Bike carbs sizing

[BobbyBreeze]

21 hours ago, Beaver said:

I always thought you get shithouse vacuum off a single runner? You’ll know more than me. Maybe different for vac advance? 

Running a vacuum balance bar actually has no real advantage in terms of max vacuum pulled. As the vacuum pulses on paired cylinders end up cancelling each other out as the other cylinder is in overlap. (same as cross talking on plenum manifolds and is the whole point of individual carbs / throttles). It should only take a few cycles to pull enough vacuum off one runner for power brakes with normal road cam timing. If you need more you can run a line off each runner with one-way valves off each to stop the cross-talk, but really shouldn't be needed on most stuff. 

I agree on repetes comment regarding pulsing for vacuum advance though. The pulses off one runner will screw with that. 

[shizzl]

Hook the vacuum advance into the balance bar?

[Seedy Al]

Yeah as @Steelies said,

I have a carb setup he built for a 4age that im looking at offloading. 

Thinking it might be easier modifying something that is already sorted,  as has a sweet cammed spindle for the throttle and everything, combined vacuum lines etc. Has been run successfully on his starlet.   Im looking at selling everything I bought with includes a fuel pump but also a 4age magic ignition box which you could sell on.

Im at $500 because that's what I paid.  Should be able to sell magic box for at least half that. 

[kiwisurf]

Fuel pressure is critical. Easy way around it is to use the fuel pump of the matching bike. They are high flow, low pressure and pressure switch automatically. 

[kicker]

Keep in mind most carby bikes use gravity feed so no pumps to be found.

[shizzl]

 

ive spoken with the guy whos got the blue hunter with bike carbs, hes gone back to the single stromberg for now, he said he went too big on the drilling the jets and never got it to run right.

 

[peteretep]

there are heaps of small things that need to be altered on bike carbs, I think lots of people who have trouble with them only change main jet sizes. Car engines work a bunch differently to bike engines, mostly with how fast they accelerate rpm's so they need to be altered to suit

[shizzl]

Yup, for sure..

I figure if I'm going to spend money on the original motor I may aswell spend a little more and do a conversion.

Or do the easiest option of the standard twin carb swap, even though they are still shit, the manifold design is 10x more efficient 

[d.p.n.s]

Bike carbs work well mate... 

Rotary would work better.

[shizzl]

indeed it would.. id go that way if I could find something affordable, but that is no longer applicable to rotaries.. also 4age's are retardedly expensive..

I would much rather have a 4age in it tbh..even a zetec on bike carbs

[d.p.n.s]

53 minutes ago, shizzl said:

indeed it would.. id go that way if I could find something affordable, but that is no longer applicable to rotaries.. also 4age's are retardedly expensive..

I would much rather have a 4age in it tbh..even a zetec on bike carbs

Man 4age motors pop up all the time on facebook.    Sometimes full rwd 4age setups.. 

The 4age would be the way I go.

[shizzl]

On 07/09/2018 at 16:14, d.p.n.s said:

Man 4age motors pop up all the time on facebook.    Sometimes full rwd 4age setups.. 

The 4age would be the way I go.

let me know if you see one...

 

 

the thought of a 46 year old motor with +40 pistons and bike carbs is rather cool...

still need a headlight for it, and a pair of M16 escort calipers, sierra/capri/escort springs...and definitely new shocks

[d.p.n.s]

3 minutes ago, shizzl said:

let me know if you see one...

 

Ive got a pair of strombergs arriving this weekend.. if it doesnt running decent enough on those ill pull the 1725 and try and find a 4age.

the thought of a 46 year old motor with +40 pistons and twins carbs is rather cool...

still need a headlight for it, and a pair of M16 escort calipers, sierra/capri/escort springs...and definitely new shocks

I'll see what I've got sitting around this weekend.

[Seedy Al]

1 hour ago, shizzl said:

4age verse

the thought of a 46 year old motor with +40 pistons and twins carbs is rather cool..

@vivaspeed

Whats your thoughts on this lol

[peteretep]

felt pretty good passing 4ages with my 50 year old engine with bike carbs TBH

[vivaspeed]

1 hour ago, Seedy Al said:

@vivaspeed

Whats your thoughts on this lol

Having gone down both paths. Modern Japanese on injection is the way of the future.

You can spend a lot of money making an old engine only half as good as a modern twin cam.

Also 4AGEs are an old engine now. Basic 16v design is 35 years old now.

MX5 engine in rwd is the go.

 

[shizzl]

my budget doesnt allow for such niceness and reliability.. no job etc etc

driving this and actually pulling out and passing said modern cars that are doing 100 is strangely satisfying even though shes pretty much screaming anything over 120.

 

[dmulally]

Hi All,

I have some bike carbs that I want to put on my 1725cc rapier engine for my commer. Basically they are the only thing I can fit under the seats of my commer. I wanted some DCOE's but it looks like too much of a pain to fit them. 

They are 34mm carbs from a Honda 600. They have a 1.5mm main jet. 

I'm about to make the manifold and have a question for those who are smarter than me. What angle should I set them at or it doesn't matter? I note on the bike they nearly point up. Also, what are the arrows pointing to in the picture? The big one top center seems to push the black choke things up when I blow on it. No idea what the two are next to it. I'm guessing the two lower ones are fuel lines. Of which I have the fuel pump from the bike.

Any help is appreciated. 

Cheers

Damo

 

[peteretep]

hey man, 90% sure the big one in the middle is connected to all the carbs, and the area above the slides. On a bike they are connected to the airbox and when that is under vacuum they open up more. For a car, especially a lazy commer motor, your engine wont increase rpm anywhere near as fast as a bike, so that can be blocked off. There will be a small hole on the bottom of the slide that 'sees' the air going past and creates a vacuum which pulls the slide up. If you dont block it off, the slides will likely 'flutter' as the revs increase, wont do much but can look and sound weird

 

For the smaller black lines, I am going to guess and say they are fuel overflow lines, typically they have little hoses that run away from the rear wheel on a bike, they can probably be left in your situation unless they will chuck fuel out onto the exhaust or something

 

I think you are a right with the lower hoses, and that they are fuel inlets, although its a bit weird having 2 inlets, but that could be because of the layout on the bike

 

For setting the angle up, I would aim to have the float needle in the vertical position, this is likely perpendicular to the bowl flange, so keep the bowl flange level and you should be about right, but check the float needle first. It is probably set up steeper on a bike due to the fuel moving backwards when the bike is accelerating which would create a false level

 

I imagine that you will need to jump up a few jet sizes, but a 1.5mm should be OK to run as is for a short time

 

You should get a carb balancer to set them all up, just takes 10 mins, and when setting up the needles, start from the top and keep lowering it until fuel stops visibly dribbling out at idle

 

also, have a look on en.impex-jp.com for spare bits for your carbs, and watch out when undoing the phillips screws not to damage them and be careful with the gaskets

[dmulally]

Thanks buddy. I might see how hard it is to pull them apart and take the sliding choke plates out. I tried to find where to plug so they stay open but nothing obvious was glaring at me. 

Much appreciated.