School Me n Keihin FCR Carbs

My Starlet offers very little room to mount carbs. The intake and exhaust manifold are both on the driver's side. DCOEs are impossible to mount unless you do what TRD did for the Starlet Cup races back in the day. They uprighted the engine by changing engine mounts, oil pan, transmission adapter and many other little things.

So, I was going to mount two 40 IDF down draft carbs, However, it looks like FCRs would be a better choice--they're very compact and from what I understand they are really easy to work on.

So, Keihin gurus, tell me what I need to know about FCRs. Did they come on any motorcycles? If so, what motorcycles should I be looking at? What's the going price for new versus used? Would Keihin's other carbs work and be cheaper? Will they put perform the Weber IDFs?

Thanks , John

4 new carbs on a rack will run you $1200-1500 Used set $450 and up. Singles do come stock on some bikes like most modern 4 stroke singles but you be looking at $150 to $250 for a used single then have to figure out how to get them synced. Check SUDCO and CarbWarehouse

I'll second the SUDCO comment. Great carbs, but not cheap. The only OEM applications that I'm aware of are some higher end 4 stroke singles, generally from KTM. There are plenty of other carbs that would work and be cheaper, but it depends on what throat diameter you're looking for and if you want an accelerator pump. I'd generally stay away from CV carbs for a custom application as well.

Dang...I can get two IDFs for about ave the price. Are FCRs really worth that much more in terms of performance?

What size are you looking at? Mikuni RS are very good as well, and can be found a bit cheaper at times.

FCR's aren't cheap. Expect to pay several hundred dollars for one, used. They came on some KTM's.

I run a set of 39mm flat slides on my Datsun 1200 I vintage race, so I will pass what I know:

First if you shop around you will not pay $$$$$; look on Apexspeed or Sportsracer netowork. Most of the former DSR/CSR P1/P2 guys are now running bike engines and most of those are fuel injected. I got mine with custom manifold for $250 back in 2009. You could probably grab a set for between $500-750 now. Put a WTB on one of the sites for sports racers.

Next Google Factory Pro Keihin flat slides, this will give you a very good guide on jetting them. Next do not do not, I repeat do not believe people who tell you that they have low end bog issues etc etc. I have a 2010 Beta enduro that uses one and all of the bike magazines described the carb as flawless, the set on my Datsun work very well. I've used them on the two different engines in my car; the heavily cammed (big overlap) 8600 rpm 1171cc buzz bomb and the current moderate cam 7800 rpm 1508cc motor. It was matter of changing jets nothing more.

As for power; the D-Sports racer guys told me changing to FCR carbs netted 10hp over DCOE carbs. Note at the power level they're at we're talking about a 6% gain. Back in the 70s New Zealand had dealer modified 1200s with Doce cars that dynoed at 55 who, running the same spec but with FCRs my car dynoed at 73 whp. Even allowing for variance in Dynos that's still a big difference. Note I've yet to dyno the 1508 motor but I'm seeing 111mph at Spring Mtn Motorsports before turn 4 on the 3.4 mile layout, which is 2-3 mph slower than a friends S2000 and on par with a good Spec Miata.

The Keihins are absolute works of art and everything is precision made. One of the big reasons for using them besides I got a smoking deal on mine is that I didn't have to move the brake/clutch master cylinders. You'll need a custom manifold and throttle cable. Also buy a complete set of 4, the dirt bike ones are slightly different and you'll cost yourself money buying the pieces you need. I've purchased parts from Sudco and from my local bike dealer. You can get all the part numbers you need online from Sudco, if you do get a set use only the genuine Keihin parts.

And yes they are worth every penny.

Tom

Well, the IDFs I was originally planning for were 40s. Looking around at FCRs they seem to be in the 39 and lower range. I found a complete set of four used FCRs off of a large Suzuki sport bike for about $650. If flat slides are really that much better than IDFs, I'll go with them. However, if the stories of FCR superiority are Internet fiction, I'll go IDF. If we're only talking 2bhp and crappy idle and driving characteristics, I can make better use of my money elsewhere like lighter wheels.

