holly carb issues???

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Dakota_Don

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the carb in question is a 770 avenger vac secondaries.

the engine is a SB 410 cid, xe274h hyd flat tappet cam 4in stroke and 4.04 bore

ported 2.02 and 1.60 valves cast iron heads eddy rpm air gap intake.. long headers.. auto 904 in a dakota with 355 gears



the carb has 72 jets, and what looks like a 8.5 pwr valve.



the truck idles like crap.. its rich and plugs are blk. and my eyes burn.

i have approx 14-16 in vac..



now do i need a pwr valve that has a lower in number?



and are the jets a good starting place? or should i change them while its apart?



float level? should the float be level when looking at the back side of the bowl? where is a good place to set the leval at since its apart?



and the idle mix screws. 1.5 turns a good starting point as well?



any other tips or suggestions while its apart?



any one use percys adjust a jet?

Timing is set approx 16
 
All the numbers you have there should be fine for it to run and idle ok. I always start the floats tilted a hair low and once running pull the sight screws and raise the fuel level until it's just at the bottom of the hole.

I do have a few questions. Has this been a issue since it was built or something that just started? What are you using for a pump? If it's the electric from the original FI engine you may need to regulate the pressure down as to not blow the needles off their seats causing the rich condition. About 5 lbs. should be plenty.
 
I would use a 6.5 power valve,and use the starting points you mentioned. A good baseline setting for float is to turn the float bowl upside down and set it so it's centered in the middle and you should be able to see the float mounting screws.
 
What is the fuel pressure? Floats; soon as a dribble comes out of the sight holes. Upside down, are the secondaries cracked a hair open with that screw?
 
OldmanRick said:
All the numbers you have there should be fine for it to run and idle ok. I always start the floats tilted a hair low and once running pull the sight screws and raise the fuel level until it's just at the bottom of the hole.

I do have a few questions. Has this been a issue since it was built or something that just started? What are you using for a pump? If it's the electric from the original FI engine you may need to regulate the pressure down as to not blow the needles off their seats causing the rich condition. About 5 lbs. should be plenty.
Click to expand...

this has been an issue since i had the carb.. so i wanna make sure everything i the cab is ok or close where it should be..
 
green1 said:
What is the fuel pressure? Floats; soon as a dribble comes out of the sight holes. Upside down, are the secondaries cracked a hair open with that screw?
Click to expand...

I didnt think about the secondaries..humm
 
OldmanRick said:
All the numbers you have there should be fine for it to run and idle ok. I always start the floats tilted a hair low and once running pull the sight screws and raise the fuel level until it's just at the bottom of the hole.

I do have a few questions. Has this been a issue since it was built or something that just started? What are you using for a pump? If it's the electric from the original FI engine you may need to regulate the pressure down as to not blow the needles off their seats causing the rich condition. About 5 lbs. should be plenty.
Click to expand...

using a 72 340 new pump..
 
From what you have posted the power valve and jetting are not a issue. I believe you have to be rich from pressure or float adjustment. If you are only running that stock mechanical pump, which i have done with Holley's many times, then i'd have to look at the float's. When you get it back together and make sure the fuel in the bowls is not above the sight holes i think you may have cured the problem. Might want to throw a set of new plugs in afterwards to get a fresh reading.
 
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