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All this talk about FCRs needs to stop.
Please stop.
My wife's wallet is begging you!
No, carry on...
Please stop.
My wife's wallet is begging you!
No, carry on...
Pros and cons of different carbs? Keihin vs Mikuni vs Amals?
- Thread starter Nortorious
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Started out with a #2, then switched to a #1What size air jet did you use?
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I'm using the latest Amal Mk1 Premier aluminum body carbs. You save 3/4 lbs per unit, compared to the zinc body originals. They are more difficult to get the throttle cables to fit the slides which were easy for the originals. (I had to disconnect the throttle lines from the two into one junction box), Other than that it went together well. I put 53 mile on the 850 today with them for starters. Still dialing them in. I will report back on how the mileage stacks up to the original sleeved Amal's that I was using.
Cheers,
Cheers,
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Did you wind the spring onto the cable after you hooked on the slide?
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I did not have enough cable/spring/mixing chamber cap and finger strength to feed the nub through the key hole in the slide. If that is what you are asking?
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From about 1.40
He's a bit fumble fingers in the video. Was easier than it looks.
Fast Eddie
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Did you ever do a dyno before after with the carbs?
Fast Eddie
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Yes and no…
Yes I‘ve had these carbs on the dyno a few times (not on their own… connected to a motorcycle)… but never in a back to back comparison with other carbs.
Some interesting learning though.
Like the fact that different length velocity stacks can vary the output by 2 bhp.
And the difference between the best velocity stacks and the stock stubs designed for filters (even without the filters) is over 4 bhp !
And that they need the next leaner needles when running the Maney replica pipe vs unbalanced peashooters.
And the fact that on my mk1 engine build, the Maney pipe added 5 BHP from the mid range upwards. And then on my mk2 build, it added nowt !
And the fact that the dyno man said it was the best fuelled carb bike he’s ever had on the dyno… and they normally see modern sports and race bikes !
I haven’t had it on the dyno yet in its latest 920 guise as covid stopped play. And now my old dyno has gone, so even when I do dyno it, comparisons between it and the previous runs and build specs are sadly irrelevant.
The trouble with playing around on a Dyno (as with any experimental endeavour) is that for every question answered, 3 or 4 are generated !!
Fast Eddie
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I’m sorry to say this… but…
IMHO, given the spec of your bike, you would see a nice improvement from fitting FCRs…
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Jim, you are not quite right.
You are right that they do not fit when you use the original curved manifolds and rubbers without any modification.
In that case the lever assy/crank bell will interfere with the frame.
As I said before they do fit with some handicraft work….
I found 2 ways to fit them on my Commando:
Easy way:
Get some nitrile plate manifolds (got mine from Allen`s performance in the UK: nitrile plate manifold „PM03“) and stick the carburetors in.
So you can use the carburetors as they are with push-pull-setup without any modification. The venturi axes is perpendicular to the engine axes….so they got quite an angle, but they work without any troubles. This was my first way to put them on. But didn`t like the look and didn`t like the short way from carburetor to valve. And didn`t like the short air intake.
The not so easy way: this is how I got my carburetors now:
Cut down the Lever assy/bell crank on the rear and upper side…..so you got only a pull cable
Get rid of the exterior throttle spring
Make a new top bracket with a holder for the throttle cable
Make a new bracket for a exterior idle screw.
Make a idle screw and a stop on the crank bell
Fit some new throttle springs INSIDE!!! the carburetors.
I use Concentric MK1 springs cut to fit…works ! throttle closes and WOT works
Shorten the curved manifolds appr. 1cm
I did the modifications with some layman tools - handsaw, file, dremel-tools and drill.
Yes, there is some work to do, but it pays….
When you got a good machine shop or lasercut tools for sure the result will be more beautiful than mine.
My result is funtional, works great and most important: DIY!
chris
Fast Eddie
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I agree Ludwig.
I thought similar when Glen posted his long life results from his Vincent.
Two things came to my mind:
1) As the Commando engine is rubber mounted, it obviously shakes about a lot, therefore carbs mounted solidly to it will shake around too. That will casue the slides to rattle around, causing wear.
2) Glen has chokes fitted, someone pointed out before that the choke slides, under tension of that long spring, will press against the slide and prevent, or reduce, rattle, and thus wear.
I don’t know if either of these ideas are real contributors to wear, but it seems logical.
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Thats some excellent R&D with good results. I don't have to go through that much redesign for the Keihin CRs so I'm not sure its worth it. But I'm interested.Jim, you are not quite right.
You are right that they do not fit when you use the original curved manifolds and rubbers without any modification.
In that case the lever assy/crank bell will interfere with the frame.
As I said before they do fit with some handicraft work….
I found 2 ways to fit them on my Commando:
Easy way:
Get some nitrile plate manifolds (got mine from Allen`s performance in the UK: nitrile plate manifold „PM03“) and stick the carburetors in.
So you can use the carburetors as they are with push-pull-setup without any modification. The venturi axes is perpendicular to the engine axes….so they got quite an angle, but they work without any troubles. This was my first way to put them on. But didn`t like the look and didn`t like the short way from carburetor to valve. And didn`t like the short air intake.
The not so easy way: this is how I got my carburetors now:
Cut down the Lever assy/bell crank on the rear and upper side…..so you got only a pull cable
Get rid of the exterior throttle spring
Make a new top bracket with a holder for the throttle cable
Make a new bracket for a exterior idle screw.
Make a idle screw and a stop on the crank bell
Fit some new throttle springs INSIDE!!! the carburetors.
I use Concentric MK1 springs cut to fit…works ! throttle closes and WOT works
Shorten the curved manifolds appr. 1cm
I did the modifications with some layman tools - handsaw, file, dremel-tools and drill.
Yes, there is some work to do, but it pays….
When you got a good machine shop or lasercut tools for sure the result will be more beautiful than mine.
My result is funtional, works great and most important: DIY!
chris
Still very much loving and recommeding the FCRs. They did take a little dialing in - I've posted my final settings somewhere here and can dig them out if helpful.
EDITED to add from a prior post:
The current settings are the result of a lot of experimentation over an extended period of time. Took quite a while, but these work great for me. Power, mileage, and plug appearance are all very, very good.
The FCRs are awesome carbs!
140 main jets (came with 152s)
Needle clip in #2 slot (from top; there are seven slots; the needle clips came in #5 slot I believe)
Stock pilot jets
Slow air screw out two turns (were originally out one turn)
Slow fuel screw out 5/6 turn (Right side was originally about 2/3 turn out. Left was originally 1.5 turns out)
Last edited:
robs ss
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Thanks for that
Would be even better if you told us about your bike (750/850, anything done to engine (mods)?)
Cheers
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Reading this post I'm reminded of an article in an early /mid seventies Motorcycle Mechanics magazine on Mick Hemmings tuning advice for Commandos , based on his proddy racer . IIRC there was a commando engine on the cover ? Anyway , he recommended and sold modified inlet manifolds that included a length of car radiator hose . Presumably this benefitted heat and vibration insulation as well as allowing inlet tract length of your choice (within reason )?
Given the number of modified components around these days compared to back then , surprised someone doesn't still make them given relative simplicity ? "Just about every carb that followed the amal Mk1 was rubber mounted .
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