dual carbs GX200

#1
Hello friends,
What would be the result of putting a T in the silicone hose used to mount a TM24 flatside and running two TM24's?
I could have a thumb throttle for both thumbs is one answer...
Go WOT on one, then the other! Might it work????

I see in some old posts that some West Bends had two mounted separately.
 
#2
Hello friends,
What would be the result of putting a T in the silicone hose used to mount a TM24 flatside and running two TM24's?
I could have a thumb throttle for both thumbs is one answer...
Go WOT on one, then the other! Might it work????

I see in some old posts that some West Bends had two mounted separately.
It would be a bear to tune and it would end up being too much carb anyway. You would be perfect with one carb.

But I'm not telling you not to try it. Just sayin' you probably won't get the result you're looking for.
 
#5
Hello friends,
What would be the result of putting a T in the silicone hose used to mount a TM24 flatside and running two TM24's?
I could have a thumb throttle for both thumbs is one answer...
Go WOT on one, then the other! Might it work????

I see in some old posts that some West Bends had two mounted separately.

So I have worked with snowmobile, dirt bikes, atv and utv engines for a few years and have seen several dual carb setups. On a single cylinder it is completely pointless in all honesty with the specific carbs you are looking at. Just too much air and fuel to efficiently burn in the combustion chamber. Kinda like fitting 10 pounds of :censure: in a 3.5 pound sack. Lol

Now that would be with dual 24mm carbs... Dual stock ones or similar sized would be a different story though. Now, the thing about bigger carbs is larger bores move higher quantity of air at lower velocities in general than smaller carbs. The opposite would apply to smaller, less air at a higher velocity. Keep in mind this is all just general info and does not always apply either so this is not the bible... The other big issue people have is the calibration with twins, specifically throttle and jet sizing. If you do not reach full throttle with both at the same time you wont reach full power and it can cause tuning issues too. I have seen jetting be off or inconsistent fueling due carbs not supplying consistent air/fuel due to the intake runner connecting the two causing irregularities in the air stream.

Hopefully this gives you an insight on making a choice. I personally would never go dual with a carb that big. I would look into smaller carbs like the newer tillitson carb that is stock sized but has tunable jets so you can tweak it. Idle is also going to be a bit of an issue with traditional jet style carbs. Good luck and have fun! Hopefully this helps! :gunsmilie:
 
#6
So I have worked with snowmobile, dirt bikes, atv and utv engines for a few years and have seen several dual carb setups. On a single cylinder it is completely pointless in all honesty with the specific carbs you are looking at. Just too much air and fuel to efficiently burn in the combustion chamber. Kinda like fitting 10 pounds of :censure: in a 3.5 pound sack. Lol

Now that would be with dual 24mm carbs... Dual stock ones or similar sized would be a different story though. Now, the thing about bigger carbs is larger bores move higher quantity of air at lower velocities in general than smaller carbs. The opposite would apply to smaller, less air at a higher velocity. Keep in mind this is all just general info and does not always apply either so this is not the bible... The other big issue people have is the calibration with twins, specifically throttle and jet sizing. If you do not reach full throttle with both at the same time you wont reach full power and it can cause tuning issues too. I have seen jetting be off or inconsistent fueling due carbs not supplying consistent air/fuel due to the intake runner connecting the two causing irregularities in the air stream.

Hopefully this gives you an insight on making a choice. I personally would never go dual with a carb that big. I would look into smaller carbs like the newer tillitson carb that is stock sized but has tunable jets so you can tweak it. Idle is also going to be a bit of an issue with traditional jet style carbs. Good luck and have fun! Hopefully this helps! :gunsmilie:
Couldn't agree more. Nice explanation!
 
#7
Honda and Yamaha, maybe others, have used staged twin carbs on bigger singles, in the past. They were 4v heads with individual ports, so a much easier setup. A 2v wouldn't have the same swirl inducing differential at low-mid throttle openings.

A 24mm carb is nearly 2.5 times the area of a stocker already. Port area and curtain area barely need a single.

But, I was toying with the idea of a large carb on a short manifold, with a small diameter Y branched off to a long narrow runner and little carb. 13mm Honda CRF50 units, maybe, or the 17mm on the 70cc.

The ever=popular Chi-kuni oval bore does some of the gain anyway, though. Smaller diameter but tall for good low speed signal and decent top end. There are bigger versions, ones with an accelerator pump, etc.
 
