Engine leaning out at 3000rpm

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moparwillybb

moparwillybb

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Hello guys it seems my engine has developed a problem now when i mash the gas my engine goes way lean like 16-17:1 pops out the exhaust and makes a hollow kinda bbbbbeeeerrrrrrrrvvvvvvvv sound ive cahanged intake gaskets 3 carbs jetted the thing as big as it can go no change its a 493 with a performer rpm intake 440 source heads checked the vac port for power brakes its good put brand new carb gaskets torqued to 80inlbs it does not idle funny runs good if i keep it under 3000rpm what the heck is going on its driving me crazy im switching to a single plane intake this weekend got the expensive hughes engines intake gaskets and a new pan and some hylomar blue so im gonna seal the crap out of it hopefully last time i took the intake off i had a little oil i the intake runners of the heads and oil in the intake bolt holes is my engine sucking air from the valley? Any help would be appreciated
 
Oh yeah i tried the ether around all the ports no change in idle listened for leaks with a hose didnt hear anything
 
What type of fuel supply system are you running? Also @ 3000 rpm I'm assuming your pretty well putting your foot in it, so if the carb is some type of Holley design does the secondary side have jet extensions on it? After three different carbs on it doing the same thing I'd be leaning towards a fuel supply issue, I'd start by figuring out a way to see what the fuel pressure is doing under load. One other thought is that engine is going to want to eat a lot under power, maybe if you're running a stock gas tank without a lot of gas in it the fuel is sloshing and uncovering the in tank pick up? Without more info on your build these are just some guesses. One other thing that may be a remote possibility, you mention popping out the exhaust, are there any exhaust leaks upstream of where the O2 sensor is located? Air getting into the exhaust from a leak can cause a popping out the exhaust upon deceleration and could be causing the AFR to show lean. More than likely the popping is just do to the mixture leaning out but just a thought.
 
Yeah thats some good stuff thanks i have a holley hp150 fuel pump pulling from a stock tank with a comp engineering sump tig welded in no pickup tube 1/2 inch fuel line holley regulator i will definately check the header bolts to make sure they are tight for the popping the bog however is what concerns me i started with a quickfuel 850 ran great but way too rich wouldnt idle right so i tried a friends brand new 750 hp the car liked it but still lean bogged not as bad tho so i bought a brand new cnc billet main body blp weekend warrior carb tuned by devane carbs wich id awesome by the way and it is better but still gets that lean bog 3000 rpms was just rolling into the throttle to pass agressively or anything for that matter much above 2800 and it starts getting lean and acting stupid pressure stays at 7psi and jet extensions did nothing to help tried every friggin power valve and pvrc jet possible no difference no matter what i do to the carb its like it has a manifold leak but i cant find one
 
This new carb is a beast i cant wait to get this crap sorted out so i can feel the new power!
 

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Oh yeah and it pops under acceleration it will push thru if i floor it but the a/f meter shows me at 16:1 itll move but its not right i understand if its sucking air through the header flange it could make it read that high too
 
Well to start with if you have almost 500 cubic inches, i will say start with an 850 cfm carb and get it tuned. Unless this is a trans brake race car you need a power valve in the primary side. I would say start with 76 jet in front with a PV and an 88 jet in the secondary side. Go out make some top end passes stop pull a plug. Jet up or down till the plugs look a nice tan brown and clean. Then squirter time. From a dead stop swap feet floor it see what car does. Keep going up in squirter size till it blows black out the back, then go down 2 sizes. Or go to the track jet for MPH and squirter size for 60 foot. This is a tried and true method. This is why i spend the extra $600 to engine dyno, then there is no guessing and you always have a base line to go back too.
 
Might try to contact Devane to see if they've got recommendations. You've got all the info they may be able to put you onto something.
 
It was dyno tuned it ran great for a while then i got an oil leak in the valley pan the 440 source style that goes under the heads so i pulled it out and put a stock valley pan in it with paper gaskets both sides oil leak went away but then i sterted with this lean stumble mess must be an intake leak right? So i messed with the carb an 850 quickfuel for a while jetted it stupid rich to stupid lean no difference when i lay into the throttle it leans out big time runs good on light throttle around here or there borrowed my buddies 750 hp same thing bought this almost 1000 buc custom carb pictures above custom built to my engine specs flows 965cfm thru a 750 base plate awesome carb same thing it has to be in the intake somewhere fuel pressure is good timing locked out at 34 degrees on an msd digital programable 6plus its been plagueing me for a month! Ive had to punk out from 3 callouts so far and it is killing me!
 
Robbie at devane has been great he is an awesome dude and local big in the race scene he has pulled his hair out with me trying to figure it out it used to run great kinda rich
 
Check your rubber hose in the fuel system.

Check the hose coming out of the sending unit that connects to the main steel line and see if it is bent and may be kinked. I've seen that restrict fuel flow. Make sure that all hoses are straight as possible and not kinking where it bends...
 
How about vapor lock fuel peculation, noticed your fuel line runs up the back make sure your not picking up excessive heat from your headers and that they are insulated where they are close to any exhaust components.
 
It does it hot or cold it never did it before i started messing with the valley pan the car rod around all over the place like 2 hour trips and stuff never had a problem i had cracked the base plate on my quickfuel and thought that was it thats before i had the torque specs and i was cranking that thing down like a champ so i tried my buddies brand new 750 hp just to see if it would give the same symptom it did with a new set of gaskets and the 80inchlb torque spec the car went from haulin *** and being awesome to this shortly after the intake valley pan swap it has to be related but i cant get no leaks from the top side eith ether propane carb cleaner etc so it must be leaking on the under side maybe ive read performer rpms being tight on the top and gapped at the bottom but you think that woul cause it to idle high or something or just drive like crap all the time thank you for all your input by the way i appreciate everyone who tries to help!
 
Im gonna change the gaskets and pan this weekend as well as swap to an m1 single plane wich is brand new so hopefully i will clear it up i got the good hughes gaskets with the silicone rings
 
It's leaning out while you're driving it or just revving it up with no load?
 
If you haven't already, you might want to disconnect the fuel line and do a flow check into a good size container.
 
If you haven't tried it already hot wire the coil to a straight 12 volts FROM THE BATTERY and see if it changes anything...... I just finished fixing a friends car that had similar symptoms and the main issue was low voltage to the ignition and a failed coil. Part of the issue was the typical bulkhead connector problem.
 
I had back firing through my exhaust. Turned out to be one plug wire terminal was corroded. Don't know why. I fixed the terminal and problem solved.
 
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