Bike Carbs

[CaMpylobacter]

Mi16 converted pug on r1 carbs

[Spencer]

Yeah I've heard that 20v ones are only 38mm anyway and from what I have seen they are more expensive. I saw a set of these on trademe recently for $350.

silvertop = 43mm

blacktop = 45mm

thats at the butterfly, have sets of both here at home. Bike carbs are a good cheap way to get throttle response and reasonable power, economy can go out the window if your not onto the tuning. Great if your running a big cam as the pulses sent back up the inlet can interfere and give a real shit idle (which sounds cool ) seperate intakes = smooth as. The only way to get correct fueling for power, economy, driveability and to get it started first pop every time is with injection. Theres pros and cons both ways cost etc

[isnowi]

there is such a thing as over throttling an engine, the bigger the throttle the longer the manifold runners need to be in order to get peak torqua at a reasonable level. I did some calculations based on a 4g63, in order to get peak torque at around 4000 rpm (rally car) using 44mm throttles required intake runners of approx 350mm between throttle plate and the inlet valves, and trumpets of around 150mm from throttle plate to lip of trumpet. Oviously if torque is not too much of a concern and you don't mind revving the tits off of the motor then compromises can be made. Also bigger throttles and short runners can actually hurt throttle response due to lower air speed through the throttles, most of the decent manifolds for quads have a pronounced vortex in them to keep the air speed up, coupled with the trumpets. Just something to think about.

[R100]

I fitted a set of Honda CB750 carbs to my hillman imp many moons ago. Seemed to work well. Good throttle response and sounded great a high revs. I fitted a 2 liter fuel tank in the rear just above the carbs because they are gravity fed. I then fitted a return line back to the tank in the front and the fuel just kept recirculating. Looked a bit rangi but at least it worked ! I have some old photographs somewhere i will post up if i can find em

[Mike-e]

if you don't mind revving the tits off of the motor then compromises can be made.

Totally. If you do swing that way then how short your intake runners are is directly proportional to the amount of fun had.

Keihin FCR's off some honda motorbikes

[CaMpylobacter]

short = neccesitates huge revs? or vice-versa?

[Mike-e]

yes, short requires high revs, longer intake runner length = more low down toruqe/response

[CaMpylobacter]

mint. thought that was the case

[mikuni]

Awesome, ^ that shit's what I like to see. Theres a calculator and a page explaining the logic floating around here somewhere.

In a perfect world it makes sense to calculate it out, but in car engines, where revs are unlikely to be climbing into 5 figures it makes sense to simply make the intake runners as long as space allows. Which in my car would only be 250mm's or so right to the trumpet tips. From memory that still equates to peak torque at something like 7000rpm haha.

[Spencer]

In a perfect world it makes sense to calculate it out, but in car engines, where revs are unlikely to be climbing into 5 figures it makes sense to simply make the intake runners as long as space allows. Which in my car would only be 250mm's or so right to the trumpet tips. From memory that still equates to peak torque at something like 7000rpm haha.

yea thats why most n/a manifolds are curved up to get the required length. I wouldnt trust most peoples calculations theres alot to it, touched on helmholtz resonance at uni, he was a on to it cunt invented heaps of cool shit.

[CaMpylobacter]

I'd be lucky to get 180mm, if that. stock manifold has culred over runners

[mikuni]

Yeah yeah. You see it on all the high po shit. B18c, Beams 3S, Opel XE, just to name a couple of the more common ones.

Low-midrange torque is great, but from what I have seen to get high revving max performance its all about shorter-medium intake runners and straight in, straight out. None of this curvy pissing about.

[tortron]

iv got a 2nd set of carbs for my bike, buy them etc

[Sparkle]

always thought bout running 3x 40s or 45s on the 5, would sound so badass.

[mikuni]

always thought bout running 3x 40s or 45s on the 5, would sound so badass.

Hell yeah do it. Or six bike carbs. Or 6 20v throttles. Would be awesome as. I think 6 bike carbs would be easier to get running right than 3 sidies.

[CaMpylobacter]

triple sidies would be easier for the experienced old cunts, they = tune sidies in their sleep. bike carbs could be a cunt, theoretically about the same though once you work out a base jetting etc. I've been reading up as much as i can bout bike carbs on pugs today. seems reasonably easy, but less actual facts set in stone are documented. there's a couple of places in the u.k that do the conversions, and tune them. most people roll with that. I've decided which cqarbs i'll use if I go that way though....

so thinned it to 3 options.

20v ITBS

bike carbs

A/Market ECU w/stock manifold

[mikuni]

Mean. Brown Brothers? are a group that does standard kits in the UK. Its pretty funny though. People with daily driven Astras and Golfs etc take them in and pay about 2000 euros to get their fuel injection pulled of and a set of bike carbs put on and thats it. I couldn't believe it but they are all happy with the results.

So thats what got me thinking about them more because for years I thought it would be cool, but to unpractical. They reckon they stay in tune under normal driving conditions for up to a year and you don't loose any drivability. I think carbs seem to have come a long way. Thats why bike carbs are the one.

[CaMpylobacter]

yeah. balancing is the only thing that should really slip....... otherwise, bike carbs will have the same downfalls, you'll likely find. can't see how mixtures changing would be any different for bike carbs.

I like how simple it is on most vehicles to construct a manifold.

[V8Pete]

Where are you guys going for your $150 custom inlet manifolds?

I've been labouring away designing one for my car intending to do as much of the work as possible to make it cheap, but if someone'll do all the dirty work for $150, I'd rather just pay 'em!

Also, what do you generally make them out of? I've mainly seen alloy, but was talking to a mate who suggested mild steel + HPC. Pros/cons...?

[mikuni]

The manifolds for R1 Carbs are simply a plate whith holes cut out the appropriate spacing for the inlet ports and some more holes drilled for the studs. Then pipes are welded on at the necersary spacing for the carbs. Its extremely simple because the carbs are just clamped on with hose clamps. I'd imagine making one for throttles would be a little more difficult.

I too was looking for hookups to get it as cheap as possible but a fabrication place that is doing some work for me offered a manifold to be made for $150, so I'll probably go with that as its surprisingly cheap. Even if it blows out a little it will still be a good price. I'm hoping to go with stainless because the added expense is neutralised buy not having to fuck around with HPC'd steel. Plus it looks pretty.