#9
Yeah a manifold with spots to mount two carbs, I would think maybe a gx390 on one and stock one or possible smaller one on the other. I would make it more like a plenum with a couple of runners though as that would give a more consistent atomizing of the air/fuel.

Here is a thought... GX390 carb on the main large runner and a Tillitson stock sized one for there 212cc race engine that has the tunable needles in it. It is the same size as stock but is fully adjustable so you could set the GX390 a bit on the leaner side and the smaller of the two could handle the rest. If there are any changes like altitude, temp, humidity or anything that would justify a slight air fuel mixture adjustment, you simply tweak the needle on the small unit.... Hmmm I may be on to something here.... :grind:
 
#10
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Wow, now that's the info I was looking for from you guys! Thanks!
I found a T with 32mm branches but only a 25mm branch for the manifold.
With all the new, fine info, I am reconsidering my daydream of duals.
Again, the feedback is appreciated for real..
 
#11
Question. How are you going to apply the second carb into the system at the correct time? Some type of staggered linkage, like a 4 barrel carb on an auto uses to apply the secondaries? Or some type of block off on the secondary carb to prevent dual fuel feed?
 
#12
Either run a thumb throttle for each carb and thumb, try to align/ mount the thumb throttles together for one thumb,
or splice the two throttle cables into one. I'm still digesting what SmoothOperator and others have said, wish I still had
some smaller stock/ SA carbs to fool around with, I have a Mikuni 22.. Maybe the T having a smaller branch to the manifold would account for not such a huge amount of air/fuel. I'm leaning toward a separate thumb throttle for each, seems control would be best that way.
 
#13
Hmm, maybe disable/block off the idle circuit on the "secondary" carb, with a closed throttle plate it would cut off any bleed from the unit.
Then when you open the "secondaries" you would get normal fuel/air mix added. Just like a 4 barrel carburetor does.

But thinking about it, normally the secondaries are larger than the primaries, so thinking you would need to do similar with the two carbs.
 
#18
Yes, I have too much time on my hands. Will let y'all know how it goes,
will be needing your help, no doubt. Thanks for all the info already offered. IMG_20181204_164445188.jpg IMG_20181204_164535846.jpg IMG_20181204_164745200.jpg
 
#19
I hate to be that guy who says it won't work. I'm pretty sure the engine will run, and maybe it will run well, but I don't think the two carbs will reach their full potentials. The main reason is that the stem of the tee going into the engine is smaller than either of the carbs. that stem will be your choke point and no matter how big or how many carbs you put before it you will not see any more flow than what that choke point can support. It's the classic "weakest link" scenario.

Here's another problem, if you open that choke point up to flow what both of the carbs can together, (lets just say 24mm carbs x 2 = 34mm stem diameter), what's the next choke point? The intake port and valves. Now it would be tough to open a GX200 or even a GX390 intake port up to flow that much. And then there's the intake valve. And then there's the EXHAUST valve, and the exhaust port, and the exhaust itself...and then at that point, can the cylinder really support that much flow at the target rpm?

Like I said, I really hate to tell you it won't be worth it's weight in power but still follow through. It is a very entertaining project/experiment and the fact that you are actually going to test it out gives it a spot in my book. RIDE ON! 1543975593607.png
 
#20
Firstly and foremostly, any man with a yellow lab in his go-kart is a friend of mine!
Also, your handle might rather be TheSharpCarbide per your mechanical insights.
Finally, the R&D on this project might push me over the edge.

Right, the carbs won't reach full potential, but won't the 25mm weakest link stem serve the purpose
of modulating the extraneous amount of fuel? Your points on port and valve size are well taken.

I guess the only way to effect a workable air flow is to use both carbs simultaneously instead of
like a 4-barrel? Maybe a velocity stack on the front carb for a ram-air effect? How much smaller
than a 140 would you jet the carbs just to begin testing? I guess the pilots will have to be changed
as well...the idle might be too high even with both idle speed screws backed all the way out?

I could go on but don't want to annoy you because I will have a ton of questions down the road.
I fully expect some or most of my questions will bring me at least a modicum of humiliation but try to go
easy on me as much as possible since it's that most wonderful time of the year..HAHAHA and HOHOHO. 20170312_175533.jpg
 

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