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Old 01-06-2020, 09:09 AM   #1
Goofle
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Keihin FCR Fitment M900

As some may remember about 18 months ago I bought some carbs from America. I've had a bit of a song and dance fitting them (not from the manner they weren't a good fit, they fitted well and reasonably easily but in the manner of I've had issues with leaks of fuel and air from the t pieces and spent a lot of time waiting for spare seals from one supplier or another). Fortunately I was in no rush and my housemate at my work digs didn't particularly mind carb bits in various states of disassembly on the table for months on end.
I've now got them fitted and managed a couple of hundred miles. I must say they do seem to make a difference. The throttle response seems crisper and there does seem to be more 'uuuumpfh' in the mid and top end (Using only the unpatented and uncalibrated 'Goofle bum dyno')! The intake noise sounds different too, more raw, which I personally don't dislike but it could get a bit tiring on a long trip I'd say (the airbox lid is drilled to match the carb set up). I'm not sure if the feeling of more umpf is just due to the noise change, I think it's quicker....
My one criticism would be the return spring for the slides is very keen - again, on a decent length trip I would say it's very heavy.
Obviously as it's rather warm at present anyhow I can't comment on starting when it's cold!
Other than the carb and airbox mods the engine is standard, a M900 from 1993, with standard gearing.
That's about it, just a quick update for anyone interested!

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Old 01-06-2020, 09:34 AM   #2
350TSS
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Can I ask what size main jet and pilot jets are you running in them? (open airbox and standard exhaust?)
I am considering them for my Monster with foam filters and an open single exhaust
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Old 01-06-2020, 01:55 PM   #3
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They're race carbs so not for really touring around on so what'd you expect? The throttle is heavier because you have more stuff to move now than you did with the girly CV's. Tuning potential has been unleashed however so now so the best thing you can do now with those carbs is get some 45/50mm headers and open cans get them set up on a dyno. The the biggest drawback with the standard setup is the standard 40mm header, will just kill it. Otherwise you won't get much advantage from them with a standard setup, just the bad stuff.
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Old 01-06-2020, 02:19 PM   #4
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Ahh! Carbs! Those were the days.

Darren's right about the headers but what sort of riding do you mostly do? Large diameter headers are great for top end power but the trade off is a loss in low end torque.

Smaller header diameters keep the gas speed up for more torque, while a larger diameter is better for higher RPM. Torque is related to the speed of the mixture passing through the engine, while horsepower is dependant on the volume of mixture that passes through. The quicker the mixture enters and leaves the engine, the more torque it'll make; the greater the volume of mixture that passes through, the more horsepower it'll develop.

So you'll need to decide which setup best suits your riding. I rarely trouble the top end of the rev range, so I won't be going large!
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Old 01-06-2020, 03:02 PM   #5
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Quote:
Originally Posted by 350TSS View Post
Can I ask what size main jet and pilot jets are you running in them? (open airbox and standard exhaust?)
I am considering them for my Monster with foam filters and an open single exhaust
I’m ashamed to say I don’t know - they were set up prior to my ownership for a m900 and indeed came with the air box lid drilled ready to go!
My riding is mainly a and B roads so I don’t really want to chase high rpm - the mid range torque is far more useful to me at present!
I’m also aware that it’s an engine rapidly approaching 30 years old - I don’t really want it red lined everywhere...
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Old 01-06-2020, 03:57 PM   #6
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With FCR's you need to tune otherwise why bother? CV's will be good enough for most even pipes and and minor headwork.
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Old 01-06-2020, 06:02 PM   #7
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Quote:
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With FCR's you need to tune otherwise why bother? CV's will be good enough for most even pipes and and minor headwork.
I totally agree - however I’ve wanted a set of flatslide carbs for ever so took the opportunity to fit them on the Monstro. I may well remove them soon / this winter and sell them on, having scratched the itch!
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Old 01-06-2020, 06:17 PM   #8
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The main reason that I bought my FCRs was because I'm told that they eliminate the carb icing that my 750 seems particularly susceptible to.
I'm also told that they give better fuel consumption, though that wasn't a major factor for me.
Extra performance was not a huge factor either .. if it had been I would have bought a 900 in the first place.

