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Single carburator!!

Jianis

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Lots of people seam to use 2 instead of 4 carburettors.
Did anyone use one carburettor instead of 4 ??.:confused:
I know its a big problem to keep the air volume equal for all 4 cylinders in a confined area but I still should like to know if anyone gave it a try and what the result was.
Thank you in advance

:cheers: Jianis
 
Lots of people seam to use 2 instead of 4 carburettors.
Did anyone use one carburettor instead of 4 ??.:confused:
I know its a big problem to keep the air volume equal for all 4 cylinders in a confined area but I still should like to know if anyone gave it a try and what the result was.
Thank you in advance

:cheers: Jianis

In theory a single carb well designed manifold should work about as well as 2 carbs.

there will be some compromise as the cam is not very conducive to either in certain ways

that would take a long explanation and you didn't ask.

keep carb as close as possible keep a small runner use a properly sized plenum

play with cam timing jetting etc.

It all has to work as a package.

2 cams would probably work best for tuning.

Like they say every time you make 1 change you need to optimize

everything. Jetting, base timing, advance curve, total advance, cam timing, jetting again.

maybe even exhaust if you have the right equipment.

I had an engine for !4 yrs that I was still tuning and making more

power (sometimes) before it suddenly and mysteriously disappeared.
 
WAY less power. Why would somebody do that?

If you don't understand 4 carbs then you don't understand 1 either, 4 is only a simple multiple of that. You just do everything 4 times and no rocket science there.

Single carb engines are dogs.
 
Hey sorry to wake this up but I am also curious about this 4 to 1 carb idea!?

In theory a single carb well designed manifold should work about as well as 2 carbs.

there will be some compromise as the cam is not very conducive to either in certain ways

that would take a long explanation and you didn't ask.

Could you give an explanation. I am interested about how the cam relates to the carbs?


WAY less power. Why would somebody do that?

If you don't understand 4 carbs then you don't understand 1 either, 4 is only a simple multiple of that. You just do everything 4 times and no rocket science there.

Single carb engines are dogs.

What do you mean by Single Carb engines are dogs?

If I had a good manifold and a large carb (say off a straight 6) would that not full fill the job of 4 carbs more the adequately?

My carb knowledge I will admit is somewhat limited I know what they do, how to take them apart, the components but I am sure there is more to them then just air and gas mix.

Cheers
Monkey Wrench
 
'In theory a single carb well designed manifold should work about as well as 2 carbs.'

Nope, nowhere close.

They print books that have shredded that idea for 50 years y'know.

Here's the simple way to look at it.

It takes so much carb hole size to feed an engine at the upper rpm levels they are capable of doing. The size is fixed in physics and easily calculated. You can take that area requirement and break it into 4 parts meaning 4 separate carbs, or leave it as one. The lower number of carbs, one in this case misses a basic tenet of the physics, that is, 4 smaller carbs are hugely more air active than one big one of the same total size. Air is much easier to move fast in smaller amounts than larger. Meaning the one carb will have fits running at lower airspeeds since it has too big a bore to activate the fuel circuits at lower rpm. The 4 carbs can do that all day long because each is smaller and the airspeed in them is much higher. To make up for that, the single carb ends up ALWAYS being smaller than it needs to be for max power, OR, you lose low speed driveability. The 4 carbs can run better down low and yet still make more power.

The rules are cast in concrete there, why you can take the single one barrel off the six cylinder and add a two barrel with each barrel smaller but the two added together are bigger and pick up 15 hp., like I did on my 258 six AMC engine. Why 4 barrel engines run harder than two as well. You ALWAYS get more efficient intake manifolds the more carb bores you add, it allows each runner to be more ideally placed for power. The less carb bores you have the more the forced crappier design of the intake. You simply never get a manifold to flow better when some of the cylinders it feeds are further away than others from the carb bore itself. The compromise doing that there utterly kills power. There are also things you can do with sonic wave tuning of the engine that absolutely do not work with a single carb. Potential BIG power increases there.

Cam/carbs relationship? Simply put, the more radical the cam is in terms of timing the more it needs better flow up high, since by the above description the flow has to suffer up high on a single carb to get good low speed running the cam's ability to make more power is sacrificed and then the extra performance disappears. Radical cam timing LOVES multiple carbs.
 
Not sure how you mean that.

If a single 4 bbl. on a bike no. You missed this completely...................

'...it allows each runner to be more ideally placed for power.'

A single 4 bbl. on bike is a manifold design disaster. There are other reasons too but if you think that basic they will be pretty much lost in the mix there.
 
Okay I might have been side tracked when you switched to talking about the AMC and 1 vs 2 bbl and 4 vs 2 bbl carbs. I just read some information on the difference between 1,2 and 4 barrel carbs.

My thought process was 4 bbls = 4 carbs

But after some research and re-reading your post a couple times, I think I have found an answer.

Please correct me if I am wrong!

In order to make a single carb on 4 cylinders work, I would need a manifold that created an equal distance from the carb to all 4 cylinders. That's one point I was missing. I understand that the larger bore also creates airflow and vacuum issues which is a problem with our high output motorcycle engines which need everything they can get.

