Looking for advise on proper jets & power valve for my Holley 2300 - 7448

Rentalman

Rentalman

Active member
Good afternoon all. I'm looking for a little advice on tuning my Holley 2300 - 7448 carb. The engine is a balanced and blue printed 345 with a isky split duration cam, Pertronix III ignition and coil with 250 miles of break in on it. The carb new out of the box came with # 63 jets and a 8.5 power valve. I believe the engine has always been running way to rich. Before I start it I have to put a piece of cardboard up to catch the black sooty splatter. Also the tail pipe is black, pictures attached. I live at 1400' above sea level if this helps. A few days ago I changed the jets to #58 and power valve to a 6.5. After the engine was completely warmed up, manual choke off I pulled out of my drive way and started up our slight incline in the neighbor hood. I noticed a slight hesitation when I put my foot on the gas pedal. As I pressed harder on the gas pedal the hesitation went away. I bulled it back in the driveway after a 1/2 mile around the neighborwood and checked the accelerator pump adjustment. It was way off where I could slide a .026 feeler gauge and still had room. I adjusted it to where I have to use a little presure to slide a .010 feeler guage between the pump lever and bolt. I took the lid off the stock air cleaner and examined the shot of gas. Gas is squirrted out of the nozzle once I accuate the throttle lever. The carb has the orange cam in the #1 position. This adjustment did not fix the issue. I drove it up our slight incline again and it stumbled. Once I give it more gas it drives fine. It has to be the power valve not opening soon enough under a load. Should I go back to the 8.5 or try a 7.5? It has always driven fine before with the 8.5 power valve, with never any hesitation.

New Tuning Specs with 58 jets & 6.5 power valve:
8 Deg BTDC
15 in vac
900 RPM at idle, 800 RPM with brakes appled (hydro-boost brakes), 650 RPM TF 727 Auto Trans in Drive with foot on brake for a minute.
Idle Mixture Screws 1 1/2 turns out
I did not adjust the distributor to get it down to 8 Deg BTDC. That changed with the curb Idle adjustment from the prior set up of the carb. If I increase the curb idle to 1000 RPM's, I'm back at 10 deg BTDC and the Auto Trans in Drive would be at 700 RPM's what is called for under tune up specs.

Prior Tunning Specs with #63 jets & 8.5 power valve:
10 Deg BTDC
14.5 - 15 in vac
700 RPM auto in drive foot on brake pedal
Idle Mixture Screws 1 1/2 turns out

My goal is just to have the engine not run so rich.

Thanks for any advise. It will be much appreciated.
 

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also--- i think you need to adjust the idle mixture, see if you can get more vacuume at idle. im at 5400 feet and i get 18 inches. you should be able to beat me.
 
Today I changed out the 58 jets for some 61's. I also put the 8.5 power valve back in. From reading a book on Holley's I need to stay with one change or adjustment at a time. Engine is completely warmed up for tuning. 10 deg BTDC, Vac is at 15", idle mixture screws 1.75 turns out, 900 RPM's at idle. Foot on brake (hydro boost) drops to 800 RPM's, TF 727 in drive with foot on brake drops to 700 RPM's. If I adjust the curb idle screw I can get the RPM's down to 800 and still pull 15" of vac. But when I have it in drive with foot on the brake RPM's drop to 600. I counted it off for 60 seconds in gear, it did not die its just nerve racking because it sounds like it wants to die. I took it for a 11 mile drive with the 900 RPM curb idle setting in our neighbor hood which has a few small grade hills to go up and down, it never stumbled like it did with the 58 jets. FDChappie you were right on the jets. I don't think I can get anymore vacuum out of this engine due to the Isky split duration cam. I've tried going leaner or fatter with the idle mixture screws, the vacuum signal drops. Also, if I have the curb idle set 700 to 800 RPM's the vac gauge is hunting between 13" to 14" vac and the engine is not smooth sounding it has a slight gallop. At 850 to 900 RPM's the engine is smooth sounding and the vac holds steady at 15", it is not hunting. After I drive it a bit I will pull some plugs and check them for color.

With my idle set a 900 RPM's does that effect the other signals of the fuel metering block when driving or is that just a seperate circuit for idling? As always, I appreciate all of the feed back. You guys always get me out of a jamb and I am learning from it. Have a great week.
 
I'm running a Comp cam and 16" at 1000' elevation. Now adjust your idle mixture slightly rich of max vacuum.
The Holley has idle, transition and primary circuits. Turn your idle down a bit so you're not trying to adjust idle mix while in the transition circuit.
 
The split duration Isky's that I have ran always tend to idle around 15-15.5" of vacuum so you're in the ballpark.
 
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