Predator 420 Carb Help

cml1of4

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Okay then... this just got inexplicably weird
I thought the 38 would be toos big. That doesn't surprise me really. It's very odd though that it now seems to have full power, if not very close, with the 34 at WOT but I cannot get the idle dialed in. I never made full power with the original intake so I feel like the new one made a difference but only on the high side. Seems to be no difference in the idle from one to another.
 

RLS_Underground

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I thought the 38 would be toos big. That doesn't surprise me really. It's very odd though that it now seems to have full power, if not very close, with the 34 at WOT but I cannot get the idle dialed in. I never made full power with the original intake so I feel like the new one made a difference but only on the high side. Seems to be no difference in the idle from one to another.
All I can say is read this old Cycle world article and maybe it will not only educate you but spark an idea of what you need to look for
 

cml1of4

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All I can say is read this old Cycle world article and maybe it will not only educate you but spark an idea of what you need to look for
Solid article. One of the few things I haven't tried is changing out the slide for a more restrictive one. It technically idles now but it very rich at idle and under smaller throttle inputs. I've got a smaller pilot jet on the way but I really doubt it'll be lean enough lol
 

Denny

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Get rid of that too short air filter. Whoever sold you that should be shot then hung and shot again. The air can not straighten out enough to go through the Venturi properly. That will screw up you mixture it is also a restriction. Take the air filter off completely and then see how it runs.
 

cml1of4

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Get rid of that too short air filter. Whoever sold you that should be shot then hung and shot again. The air can not straighten out enough to go through the Venturi properly. That will screw up you mixture it is also a restriction. Take the air filter off completely and then see how it runs.
I dont think thats it. I've run it without a filter and I've used this style filter on many things. They look dumb but they're fine especially when space is a big concern.
 

RLS_Underground

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I dont think thats it. I've run it without a filter and I've used this style filter on many things. They look dumb but they're fine especially when space is a big concern.
FWIW: Denny hasn't lead me wrong outright... we've had a minor difference of opinion on maybe one thing.

I myself have has issues with over restrictive air filters. Specifically the big ones (like below) that a lot of sites pedal for Karting with a velocity stack adapter to use them on a stock type (Hauyi) carb
20220806_222041.jpg
I dont think thats it. I've run it without a filter and I've used this style filter on many things.
I'm going to point out what should be obvious...NO 2 ENGINES RUN EXACTLY THE SAME EVEN WHEN THEY LITERALLY ARE EXACTLY THE SAME.
My advice (you've said I have been extremely helpful this far) is just try it without the filter instead of assuming. Realistically what the hell do you really have to loose from some testing!?!?

I may be harsh and brutal on occasion, but I look at logic and facts, not assumptions and maybe if's.... I also look at all options and logical possibilities ESPECIALLY those not common or those that require out if the box thinking.

In my experience a too restrictive filter is going to mess with idle the absolute worse. The reason is simply because it does. The intake velocity, volume, and pressure are all at their weakest signals during idle and don't start picking up noticablly (to you) until around the quarter throttle mark
 
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RLS_Underground

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Ok, good luck.
I dunno about you Denny, but one of my biggest pet peeves is someone who definitely needs help, asks for help or advice or however you choose to phrase it (anything but a meaningless opinion)

And then would prefer to continue doing everything they've already done that doesn't work as if by some grand miracle it will suddenly work.
Yeah okay sure it happens occasionally... but generally speaking it turns out it's ALWAYS because of something else got corrected unnoticed in the process of doing that thing that didn't work before.
 

RLS_Underground

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I dont think thats it.
If you can grasp simple physics it becomes obvious that overly restrictive filter is a problem.

Vacuum is still (negative) pressure and like positive pressure (a tire) it will always seek the path of least resistance to equalize indiscriminately. A carb bowl is vented to atmosphere to prevent negative pressure build up... same as a fuel tank is.

If an airfilter doesn't allow proper airflow, then the negative pressure created by the process of a running engine builds up and seeks to equalize by any means possible... which inadvertently means through the pilot jet, which leads straight into the bowl restricted only by the jet size, which as previously stated is vented to atmosphere.

The physics are quite comprehensive when you leave the complex mathematics aside and focus solely on the how and why aspects.
 

cml1of4

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If you can grasp simple physics it becomes obvious that overly restrictive filter is a problem.

Vacuum is still (negative) pressure and like positive pressure (a tire) it will always seek the path of least resistance to equalize indiscriminately. A carb bowl is vented to atmosphere to prevent negative pressure build up... same as a fuel tank is.

If an airfilter doesn't allow proper airflow, then the negative pressure created by the process of a running engine builds up and seeks to equalize by any means possible... which inadvertently means through the pilot jet, which leads straight into the bowl restricted only by the jet size, which as previously stated is vented to atmosphere.

The physics are quite comprehensive when you leave the complex mathematics aside and focus solely on the how and why aspects.
Lol. I literally said I did run it without the filter. It's been on/off the entire time I've been working on it. I've been taking it on or off to check impact.
 

RLS_Underground

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Lol. I literally said I did run it without the filter. It's been on/off the entire time I've been working on it. I've been taking it on or off to check impact.
The only thing fits the symptoms, and makes sense is a problem with the enrichment plunger not sealing fully.

There was an issue similar on my PWK24, the enrichment plunger was just not threaded into the carb body fully... I fixed it without fully realizing it was the problem because I ended up taking the carb fully apart after accidentally dropping in a bucket of old motor oil that I'd been using to quench parts after heating and shaping them
 

RLS_Underground

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At the end of the day there's only 4 things that's going to make your pilot flood uncontrollably

1. Too restrictive filter
2. Malfunctioning/damaged enrichment circuit
3. Too big of a pilot jet
4. Too small of a carb (this will effect both the main and pilot)

I would say 5 things, but a stuck float or a float set too high would just dump fuel out of ALL it's orifices.
 

cml1of4

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At the end of the day there's only 4 things that's going to make your pilot flood uncontrollably

1. Too restrictive filter
2. Malfunctioning/damaged enrichment circuit
3. Too big of a pilot jet
4. Too small of a carb (this will effect both the main and pilot)

I would say 5 things, but a stuck float or a float set too high would just dump fuel out of ALL it's orifices.
I'm gonna put it away for a week. Come back fresh. I emailed GPS about the carb being bad. I've also got a smaller pilot jet on order. It's the smallest I could fine.
 
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