The 510 Realm

Hi, i just bought some bike carbs and would like to know if someone could help me a little..

I have a stock a12 with headers and the carbs are from a cbr900rr so are a little big, and would probably need rejetting but don't really how to start..

I know how to make the manifold, thats not a problem i just know nothing about the tunning. If someone has informations it would help me.a lot.. thanks !

Get a WBO2 sensor and gauge. Get spare jets for your carbs. Jets'll be bigger or smaller than what you have in the carbs. Baseline your OE jets with the WBO2, then go from there. Same as figuring out the tune on any other sort of carb setup. No one here's going to have the magic setup for your particular engine/carbs, probably no one has run them. But the basics are the same no matter, just get stuck in. Good luck.

Thank you really much, i'm new to the carbs world, i'll find informations about them first and after that i'll go from there, thanks !

What are the carbs? FCR?
Also remember that bike carbs run on very little fuel pressure. Holley sells a low pressure kit that works with their bypass style fuel pressure regulator, if you can't fine tune whatever fuel pump you're using just right.
Also, on A and L-series engines running bike carbs, I highly recommend running a heat shield between the carbs and the exhaust headers, as your float bowls are literally right above the headers. Many A-series bike carb manifolds I've seen in Japan raise the carbs up considerably, away from the headers.

I'm currently in the fine tuning stage of running Yamaha R1 Mikuni bike carbs on my L20B. I've done everything myself, except having the intake custom made by Bogg Bros. in the UK. It has been a real learning curve, but there seems to be quite a bit of info about running R1 bike carbs. I'm not sure about your carbs, but I'm sure the principle is the same. Mine are 40mm CV carbs. They work real well, but it's been a lot of trips around the block to figure things out. The WBo2 is my next addition. This will really tell what is going on in the rich/lean department. You have to run a fuel pressure regulator whether run run electric or mechanical fuel pump. These bike carbs don't like any more than 3psi. If you have any questions, I can try to answer them.
http://www.boggbros.co.uk/
www.youtube.com/watch?v=dQOG_KYIPGQ

I do have a general question about bike carbs - generally you see them mounted horizontal in their original configurations. The photo above shows these cars at a pretty extreme angle. Having worked on many cars with side drafts, Webber DCOE, Mikuni PHH, Delorto DHLA's ect - and all need to be mounted within a few degrees of horizontal to work well.
Is this not the case with bike carbs?

Thanks.

Byron

Bike carbs are designed to run under very aggressive positions. Car engines pretty much stay in the same position. If you look at the line at the top of the float bowl, it is horizontal to the engine or close to it. The body of the carb is actually on an angle to the engine, not the float level. This is why I had my intake made by Bogg Bros.They have all the angles figured out for R1 to Datsun motors.

That does make sense, as it's the float chamber, emulation tubes and air correction ports that need to be in the right relation to horizontal. The throttle plates could run at any angle and are irrelevant. Having not held these carbs in my hand, I hadn't noticed that the float chambers were actually mounted level.

Thanks for the installation photo - they do look good.

Byron

Loryde520 wrote:You have to run a fuel pressure regulator whether run run electric or mechanical fuel pump.

The 280ZX electric fuel pump that has the gerotor style pump section that can be disassembled externally, and have the pressure relief spring fine tuned to drop down to a consistent lower fuel pressure. Granted, it's...a lot of work, but it can be done. For pretty much all other electric fuel pumps though, that is correct, and a regulator will be required. I only bring up the 280ZX pump as it's my personal favorite pump for any carbureted Datsun.

Thank you very much for all your responses, i bought a set of cbr600 since i won't have to mess with the jetting (for what i read)

I'll keep the cbr900 for another future setup on my 510

Hakosuka510 wrote:

Loryde520 wrote:You have to run a fuel pressure regulator whether run run electric or mechanical fuel pump.

The 280ZX electric fuel pump that has the gerotor style pump section that can be disassembled externally, and have the pressure relief spring fine tuned to drop down to a consistent lower fuel pressure. Granted, it's...a lot of work, but it can be done. For pretty much all other electric fuel pumps though, that is correct, and a regulator will be required. I only bring up the 280ZX pump as it's my personal favorite pump for any carbureted Datsun.

Interesting, that's the same pump that I used to run on my carbureted turbo setup. Excellent pump for my application - not too much pressure. Never knew those pumps could be modded to run at lower pressures, very cool.

James

I make a set of FCR manifolds for the A12