P11 and a hacksaw for FCRs

What follows is of no value to people doing P11 restorations unless they want to go way off script. Tuners might find it interesting.

Last time I messed around with my intake manifolds for FCR carburetion on my P11 I made them about 1/8" too long. Getting my K&N air filters on scratched the paint up on the rear down tubes that come down from the main backbone of the frame. Kinda ugly and it made getting the air cleaners on a pain. Anywho, six months later yesterday I took the carburetors and intakes off and cut 1/8" off the length of the manifolds using a hacksaw. I also used a 1/8" shorter length of hose for the spigot attachment between the intake manifolds and the carburetor body. I put it back together and it's a bit easier to start and responds to throttle events extremely well. And if I'm careful I can get the air filters on without scratching anymore paint off the frame. Essentially the length is just right for the squirt from the accelerator pump. Amazing difference. No dyno was used to determine it runs better. It's kind of obvious to me.

I'll shoot a video of some throttle blipping and stick it in this thread later. Give you something to make fun of.

This is what the manifolds sort of looked like before I started hacking on them. And yes that is epoxy holding the extensions on. Epoxy is also on the inside of the manifolds. Very strong attachment as long as I don't hit them with a hammer.



The two rings below are what I cut off of the extensions with a hacksaw. Fortunately I have another head I can bolt the manifolds to in order to hold them in place so I can do the hacking with a hacksaw by hand.

Did you check ot the shorter adapters? They do the same thing without needing a hacksaw : https://www.accessnorton.com/Norton...do-with-your-commando-today.33718/post-705873
Could give you even more room!
Read related posts 3909 & 3915
Cheers

EDIT I brecently bought a spare pair -

robs ss said:

Did you check ot the shorter adapters? They do the same thing without needing a hacksaw : https://www.accessnorton.com/Norton...do-with-your-commando-today.33718/post-705873
Could give you even more room!
Read related posts 3909 & 3915
Cheers

EDIT I brecently bought a spare pair -

https://mikunioz.com/shop/mikuni-rubber-carb-mounting-sleeve-40mm-id-both-ends-extra-short/?v=8bcc25c96aa5

Click to expand...

Cool but...

If I used that type of premade rubber adapter with the center step up inside between the carburetor spigot and intake manifold spigot, I would have to cut 1/4" off the intake manifolds to get the same length I have now. Plus they probably would not work as well. Not as much rubber over the metal on either side. I prefer what I did. Funny that way I am.

I cut my own rubber adapters out of automotive fuel tank filler hose. I can make them any length I need. I won't make them any shorter though. My FCR setup is as good as it gets on a P11. Not that anyone else has actually done it to compare to. Gotta get the video done so people can listen to how quick my engine revs and the sound it makes with the 2 into 1 exhaust. Nothing really new for a race build, which my engine actually is, but kinda different for a street oriented P11.

I did start with 32mm Commando MkII intake manifolds, which I modified several times to get the right length, angle, and clearance to the fuel tank. Commando intake manifolds left alone would have the FCRs pointed down at the rear, and be too long.

My slides haven't fallen apart yet either. With the shorter length manifolds and shorter rubber adapters they weren't rattling like they were previously. May have something related to resonance and the intake pulse, but I don't have time to waste investigating the techno side. I'm a doer not a theoretician and closet engineer. Plus they might start rattling again anyway when the weather warms up. lol

Thanks for the thoughts

If you've got rattling going on I'd keep an eye on the condition of the vacuum release plates (the ones that spigot onto the fronts of the slides) if I were you.
If they break then disaster (valve stuck open) could strike.
Not difficult to pull out and inspect.
Apparently the seal between the plate and the slide is the first to go.
Cheers

I've seen your discussion of the vacuum release plates cracking. I'm going to try using positive thinking to keep it from happening. To me right or wrong it sure seems like more of a problem for off road single cylinder thumpers that take a hell of a pounding. I only have maybe at most 4K street only miles on the FCRs. I'll be sure to remind myself that you warned me about it if it ever happens. Thanks Rob