carb tuning issues HELP PLEASE
05-29-2013, 10:32 AM
#1
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carb tuning issues HELP PLEASE Ok im about ready to push this piece of **** into the garage and burn the garage down.
HOLLEY 700? DP
5.3 WITH VIC JR LG 5GX1 cam
Front
jets 67
50cc pump
Yellow cam
#37 squirter
Rear
Jets 73
30cc pump
Brown cam #2 position
#47 squirter with different screw
Timing 15°start straight ramp to 36°@2600rpm
No vacume advance
Between 2-3000 rpm I have a dead spot (lean wideband installed)
Ive gone up and down with cams and squirters
When I dissconnect the linkage (front and back) and rev seperate everything is good. Connect them togther in neutral and all is well a/f 12.5-13.
As soon as im under load on dry pavement or cruising in second it goes lean untill the carb catches up or I let off the throttle a little and mash it again.
Please help!!
HOLLEY 700? DP
5.3 WITH VIC JR LG 5GX1 cam
Front
jets 67
50cc pump
Yellow cam
#37 squirter
Rear
Jets 73
30cc pump
Brown cam #2 position
#47 squirter with different screw
Timing 15°start straight ramp to 36°@2600rpm
No vacume advance
Between 2-3000 rpm I have a dead spot (lean wideband installed)
Ive gone up and down with cams and squirters
When I dissconnect the linkage (front and back) and rev seperate everything is good. Connect them togther in neutral and all is well a/f 12.5-13.
As soon as im under load on dry pavement or cruising in second it goes lean untill the carb catches up or I let off the throttle a little and mash it again.
Please help!!
05-29-2013, 10:39 AM
#2
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I've got the same issue now too. I changed my idle feed restrictors to smaller and opened up my 4 corner adjusters alittle and it helped alittle but didn't fix it. I think it's just goin dead lean between the idle circuit and main circuit. My next thing will be to put a different power valve in it so it opens earlier. Any thoughts on this?
05-29-2013, 10:47 AM
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Get the power valve eliminator and jump it up a few jet sizes, start at 2 sizes larger and see what happens. Do you still have vacuum when you let off ? hook up a vacuum gauge to see where you stand first.
05-29-2013, 11:23 AM
#4
That is your transition circuits. You tune those by adjusting the idle feed restictors and idle air bleeds.
What power valve do you have? What is your AFR and MAP pressure when cruising (but not accelerating) at say 2000 RPM? Is it stable or fluctuating around a bit? Can you tell if the power valve is opening at the correct vacuum? Does your wideband record?
My first guess is you need to reduce the idle air bleeds a step or two. If yours aren't replaceable and you aren't quite ready to drill out the press in restrictions and tap the carb for set screws, then you can try bending a narrow piece of wire in a T shape and sticking those into the bleed holes to reduce their size that way. I've done this with IFR but never an airbleed, not sure how you secure them in an airbleed.
Out of the box my idle air bleeds on the primary side were the size of a #49 drill bit (0.0725"). I reduced them to the size of a #52 drill bit (0.0625"). So you need a very small diameter wire, like off a stainless steel brush or just a strand of copper wire. Not to insult you but make sure you do both sides the same way.
Going down two sizes on the idle air bleeds made all the difference in how my car runs. If you get the bleeds and IFR right you might be able to ditch the 50 cc accel pump like I did.
Before you do anything make sure all your gaskets are good, no vac leaks, base plate gasket is good, float level and fuel pressure are right, no gunk in the carb or blocking any internal passages.
What power valve do you have? What is your AFR and MAP pressure when cruising (but not accelerating) at say 2000 RPM? Is it stable or fluctuating around a bit? Can you tell if the power valve is opening at the correct vacuum? Does your wideband record?
My first guess is you need to reduce the idle air bleeds a step or two. If yours aren't replaceable and you aren't quite ready to drill out the press in restrictions and tap the carb for set screws, then you can try bending a narrow piece of wire in a T shape and sticking those into the bleed holes to reduce their size that way. I've done this with IFR but never an airbleed, not sure how you secure them in an airbleed.
Out of the box my idle air bleeds on the primary side were the size of a #49 drill bit (0.0725"). I reduced them to the size of a #52 drill bit (0.0625"). So you need a very small diameter wire, like off a stainless steel brush or just a strand of copper wire. Not to insult you but make sure you do both sides the same way.
Going down two sizes on the idle air bleeds made all the difference in how my car runs. If you get the bleeds and IFR right you might be able to ditch the 50 cc accel pump like I did.
Before you do anything make sure all your gaskets are good, no vac leaks, base plate gasket is good, float level and fuel pressure are right, no gunk in the carb or blocking any internal passages.
