Advanced Hemi 212cc Predator Build

[Denny]

Bob,
Speaking from experience at this point you need to stop changing things or doing anymore to the engine and just concentrate on optimizing what you have. Right now even you admit you don't know if you have hurt or helped performance and if so by how much. The best advice I give novice engine builders is to only change one thing at a time then figure out how the engine responds. If successful you will know to do that again to the next one, if not then you know not to do it again. Then move on to the next change and so on an so forth.

Good Luck,
Denny

 

[Poboy kartman]

Denny makes a good point....there have been people that come oj to the forum and ask what's wrong with my engine and have a long laundry list of stuff they've done....any one of which could potentially be the problem. As much as I like to get a bunch over with in one sitting when working on cars...I may change gaskets, work on brakes, change oil....whatever, but if it's a problem...and potentially two different causes, I never do them together....it just means more diagnostic work if it fails!

 

[bob58o]

I understand completely about changing one thing at a time. But before I start taking stuff off, I am going to try to get this "Copy and Paste" set up to work. This build is based off other Engines I've seen (read about) by experienced builders who did dyno testing (I think that means they raced a T-Rex). So I think the parts I have should be able to make good power if installed corrected and tuned.

Lets fix the manifold leak first, then work on jetting and timing.

If I am not getting anywhere, I can go back to old carb. I have a stock 0.045" or 0.041" head gasket coming too with a gasket kit.

Only thing I can't un-do is un-port the intake.

TAKE A DEEP BREATH EVERYBODY!!!!
I feel like you guys are starting to panic. lol I should be panicking, not you, but I'm not.
Don't worry, It'll be fine. We will be making neighbors scared for their bushes again soon.

AND I wasn't implying I wrote the textbook. I thought you guys wrote it. You did write the internet, right? I was just trying to copy.

 

[bob58o]

Thinking... How difficult it would be for ME to mod the frame for an engine? Buddy is willing to donate it to me.
Maybe this could be part of a future project or BE a project.

 

[bob58o]

They sent wrong gasket kit. So no valve cover gasket.

 

[bob58o]

I got lots of extra gaskets!!!
MainJets now in Arsenal include:
.036, .037, 041, .042, .043, .0455 x 2, (They also didn't send the .059 jet), and .063 (alcohol) plus stock 212 and stock 390 jets.

Low jet I ordered is #60 or 0.024" (said for alcohol but lots of gas jet combo recommendations had similar size low jet)

I have lots of playing to do!

This is the good stuff!

 

[bob58o]

This is just me trying to organize some of the info I found:

Predator 212 / gx390 carb?
Wanna get input on what jets to start out with to run on gas/alky? What seems to run the best?

Alky by far...
A stock untouched 390 carb with stock Etube...
Alky a good start is pilot jet .035-.040, and main .065-.068

A .038-.040 pilot jet is going to give you a very rich idle but gives a good punch out of the hole may milk the oil, a .065 main will have head temps around 350-380*f under heavy load...

You may want to start a bit leaner say a .030 pilot and .060 main...on Alky and go up from there...
All depends on altitude and air density...

I ended up with these jet sizes from track temps, and my afr,rpm and temp gauges at home...

FOR ALCOHOL - 0.030" to 0.040" Pilot, 0.060" -0.068 Main"
.038 Pilot, .065 Main (Rich Idle, Good Punch out of hole, may milk oil)
.030 (0.75 mm 75) Pilot, .060 (1.52 mm 152) Main - "Lean" for Alky

Best carb for a mod predator 212cc
want to buy a awesome carburetor for my predator 212cc

engine rebuilded parts help me choose whats best for my motor I mean one that will scream

billet rod long
wiesco piston flat top standard bore
mod 2 cam
1.3.1 rockers
25 intake stainless steal
24 exhaust stainless steal
14cc hi performance head
billet flywheel

Big carbs have poor low speed performance.
I have worked at this an its real hard to fix.

Its a velocity issue, air blowing threw is too slow relative to venturi and throat diameter.
when you open it right up the velocity picks up faster than the fuel flow.
Its a game of catch up until you cam pull the fuel along to get it to run decent.
A couple of fixes:
higher idle speed and richer mixture on the low side.
Your going to have to tap the throttle to keep it from drowning out at low speed with all that fuel.

I have that issue and can't say there is anything else to do.

Racing carbs do not idle.
Race engines race.....

When your running it ( actual race ) and you get off the throttle the high vacuum you pull draws a rich mixture into the engine.
When you come out of a corner or down a hill the engine is loaded down with fuel.
Your primed for the next time you crack the throttle wide and no bog.

But if your just coming off the idle and your set lean for a clean idle you lack that cushion of extra fuel.
Watch the drag bikes on Anna street videos.
All the guys are tapping the throttle and you can hear how fat the mixtures are.
Modified Karts same thing especially the ones running tillotsons.
They need to lean up for the parade laps and warm up.
But if you watch once they are ready to drop the flag those low speed circuits are set real fat again.
On a yellow when they have to drop back and cut the power the drivers are all tapping the throttle to keep the plugs clear adn keep from drowning...

If you have a tillotson carb dialled in correct and everything is working just right that is the closest thing to fuel injection out there.

More on same
Even in the WKA and AKRA kart racing with a .615 bore stockish carb we run a .24-.28 low side jet and have to blip the throttle to keep to from loading up.
But it does not stumble coming off the corner.

