Ok so im having an issue with my new 351w thats been running rich.This is a new motor.Its a 1972 351w block with stock ported heads comp cams 512 hydrolic flat tappet cam performance products intake and a quickfuel 750 carb.The car starts and idles fine but you smell fuel and if you look under the car its just smokey in general.My fuel pressure is weird.I am running a holley fuel pressure regulator into a summit dual feed line.I have 1 fuel pressure gauge on the summt line by the carb and the other on the fuel pressure regulator.Now if i have 3psi at the regulator i have about 13 psi at the summit dual feed line.If i have about 1psi from the regulator im running 7 1/2 psi by the dual feed.Why is this?Which is most accurate?I dont know what else to do in this case.I looked at my quickfuel calibration sheet and it says the following
Pri Jet: #74
Sec Jet: #84 W/Jet Extensions
P.V. Pri: #45
P.V Sec: Plugged
Pri Nozzle: #31
Sec Nozzle: #31
Acc Pump: 30cc Pri and Sec
Pump Cam: Pink Pri and Sec position #1
Idle Air Bleeds: .070" 10-32 Screw-in Type
High Speed Bleeds: .033" 10-32 Screw-in Type
Floats: Brass Primary,Nitrophyl Secondary (nothed for jet extensions)
Anyone with any imput please give me a hand.Im not sure if this is a jet issue or not so any detail and help is much appreciated
Hiya, welcome to the site.
My opinion, that 750 is too big to begin with. You'd do much better with a 650 mechanical secondary. Plus you add in those jet sizes and that's wayyy too much for it. According to Holley, a 650 is the way to go. You could try stepping down the carb jets first, see if that helps because I know another carb isn't cheap.
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Thanks for the greet.What jet size do you think i should go with?Should i leave the secondary jet size be and not touch that since that only comes into play when im full throttle?My jet size for the primary is 74.please let me know what you think
At the carb you'd want no more than 6psi. Tube inside diameter has an impact on line pressure.
In your situation I would do some tests first to see where you are.
1. Put a vacuum gage to your setup and see how much you're pulling at idle.
2. You didn't post if the carburetor is new or old... that does make a difference. Especially if the carb is dialed in for another setup.
3. Adjust your mixture screws for the greatest amount of vacuum.
4. Initial timing does have a play in carburetor signal as well as camshaft timing. Those have to be correct in the first place.
5. Install new plugs in #1 and #3 and run it at idle for a few minutes, shut off, pull and read them. You can do this for part throttle and WOT... that's when the jets really start to play a part.
I'm not really a believer in a carburetor being too big for a said cubic inch engine. It's all about carb signal, venturi diameter, tuning, and the throttle blades are the restriction at any time other than WOT. So it is my opinion either 650 or 750 will work well... and I have experience that a larger carburetor makes more power when installed on the same engine when originally setup with a 650 (both Holley).
This carb is new.The funny thing about the fuel pressure its it worls really weird.I have a holley fuel pressure regulator with one end blocked off but with a npt port with a fuel pressure gauge on one side and on the other side of the regulator i have the fuel line going up into a summit dual feed line for the carb with a fuel pressure gauge right next to the primary side.Now heres my situation.On the side of the regulator with the pressure gauge that will always read about 6psi lower then what the gauge to the carb is reading.So if my fuel press gauge on the regulator is reading 3 psi my gauge by the carb is reading about 10 psi.I dont know what the hell is wrong here.I can get the gauge to go any lower then 1 psi on the gauge by the regulator bu the one by the carb reads 7 1/2.Im confused...If you want i can go get a video of the car running right now and i can also post pics of the gauges reading different #s
Yes, a larger carb will make for more power but in the higher rpm range. A smaller carb will give better engine output in the mid range and cut out on the consumption. That's wayyyyy too big. And by the way, those vids were so blurry I couldn't see detail up close but I could see at least the pressure was steady.
I'd say step down the jets to 72's, front and back. That should help.
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did you see the last vid of how smokey it was?Its really aggrivating i cant pinpoint my problem.So 72 for both prim and secondarys and everything should be running better and less smokey?
I could see the last one, about how smoky it is, yes. And the smaller jets should help, maybe not totally remedy the problem but they should help some.
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I'm QuickFuel ignorant so please inform me a few things here;
Does your carburetor have idle circuits? If so, then they need to be looked at. For example, the Holley has a powervalve which if incorrect or blown will allow too much fuel to pass during idle.
The idle circuit has it's own fuel metering which although pulls fuel from the bowl through the mains but is not determined by the mains.
I don't see how "jetting" down on the "mains" affects the idle circuit.
If there is not enough signal to the carburetor, then the engine will not run well... especially at idle.
Would it not be best to check for existing factors first before changing carburetors?
I'm assuming there is are seperate circuits from Fatal's first post.
Im not sure about that.I Don't know whole lot about carbs and their featurs.I know idle screws and the basics.This carb is basically new.I just spoke with summit tech support and he said thats a whole lot of carb for a small block.He said you can start by jetting it down but i should call quickfuel.If it helps im gonna go take some pictures of the carb for you guys and this way you can tell me what would need to be adjusted and if my carb is equiped with making my tune easier.I will be back momentarily
Fist of all, what brand/style of fuel pressure gauges are you using, and what size fuel line both to, and from the regulator?
Second, jets have nothing to do with the idle circuit.
Start tuning by adjusting the floats first. You want to set them just below the sight window, so that fuel will trickle out when you give the car a slight bump with your hip. Next, set your base timing, then proceed to setting the idle speed.
Next up is the idle mix, use a vacuum gauge as has been suggested, and adjust both sides equally until max. vacuum is achieved. Re-adjust idle speed if necessary.
I'm willing to bet that a 4.5 pv is wrong for you. Choose a pv rated around 1/2 of the idle vacuum. As an example, if you have 15 inches of vaccum at idle, run a 7.5 pv.
Fist of all, what brand/style of fuel pressure gauges are you using, and what size fuel line both to, and from the regulator?
Second, jets have nothing to do with the idle circuit.
Start tuning by adjusting the floats first. You want to set them just below the sight window, so that fuel will trickle out when you give the car a slight bump with your hip. Next, set your base timing, then proceed to setting the idle speed.
Next up is the idle mix, use a vacuum gauge as has been suggested, and adjust both sides equally until max. vacuum is achieved. Re-adjust idle speed if necessary.
I'm willing to bet that a 4.5 pv is wrong for you. Choose a pv rated around 1/2 of the idle vacuum. As an example, if you have 15 inches of vaccum at idle, run a 7.5 pv.
Worry about the jetting last.
Absolutely agree!
I assume QuickFuel Carburetors are VERY similar to Holley mainbody and bowls?.
Need help with carb running rich, jet size maybe? 
