Sputtering issue with new carb/motor. Need advice. Bad Carb?

[cudablue]

Hello gang,
When diving the carb will sputter. I can cruise at any speed (40 to 80 mph) consistantly and out of the blue,,, it sputters for a split second and then is fine. It will do this at various times, but approximately every 45 seconds to a minute.
Here are the facts. Heads up ,, I'm a novice here. IF I need to give more info just fire away.
We do have it running rich with 82 size jets (we went higher but had to come back down) and performance power valve. Motor build is excellent. Runs and idles great. It does good banging through the gears. Build came over to adjust the carb and timing.
Got 115 miles on new engine. The previous fresh rebuild with this same carb did the same thing. I had a cracked block in previous engine.
New 870 Holley(4150) vac secondary. square bore.
Intake is Edlebrock performer dual plane (spreadbore) has 1" adapter plate to square bore.
Mallory electonic distributor.
360 block with 318 heads. computer specs with this build shows 450 peak HP (5000 RPM), 540 peak torgue(4000).
Lunadi hyd cam 30405 , Duration (.50) 224/234 , lift .318/.338
Bored .30 KB 107 pistons.
New Carter mechanical fuel pump 120 gph. 3/8" to carb. 6 psi.
5/16th line from tank to pump.
160 degree T-stat. Engine runs exactly 160 degress.
Headers
3" stainless magnaflow.
4 speed / 3.23 SG.

Hopefully this gives enough info.
thanks!

 

[Rob C]

Sounds lean if not an obstruction in the carb.

 

[Chryco Psycho]

the first change I would make is to install a 180* T stat
I assume the power valve is rated approx 2" below engine vacuum in gear at idle ?
are you using vacuum advance , the engine should have approx 36*@ 3000 rpm with idle around 14-16* , most engine run better without vacuum advance as this allows for more initial timing .
the 3" exhaust on a small block is overkill LOL

 

[moparleo]

Ditto

 

[cudablue]

Hey guys,
no vacuum advance. At idle I believe vac it is 13. I don't know what 3K RPM is, but will check and get back to you.
I have been reading alot about the 180 vs 160 and more confused before I started . I will install the 180 first.
I do have a couple of Carb options. I have a brand new 670 Holley Street Avenger and access to my buddies Edlebrok 750. Maybe I'll try that next.
In retro, I would go with 2.5 tubes, Part of ignorance. ' just assumed bigger is better. Every day is a learning process.
thanks

 

[Chryco Psycho]

870 cfm is large for a 360 , I far prefer the Holley carbs & would try the 670 just to see how it runs with it first

 

[cudablue]

I put the 670 on and rejetted it to 70 primary and 71 secondary. It ran perfect! but very lean and the temp went up about 20 degrees.
I called Holley and they said its not recommended to go up more the 4 to 6 sizes.
It came with 63. Can I go higher that 70?
Today I will try the 870 again and lower the jets from 82 to 78.
What do you think?

 

[Chryco Psycho]

generally the secondary is jetting approx 6 sizes larger .
if it is lean you can up jet , what vacuum are you making ? Usually a smaller carb will be very responsive & have no problems pulling in fuel & would not need to be up jetted that much , but if it is lean increase jet size .

 

[cudablue]

Update:
I jetted the 870 to 78 instead of 82. The hiccups got better. I'll try 77 next.

 

[moparnut74]

Hello. I have same problem with my 750 double pumper. Holley told me to change the squirter nozzles to a 35