[chevyman72]

i have a 85 chevy truck with a 1979 350sb in it .it is a stock engine i have a holley 600 cfm carb on it which i had rebuilt less than 2 months ago. it ran rich even when i adjusted it correctly. it had 64 main jets in it . i dropped the jet size down to 60 and now it has a slight surge at low speeds (around 30 mph or so) is this too lean for this motor ..what size jets should i use to eliminate this problem

[vinniekq2]

try raising the float lever slightly or 61/62 jets

[chevyman72]

i'll order up the jets tomrow just in case.the float is adjusted to u can just see the fuel at the bottom of the sight hole

[kleen56]

Sounds lean to me. Usually dropping 2 numbers on Holley jets makes a big difference. Holley recommends you don't go lower than 4 numbers when jetting. I'd use a 62 jet and see if it improves. You can play with the idle fuel mixture screws on the side of the bowls. When seated gently, turn them out 1.5 turns as a starting point for adjustment. I use a vacuum gauge to achieve the highest vacuum reading while adjusting the carb. I'd also check the timing.. you may be either advanced or retarded.

[chevyman72]

i kinda figured it was too lean kleen..i just ordered #62 jets from summit i should have them by saturday...ill give a whirl again when i get them

[cobalt327]

Originally Posted by chevyman72

i have a 85 chevy truck with a 1979 350sb in it .it is a stock engine i have a holley 600 cfm carb on it which i had rebuilt less than 2 months ago. it ran rich even when i adjusted it correctly. it had 64 main jets in it . i dropped the jet size down to 60 and now it has a slight surge at low speeds (around 30 mph or so) is this too lean for this motor ..what size jets should i use to eliminate this problem

I'd be looking closely for a vacuum leak. Running at light throttle/30 mph you're not on the main circuit of the carb- you're still on the idle/transition circuits, and changing the main jets might not be effective at ridding it of a lean condition- but I do believe the stock jetting should be closer than 60 jets.

How is the timing set up on this engine- how much initial and total, w/o adding in the vacuum advance?

And is the vacuum advance being used and if so is it connected to manifold or ported vacuum? It should run better using manifold vacuum...

[cdminter59]

Here is the manual for the Holley 600 carbs. According to the manual the carb came with 65 jets in the primary and secondary. http://www.holley.com/data/Products/...7948-5rev5.pdf. Check your vacuum the engine makes at idle. If 12 or over use a 65 power valve.

[chevyman72]

i'm not too sure on the timing..i dont belive there is a vacum leak i had replaced all the vacum lines..i'm picking up a vacum guage in about an hour i belive the proper vacum for this engine should be between 19-21hg i have a set of #62 jets comming from summit tommrow.hopefully something gives..its getting frustrating