Bike Carby's

[Jono.C]

Hey guys, Getting back to building my 5k for my white ke10.

 

Want to go the bike carby route, just for something different, trying something new and the sound.

 

The thing i'm not sure is, Is there a way to work out what carby's will be suitable which aren't?

 

I was talking to Jordain on facebook about it earlier and just got lost, he mentioned about going off throat sizes..

 

He also said he had cbr600 carbs on his 4k, Guessing this would lean out on a 5k?

 

 

It's going to be pretty mild, heads done to 10.1:1 compression, mild porting, will cop valves and valve springs as well and be run on 98..

 

Any idea's on how to work it out, or what would be suitable?

 

Cheers

[Taz_Rx]

Think about the rpm that the 600 pulls, not just its capacity!

[Jono.C]

Yeah but the thing with motorbikes is they all rev to like 12k

 

My slightly less shit than stock 5k wont go anywhere near that.. So i should be right for pretty much might carbs by that standard

[azza91]

don't forget you can mess around with the carby jets too

[ke70dave]

yeah the jets is the big one.

 

using purely theoretical ideas...and how i would approach it from a standing start...

 

you would need to ensure that the carby can flow the requied amount of air (assuming maximum VE @ maximum revs for a conservative approach). you may find that a 600cc @ 12,000rpm, might be in the ball park of a 1300cc @ 7000rpm. which it probably is quite close so hopefully only small mods are required.

 

And at that amount of air flow, ensure you can modify whatever you need to to ensure the carby can supply that fuel at that air flow.

 

Carbys are amazing yet fairly simple devices to modify if you know what you are doing.

 

might even be worth dropping down to your local bike tuning shop and see what they reckon on the limitations of bike carbs, they might even be able to suggest a specific carby that is easy to modify or can get you close to your goal from the get go.

 

what i would avoid doing is buying a set of bike carbs, slapping it on, and hoping for the best. do all your research before spending a dime!

[coln72]

Used to be a Civic rally car running bike carbs in Ballarat. It used a header tank that the fuel was pumped into. The carbs were then gravity fed from this as they wouldnt handle the fuel pressure of the pump.

[snot35]

I've been debating bike carbs lately. I think it's quite do-able, and the CBR 600 carbs can be had so cheaply.

 

I think the real way to look at it is HP. Ultimately you need to flow enough fuel and air for X number of HP. The CBR600F2 is rated for 74kw, how close do you think you'll be to that? There is probably some leeway either way too. They're supposedly 34mm (F2) to 36mm (F3) carbs. Given they have fairly clear throats they should be fine with the roughly 27mm ports of the 5K if you're only giving them a mild tidy.

 

Definitely budget for tuning. If you're doing it yourself you might be OK. If you want someone else to do it you may want to make sure they can get their head around jetting a bike carb for a car. They may freak out :)

Edited July 1, 2012 by snot35

[rollalicious]

there is a thread elsewhere on here about this, but all the good stuff and links is on the club k forums. quite a few New Zealanders doing it well. and the gravity feed thing is ancient technology, but you will need a specific bike fuel pump.

[Figjam14]

We have a datto a12 engine running bike carbs at tafe, was mucking around with it the other week. It had quad 450cc carbs that ran quite well.

[azza91]

i was going to run r1 carbs on my 4ag before i decided to just run twin webers

[MRMOPARMAN]

look at what similarly modded 5k's with webers run in the way of choke sizes, then run somewhere around that sizewd carb. i think around 36mm would be the go. if going flat slide carbs or barrel carbs you could go a little smaller.

 

also look for something that has an accelerator pump, or ones that can get off the shelf kits added. will make, making them work a lot easier.

[altezzaclub]

also look for something that has an accelerator pump,

 

Good point- how do bikes get around the lack of a pump jet? The SUs have the oil dashpot delay the piston rising so it immediately richens for a second or two when you boot it, but I haven't seen those on bike carbs.

 

you may find that a 600cc @ 12,000rpm, might be in the ball park of a 1300cc @ 7000rpm. which it probably is quite close so hopefully only small mods are required

Surely max air flow should be-

max revs X 1500=12000 X 600.... so max revs=12000X600/1500 or about 4800rpm on your 5K will suck the same air flow as that Honda pulling 12000rpm. Those carbs could be a bit small.

[Trev]

I have a spare set of 4 cylinder 250cc bike carbs here that I am willing to donate to someone for flow testing purposes, they have a 27-28mm throat.

[Trev]

Good point- how do bikes get around the lack of a pump jet? The SUs have the oil dashpot delay the piston rising so it immediately richens for a second or two when you boot it, but I haven't seen those on bike carbs.

 

This is the carb breakdown from my parts manual, not sure if it will help or not.

 

[snot35]

Doesn't the spring provide that initial resistance that will enrichen the mixture? It would have to build enough vacuum to overcome the spring resistance, I thought the pot oil damped this movement much like a car damper prevents oscillations in the springs. Yes they contribute to the resistance as well, but there's a bit of cross over there.

 

Reading into it, it seems the bikers adjust the size of the vacuum bleed port into the pot to adjust accel enrichment. So there's the option to drill it out or put in restrictors to modify the accel characteristics. It seems some of the dyno jet kits include restrictors.

Edited July 11, 2012 by snot35