FCR's on A12

[alex476]

Hi everyone 

 

Im having trouble finding any information on FCR's on a A12. 

i have an A12 bored to 1204.4cc with the A14 h89 head. The original plan from the previous owner was to efi and turbo but id like to go down the road of FCR's 

The only problem im having is knowing what size i should go for the FCR's. 34, 36, 38mm etc and what jet size should i go. Ive read on other forums that someone else had 34's to 38's and then when back to 36's. 

Some people say cause they are bike carbs and they are made for a higher revving motor that a 36mm or 38mm would be fine but 39, 40mm is pushing it.

Manifold im getting made of billet from a guy in the US and i know i should get a carter fuel pump at 3psi no more with a regulator etc, so ive done a fair amount of research but im stuck with what size. Sort of leaning toward 36mm but then i find kits in japan and they are for A12 at 41mm.

cheers 

[datzenmike]

I would guess that the intensity of the build would determine the size of the carbs. A full out racing A12 would need and use a larger set than just a 1204 and stock head and cam. Generally, never over carb your engine. Better to have slightly small and wish it were larger than to have too large and wish it were smaller. Too large is hard to live with for driving around.

[Morrisun]

From datsun1200.com site...under Bike Carbs on an A14.

 

I run 39mm Keihin FCR Flatslide carbs on the coupe I race. I bought the set up complete with manifold several years ago. Note this very same type of carb is on my Beta 520RS enduro bike, which is street legal and the bike runs flawlessly. I mention this because do not buy into people telling you they bog or have flat spots. The should work as well as any carb if not better.

It has been mentioned but much more than 2psi and the float bowls will overflow.

I ran the 39mm carbs on my A12GX that other than the ports being cleaned up was stock and it made 73 HP at the wheels. That is nearly double the stock WHP. I am still using this set up but now have an A15 in the cat. An 14 will easily support the R6 carbs.

As for jetting start with the mains and work down from there. Do a google search for FCR carbs and Factory Pro, there is a explanation on jetting Keihin bike carbs that is a good guide regardless of what brand of slide carb you have.

Naturally having raced bikes before cars I am biased but I think motorcycle carbs are made to a higher standard.....this doesn't mean other carbs are rubbish but non CV slide carbs just flow more.

 

You MAY want to search datsun1200.com for more info on running bike carbs on an A14.
 

 

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