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predator carb help

T

Time Bomb Tom

Member
Can someone explain the Predator carb to me? I read about people using the gx140 emulsion tube and a bigger jet. What is the difference between the stock tube and the gx140? I keep seeing people talk about the main jet and the low speed. This carb only has 1 jet as far as I can see. Do I just drill out the main jet 1 size and keep the stock tube or change to the gx140 tube? This is on a hemi predator that has a thin head gasket and a bsp3 cam with 18 lb springs, 3 step header and k&n style filter. Everything else is stock and it wont see more than 4500-5000 rpm. Any input would be appreciated.
 
The little black thing under the idle screw is the low speed jet.
Unscrew idle screw and it pulls out.
Best to buy this pre drilled or reamed.
 
Graphic of carb has been a help to many:


The emulsion tube controls the air fuel mixture in concert with the main jet. The number , location and size of the holes in the tube regulate how the fuel is broken up before it reaches the venturi. The GX140 is an early engine before EPA rules affected small engines. In later years these engines must meet emission rules for import, one way is to run them lean, thus E tubes with many air holes.
 
so will the aftermarket gx140 emulsion tube from NR work better for me than my stock tube? can I simply drill out my existing tube or should I buy an actual genuine Honda tube? hate to ask these questions, but these carbs aren't my thing. I would be good if there was a manifold where I could just mount a Holley on it. :)
 
The gx140 etube has less holes, providing a richer mixture than the stock etube, so you would most likely want smaller jetting than what is in it now. We usually use about 2 sizes smaller main jet with the gx140 etube than we would use with the stock etube
 
Time Bomb Tom said:
so will the aftermarket gx140 emulsion tube from NR work better for me than my stock tube? can I simply drill out my existing tube or should I buy an actual genuine Honda tube? hate to ask these questions, but these carbs aren't my thing. I would be good if there was a manifold where I could just mount a Holley on it. :)
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Get you a manifold and a Tillotson 304wx carb for it if you plan on building this engine up with a better cam, springs, valvetrain, flywheel and rod. You can adjust the tillotson from the seat of the kart with your hand just by turning one of 2 needles....huge advantage over fixed jetting when you learn to do it right, and more power to be had when you can get the mixture just right. Only bad thing about the tillotson carbs that i have found is that they are not very good for when you ride around at part throttle at low rpms, they wouldnt be good for something like a yard kart or a minibike, but more for a racing kart or a mini drag bike.
 
W5R said:
The gx140 etube has less holes, providing a richer mixture than the stock etube, so you would most likely want smaller jetting than what is in it now. We usually use about 2 sizes smaller main jet with the gx140 etube than we would use with the stock etube
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I know nothing about these carbs, but I'm trying to learn, so I'm having trouble imagining that recommendation. Fewer holes give you a richer mixture? How is that? I'm guessing with fewer holes they might be bigger holes? Have you ever calculated the area of the holes? What are the hole sizes, do you know?

And two jet sizes? Are we talking like .037" to .039"? I ask because that's about an 11% increase in jet size.
 
Al if you look at the picture of the circuits I will post. The holes in question are air holes, the emulsion tube has a series of holes that direct air into the fuel charge after the main jet and before the Venturi. The more air that is forced in helps to break up,(emulsify) the fuel. An emulsion is usually two liquids but for this case we will use a liquid and droplets of air. To meet EPAstandards engines are now tuned leaner, cleaner emissions. By using an Emulsion tube with less air holes the fuel reaches the venturi in a more liquid form before it becomes broken up (atomized). It is easier to direct the fuel upward also imagine a drinking straw with less holes in it. I circled the E Tube
 
Kart43 said:
Al if you look at the picture of the circuits I will post. The holes in question are air holes, the emulsion tube has a series of holes that direct air into the fuel charge after the main jet and before the Venturi. The more air that is forced in helps to break up,(emulsify) the fuel. An emulsion is usually two liquids but for this case we will use a liquid and droplets of air. To meet EPAstandards engines are now tuned leaner, cleaner emissions. By using an Emulsion tube with less air holes the fuel reaches the venturi in a more liquid form before it becomes broken up (atomized). It is easier to direct the fuel upward also imagine a drinking straw with less holes in it. I circled the E Tube
Click to expand...
Perfectly described.
Another way to richen the mixture is to restrict the air bleeds that supply the air to the emulsion tube. When I first started experimenting with nitro I had a hard time getting enough fuel to supply the engine, after plugging the air bleeds completely I could run as high of a percentage as I wanted and just regulate it with the pilot and main jets.
 
We used to tap the air bleed hele #6 24 them make sets of drilled brass set screws to act as jets, we did it on both side the bleed for the emulsion tube, and for the pilot idle circuit. The hours on the dyno testing and tuning all of the variables would make your eyes fall out and your ears ring.
 
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