Billet FCR Velocity Stacks

[CosentinoEngineering]

Hillbilly,

Thanks for the compliments. So far I am making stacks for the KTMs and ones for the modern Triumph twins are in the works. Depending on the under tank space either or both of these may fit on the Duc. One downside to that approach is that the KTM and Triumph are optimized for each particular engine. If there was a market for these in Ducland I would prefer to make a M900 specific set and as you say a nice fat torque curve is preferrable to a couple of extra Hp at the very top.

Whereabouts are you?

[B02S4]

This may be all the incentive I need to run FCR39's on my 07 Triumph 865/270...

[kamanya]

Some feedback.

Beautiful engineering!

I have a 990 Super Duke engine (with an adventure gearbox) in a 2004 adventure chassis. I am using the 950 headers with a free flowing aftermarket exhaust.

I have spent 2 sessions on a dyno with a very experienced operator to get to where I am now.

Used to have a 150mm unifilters with foam skins setup on the OEM FCR carb. I had 142 140 main jets, 52 pilot jets in it. This was setup by the same dyno guy.



When the velocity stacks arrived, I mounted them with 155 mains that were supplied. It was way too rich. I went back to the 142 140 with the needles on the 4th clip from the bottom and then sent the bike off to the dyno.

What I came back with and am at the moment;

140 front 138 rear main jets
Needles second clip from bottom
50 pilot jets
198 air jets
2 ½ turns out on the air screw bleed
1 ½ turns out on the fuel screw bleed.









I have left the outer foam socks on until my filter skins arrive. (we dyno’d the filters with the foam on and off – it made negligible difference to the AFR’s)

The billet throttle position sensor works very well and looks factory;



Starts instantly, even when cold. Seldom have to re-thumb the starter button. Very torquey and snappy. Angry even. With my 95kg’s and 25 litres on board it was roll on wheelies in 2nd. Precise throttling. Some patience is needed balancing the carbs both at idle with the adjusters and at 5k revs with the cables. Slow technical riding is brilliant, it will tractor through at low revs and is very hard to stall. This is very cool as I am short and having to dab from a stall always means a trip to the ground. The rear tire is not very happy.

My dyno guy has been a bit slack (too busy) in sending me the dyno charts, but will post them up when I get them.

We are not sure why there is such a discrepancy between the USA main jet experience and my South African one. I am the only one I am aware of that has these stacks here so can’t explain why. Unless you have a dyno with exhaust gas analyser, or, you have huge experience and skill in tuning, then these stacks are maybe not plug and play. In anycase, I can’t imagine anyone would buy these carbs and not expect to have to go visit a dyno. Not doing so, in my opinion would be foolhardy.

It has been a long road with these carbs and I am done fiddling now… I think… I spied a 2 wheel drive project somewhere?

[666]

I know that it may be a very strange question to ask about this setup, but how much mpgs suffer, if any on 950? Now I have 35-40mpg with headwinds setup on 950.

Do you need longer mixture screws, so they can be adjusted without gas tank removal?

I remember converting 640 to FCR and actually improving mileage a little and adding excellent midrange.

[kamanya]

Originally Posted by 666

I know that it may be a very strange question to ask about this setup, but how much mpgs suffer, if any on 950? Now I have 35-40mpg with headwinds setup on 950.

Do you need longer mixture screws, so they can be adjusted without gas tank removal?

I am not the best to answer, not much time on them in this configuration. They are very sensitive to abuse. Baby it and they can do comparable figures to the CV's... I believe. But I seldom, if ever baby it and twist it's ear a lot and often ride in thick sand - worst I've seen is 9 km/liter, best I've got is about 14km/l but I haven't done much cruising on them.

I don't have the longer screws.

[CosentinoEngineering]

Andrew, thanks for the update and glad to hear some dyno work got it sorted out. I was thinking maybe the gas could make a difference? In the US there are various percentages of ethanol blended in to the gas depending on the season and location. Do they do this in SA?

I was hoping for a plug and play solution but with anything but a completely stock configuration it may be hoping for too much. As you say a dyno tune is a good idea whenever changing components anyway.

>>but how much mpgs suffer, if any on 950?

Our only data point so far is for Flanny changing from a Sudco FCR setup to my FCR setup and it increased gas mileage for his trip from NYC back to the Great White North. YMMV quite literally. CV to FCR? Good question.

>>I think… I spied a 2 wheel drive project somewhere?

Yes, that is about to start in earnest. Keep tuned to Sakurama's 950 refresh (yea, refresh!) thread.

[Flanny]

For street riding, my FCRs are now getting the same mileage as my stock CV carbs were at 17 kms/litre or just about 39mpg. I think I can squeeze a little more out, because I think it's a bit fat on the pilot circuit still.

Off road all bets are off. Economy can get down to 12kms/l or about 27mpg, but then again, usually when we're doing that kind of riding, I'm not the least bit concerned with fuel milieage, and more concerned with just staying alive...

Getting the velocity stacks improved fuel mileage by 10% based on the before trip to NYC and the after trip from NYC under the same conditions (I was getting 35mpg on the way down). For transparency sake, this is probably not 100% attributed to the stacks/filters because of the small jetting changes we also made on the main, but my guess is that the intakes did contribute a lot to better steady-state cruising mileage...

Originally Posted by CosentinoEngineering

>>but how much mpgs suffer, if any on 950?

Our only data point so far is for Flanny changing from a Sudco FCR setup to my FCR setup and it increased gas mileage for his trip from NYC back to the Great White North. YMMV quite literally. CV to FCR? Good question.

>>I think… I spied a 2 wheel drive project somewhere?

Yes, that is about to start in earnest. Keep tuned to Sakurama's 950 refresh (yea, refresh!) thread.