambow now also has or can get some shorter carb spigots to create a touch more room but the originals do work. I finagle them in there while holding my tongue out of my mouth in just the right position.....
 
Schwany said:
You can buy a version of the FCR that is designed for a steep angle. They made them for inline 4's that had downdraft heads much steeper than the Norton Commando angle. I had a set on an FZR400. The 35mm FCRs I have probably would not work that well at that angle. That said, didn't Greer put FCRs on straight intakes on the 880? Ask GP what he thinks. Not a Seeley frame though.
Click to expand...
Kenny Flowed some Mk 2 manifolds for the FCR's.
And removed the cross plate, gusseted the sides.
I believe he was first to use the FCR's.
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The Kenny Dreer VR880 undressed

I have been planning on doing some kind of blog on this bike for Jerry. As you'll see, it's somewhat apart now so I don't have any clean pix of the whole bike. It may be awhile till I get it back to photo stage, so here is what it looks like under the skins. Just so everyone knows these...
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