So the thing I guess I am still fumbling with is the barrels. So from what I understand a single stage 2 barrel carb is essentially 2 single bbl carbs using the same air trumpet, but a 2 stage 2 bbl carb has a primary and secondary bbl. 4 stage carbs have 2 primary and 2 secondary bbls.

So say we have 2, single stage, 2 barrel carbs, set up with a perfect manifold would we essentially running 4 carbs? or do we still have the Airflow/vacuum issues due to the larger/shared air trumpet

Sorry I am just trying to completely wrap my head around this. I have a picture of having one massive carb under my fuel tank being fed by a massive cone air filter under my seat. But while I am thinking more about aesthetics here then trying to improve performance, if all I am going to do is ruin the performance of my bike I might just go the otherway and get CR 29's and rip.

If you have any sites or reading materials I can look further into that would be also appreciated!
 
Okay I might have been side tracked when you switched to talking about the AMC and 1 vs 2 bbl and 4 vs 2 bbl carbs. I just read some information on the difference between 1,2 and 4 barrel carbs.

My thought process was 4 bbls = 4 carbs

But after some research and re-reading your post a couple times, I think I have found an answer.

Please correct me if I am wrong!

In order to make a single carb on 4 cylinders work, I would need a manifold that created an equal distance from the carb to all 4 cylinders. That's one point I was missing. I understand that the larger bore also creates airflow and vacuum issues which is a problem with our high output motorcycle engines which need everything they can get.

So the thing I guess I am still fumbling with is the barrels. So from what I understand a single stage, 2 barrel carb is essentially 2, single bbl carbs using the same air trumpet, but a 2 stage, 2 bbl carb has a primary and secondary bbl. 4 stage carbs have 2 primary and 2 secondary bbls.

So say we have 2, single stage, 2 barrel carbs, set up with a perfect manifold would we essentially running 4 carbs? or do we still have the Airflow/vacuum issues due to the larger/shared air trumpet

Sorry I am just trying to completely wrap my head around this. I have a picture of having one massive carb under my fuel tank being fed by a massive cone air filter under my seat. But while I am thinking more about aesthetics here then trying to improve performance, if all I am going to do is ruin the performance of my bike I might just go the otherway and get CR 29's and rip.

If you have any sites or reading materials I can look further into that would be also appreciated!
 
2 barrel automotive carbs can be made to work...just look at the weber carb setups for the 750 from the 70's. Granted they are not just a simple 2 barrel webers are fairly complex as far as carbs go. The carbs do work well because they had been sized to the engine size and each barrel does work as an individual carb. This setup does increase power and performance over the stock carbs, it has been tested and proven to work. RC engineering did a lot of testing and tuning of this setup in the 70's and made them work very well and are very desirable...if you can find and afford one of the setups. I suggest you go with the CR29's if you want to ditch the stock carbs, dont go any larger unless you make the motor bigger.
 
The only reason besides the small venturis the Webers work is because they come in a bore spread that you find virtually impossible to get with other 2 barrels. One other reason is the 15 gigamillion different parts that can be had for them, no other 2 barrel carb has that sort of backing.

When you start bending ANY manifold port around to fit up with a carb bore you have pretty much gone down the route of less power.

Uh, there were flowtests that showed the Keihin 28 mm. carb supplied on SOHCs actually outflowed the 29 mm. smoothbores by a small amount (possibly due to the adapters used on the 29s) but they reportedly didn't track quite as well, that could easily have only been how far somebody wanted to go with dialing in airbleeds or slide cutaways before giving up.
 
But the fact is the webers work...and they work very well, doesn't matter what the reason is. The new cr29's flow much better and have better drivablility than the stock carbs. Flow isn't everything either, fuel metering accuracy, atomization, and mixing of air and fuel are much more important to making good drivability. Yes I have seen the old flow test done back in the 70's comparing the stock carbs and the "old"29 carbs. RC also used to bore the stock carbs to get them to work with the big motors...until they found webers and used them instead of the bored carbs as they found they produced much more power then the stock bored carbs. But to each there own, the fact is 4 carbs works better then most any other setup so for most people stock carbs will work fine and most people are just after a "look". :shrug:
 
There you go...............the look thing. Why on the DOHCs they so screw the motors up looking to put those pods on there. Pods and CV carbs are not one of the better combinations although I personally had pretty good results with them once you learn to toss a few ideas that are out there. Them CVs are something else.

I played with the 'weber' carbs (the staged 2 bbl. ones) on Ford 2.3 SOHC motors when Holley was licensing them (the 5200 series) for OEM production, they had scads of tuning parts available, what made them so good to work with. Or you could easily mod existing parts to get more out of them. I could get them to pass emission specs all day long even with hot rod parts on the engines.
 
There you go...............the look thing.

Ha ha isn't that at least 50% of why we do this? So we look awesome!

Why on the DOHCs they so screw the motors up looking to put those pods on there. Pods and CV carbs are not one of the better combinations although I personally had pretty good results with them once you learn to toss a few ideas that are out there.
Yea I am running stock carbs with pods and a 4 to 1 exhaust right now, and for some reason it runs.... wellish. Might have to do some tuning once I get the engine back together... But we'll see!

Thanks for the info!
Maybe Ill just go CR's for now, or mess around will the stock carbs, and then play around with the 5200's or something over the winter. I just wannnnna ride while the suns out!
 
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