Dan Georgino
Well-Known Member
Wooo, 750cfm is way to much carb. 600cfm is plenty. Then play with your jets till you get 18 to 20 vacuum inches at idle. What is your vacuum at idle now?
My 340 getting 6 mpg
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Dan Georgino
Well-Known Member
Correct
Dan Georgino
Well-Known Member
3.73 very high. 3.55 or 3.23 a bit better
Dan Georgino
Well-Known Member
Don't forget, it's still breaking in, mostly around 3,000 miles it will relax and give you the correct mileage per gallon .
Last of the Fast
Active Member
I have a 340 Duster running a Holey 750 double pumper primary jets 72, secondary jets 76 power valve 45 Edlebrock LD340 intke. Your jets are too small so you have to push the throttle so far that you are always into the power valve. What is your elevation? I'm in southern California pretty close to sea level. Your cam sounds like it is a little too hot for the street (Sig Erson hyFlow 2?) The Sig hyflow 1 is a better choice. My Duster gets 12mpg with 3.55 gears with posi and the stock cam (hydraulic). I have a 4 speed. It turns low 12's/high 11's depending on the track.
If you have an automatic, what is the stall speed on the converter? My V-8 Vega has a 700R4 2200 rpm stall, 3.08 gears with posi and Sig Erson HyFlow1 cam with Fuel Injection. Both cars have headers.
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MILO
Well-Known Member
I have had carter afb also carter theromoquad carbs that ran good and mileage was not bad
Newbomb Turk
Well-Known Member
There is nothing wrong with your carb other than FST pays low IQ morons to put them together.
I can tell you without looking at it that:
It has too much emulsion.
The idle feed restriction is up high when it should be down low.
The main air bleed is too big.
It needs T slot restricters.
You’ll need a timing curve with 24 initial and a curve that is slow through peak torque. Vacuum advance would be a bonus.
I see all the Carter boot lickers have been here. That’s the LAST thing you’d want.
I had a 350 Chevy on the dyno Tuesday (a 1406 Edeljunk turd) and it was so lean neither one of us had the jets or metering rods to even get it to make a pull.
Learn to tune and fix what you have. Ignore the knaves who tell you that a Holley won’t get fuel mileage.
I can tell you without looking at it that:
It has too much emulsion.
The idle feed restriction is up high when it should be down low.
The main air bleed is too big.
It needs T slot restricters.
You’ll need a timing curve with 24 initial and a curve that is slow through peak torque. Vacuum advance would be a bonus.
I see all the Carter boot lickers have been here. That’s the LAST thing you’d want.
I had a 350 Chevy on the dyno Tuesday (a 1406 Edeljunk turd) and it was so lean neither one of us had the jets or metering rods to even get it to make a pull.
Learn to tune and fix what you have. Ignore the knaves who tell you that a Holley won’t get fuel mileage.
MILO
Well-Known Member
Holley oh forget it not going to start a argument to each there owe and what they had the best luck with and that is the best to stick with
Dan Georgino
Well-Known Member
One main problem, stop using Chevron.
Dan Georgino
Well-Known Member
Chevy, no wonder you have no clue.
Rug_Trucker
Love my 3.8 Buicks
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Why? What do you know about the fuel business?
Newbomb Turk
Well-Known Member
He doesn't know dick about anything.
Newbomb Turk
Well-Known Member
750 is correct for a 340. You can use a spread bore for better fuel econ. but you need to ck the rest out first.
MOPAROFFICIAL
Oogliboogli
Timing is 24/34
Plugs all cleaned up, jets were 65/75
One pv 6.5, vac at idle 10.5-11, good enough.
Jets are Now 68/78, for now.
Plugs all cleaned up, jets were 65/75
One pv 6.5, vac at idle 10.5-11, good enough.
Jets are Now 68/78, for now.
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Dan Georgino
Well-Known Member
No, no, no
Dan Georgino
Well-Known Member
Nothing about the Business, but I do know about gas it's self. I do know Chevron is the reason California gas prices are so high. And the gas is bad. Most if it is chemical cleaning additive.
Dan Georgino
Well-Known Member
You don't even know what his Horsepower is. 340 means nothing. Even a 360 a 750 cfm is too much.
Dan Georgino
Well-Known Member
Glad you know all about dik. Lol
Newbomb Turk
Well-Known Member
Glad to know you don’t know **** about anything. All you do is run your mouth with useless drivel.
Hartman-52
Hartman-52
Geeses, semi tractors pulling a full trailer are getting better mileage than that. Check for hole in gas tank.
I see the ignorance of Newbomb Turk rises to the top in post #107 like cream rising to the top.
Larger main air bleeds will lean the mixture, not richen it. Same dope blames the carb he has on the dyno because he does not have the jetting parts on hand to jet it. It's the carb's fault!
As I said earlier in this thread, I believe the carb being used has some fundamental internal problem & a different carb should be tried if possible.
Below on air bleed function is from the Holley book, by Holley Engineer Mike Urich
Larger main air bleeds will lean the mixture, not richen it. Same dope blames the carb he has on the dyno because he does not have the jetting parts on hand to jet it. It's the carb's fault!
