[rattus]

My carb is a holley 830 cfm dp and came with 78 jets all around (and front and rear 6.5 power valves). I swapped the primary power valve for a 4.5 (my motor makes about 8.5" at idle), plugged the secondary power valve and changed the secondary jets to 84's. It seems from searching various threads that my current jet setup is somewhat on the lean side.

My motor specs:

461 ci, 9.6:1 comp. ratio
ported e-heads
288HR cam
torker II intake
Holley (9381) 830 cfm (primary: 78 jets, 4.5 power valve, secondary: 84 jets, plugged power valve), 30 cc accel pumps (primary and secondary).

Is my current jetting too lean? Any other suggestions on my carb setup?

[shaker455]

That sounds like pretty bad vacuum @ idle for the XR288HR as thats a good cam and should have you in the 10-12"Hg range.

How many turns out are you idle mixture screws?

how about some more details about you combo and exhaust?

To start you may want to try 80's in the front...need more info

[rattus]

The idle vacuum may be a little off (I have three cheap vac. gauges and they all differ by about 1" or so), but I'm pretty sure its under 10". Comp Cams has dyno info on a sbc (running the xr288hr) that pulled 9.5" at 1000 rpm.

The idle mix screws are 1.5 turns out.

I'm running Doug's headers (1-7/8" primaries, 3.5" collector) 2.5" pipes w/ glasspacks. The header back exhaust is temporary until I install a 3.5" x-pipe system.

Rockers are 1.6 ratio. I had the cam spec'd out (cam doctor) and the duration @0.050" was 239/246 (a little more than comp cams specs of 236/242).

[02Hawk]

Usually a good rule of thumb on powervalves is, if you block em off go up 10 jet sizes

[hal101]

what do the plugs look like ?

you said came with 78 front and back and power valves front and back

if you mean came with NEW like from the holley factory then i would say that is prob
verry close
holley's hav a rep of coming out of the box a litle rich not lean

O2Hawk is right if you take out the power valve you go up (8-10) jet sizes to compensate

[shaker455]

Hal,
Your right about how close they come out of the box, but in the case of an annular that produce a strong vac signal like Rattus I've seen them be a little skinny and I think he may be right about the jetting.

Rattus,
Thanks for the info, if you don't know how much transfer slot is exposed both front and rear then I'd say start by taking the carb off and set the blades so only about .020" of the transfer slot is exposed....it will look like a little square when your done and this may explain your vacuum reading as the blades may not be in a good spot to produce good vac....

I like to see about 1 turn out on the mix screws so your close but I'd recomend a jetting of 80/86 to start as you have plently of head flow.

What are you noticing about the car that you think it's lean and what tranny you got and if auto what stall?

[Skip Fix]

I've gt a flat tappet hydraulic 239/247 @ 0.050 that is pulling 12 " @ 900, sounds awful low for that cam on vacuum.

Timing setting? Vacuum advance?

[rattus]

Thanks for the responses. I'm not sure that its running lean, the plugs are tan. It just seems that the jets I'm using are smaller than what I've seen in other threads... just looking for a good place to start w/ out running too lean and hurting something. I'll check the transfer slot and up the jets to 80/86. I'm running a TKO 600 trans.

I'm running 12 deg initial (38 deg total, in at ~3500 rpm). Vacuum advance is hooked up to manifold, limited to 8 deg (crank), and comes in at ~7" Hg. With vacuum advance it idles at 18 deg at 950 rpm.

[shaker455]

Rattus,
That cam will take as much intinal timming you can give it and it would be nice to see it atleast 18....what dist do you have?

I personally run my vac adv on a ported source so it only working at part throttle/ cruise.....

Remember to also check the float level...bottom of the sight