Carburetor trouble

[Matt510]

I have a holley 650 brawler 4 barrel on my 318, can't seem to get it tuned right. I cant get more than 15psi vacuum and it is either falling flat on its face off idle or backfiring through the carburetor. I put 68 secondary jets in it and went through and cleaned it because it had sucked some stuff out of the gas tank. I have gone back and forth with tuning this carb and messed with timing too, and I am completely lost. It doesn't help that I don't know much about the motor, because I didn't build it and I have only had the car for about a year, and have been mainly focused on putting an interior back in it as when I bought it it had almost nothing there. Any help would be much appreciated.

 

[RustyRatRod]

The jets are on the power circuit so if you're trying to tune the idle by changing jets, that's not gonna work. Vacuum is measured in hg, not psi. What I would do is put the carburetor back stock. Then concentrate on the timing. You don't know anything about the engine, but you can tell us how it sounds. Does it sound stock with a smooth idle? Does it have a slight lope? Does it have a hard lope? You're gonna have to have some skin in this game if you want some help.

 

[Matt510]

Ok, I can tell it is not stock and I think it has a decent cam in it. I put different jets in it because no matter what I did with the mixture screws it kept overfueling and still is. When taking it apart I noticed the front needle and seat is sticking sometimes, does that need to be replaced?

 

[MOPAROFFICIAL]

I have a holley 650 brawler 4 barrel on my 318, can't seem to get it tuned right. I cant get more than 15psi vacuum and it is either falling flat on its face off idle or backfiring through the carburetor. I put 68 secondary jets in it and went through and cleaned it because it had sucked some stuff out of the gas tank. I have gone back and forth with tuning this carb and messed with timing too, and I am completely lost. It doesn't help that I don't know much about the motor, because I didn't build it and I have only had the car for about a year, and have been mainly focused on putting an interior back in it as when I bought it it had almost nothing there. Any help would be much appreciated.

You're going to have to tune the pump shot, the power valve and the primary jetting. Start with tuning the idle, if it's an automatic do it in gear with the brakes on as in you'll need somebody else to help. Remember to make each idle screw the same amount of turns
Buy a book

 

[318willrun]

Ok, I can tell it is not stock and I think it has a decent cam in it. I put different jets in it because no matter what I did with the mixture screws it kept overfueling and still is. When taking it apart I noticed the front needle and seat is sticking sometimes, does that need to be replaced?

No carburetor will function right with sticky/leaking needle-seats. Cheap and easy to replace. Float level is the first place to start.

Is there an electric fuel pump that might be pushing the gas past the needle n seats?

 

[Matt510]

No carburetor will function right with sticky/leaking needle-seats. Cheap and easy to replace. Float level is the first place to start.

Is there an electric fuel pump that might be pushing the gas past the needle n seats?

No, mechanical fuel pump, I know there are different needle-seats sizes. Would it be worth it to go up or down a size or will it make a difference.

 

[318willrun]

No, mechanical fuel pump, I know there are different needle-seats sizes. Would it be worth it to go up or down a size or will it make a difference.

No, just replace it with what it came with.
As for your vacuum, 15 hg may be just fine if it has a bigger cam in it, but so much depends on what's all what with the engine. But, either way, the 650 should work just fine.

 

[Newbomb Turk]

I have a holley 650 brawler 4 barrel on my 318, can't seem to get it tuned right. I cant get more than 15psi vacuum and it is either falling flat on its face off idle or backfiring through the carburetor. I put 68 secondary jets in it and went through and cleaned it because it had sucked some stuff out of the gas tank. I have gone back and forth with tuning this carb and messed with timing too, and I am completely lost. It doesn't help that I don't know much about the motor, because I didn't build it and I have only had the car for about a year, and have been mainly focused on putting an interior back in it as when I bought it it had almost nothing there. Any help would be much appreciated.

Before you do ANYTHING else pull the primary float bowl off the carb and take a picture of the front of the metering block so we can see what you have.

Those Brawler carbs have about 20 different tune ups in them from Holley. They bought out Quickfuel and just wrecked the whole line of carbs.

A 68 secondary jet is WAY TOO LEAN for that Venturi diameter.

 

[Syleng1]

Good morning Matt510-
These guys are good and when they ask for you to try something- try it and report back. Sadly you sound very lean (popping back thru the carb) but there are so many other items like tune or distributor issues also fall into the mix.
Sorry you are having this issues. We also do not know how much you know about engines or cars in general.
So hold tight.
Syleng1

 

[67Dart273]

I can't believe you guys have not addressed/ questioned TIMING

(I see Rob mentioned it)

 

[Matt510]

I can't believe you guys have not addressed/ questioned TIMING

(I see Rob mentioned it)

Good morning Matt510-
These guys are good and when they ask for you to try something- try it and report back. Sadly you sound very lean (popping back thru the carb) but there are so many other items like tune or distributor issues also fall into the mix.
Sorry you are having this issues. We also do not know how much you know about engines or cars in general.
So hold tight.
Syleng1

I have thought about timing and other issues, I want to rule out the carburetor first before I tear into my motor. And I am still very new to cars, this is my first hot rod and I have only had it for a little over a year, and I am learning as I go. I will do some testing as soon as I get home from work and share what I've figured out.

 

[Newbomb Turk]

I have thought about timing and other issues, I want to rule out the carburetor first before I tear into my motor. And I am still very new to cars, this is my first hot rod and I have only had it for a little over a year, and I am learning as I go. I will do some testing as soon as I get home from work and share what I've figured out.

Someone way smarter than I will ever be said most carburation issues are really timing issues.

 

[67Dart273]

I have thought about timing and other issues, I want to rule out the carburetor first before I tear into my motor. And I am still very new to cars, this is my first hot rod and I have only had it for a little over a year, and I am learning as I go. I will do some testing as soon as I get home from work and share what I've figured out.

YOU CAN NOT ADJUST carb idle RPM or mixture if the timing is wrong for the engine.

Engine MUST be fully warmed.

Timing MUST be correctly set, and in a "cammed" engine this may require some experimentation. If you don't know the history, the distributor may not be/ not ever properly recurved, may not ever have know the optimum advance. And don't just advance a stock dist. for idle, because then it will OVER advance at high RPM.

THEN set idle RPM temporarily, adjust idle screws for mixture, and then, finally retouch carb idle RPM and mixture.

 

[Matt510]

Didn't get the chance to do any testing tonight, will try tomorrow and figure some things out, I am new and dumb and I appreciate any help I can get.