Fix my carb!

[dammitmitchell]

hey gentle men i need your help.
simply TELL ME what powervalve jets and vac secondary spring i need on my holley 670
unfortunatley the 670 has to stay cant afford to swap down to a 630.

im having issues at half to full throttle with "popping" as in it feels the same as a lack of fuel delivery.

so here's the specs
block
350 bored .060 over

Federal Mogul 350 cast pistons .060 over

crank is
3932442 3.48 69-85 2.45/2.10 cast large journal

heads are casting number 462624
76-87 1.94/1.50
& 2.02/1.60 76 CC Chambers

cam
RENEGADE PN 158881
dur@.050 Int 234 exh 244
vaulve lift int .488 exh .510
cam produces 18 lbs of vaccum on my set up. which is alot for the style of cam it is..

intake edlebrock perfromer RPM highrise

spacerplate (1in)

msd street fire distro
timing is currently set at 12 degrees
with the silver accel spring kit springs same as "stock" for the distro)
and accel shorty header plugs.


carb holley 670 carb with 73 primary jets and 74 secondary
i do believe i have a 65 powervalve installed (need help HERE!)
manual choke





now what powre valve , secondary spring and jets do you reccomend?

please dear god help because ive confused myself so bad on this carb im just restarting over.
and also do you think i should switch to a higher volume fuel pump? im running a stock and i beleive it's off of the "old 305" that was in the truck, but hell it was new so i kept it.
thanks!

[sv10001975]

I would probably start out with the stock set up for this carb which is 65/68 jets FT/RR and a 6.5 power valve. from previous experience, if you have that much vacuum you will need a 8.5 or 10.5 power valve. the jetting sounded very high for this carb and after looking it up on holley's site the above is the as shipped jetting for a 81670. i am making an assumption that this is your carb, but verify that this is the number on the choke horn. I think this should be a good starting point. you can't tune the secondary spring until you get the rest of the carb right, so i would just put the stock silver spring in it, if it is too stiff it will just make secondary come in late. they will still open if there isn't something else wrong with the carb. Hope this helps you out.

[dammitmitchell]

thank you.

[cableguy0]

We also need to verify the total timing. Initial timing doesnt really mean anything. We need to know how much timing it has total @3k rpm. You should be at 36 degrees. The stock springs in the distributor are usually pretty tight and dont allow full advance and usually wont be fully advance until way high in the rpm range.

You says its popping? Is it popping through the carb or through the exhaust and when exactly is it doing it? Is it when you go to wide open throttle? Does it do it from a standing stop if you stomp the throttle?

[dammitmitchell]

under partial throttle (about 2k rolling) it'll "pop" like as in a fuel delivery issue feel.. then it'll come back to life. it'll do this sporadicall under partial throttle.
(this is why i thought it was a vac secondary issue at first)
under full throttle 3200=3500 ish. no power and sounds like it's outta gas, tach needle jumps also.
but then comes to life and has full power again until about 5 k..


I will (later this week) reset the carb back to factory settings.
but i was really looking for a recommended setting from yall besides factory.
like jets , powervalve and spring combo..

[cableguy0]

Generally they are very close out of the box. The carb flows x amount of air. X amount of air requires x amount of fuel. Jetting is normally dead on out of the box. Are you positive the ignition isnt breaking up a bit? are all the parts fresh. A lot of times people go after the carb and chase a ghost because the problem lies in the ignition system. Are you sure that the floats are set properly and that fuel pump is supplying enough fuel? What size fuel line does it have? Is it a stock mechanical pump?

[dammitmitchell]

stock mechanical pump and a NEW msd street fire.
this is why im asking.

I felt at first it was the fuel pump but why would it "come back to life" after a certain point.

so that's why im asking because after tweaking and fixing and so forth im at a loss.

thank you for you input. im really hoping to get this done without throwing a bunch of cash at it.

wednsday i'm putting on new wiring for the pos lead on the distro, pulling the cap and rotor and doing new plugs, wires are msd's and 6 months old.
the carb is two years old and i got it "second hand"....
and the floats are set and compensated for the angle of the motor (t case drop installed to compensate for the 8 in lift)
she will be getting jet extensions and springed floats also to compensate for "bouncing" while mudding.

this is just plain out kicking my butt.. thank you for the input

[Captainfab]

I don't have any personal experience with them, but I've read several posta on various forms from guys saying that the MSD Streetfire HEI's are a POS. I don't remember just what the issue is with them, just thought I'd throw that out there.

[cableguy0]

I was going to say the same thing but hadnt gotten around to posting again. Do you have a spare distributor laying around? The msd streetfires are chinese made hence the price. I would personally try a different distributor or at least take your apart and make sure there arent any loose wires especially at the module or pickup coil.

[rjs53]

not to throw confusion into the mix but along with the timing issues the cam you have is no slouch how much stall do you have in the converter? what ratio in the rear? no stal, low gearing and quick timing and detination will happen

[dammitmitchell]

4.56 gears on a sm465
=-)
and thanks for the compliment on the cam.
wedensday i'll update again after checking things out.
new cap rotor and plugs..
and i found my 8/5 power vavlve on the table.. So i probably have the 6/5 installed
so with the18 lbs of vaccum, there's a chance the static manifold pressure dosent drop to what it needs to...

so im going to start there...

and with the tune up..

=-) wish me luck!

[dammitmitchell]

FIXED IT!
woot!
turns out during a rush a few weeks ago when i lost seals on the side ofthe road the powervalve that was reinstalled was a 3/5... opppps...

so now the 8/5 is in she runsto 6grand, smoothly under all conditions..
and she is still a freaking beast .. i loveit

[sv10001975]

glad you got it sorted out!

[dammitmitchell]

i about pooped myself because i could have sworn that i had the stock 6.5 in it.
long story short it wsa very hot very bad day and my truck swered gas everywhere. and i could have sworn during "oh crap gotta fix it NOW "type repairs i swappedtothe 6/5 PV..
welp.. grr.. thanks for the input!

[cableguy0]

At least it was a cheap and easy fix

[sv10001975]

cheap easy fixes are the best kind, these old trucks cost enough as it is without something unexpected costing a fortune.