As I said earlier in this thread, I believe the carb being used has some fundamental internal problem & a different carb should be tried if possible.
Below on air bleed function is from the Holley book, by Holley Engineer Mike Urich
MOPAROFFICIAL
Oogliboogli
Dude , are you ok?
Newbomb Turk
Well-Known Member
I've already proven you a liar. I can do it again.
I explained it above, like it works in the real world. I'll say it a different way. I doubt that will help you but someone else may learn.
Because of the position of the MAB and the fact that the MAB is connected to the main well and the nozzle, at low air flow rates the main air bleeds functions as an emulsion jet. And it behaves in that manner until the nozzle is activated. And what activates the nozzle (booster)?
As the airspeed increases and the fuel starts to flow from the nozzle, the MAB now acts like an air bleed and starts to do what it's name says it is. It starts to bleed off flow from the booster.
The MAB is needed because the booster can deliver more fuel than the engine needs. You wouldn't use the same emulsion and MAB for a straight booster as you would with a down leg booster or the same emulsion with annular boosters.
You are trimming the fuel with the MAB at high air flows.
If you were to look at it on a graph, assuming that the emulsion is correct and such, you'd see that a .034 MAB would have a different curve than say an .026 MAB.
The difference would be the bigger MAB will tilt the curve rich at low air flow and tilt the curve lean at high air flows.
The smaller MAB will tilt the curve LEAN at low air flows (because the smaller bleed, acting like an emulsion bleed isn't adding as much air to the main well and the fuel in the main well) so the booster starts later (making it leaner at low air flows) and at higher air flows (the booster has started) it will tilt the curve rich because its not bleeding off as much signal.
It's pretty simple really unless you don't think for yourself. Bewy thinks that because the MAB reduces the signal to the booster, making the curve tilt lean at higher air flows that it must do the same at low air flows.
It doesn't. It works exactly as I outlined above. It's easy to see with O2 sensors on the dyno.
What I can't explain is why some of the carbs come with huge MAB's in them, other than they have so much emulsion they are trying to kill more signal to keep the fuel curve half assed close.
Always remember, at low air flows the MAB acts like an emulsion jet which is adding air, which makes the fuel in the main well lighter, which causes that fuel to flow to the nozzle (booster).
Big air bleeds and too much emulsion have caused as much grief as setting power valve timing at half idle vacuum. Another Bewy tuning error.
As for the junk **** edeljunk carb on the dyno, it was over 16:1 with the stock jets and rods. I have a full Carter strip kit and he had some loose jets and rods but neither of us had rich enough jets and small enough rods to get enough fuel in it to make a pull.
I don't tune junk that is a power loser.
MOPAROFFICIAL
Oogliboogli
The carb is decent, except for the throttle plate... its cheese. The accelerator pump arm screws wobbly pos's and you watch the throttle raise then dip while turning the speed screw in. Trash. The idle changes speed after driving it, raises.. lowers. When yoy come back from a test drive it's gone from 850 to 1100... then you push close the throttle and it's back to normal. It took enough return springs to necessitate standing on the throttle to open it.. I said take those springs off and buy a new throttle plate for this shitter. The thing is nice.. except for that part.
It got dark... so that's why we stopped with the tuning, for now. Going to drive it a little now and check plugs, check milage etc .
it pulls much harder, acceleration is smooth...and it has balls up top now it's not starving for fuel.
I like newbombs guesstimate of timing because that about as high as you would want it while still maintaining an advance curve. 8 to 10 advance is nice. His is all in by 2800 fwiw.
I normally will spend most of an afternoon test n tune with jetting and playing with pump shot.. but I got there a little later in the afternoon. It'll probably pick up 5 mpg immediately but expect it to get closer to 15 mpg. The higher initial means less fuel/pedal to get moving aka more power, less stink being cleaned up idle... not feeding from the mains... lowered throttle position. The timing shows a nice right before the bend initial and total burn mark.
It initially surged with the 65 jets, so immediately I went to 68's. Going to jet up depending on the plugs and feel... then he has a wide band he wants to get working..so that can aid his final jetting
It got dark... so that's why we stopped with the tuning, for now. Going to drive it a little now and check plugs, check milage etc .
it pulls much harder, acceleration is smooth...and it has balls up top now it's not starving for fuel.
I like newbombs guesstimate of timing because that about as high as you would want it while still maintaining an advance curve. 8 to 10 advance is nice. His is all in by 2800 fwiw.
I normally will spend most of an afternoon test n tune with jetting and playing with pump shot.. but I got there a little later in the afternoon. It'll probably pick up 5 mpg immediately but expect it to get closer to 15 mpg. The higher initial means less fuel/pedal to get moving aka more power, less stink being cleaned up idle... not feeding from the mains... lowered throttle position. The timing shows a nice right before the bend initial and total burn mark.
It initially surged with the 65 jets, so immediately I went to 68's. Going to jet up depending on the plugs and feel... then he has a wide band he wants to get working..so that can aid his final jetting
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