carburetors....modification question

[Anonymous]

as most gs bikes there is a carb for every cylinder....mine particular bike is a 1978 gs400 twin........ could somone tell me what is the advantage of this and what would happen if i tryed to run two off of one carb with a custom intake whether it be stock and i jetted tha hell out of it or if i got a bigger carb would this work and would it boost drop or maintain performance

your help would be greatly appritiated

Mike

[Dink]

the main advantage of a carb pre cylinder is precision, precision of adjustability etc.
Yes you can swap to a single larger carb, on a custom manifold, but why you would is beyond me, it will lower performance, only slightly if at all increase fuel economy, and offers up the potential for all sorts of weird and wonderful mixture problems.
Dink

[Anonymous]

carbs

ohh ic thanks for the input i just thaught it wouldnt make a difference in performance because only one cylinder breaths in through the carb at one time anyway plus the big v twins you see on choppers only run a single carb.

[Dink]

Re: carbs

ohh ic thanks for the input i just thaught it wouldnt make a difference in performance because only one cylinder breaths in through the carb at one time anyway plus the big v twins you see on choppers only run a single carb.

But big V-twins are not about performance!!! They are all about torque and pose value.
Dink

[Nerobro]

A single carb can very well improve drivability. And can actually take some of the guesswork out of carburation. It also allows you the option of tuning the intake tract lengths so you can get more horsepower, or at least move the horsepower to a different spot in the powerband.

Also with one carb... There's no problems with carburator syncing.

It would be an interesting project. And not the first time I have heard of it.

[Anonymous]

so if i were to make a manifold and use one carb could i use one of the stock carbs and rejet it??

[Nerobro]

You'd need at least two of the stock carbs. BAsic rule of thumb is that when you go from a single carbuator one carb per runner you need to doubble the total cfm of the carburators. So you'd be doing the oppiste, going from individual carbs to a manifold setup. :-)

[Anonymous]

carb

some of what neobro says makes sense but the rest???? you can run a single carb,on a twin carb engine, triump and bsa have been offering both in the same models, for 25 years, you can use one of the old carbs you will have to jet up about 15%, you will gain low end power, ease of adjustment,ans some milage improvement, the down is a big loss off top end power, some can be made up by going to a slightly bigger carb like from a 28mm to 32mm i.e, if you jump to big then you will have a bogging problem, as far as tuning the manifold its not going too happen do to room constraints and the fact you have to split the runner

[Nerobro]

So what you say is that the mfg's work agrees with what I said. Now, jetting changes have nothign to do with this whole setup. So we'll not considder actaully tuning the engine.

With a properly deigned intake manifold you shouldn't have a huge loss of horsepower. At this point the people wanting the most hosepower with v8's are still running pleanum manifolds and not single carb per cylinder.

Now I won't go into a tirade over the truely crappy designs that the brittish have come up with for intake manifolds, but I'll leave you with this. The intake manifold on a v-12 jag looks like a roundabout.

We actually have quite a bit of room to build a good manifold on a GS. Keep in mind that we wouldn't need an airbox anymore, and we could bolt to the head instead of using rubber adapters like we do.


Though making a good "wet" manifold is much more difficult than making one for efi (in other words a dry) manifold. We have a buttload of space to work with. Though that does bring up the thought of going EFI with just the throttle body off of like a cavileer or other car with similar horsepower potential.

As for bogging issues, needle changes and dashpot/accelerator pumps are there to fix those :-) As are CV carbs.

[Anonymous]

Are you saying i could make my bike fuel injected?...if i had a small throttle body and some injectors i would need some sensors and a computer for all that wouldnt i?

[Anonymous]

I dont understand this carbureted sh** personally hate them....how will one carb make me lose power on top end and how will the length of the manifold effect the power....on a twin cylinder one piston draws in at a time doesnt it so why wouldnt one stock carb work?....

[Nerobro]

Well... I can't vouch for the triumph mainfolds, but I"d assume they'd have longer runners. Longer runners increse torque at lower rpms. Shorter runners, like those you'd get when you have individual carbuarotrs, will increse torque at higher rpms.

Yes, you coudl go efi. http://www.megasquirt.info/ is an answer.

The runner length is important for both carbuarted and efi bikes.