Box Stock

advice on boring carb on 212 pred

1

1987kpf

New member
Have a hemi predator, have ported it out, assuming ive improved the airflow. I want to bore the stock carb. I havent done it before so im looking for tips and advice. I have multipul carbs so im not to worried if i dont get it the first time around. I know i will have to rejet the carb. Im running arc intake, free flow exhaust (home made), bsp3 cam. Any help is appreciated.
 
Bore it out but dont focus so much on making a perfectly round bore as big as you can or you will break thru the casting. You will likely break thru on a couple carbs before you see where the thin spots are. Ill go ahead and give you a head start...the most likely places you will break thru the casting first is if you look thru the choke side into the bore, on the left side where the low speed jet sits is usually one of the first places that break thru, along with the top of the bore directly below the top of the carb. Id suggest taking an old carb and boring it strait thru as big as you can so you can break thru in the weak spots and see where they are, this will show you where to focus your boring. Try to go for a more square shaped bore than a perfectly round one.....that has given me the best results. I have one here now that is .685 with no break thru's, but i broke thru several carbs before i learned how to do it right. The ones i like to use are the SP carbs that come stock on the Hemi predator engines, they seem to have a thicker casting in the weak area's.
 
W5R said:
Bore it out but dont focus so much on making a perfectly round bore as big as you can or you will break thru the casting. You will likely break thru on a couple carbs before you see where the thin spots are. Ill go ahead and give you a head start...the most likely places you will break thru the casting first is if you look thru the choke side into the bore, on the left side where the low speed jet sits is usually one of the first places that break thru, along with the top of the bore directly below the top of the carb. Id suggest taking an old carb and boring it strait thru as big as you can so you can break thru in the weak spots and see where they are, this will show you where to focus your boring. Try to go for a more square shaped bore than a perfectly round one.....that has given me the best results. I have one here now that is .685 with no break thru's, but i broke thru several carbs before i learned how to do it right. The ones i like to use are the SP carbs that come stock on the Hemi predator engines, they seem to have a thicker casting in the weak area's.
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Thanks for the advice. I have two hemi carbs and one from a none hemi. So im guessing the part were ppl talk about using epoxy is when theyve went through. Any suggestions as far as rejetting for atleast .650 on the bore?
 
At .650 you shouldn't break through... Especially if you start boring at the bottom right...or left depending which way you look at it.
Assuming you have not done anything else to the carb beside boring, and you are running gas
Start at a low jet of .024, and high jet at .038
 
Yakattack said:
At .650 you shouldn't break through... Especially if you start boring at the bottom right...or left depending which way you look at it.
Assuming you have not done anything else to the carb beside boring, and you are running gas
Start at a low jet of .024, and high jet at .038[/QUOTE

Now i do have the gx140 emulsion tube, would that affect the jetting. I know it has a larger main bore and less air holes. I am running 93 gas. Is there anything else that i should know as far as mods, or not to do's?
Click to expand...
 
1987kpf said:
Yakattack said:
At .650 you shouldn't break through... Especially if you start boring at the bottom right...or left depending which way you look at it.
Assuming you have not done anything else to the carb beside boring, and you are running gas
Start at a low jet of .024, and high jet at .038[/QUOTE

Now i do have the gx140 emulsion tube, would that affect the jetting. I know it has a larger main bore and less air holes. I am running 93 gas. Is there anything else that i should know as far as mods, or not to do's?
Click to expand...

Go back to 87 gas, you will see zero gains from using anything higher octane than 87 unless you increase compression to around 11:1, 93 will just carbon up your head and ports even more and hurt performance. I'd suggest starting a bit lower on the main, like .036 or .037 instead .038
Click to expand...
 
8:1 CR recommends 85 Octane stock AKRA engines have 8.4:1 CR because you have increased the flow and enriched the mixture the actual cylinder pressure is higher than than stock, so 93 octane will not hurt in this case.
 
Hey guys, well i was aiming for .650, i went past it. I dont have a micromiter to measure that way. So if placed one item in the venturi, which is 5/8" so .625. Then with the object inside the venturi, looking through with measuring tape on opposit end theres a 1/16" .0625 difference so ive added the difference to .6875. I know the size is not exact, but the point is im in need of advice for jetting, good starting point. Thanks guys
 
I already posted what a good starting point was for jetting...
I can run a stock carb, or board carb, or bored with a bigger butterfly...pretty much the same jetting...

Now if you start messing with other things it is different then...
 
Yakattack said:
I already posted what a good starting point was for jetting...
I can run a stock carb, or board carb, or bored with a bigger butterfly...pretty much the same jetting...

Now if you start messing with other things it is different then...
Click to expand...

Sorry im new to mods like this. Thanks for your help.
 
1987kpf said:
Hey guys, well i was aiming for .650, i went past it. I dont have a micromiter to measure that way. So if placed one item in the venturi, which is 5/8" so .625. Then with the object inside the venturi, looking through with measuring tape on opposit end theres a 1/16" .0625 difference so ive added the difference to .6875. I know the size is not exact, but the point is im in need of advice for jetting, good starting point. Thanks guys
Click to expand...

I would start with a .026 pilot, and a .036 main with a 140 e tube, .038 main with a clone etube.
 
When im setting my jets what are some tips on knowing which jet i need to adjust? As far as how the engine is acting. I have it running, so thats a plus but it smells lean. Thanks in advance for the help.
 
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