Tbh I was undecided about them but an opportunity came up to grab a brand new pair at a bargain price just before the post-brexit price jump.
I still haven't fitted them. (but no, they're not for sale)
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Old 01-06-2020, 11:44 PM   #9
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Jezz starting is a whole handling with these I’ve to twist the throttle 10 times or more before I hit the button
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Old 02-06-2020, 07:46 AM   #10
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Yea, you need to prime them, my Dell Ortos are the same, even with a choke. Good point about carb icing that would be a real benefit in addition to the induction noise!
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Old 14-06-2020, 05:25 PM   #11
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36mm on my 98 m900-K&N cone filters,Arrow cans(not too noisey),quick action twist grip,two pumps first thing(even down to about minus 5) let her warm up and then enjoy-pulls like a train with no flat spots till flat out,good steady tick over even when she"s so hot you can"t get near her and will still pull with no flat spots or hiccups to an indicated 130.Can"t tell what the set up is coz they where on there 3 years ago when I bought her and I"ve had no reason to delve inside.Having had Guzzis for years I don"t find a problem with a heavy throttle (it is still twin cable set up) runs V Power and at 60 I"m a firm believer of if aint broke don"t fix it.
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Old 14-06-2020, 05:46 PM   #12
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Mine has 41mm FCR split singles, to start it needs a couple of twists to prime the cylinders and then needs 'tickling' for a while until there's some heat in the engine otherwise it'll stop.

To help with this I fitted a 916 throttle/twistgrip which has a 'switch' that holds the throttle part open so it'll idle around 2,000 rpm.

Once warmed up they run really well, lightning fast throttle response - probably a little too 'on/off' initially but fitting a TPS to one of the carbs helped smooth it out. I think this was mostly down to the Ignitech advance being too 'keen' and having the TPS better synchronises the timing/fuelling setup.

Can be very thirsty if you've got a heavy right hand though...
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Old 23-05-2021, 08:59 PM   #13
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Dukedesmo. you used the 916 throttle assembly to help idle, can I ask how you did it. I’d love to do this but my 916 has 1 cable and my monster is a 2 cable job. So is it just the 916 throttle case with the fast idle button you used.
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Old 23-05-2021, 11:38 PM   #14
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Quote:
Originally Posted by Davy View Post
Dukedesmo. you used the 916 throttle assembly to help idle, can I ask how you did it. I’d love to do this but my 916 has 1 cable and my monster is a 2 cable job. So is it just the 916 throttle case with the fast idle button you used.
When I bought the FCRs they were supplied with a 'Motion Pro' twistgrip and throttle cable and I used this for a while.

The Motion Pro has 2 cables - an opening and closing cable both of which split into two again, so 4 cables to open and close each carb individually.

I used a 916 throttle/twistgrip with a single cable but made a new cable setup using the 1 into 2 opening cable part of the Motion Pro - basically attached a single cable from the twistgrip to a splitter which already had the correct ends at the correct length to fit the carbs. There is no provision for the closer cable but it's not needed either as the FCRs have strong enough springs to close by themselves (I think the closer cables are a US 'liability' thing anyway?).

916 throttle has a faster action than the Motion Pro and so it was a very short throttle pull so, to this end I fitted a 'throttle tamer' cam into the twistgrip that smooths out the action, it is still a very quick action throttle - about the same as my 916 which has a quick action cam fitted, only much heavier due to the carb springs.

It works very well and I like it like it much better than the Motion pro setup.
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Old 24-05-2021, 07:35 PM   #15
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Thanks for that. I’ll have a look at what’s what on the monster. And I’ll try and get my hands on a 916 throttle assembly with the fast idle button.
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