Predator 420 Carb Help

[Rat]

The problem is exactly as I expected
There should be another hole there! The holes are supposed to be equidistant along the tube essentially one for each quadrant of the throttle range. This is actally cause for tuning problems on the OKO carbs (Keihin PWK copy).

The easiest fix is having a hand drill with the itty bitty bits, figure out which one matches the holes as close to exact as possible, and then reaming them all out the next size up and then ride testing the difference. If it still acts flat open the top pair of holes one more bigger and go from there.

The correct way is getting the correct emulsion tube because hand drilling the brass precisely is nearly impossible with that small of a bit.

 

[cml1of4]

The problem is exactly as I expected View attachment 133885
There should be another hole there! The holes are supposed to be equidistant along the tube essentially one for each quadrant of the throttle range. This is actally cause for tuning problems on the OKO carbs (Keihin PWK copy).

The easiest fix is having a hand drill with the itty bitty bits, figure out which one matches the holes as close to exact as possible, and then reaming them all out the next size up and then ride testing the difference. If it still acts flat open the top pair of holes one more bigger and go from there.

The correct way is getting the correct emulsion tube because hand drilling the brass precisely is nearly impossible with that small of a bit.

Do you know which one to get? It's a Chinese 32mm flat slide.

 

[Rat]

Do you know which one to get? It's a Chinese 32mm flat slide.

Most of the Chinese copy carbs use Keihin jets and other internals for what ever reason, beyond that not really which is why buying genuine is so damned important.

My PWK24-pj is about as exact as clones get in both appearances and function, right down to being interchangeable with everything a GENUINE PWK28 is... 28 is the smallest Genuine PWK size. I'm not entirely convinced it's NOT genuine but I've not found any supporting info that it is... and more than enough that says it's not

I decided to delete the power jet on mine and need to get some JB aluma-weld to fill the hole and smooth the bellmouth out

 

[cml1of4]

Most of the Chinese copy carbs use Keihin jets and other internals for what ever reason, beyond that not really which is why buying genuine is so damned important.

My PWK24-pj is about as exact as clones get in both appearances and function, right down to being interchangeable with everything a GENUINE PWK28 is... 28 is the smallest Genuine PWK size. I'm not entirely convinced it's NOT genuine but I've not found any supporting info that it is... and more than enough that says it's not

I decided to delete the power jet on mine and need to get some JB aluma-weld to fill the hole and smooth the bellmouth out

I can't seem to find any emulsion tubes that match mine. Even the rebuild kits don't seem to have them.

 

[Rat]

I can't seem to find any emulsion tubes that match mine. Even the rebuild kits don't seem to have them.

I looked at it again that's a Keihin style tube and looks exactly like the one they put in the OKO's as well as what was in mine... I just enlarged all 8 holes and 95% of my tuning issues went away. I was able to get the jets nailed to a size that was nice and crisp even though the [now deleted] power jet was making it a little rich at WOT

 

[cml1of4]

I looked at it again that's a Keihin style tube and looks exactly like the one they put in the OKO's as well as what was in mine... I just enlarged all 8 holes and 95% of my tuning issues went away. I was able to get the jets nailed to a size that was nice and crisp even though the [now deleted] power jet was making it a little rich at WOT

I've been looking all over Amazon for a replacement emulsion tube. I can't find one and I'm a little hesitant to drill holes in the only one I have lol.

 

[Rat]

I've been looking all over Amazon for a replacement emulsion tube. I can't find one and I'm a little hesitant to drill holes in the only one I have lol.

Totally understand... so was I

 

[cml1of4]

Totally understand... so was I

I think it's getting better everytime I increase the main. I'll just keep at that until I build a new I take.

 

[Rat]

I think it's getting better everytime I increase the main. I'll just keep at that until I build a new I take.

It will still have a flat spot at or around ¾ with that E tube, but jetting up will help mask it to a limited extent

 

[cml1of4]

It will still have a flat spot at or around ¾ with that E tube, but jetting up will help mask it to a limited extent

http://imgur.com/a/0fMPq4y

The too end is amazing now with this intake. Chasing a vacuum leak from my **** welding because idle is still not great.

 

[Rat]

The too end is amazing now with this intake.

Longer intakes are natural torque boosters especially if you purposely go through all the math (way beyond above my education level) to tune the length specifically to your most used rpm range.
A tuned length long intake runner on a 4cycle engine done well does the same thing as an expansion chamber exhaust on a 2stroke... and that would be using the port resonance to create a fuel/air ramming effect much like a Roots or twin screw supercharger on a V8

Chasing a vacuum leak from my **** welding because idle is still not great.

Something I've done that has worked extremely well for pinholes and weeping is to give it a light grinding and smooth it up around the weld (knock off any spatter the chippy didn't) then butter it with some steel stick epoxy putty.

Mash it into any divots, and work it out past the weld by a half inch or so. You'll find it cures pretty fast and becomes tacky and warm, best way to smooth it in real good is a dish of water to dip your fingers in (a lot like working with clay)

Once it's cured solid, you can file, sand, smooth, and blend it into the pipe so that the weld becomes permanently sealed and completely invisible especially if you use a fuel/solvent resistant automotive engine paint to cover it all up.

