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Fuel mixture problem

  
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Fuel mixture problem

 
Mongoose78 Mongoose78
New User | Posts: 16 | Joined: 06/12
Posted: 10/28/13
08:40 PM

I have got a fuel mixture problem
This is 383 forged flat top pistons hydraulic roller pro comp cylinder heads with 220 intake runners 64cc chambers
Pro comp intake port matched to the heads running 34 degrees total timing 750 dp proform carb
The problem is 1and 2 cylinders are a little lean 3 5 4 6 are about right 7 and 8 are to rich 8 being the worst
Ran compression running 205 to 210 on all cylinders don't remember ever seeing such a imbalance
Anybody ever ran in to this thanks for thr reply  

wayne712222 wayne712222
User | Posts: 195 | Joined: 10/13
Posted: 10/28/13
10:13 PM

that should have idle mixture screws on both metering blocks..


take the metering blocks off...

check the emulsion jet sizing. that nobody changed it..

check the idle transition feed restrictions ..

check the air bleeds inside the main body.. that nobody messed with them...

call proform and find out what the baseline jetting for those was on that carb...


remember... the idle feed restrictions effect fuel mixtures

sometimes cut away views help...

Metering Block Clear Zpsb13473b5

Holley Main Circuits Zps75c9f9b1

Holley Off Idle Zps85779e58


Holley Atidle Zpsbdbaea76


have you hooked up power brakes to the back of the carb.. and a PCV to the front???

do you have a tachometer???  or a digital tachometer either in a digital volt meter or timing light.   pinch off the PCV hose at idle.. the RPMS should drop between 50 and 70 RPMs if the PCV is the proper calibration size for the engine...

if it drops more..  then the PCV has too much flow and a smaller calibration is needed.. if it drops less that 50.. then you need more...

another thing.. does the carb you have.. use a idle speed /air bypass screw thats under the air cleaner stud???  

Mongoose78 Mongoose78
New User | Posts: 16 | Joined: 06/12
Posted: 10/29/13
01:36 PM

Hey thanks for the info you gave me a lot to look at  

Mongoose78 Mongoose78
New User | Posts: 16 | Joined: 06/12
Posted: 10/29/13
01:49 PM

Well this might be it then PVC and power brake teed off the only port I have on the rear of carb
This is on a vette so I can't run a spacer plate to add another port any suggestion would be welcome  

wayne712222 wayne712222
User | Posts: 195 | Joined: 10/13
Posted: 10/30/13
04:20 AM

how about some history on the carb????


new out of the box...

used...

loaned out to somebody who returned it??? perhaps they modified it.. i have seen that done too many times..

when you adjusted the idle mixture.. and the idle speed..

did you adjust all 4 idle mixture screws...

did you adjust the secondary throttle plate opening...

does YOUR carb have the center idle air bypass adjustment under the air cleaner stud???  that if closed would require you to play with the throttle openings...

the reason to chart all the jet and bleed sizes is to see if its set up WRONG..

is the carb dirty??? been run without an air cleaner... might have pulled dust into the air bleeds ... or worse... fiberglass from the underhood insulation..  i had 71 camaro.. acted really strange.. when i ran the engine without the air cleaner housing and lid.. it would stall when i jumped on it..  it pulled the insulation right down and suffocated the carb...

the air bleeds actually have significant suction on them and will drag dirt or debris into them... this  could cause weird mixture problems..

and i am taking that you don't have any vacuum leaks from the intake not fitting properly against the heads... .. need to examine the impressions left in the intake gaskets..

i am going to step back and wait to see what the other forum members sayd..  

Dave632 Dave632
Addict | Posts: 2217 | Joined: 07/08
Posted: 10/30/13
01:09 PM

Wayne I see you are aware of the center idle air bypass under the air cleaner stud. I think it is the BG Demon or King Demon carbs that have that excellent feature.
Few I have talked to are aware of that adjustment as it is pretty well hidden.  
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wayne712222 wayne712222
User | Posts: 195 | Joined: 10/13
Posted: 10/30/13
06:10 PM

Icon QuoteDave632:
Wayne I see you are aware of the center idle air bypass under the air cleaner stud. I think it is the BG Demon or King Demon carbs that have that excellent feature.
Few I have talked to are aware of that adjustment as it is pretty well hidden.


oh yea...

i know about that.. take a look at some of the images above.. you will see that its included in the images of a 4150EG governor carb from an international application in the mid 60s thru mid 70's as thats where the images came from...  

Dave632 Dave632
Addict | Posts: 2217 | Joined: 07/08
Posted: 10/30/13
07:38 PM

I was not aware that Holley used that feature on any of their carbs.  
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