Are there any printed tuning books for FCRs or Keihin's? I'm pretty good with Webers but FCRs are a whole new game...even though they look simple.

For tuning try this: http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

As for Internet myth, they do flow more but depending on what trim or motor you have (K or 4AG) it may indeed not be worth it. If you have the ability to fab a manifold or you find one for you're motor than it's worth it. The manifold I have used part of a stock Datsun manifold and short rubber hoses that join the ca bs and manifold. (fuel filler neck I think) My take is if you had a bone stock Starlet and bolt these on you'd probably see 5-6 hp. If you were cleaning up the ports adding a moderate cam and performance exhaust they'd probably be worth an extra 10-12hp.

As I said in my first post; the car should idle perfectly. Note my carbs have no enricher circuit so cold starts involve pumping the carb 5-6 times, I live in a hot climate and it's not a street car. If I had an air box the choke problem would be easily solved. The set you saw may have an enricher, again mine doesn't.

I'm getting about 2-3 mph more than other 1200s in similar trim and the only difference is the FCR carbs

Thanks Tom. I have a 4KC with the following:

Fresh rebuild with OEM Toyota parts throughout Ported intake and exhaust runners with minor reshaping of the combustion chamber Fully balanced rotating assembly Lightened crankshaft Weber 38/38 Carter fuel pump Holley FPR keeping fuel at 3.5 psi Big port K series intake manifold matched to cylinder head runners Kelford 290 degree cam Martelius Headers 2" exhaust that dumps out the side, no muffler or cat Kameari Flywheel AC Delete MSD 6A Recurved timing in the dizzy 15 at idle and 35 all in by 3000rpm ARP head studs Denso Iridium plugs (work the best for me...YMMV) Denso wires 3.9 rear gear (stock was 3.2) Fancy blue oil cooler EGR and emissions delete 10:1 comp

I think that's it for the engine....for those curious, the rest of car is as follows:

Celica Supra wheels Tokico Blues front and rear (will up grade to Konis) Front strut and brake conversion from a 87 Corolla GTS I made the fronts adjustable coilovers with Tanabe springs and T3 camber plates Rear springs are cut 91 MR2 springs Awesome Autopal headlights with the classic PIAA yellow bulbs Old School Hella 500 driving lights to throw light as far forward as possible when in rural areas SS Braided Brake lines Brake Master cylinder delete Sonic Motors fixed buckets (these are rad seats for super cheap and they're incredibly light...if you need good cheap seat call Sonic Motors, ask for Zach, and tell him "John with the Starlet sent you." Four point cage/bar I did myself. It was the first one I had ever done and I think it came out well. May not win any awards but it's safe and made right Sabelt cam lock harnesses

I just pillaged a 87 Corolla GTS for its sway bar, tension rods, control arms, brackets, rear disc brakes. I plan to do something very similar to what T3 offers as a KP to AE86 front suspension swap-- tubular control arms, heim joint ends but I'll be using a stock AE86 front and rear sway bar. And now that I have AE86 rear brakes, I'll be retrofitting those soon.

With all that said, will the FCRs give me somewhere near 10bhp. I know that's impossible to tell but let's hazard a guess. I would say the car is up from its factory 57bhp to about 80. I've been told that's pessimistic but without a dyno that's my best guess.

Sorry for the late reply: here is the rub as you'd be going from 2 38mm barrels,to 4 39mm barrels I would expect a 10hp gain. The rub is that a set of webers would also give a boost as well. Given the spec you listed the carb would seem to be the restriction.

I'd figure out the cost of webers versus the FCR carbs, make sure you cover everything from any motor mounts to custom throttle cable. Let's say the FCR carbs make 10hp more than the webers, if it's going to cost $400 more than the webers is it worth it for the way you intend to use it.

Finally given the specs you have, after adding some type of side/down draft carbs, I'd expect about 85-90hp at the wheels.

Tom