 

[cml1of4]

Longer intakes are natural torque boosters especially if you purposely go through all the math (way beyond above my education level) to tune the length specifically to your most used rpm range.
A tuned length long intake runner on a 4cycle engine done well does the same thing as an expansion chamber exhaust on a 2stroke... and that would be using the port resonance to create a fuel/air ramming effect much like a Roots or twin screw supercharger on a V8


Something I've done that has worked extremely well for pinholes and weeping is to give it a light grinding and smooth it up around the weld (knock off any spatter the chippy didn't) then butter it with some steel stick epoxy putty.

Mash it into any divots, and work it out past the weld by a half inch or so. You'll find it cures pretty fast and becomes tacky and warm, best way to smooth it in real good is a dish of water to dip your fingers in (a lot like working with clay)

Once it's cured solid, you can file, sand, smooth, and blend it into the pipe so that the weld becomes permanently sealed and completely invisible especially if you use a fuel/solvent resistant automotive engine paint to cover it all up.

So I got that fixed. It's still running great at WOT but it going rich again at idle. I was using a 22.5 pilot and went down to a 12.5. The air screw appears to do nothing and the idle really isn't that consistent. It moves around a bit. I've got all the vacuum leaks fixed. Carb is getting good fuel. Anything else you could think of that could still be causing this? I also checked the float level. The lever the floats push against is dead level with the carb when I flip it upside down. I've also noticed the filter has some unburnt fuel in it when I take it off. Clearly way rich.

Also, the idle air screw appears to do nothing.

 

[cml1of4]

Longer intakes are natural torque boosters especially if you purposely go through all the math (way beyond above my education level) to tune the length specifically to your most used rpm range.
A tuned length long intake runner on a 4cycle engine done well does the same thing as an expansion chamber exhaust on a 2stroke... and that would be using the port resonance to create a fuel/air ramming effect much like a Roots or twin screw supercharger on a V8


Something I've done that has worked extremely well for pinholes and weeping is to give it a light grinding and smooth it up around the weld (knock off any spatter the chippy didn't) then butter it with some steel stick epoxy putty.

Mash it into any divots, and work it out past the weld by a half inch or so. You'll find it cures pretty fast and becomes tacky and warm, best way to smooth it in real good is a dish of water to dip your fingers in (a lot like working with clay)

Once it's cured solid, you can file, sand, smooth, and blend it into the pipe so that the weld becomes permanently sealed and completely invisible especially if you use a fuel/solvent resistant automotive engine paint to cover it all up.

I also tried a 38mm. Still super rich at idle even with the leanest pilot I have. I tried a few others too. It also doesn't want to rev out with the 38 but I haven't touched the main or needle.

 

[Rat]

I'm wondering if there's an issue with your enrichment circuit.
It seriously seems like you are trying to tune with a closed choke, but with your carb it would be an open enrichment circuit.

Air screw being ineffective points to being puke rich just as much as an airfilter full of fuel and all your other symptoms do

 

[cml1of4]

I'm wondering if there's an issue with your enrichment circuit... because it seriously seems like you are trying to tune with a closed "choke"

That's where I am right now. I bought the carb from GoPowerSports and they are right down the road from me. Funny enough, the first mikuni I got from them was bad, the slide was manufactured backwards. I'm thinking they maybe got a bad batch since it's a legit Mikuni. I sent them an email and I'm gonna stop by this week and possibly swap it out. I get the 38 being fat, it's too much carb I think. I only have a mild cam and don't rev over 5k.

 

[Rat]

You keep referencing 2 different carbs and I can't keep track anymore.

If you haven't tried tuning the 38, you should.

 

[cml1of4]

You keep referencing 2 different carbs and I can't keep track anymore.

If you haven't tried tuning the 38, you should.

Sorry lol. I tried tuning the 38 pilot jet for a while. Idled worse than the 34. Didn't really mess with anything else.

 

[Rat]

Sorry lol. I tried tuning the 38 pilot jet for a while. Idled worse than the 34. Didn't really mess with anything else.

Worse how, Rich or lean? At this point lean is going to be easier to tune out

 

[cml1of4]

Worse how, Rich or lean? At this point lean is going to be easier to tune out

Real fat. Eyes watering from being near the exhaust lol. I went all the way down to the leanest jet I had (stair stepped), not much difference.

The thing that is bothering me most is that the 34mm should work. The vast majority of kits for the big blocks use a 34mm and I can't find much info on anyone else having any kind of major issues like I am. I've evn read through a bunch of user reviews on them. Almost everyone it's plug and play.

 

[Rat]

Real fat. Eyes watering from being near the exhaust lol. I went all the way down to the leanest jet I had (stair stepped), not much difference.

The thing that is bothering me most is that the 34mm should work. The vast majority of kits for the big blocks use a 34mm and I can't find much info on anyone else having any kind of major issues like I am. I've evn read through a bunch of user reviews on them. Almost everyone it's plug and play.

Time to assume the 34 is a hunk of S××t then.

The odd thing is if the 38 were in fact too big it would lean out really bad from the weak signal... have you tried it on the new intake yet?