weber 48 IDA, idle & progression theory ?
03-22-10, 10:40 AM
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weber 48 IDA, idle & progression theory ?
So after many attempts at setting this carb right i am starting to realize that most of the issues that I cannot overcome seem to be from the factory progression holes location. I have tried various etubes, and even custom drilled ones, several varieties of idle air bleed/fuel jet sizes with various results but nothing that is even close to right on acceleration with out cruising on basically liquid fuel<10 afr. from what i have read in various weber books, and what I see hapening in my carb is I cannot get the progression circuit right with out a 1500rpm idle. this is a problem for me because at that rpm I feel I am consuming much unneccesary fuel in traffic, and the car sounds like it should be on the track not the street.
I can set it to idle smooth at like 750/800 rpm, but this puts the throttle plates too low in the bore("offset upstream, resulting in a positive head." quoted from -weber carburettors tunning tips and techniques p.49), this ends up resulting in a huge flat spot just off idle and making off the line acceleration very rough. Through out today i am going to do some further testing, starting with the throttle plates set to the appropriate level acording to the progression holes (1500 rpm idle), once I am sure that this cures the stumble/ or does nothing for it, I will be back to look into throttle plate modification(possibly closing the tab a little to let the throttle plates sit where i want the idle, and in appropriate relation to the lower progression hole).
I have tuned the low end stumble out with a few different settings, but it always causes other issues through out the rpm range, usually way too rich every where else.
anyone else been down this path with there IDA, any fixes other than really rich idle jets, or modifing throttle plates?
I can set it to idle smooth at like 750/800 rpm, but this puts the throttle plates too low in the bore("offset upstream, resulting in a positive head." quoted from -weber carburettors tunning tips and techniques p.49), this ends up resulting in a huge flat spot just off idle and making off the line acceleration very rough. Through out today i am going to do some further testing, starting with the throttle plates set to the appropriate level acording to the progression holes (1500 rpm idle), once I am sure that this cures the stumble/ or does nothing for it, I will be back to look into throttle plate modification(possibly closing the tab a little to let the throttle plates sit where i want the idle, and in appropriate relation to the lower progression hole).
I have tuned the low end stumble out with a few different settings, but it always causes other issues through out the rpm range, usually way too rich every where else.
anyone else been down this path with there IDA, any fixes other than really rich idle jets, or modifing throttle plates?
03-22-10, 11:41 AM
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Hopefully this thread will help: https://www.rx7club.com/1st-generation-specific-1979-1985-18/45-dcoe-info-references-882842/
03-22-10, 01:19 PM
#3
Get the third progression holes drilled. And....the idle fuel jet and idle jet holder are the only two jets that determine progression mixture..
I sent my carb to JayCee and he sent it back modified and ready to go. Increased the float bowl and ground down the fuel inlet where the little filter goes. Cost $50 + shipping.
http://www.jaycee-ent.com/
I sent my carb to JayCee and he sent it back modified and ready to go. Increased the float bowl and ground down the fuel inlet where the little filter goes. Cost $50 + shipping.
http://www.jaycee-ent.com/
03-23-10, 11:02 AM
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alienteabagger-- good thread, lots of info/and good pics of operation(DCOE), also many good links posted through out
DriveFast7-- I did third progression hole a couple of years ago and it makes a world of difference, I did not inlarge the fuel bowl, but do run a 3.3 glass ball inlet, and have modified the inlet where the screen goes. I have also changed from the spring retainers for the aux venturies to set screws to get rid of rattle/loose fitting, and polished choke tubes. I checked out JayCee and they seem to be the place to go, but i am already moded, but he does have some nice parts.
Hyper4mance2k-- I have a bypass style regulator, with 3/8" fuel line run from in the tank to carb and back, so I should have lots of volume at low pressure, by check valve in the carb do you mean the acc pump bypass valve just under the float, I have a 0 right now but have not opened the carb recently to see if it is checking or bypassing. You have given us all many very good tips, but I am just getting a bit picky about things, I have followed your thread, and even posted in it when i started playing with e tubes myself, but what i have found is that this carb will run one of 2 ways, very responsive and full of power, but stinkling rich at a cruise, or poor throttle response no power down low, good mid/top end power, and a cruise at a reasonable afr.
