Jet size carb

W

Whitetiger289

New forum user
CAT Member
Messages
3
I have stumbling from idle, poor gas mileage, and running rich. Engine is a 289 Hipo with a Holley 4160, 600 cfm. The jets are most likely what came from Holley, size 66. Does anyone else have this configuration and know what size jets work well?
 
I was pretty happy with 63s in the 600cfm 4160 in a Hi-Po.
I'm happier with the 465cfm 1848-1 with 55s.
I will probably next experiment with the 1848-2 next (which offers improved vacuum ports over the 1848-1).
 
Working on the same problem certainly will keep in touch . Alas other cars and duties in the way.
Is this a vintage carburetor or a newer one Whitetiger289?
 
Too many factors to opine from long distance. Cam timing? High or Low port vacuum? Points or module? Ad infinite carb items here! Once had a 950 3-bbl Holley on the Tiger perched on an Offy 360 intake. Really good gas miser until that 3rd barrel swallowed.
 
Sounds like more than 1 problem, the 'stumble from idle' is from overexposed transition slot. This is common when the engine isn't quite running right and the idle speed is increased to compensate. When the idle speed is increased the throttleblade angle increased and that overexposes the transfer slot, the transfer slot is in the main body adjacent to the idle discharge hole, it is a thin slot extending up from the throttle blades. When the idle is proper the slot exposure will be about square below the throttleblade. The function of the slot is to provide fuel as the throttle blade sweeps open (called 'tip in') the slot see vacuum and reacts in milliseconds providing additional fuel to the engine until the squirter shot kicks in.
When the slot is overexposed the motor will stumble then the accelerator pump covers it up.
If you have big cam and need high idle you can open the secondary throttleblades a little and then close the primary blades down a little to keep the higher RPM without over exposing the transfer slot. There is a little screw in front of the secondary pumpshot plate that is accessed by turning the carb over, the screw is down in that hole.
 
I have exactly the same problem which I am working on at present. The 4150 carb I have had a 1/8" hole drilled in each primary butterfly. In my wisdom I blocked these holes off with screws, but now realise that this wasnt the best thing to do. I am waiting on a heat sheild to go under the carb, and when it is off I will remove the screws and reset the carb. The holes assist the idle speed without having to screw the idle adjuster in too far. I will advise progress once this is done.
 
grelley said:
I have exactly the same problem which I am working on at present. The 4150 carb I have had a 1/8" hole drilled in each primary butterfly. In my wisdom I blocked these holes off with screws, but now realise that this wasnt the best thing to do. I am waiting on a heat sheild to go under the carb, and when it is off I will remove the screws and reset the carb. The holes assist the idle speed without having to screw the idle adjuster in too far. I will advise progress once this is done.
Click to expand...
the holes are overly large, I make them about .080, that should get your idle about right, with a .125 hole the idle speed could be high enough to get flow thru the main boosters - you'd see dribbles of fuel if looking down into the carb, at idle you should not be able to see fuel anywhere. I just did a set where I had to weld the .080 hole and redrill to .055 to get perfect idle without stumble at throttle whack or hesitation pulling into the passing lane.
 
I have just installed a Holley heat shield under my carburettor and the carburettor runs much cooler. I checked the position of the throttle plates in relation to the progression groove and approximately 2/3rds of the groove was exposed. I removed the 3.0 (.120") screws I had installed previously, from the throttle plates and reinstalled the carb. I have reset the idle to 1000 rpm and the mixture screws are 11/2 turns out, and runs at 10-11 hg. It has a .345 lift cam with 258 deg. duration @ .020" lift roller cam and 1.6 roller rockers. With the .120" holes in the plates the carb still has plenty of adjustment The car certainly idles much better and is much smoother on smaller throttle openings. There is no sign of fuel entering the carburettor at small throttle openings. I think the holes in the throttle plates may have been the factory set-up specified for the car. If I was drilling the throttle plates I would certainly start smaller.
 
You must log in or register to reply here.
Back
Top