Dave I do think the Keihin FCR carbs make more power based on a couple of things:

When both SCCA D-Sports Racers and GT-5 / Lites used A-series motors , the DSR A-series made more power. The major difference being the FCR carbs. Additionally SCCA has banned motorcycle carbs for GT-cars.

The claimed power outputs of Sunny race cars........anecdotal of course.

Most importantly the Keihin carbs flow more.


The webers do have an advantage in that there are loads of tuners who know them well and can get the most out of them. As a motorcycle racer first I was familiar with how they worked (my new Beta 520 Enduro uses the same carb). If you're familiar with SU's you'll understand the concept of needles, all the rest is pretty much the same. The biggest thing I'd recommend if you tune them yourself is an air fuel ratio meter..................attempting to differentiate between lean stutter and rich flutter by ear is a bit dodgey if you palyry with carbs much.

The Factory Pro site helped a lot, my biggest issue was with GX cam the pilot jet and needle needed to be a kinda fat, I ended up with 3 sets of needle getting it right. Then as soon as I went to the cam with 280 duration and .460 lift that same set up made the pilot jet 6 steps to rich but the main only went up three steps. I also leaned out the low speed air correction jet but the high speed air correction stayed the same....................know different the webers. The myth about the flat slides, that you can't just whack them open is really a case of tuning. You can know do that on my motor.................it's now goes rrrrrrrRRRRRRRRRWAAAAAAAA, instead of falling on it's face. The camshaft on the other hand is now happy if you try to pin it below 4K.

http://www.factorypro.com/tech/tech_t ... ocedures/tuning_FCR_Burns,Pat.html


Finally I'm working on the A15 and the 39mm carbs are much better suited to the bigger displacement then the A12.

Tom

there where some old mikunis the other week on ebay that i went to look at in the car. they werent tuned real well, but made a noticeable topend increase in power. they were on a stock 1200. there are some keihin fcr pumper carbs on ebay at the moment. they are the most awesome carb ever!! so many adjustments, nust need to spend the time getting them right. helps if you know a motorcycle tuner.
http://www.ebay.com.au/itm/datsun-120 ... ories&hash=item23190b6887

Tom, do you think there are any power gains over twin DCOE?

yes i should have clarified that. The "don't work well" part is just bolting on bike carbs. Multiple guys found out they run terrible until tuned. Contrast that with your average DCOE or DGV, bolt on and it runs pretty good. Tune it and it runs excellent.

Bike carbs on a car engine often don't work well at first -- but can work well after tuning. You are the only guy I know that tuned his to work great. Others 1200 fans either never get em going great, or pay a tuner to get it done.

I've had the bike carbs for bit, Keihin FCR flat slides 39mm. On a stock or stockish motor you're not gain to see a great gain, it may even go slower. Before I installed a more aggressive camshaft , the motor was borderline over carbed under camed. With the GX cam it did, as you'll see in the link Dave posted, make 73 RWHP. The addition of the carbs was worth at least 10HP, maybe more. At the track I run the speed at the end of the longest straight was almost 5 mph more. I've yet to dyno the car with the new cam, but it's likely up to about 80RWHP as I've picked up a couple hundred more RPM.

The reason I used bike carbs is due to left hand drive cars requiring moving the brake master cylinder in order to fit webers. I also got the whole set up for less money then the cost of a weber DCOE manifold.

Dave clarify the "don't work well" part of bike carbs.

For me they work great but I only use it on the race track. Also the bike carbs require a little more work as they are less common so not as much knowledge about them floating around. Basically it will require a custom manifold

Tom

They went really well when tuned well (not by me!) but you have to be careful as too rich and you can glaze your bores.
Andy you got the butch "D" tuned ones :( night and day compared to the ones I had setup professionally on the works high comp A16 I gave up on after 2 split bores.
They go hard though, isolating the pulses for each cylinder helps more than I thought it would.

I had them on an A15 courtesy of D and can vouch that they go very well, best thing this side of fuel injection, better really cause there is no computer to dick around with.

There is definitely a gain going for 4 individual carbs that are well tuned with good ignition. I guestimated 15hp over the stock carb and 5hp over twin sus with my old setup but made sure I had more compression also all else close to stock.
You have to make sure the runners are long enough for extra response down low to suit engines that run at halve the revvs from the bikes they came from.
Otherwise extra long velocity stacks also help.

Bike Carbs yeah they don't work very well, but look very cool

do a search its been covered plenty