In regards to my previous post I have noticed a conciderable increase in throttle response when setting the throttle plate in relation to the progression circuit, not idle speed, no matter what the jetting this seems to improve throttle respnse.
does this setting typically get overlooked when running the ida on our engines, is there a reason for not having this correct or is it just not a concern?
DriveFast7-- I did third progression hole a couple of years ago and it makes a world of difference, I did not inlarge the fuel bowl, but do run a 3.3 glass ball inlet, and have modified the inlet where the screen goes. I have also changed from the spring retainers for the aux venturies to set screws to get rid of rattle/loose fitting, and polished choke tubes. I checked out JayCee and they seem to be the place to go, but i am already moded, but he does have some nice parts.
Hyper4mance2k-- I have a bypass style regulator, with 3/8" fuel line run from in the tank to carb and back, so I should have lots of volume at low pressure, by check valve in the carb do you mean the acc pump bypass valve just under the float, I have a 0 right now but have not opened the carb recently to see if it is checking or bypassing. You have given us all many very good tips, but I am just getting a bit picky about things, I have followed your thread, and even posted in it when i started playing with e tubes myself, but what i have found is that this carb will run one of 2 ways, very responsive and full of power, but stinkling rich at a cruise, or poor throttle response no power down low, good mid/top end power, and a cruise at a reasonable afr.
In regards to my previous post I have noticed a conciderable increase in throttle response when setting the throttle plate in relation to the progression circuit, not idle speed, no matter what the jetting this seems to improve throttle respnse.
does this setting typically get overlooked when running the ida on our engines, is there a reason for not having this correct or is it just not a concern?
03-23-10, 12:16 PM
#6
You definately don't want to idle on the progression circuit if that's what you mean. What is your jetting and choke sizes? Also remove the accelerator pump spring and make sure it's clean down there. Crud accumulates and reduces the accelerator pump squirt. Take the lid off the carb and pump the throttle. The bypass valve in the bottom of the float bowl should seal instantly and not leak. I had one crack and it leaked horribly - air bubbles and all. You're using the 0 which is correct.
What is your fuel pressure and where is the gauge located in the fuel line?
What is your fuel pressure and where is the gauge located in the fuel line?
03-23-10, 07:04 PM
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sorry I have not been as clear as I could have been the carb runs great, I want to make it better first i want to get rid of the overly rich idle fuel jet used to hide this issue below,
my chokes are 38.5mm polished,fuel psi 6, pump bypass has no leaks checked today, I run an AEM wdeband o2, and jet according to it, no stuff in the pump chamber, i did a full rebuild not even 2 years ago, all is clean, and work well but could be better I feel.
I know that you dont idle on the progression curcuit, I have had this carb for a long time, and have read more on it than I can begin to explain. I have had plenty of good tunes on it but I am getting picky.
Now i would like to ask all who run webers has the calibration in the picture below ever been concidered as the cause for off the line stumble,
what I am getting at is that the throttle plates in my carb when adjusted properly according to at least 2 weber specific books causes my car to idle at 1600 rpm,
when the idle is adjusted down to a reasonable level, the throttle plates do not sit properly in regards to the lowest progression hole, I have issue B in the picture.
my chokes are 38.5mm polished,fuel psi 6, pump bypass has no leaks checked today, I run an AEM wdeband o2, and jet according to it, no stuff in the pump chamber, i did a full rebuild not even 2 years ago, all is clean, and work well but could be better I feel.
I know that you dont idle on the progression curcuit, I have had this carb for a long time, and have read more on it than I can begin to explain. I have had plenty of good tunes on it but I am getting picky.
Now i would like to ask all who run webers has the calibration in the picture below ever been concidered as the cause for off the line stumble,
what I am getting at is that the throttle plates in my carb when adjusted properly according to at least 2 weber specific books causes my car to idle at 1600 rpm,
when the idle is adjusted down to a reasonable level, the throttle plates do not sit properly in regards to the lowest progression hole, I have issue B in the picture.
