Help With My Weber Carb
08-24-2005, 02:09 PM
#1
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Join Date: Mar 2005
Location: L.I NY
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I have the weber 48 DOC carb on my N/A rx-7 right now and I think it may be running to lean. When its idling it runs perfectly fine then when I go to wot (wide open throttle) it hesitates for a second then revs up fine. Right now my accelorater pump jet is a 45. and thats how it came. I was wondering if I should go up to a 50 or down to a 40?
08-25-2005, 09:11 AM
#3
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Location: Boston Ma.
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Thy in "1st Generation Specific" forum.
I dont know much about webbers, but have a spotter check to see if you get a puff of black sooty smoke when you accelerate. That usually means your accel pump jet is too big.
I dont know much about webbers, but have a spotter check to see if you get a puff of black sooty smoke when you accelerate. That usually means your accel pump jet is too big.
08-28-2005, 03:47 AM
#4
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08-30-2005, 07:37 AM
#5
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Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
[quote name='bansheerider29x' date='Aug 24 2005, 07:15 PM']Does anyone know anything about these carbs?
[/quote]
I have been using the 48MM Weber since 1980. I have never done anything to the idle circuit.
For general trouble shooting, I would alter the fuel pressure. This makes a big range of mixtures available without getting into the jets at all. I don't have the numbers on our idle jets, but they are suppling a huge amount of fuel.
Since we premix top oil, we need the extra fuel/oil on a long spool down from speed to keep the housings oiled.
It also puts out huge fire ***** and the crowd loves that. At any rate I didn't want to just let you hang there with few answers. The butterfly plates have 5/16" holes in them so we can idle at 2,200 RPM and still have the edge of the plate in the correct location to pick up all of the transition holes coming off idle.
A high energy ignition system at least on the leading plugs will cover up quite a bit of the rich/lean tuning problems.
If the problem is worse when the outside air temp is lower, then its too lean. The hotter it is the leaner will be the mixture that runs well.
Sorry I don't know more. It just never came up.
Lynn E. Hanover
[snapback]751736[/snapback]
[/quote]
I have been using the 48MM Weber since 1980. I have never done anything to the idle circuit.
For general trouble shooting, I would alter the fuel pressure. This makes a big range of mixtures available without getting into the jets at all. I don't have the numbers on our idle jets, but they are suppling a huge amount of fuel.
Since we premix top oil, we need the extra fuel/oil on a long spool down from speed to keep the housings oiled.
It also puts out huge fire ***** and the crowd loves that. At any rate I didn't want to just let you hang there with few answers. The butterfly plates have 5/16" holes in them so we can idle at 2,200 RPM and still have the edge of the plate in the correct location to pick up all of the transition holes coming off idle.
A high energy ignition system at least on the leading plugs will cover up quite a bit of the rich/lean tuning problems.
If the problem is worse when the outside air temp is lower, then its too lean. The hotter it is the leaner will be the mixture that runs well.
Sorry I don't know more. It just never came up.
Lynn E. Hanover
08-30-2005, 05:48 PM
#6
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Join Date: Jun 2004
Posts: 524
Originally Posted by Lynn E. Hanover' date='Aug 30 2005, 04:37 AM
The butterfly plates have 5/16" holes in them so we can idle at 2,200 RPM and still have the edge of the plate in the correct location to pick up all of the transition holes coming off idle.
Am I reading that right, 5/16" as in .3125"?
08-31-2005, 11:54 PM
#7
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Join Date: Jan 2004
Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
[quote name='heretic' date='Aug 30 2005, 02:48 PM']Am I reading that right, 5/16" as in .3125"?
[/quote]
Yes.
It's a trick so that you can have a large amount of idle fuel flow at high vacuum
(butterflys shut tight) as in braking down from flat out in 5th gear, and when you need power, the whole transition circuit is still available.
Without the hole trick, you would have the butterflys propped open with the idle ajustment screw to hold your 2,200 RPM idle, and none of the transition circuit holes will be in service. They begin just off idle.
So, at idle the oversized idle jets are fine for the amount of air going through the hole in the butterflys.
From high RPM, the holes are not a factor flow wise and the big idle jet supplies extra fuel (and oil) during spooldown.
Carbs have trouble at very high RPM keeping mixtures rich enough. Worse, we chop things off here and there that gets the booster signal to the poor side, in order to improve flow (more power). If you lean way out at the top, and a high energy ignition is keeping it running even though its too lean, it is also going lean on the top oil supply. Bad mojo.
So offering jetting ideas based on what I run is worthless unless you have hacked up some of your parts. My carb is of no value at all for street use.
Lynn E. Hanover
[snapback]753672[/snapback]
[/quote]
Yes.
It's a trick so that you can have a large amount of idle fuel flow at high vacuum
(butterflys shut tight) as in braking down from flat out in 5th gear, and when you need power, the whole transition circuit is still available.
Without the hole trick, you would have the butterflys propped open with the idle ajustment screw to hold your 2,200 RPM idle, and none of the transition circuit holes will be in service. They begin just off idle.
So, at idle the oversized idle jets are fine for the amount of air going through the hole in the butterflys.
From high RPM, the holes are not a factor flow wise and the big idle jet supplies extra fuel (and oil) during spooldown.
Carbs have trouble at very high RPM keeping mixtures rich enough. Worse, we chop things off here and there that gets the booster signal to the poor side, in order to improve flow (more power). If you lean way out at the top, and a high energy ignition is keeping it running even though its too lean, it is also going lean on the top oil supply. Bad mojo.
So offering jetting ideas based on what I run is worthless unless you have hacked up some of your parts. My carb is of no value at all for street use.
Lynn E. Hanover
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