FYI a stock carb with a little work done.. ie...bored to .670 will support 17-20 hp... And they are super easy to tune.

The 390 carb. Needs at least 27/25 valves on the head with a good port and polish to get even close to running decent... The 390 carb is a bit of a pain to even get running somewhat right on gas...
If running Alky it is easier to tune the 390 carb.

 

[rk970]

They sent wrong gasket kit. So no valve cover gasket.

Use this stuff...
https://www.permatex.com/products/gasketing/permatex-anaerobic-gasket-maker/

Oh Yeah,, BTW.. Mikuni VM22..

 

[bob58o]

Use this stuff...
https://www.permatex.com/products/gasketing/permatex-anaerobic-gasket-maker/

Oh Yeah,, BTW.. Mikuni VM22..

The 22mm Mikuni is larger than the 390 right? The 390 is 21 mm, I think. Stock predators are 16 or 17 mm I believe.

Everybody seems to love that 22mm carb though.

 

[bob58o]

When work is slow. Paper Air Planes..

 

[cavfire]

Reading some of the pitfalls of the GX390 carb on a GX200 is one of the big reasons I went with the GX270 carb. Best information I've read puts it at a .660" venturi. Definitely larger than stock, and driveability wasn't affected. Actually helped out the low end as well. The GX390 carb is something I think would be more suited to racing or maybe a modified mini bike where the revs are typically higher than a yard kart considering the weight. I would still like the think you'll get the GX390 carb to work, but it might be finicky on the low end. Stopping the intake leak is still the first step though.

The 22mm slide carbs are more tuneable than a run of the mill OPE butterfly carb.

 

[bob58o]

QUOTE=cavfire; The GX390 carb is something I think would be more suited to racing or maybe a modified mini bike where the revs are typically higher than a yard kart considering the weight.

Seems to be true. Set the idle high, set the clutch higher, ease into WOT, and stay there!

Now I can have a screamer carb for the neighborhood streets with no brakes Perfect for top speed testing and police evading.

And the stock carb (perhaps better for low end) to be used when I want to climb mountains (and police evading).

I'm up to the challenge of trying to slay the 390 carb. lol
FUN!!!
I have compiled all of the suggestions for jetting this carb.
Hobbytown sells individual bits for $0.99 each #61-#80.

Reading threads and posts from Jody at ARC, youngengines, Prowler08, OND, and a bunch of other ppl on these forums.... I got this. Mostly for minibikes and racing karts I think.

BUT I KNOW A DIFFERENT SOLUTION TO TO HELP THIS CARB WORK!!!!

JACKSHAFTS!!!! BUT HOW MANY???? JK, kinda.
1.2:1 JS might not be a bad idea to use with 18.5" wheels.

 

[bob58o]

Two engines, two torque converters
http://youtu.be/Ynhklod-ejA

 

[cavfire]

Kinda late in the day looking at that gasket set, but if the gasket sealing problem turns out to be a flatness issue on the head's intake you could always try making a gasket out of 1/16" sheet neoprene. Gas resistant and able to seal up imperfections. Double oem gaskets may help as well.

 

[bob58o]

Kinda late in the day looking at that gasket set, but if the gasket sealing problem turns out to be a flatness issue on the head's intake you could always try making a gasket out of 1/16" sheet neoprene. Gas resistant and able to seal up imperfections. Double oem gaskets may help as well.

I've read that double OEM gaskets should seal it up pretty good. I'll try that first.

Thanks for the help!

 

[bob58o]

Let's seal and jet this SumnaB.
0.018
0.020
0.021
0.0225
0.024
0.025
0.026
0.028
0.029
0.031
0.032
0.033
0.035
0.036
0.037
0.038
0.039
0.040
Pre drilled 0.041, 0.042, 0.043, 0.045, (Methanol - 0.063")

 

[bob58o]

Finally got Russel at NR Racing on the phone!

He is going to send me a 0.027" Head Gasket (I got sent a 0.018" by mistake). Also sending correct valve cover gasket for Hemi.

The Gasket Kit I ordered doesn't come with stock 0.041 / 0.045" gasket. It comes with thin 0.009" gasket. I can stack these to get the 0.027" He told me to send back what I don't use.

I think MLS gaskets need nicely machined surfaces to work?????????
I was hoping I got a stock gasket in case my sanding is not perfect (I'm sure it won't be).
Still trying to find a shop to chop the top if I need. lol

 

[Poboy kartman]

Two engines, two torque converters
http://youtu.be/Ynhklod-ejA

Sir....please place your posts in the appropriate threads!!! This obviously should have been posted in a FR thread!!!

(He needs all the chances we can give him to say something dumb! )

 

[bob58o]

Sir....please place your posts in the appropriate threads!!! This obviously should have been posted in a FR thread!!!

(He needs all the chances we can give him to say something dumb! )

Did you watch this? I was actually very impressed.
Seems like a monster!

 

[Poboy kartman]

Did you watch this? I was actually very impressed.
Seems like a monster!

Of course I watched it....and it was Fing awesome and Fing yard destroying and Fing every thing else! Are you Fing kidding me? (Just a little dig at the bad language! )

BTW: I'm hoping FR gets the idea to jump up and down like they did! His will do exactly the same thing..(except it won't come back up!)