2 into 1 intake jetting issues

It runs pretty good . Alittle rich. Lots of power but no topend . Im waiting on the main jet because it came with a 175 main. Soon as my metalflake tank is done and the jet is in , Off I will be into the sunset . :)
 
I have a feeling you'll never get the thing just right. This is why, your left cylinder and your right cylinder are never going to be equally fed. you would have been better off using a much shorter 180 with the carb centered to help balance out the flow. I see the left being rich, and as soon as you dial in the jetting on the left your right is going to be lean.

or maybe i have no idea what im talking about and it'll work just fine? hahahaha

all i know is every intake ive seen has been engineered to equalize flow to each cylinder regardless of what it is on, and this doesn't do that.
 
xb33bsa said:
you know with a slight lowering mod to that lashup you could use the carb as a rearset
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ROFLMAO!
I damn near coughed up a bronchitic lung when I read that!

Maybe that should be WOFLLO (Writhing On Floor Laughing Lung Out)
 
D4N63R said:
I have a feeling you'll never get the thing just right. This is why, your left cylinder and your right cylinder are never going to be equally fed. you would have been better off using a much shorter 180 with the carb centered to help balance out the flow. I see the left being rich, and as soon as you dial in the jetting on the left your right is going to be lean.

or maybe i have no idea what im talking about and it'll work just fine? hahahaha

all i know is every intake ive seen has been engineered to equalize flow to each cylinder regardless of what it is on, and this doesn't do that.
Click to expand...
This assumption is widely used and there are many people who would argue this on both sides. So far the slight offcenter hasn't effected the flow of fuel .If it has, it isn't enough to make a dramatic difference. My 2 cents : )

I think some motors have different rotation times which can cause this intake to not work equally. My engine never has both cylinders open at the same time. It one fires tdc while other is on its bottom stroke.
 
Clearly, there is a great deal that you do not know about fuel/air induction, the timing of intake pulses and how they can work together, or not. I applaud your spirit of experimentation, but better keep your day job.
 
Yeah, I'm 20. Not trying to prove anyone wrong or be ignorant. Just saying it seems to be working good so far. If I run into any problems though, I would be lucky to get help from guys who know a lot more about air and fuel jetting/flow. With that being said there is a slight flat spot on 1/4 throttle opening. If anyone wants to crack some codes
 
Schmeck750 said:
It runs pretty good . A little rich. Lots of power but no topend .
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Any possibility that the intake is the problem? A little rich is good for power.

The KZ-750 is a 360 timed engine. that means the left and right cylinder alternate firing every 360 degrees of crank rotation. This means the intake pulses are evenly spaced. So a balanced intake would get the best results. In addition, sharp, right angle turns increase pressure drop, reducing flow. A "Y" intake would allow more flow.

I am not saying your design will not work, only that from a performance point of view, it is very sub optimum. The length of the tubing determines the RPM at which the most effect is given with the velocity the intake charge. That is why some modern bikes have variable intake lengths. My old Ford Contour had double intake tubes, a short one and a long one for each cylinder. This allowed better intake pulse timing for both lower and upper RPM ranges.

What this means is your left cylinder is better tuned for one RPM and the right for another. Which means you will never have a point where both cylinders are performing the same. This is sort of like having the ignition timing different for each cylinder. the engine will run, but not perform it's best.

Intakes should resemble exhaust headers in some respects. Equal length. smooth turns. You seem to have some really good fab skills. With skills like that, you could do a better job....
 
Ill definently look into the equal flow issue . I probably should look into shortening the intake so the cable isnt in the way . Thanks for the advice and I think compliment ?

-Schmeck
 
I like the Y intake idea . How could I make that centered considering I already have a hole cut at an angle on this one ? Any thoughts anyone ?
 
You either need to make it shorter. So that the carb centers in front of the backbone. Or longer and have it join up behind the back bone.

In its simplest form. Short runners are usually better for high rpm HP Longer runners increase bottom end torque.

If you wanted to get fancy you could do a balanced plenum intake like a car uses. But they are wry very hard to effectively make at home.

That's why suggested another intake that is much shorter ten your current one, allowing you to mount the carb right in the center of the loop.
 
I have an observation based on knowledge acquired from years of car racing, plus having built a few intake systems from scratch myself.

The carb size is really irrelevant until the motor rpm exceeds the carb's flow capacity. It'll run good up to a point then flatten out if the carb is too small. It will bog badly and not respond to throttle quickly if it is too big.

On the intake design....D4N63R is right. Too long. A couple things need to happen. First, and most importantly, it needs a carb with an accelerator pump. The idle may in fact be too rich, but it does a lean pop and back fire because there is a "hole" in the fuel delivery. The time it takes between crackin' the throttle open and the time fuel actually flows. Once you crack the throttle, manifold vacuum drops and it stops pulling fuel.

The "BigThing" about an intake that long. Fuel puddling and separation. Until it gets good and hot, the fuel will collect on the sides of the intake runners and simply make a puddle. If you look at virtually every intake manifold on a production vehicle with a single carb feeding multiple holes, the manifold gets heated. This keeps the fuel vaporized so that it is available to burn.

In the motorcycle world, Harley's have a single carb. BUT, (big hairy but) the intakes are short and the carb has an accelerator pump. You can probably make it work with a carb that doesn't have an accelerator pump, but the intake is gonna have to be short. As short as possible. And the carb size should probably be close to what size would work on it with individual carbs. It will ALWAYS have a off idle bog tho.

Just my opinion based on 40 years of building and racing cars
 
Okay I think I understand where you all are coming from. I didn't really know about the whole accelerator pump thing. I learn something every day I'm up here. My carburetor does have a power jet but I don't know how to hook that up because I think it connects to a Cdi which my bike does not use. I will see if making the intake shorter helps any, thanks.
 
the power jet is just to Split the function of the main jet for smoother transitions from half to full throttle

it is not electrical but it does involve a extra jet and some fiddling
 
power jets were developed at first for 2 strokes running continous wot ;D whereas the venturi effect of the slide is no longer even happening as they are smooth bore at wot
pressure drop at the main jet relies strictly on the airbell of the carb to speed up the air
lean afr conditions and the wot seizures were an issue,specially at high speeds :'( that that forced the developement of a powerjet into use i think it was sparky at lectron that actually perfected the deal
the ones i am familiar with are not wired, they simply work by pretty much inventive genius
 
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