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Unread 02-10-2013, 01:32 AM   #1
befumo
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Weber 38 progression circuit / drivability issue

I have a new Weber i bought through Redline, everything seems to be fine with the exception of driving away from idle or really at any speed in the RPM range of 1000-1500. At 1500 the engine immediately stops with the 'bogging' or 'sputtering' and pulls, smoothly to any speed i want.

According to my research this is a problem with the progression circuit. I took the carb off and took a look at the holes drilled into the wall of the carb and to see where the throttle plates were and they are sitting to high according to the book i have.

Anyone else experienced this problem? The fix according to the book is to drill holes in the throttles plates to counter the rich condition. Im skeptical on drilling a hole in the new carb and would almost rather return it and get another.

Both throttle plates and progression circuit holes with the throttle completely untouched.




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Unread 02-10-2013, 07:15 AM   #2
blown50
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If that is where ur blades are sitting at idle, then you need to readjust your idle settings! As the idle setting is the most critical on a weber. And no don't drill any holes unless you have a narrow lobe separation cam! AKA BIG CAM! And I'm sure you don't . Try the idle adjustment, it should be in the papers with the carb, did you recheck your timing? Fuel pressure? Go back through the install one more time, I bet you will find what is wrong. Webers are good carburetors, but I'm sure there can be bad ones, but do the recheck first! Also check the PVC and be sure it's working If its not working or not hooked up this can cause you to have to idle the carb too high. But read and re read the idle setting adjustment, it tells you what to do step by step. If it doesn't idle with the plates where they should be, then it may be time to send it back
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Unread 02-10-2013, 11:38 AM   #3
befumo
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Timing is at 12*
Fuel pressure wants to sit at 1-2 psi with Holley FPR
PVC i have with a stand alone aftermarket breather (should i route it to the air cleaner?) and then i have it going to the charcoal cannister / base of carb.

Also its not just that its idling high, it sputters or bogs when coming off the highway when you put it in gear or anywhere from 1-1.5k rpm.


I did not get the idle down specifically and i will definitely re-check it. But i am a little annoyed that the $400 carb has the progression holes open at idle. That's what i am probably going to do is just return it and get a new one.
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Unread 02-10-2013, 01:30 PM   #4
blown50
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Quote:
Originally Posted by befumo
Timing is at 12*
Fuel pressure wants to sit at 1-2 psi with Holley FPR
PVC i have with a stand alone aftermarket breather (should i route it to the air cleaner?) and then i have it going to the charcoal cannister / base of carb.

Also its not just that its idling high, it sputters or bogs when coming off the highway when you put it in gear or anywhere from 1-1.5k rpm.

I did not get the idle down specifically and i will definitely re-check it. But i am a little annoyed that the $400 carb has the progression holes open at idle. That's what i am probably going to do is just return it and get a new one.
On the Pcv I'm talking about the valve, the one that sucks from one end of the valve cover. The one you are referring to is the breather side. The Pcv valve regulates a metered amount of air into the intake, therefore you don't have to open the blades as wide to make it idle, think of it as a metered intake leak it will need to work for the carb to function properly
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Unread 02-10-2013, 04:06 PM   #5
befumo
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Oh no I understand what a PVC does. It was working before. I am going to send this carb back for another 38. Other than this it has definitely met expectations.
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Unread 02-11-2013, 02:59 PM   #6
uptillnow
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Quote:
Originally Posted by blown50 View Post
If that is where ur blades are sitting at idle, then you need to readjust your idle settings! As the idle setting is the most critical on a weber. And no don't drill any holes unless you have a narrow lobe separation cam! AKA BIG CAM! And I'm sure you don't . Try the idle adjustment, it should be in the papers with the carb, did you recheck your timing? Fuel pressure? Go back through the install one more time, I bet you will find what is wrong. Webers are good carburetors, but I'm sure there can be bad ones, but do the recheck first! Also check the PVC and be sure it's working If its not working or not hooked up this can cause you to have to idle the carb too high. But read and re read the idle setting adjustment, it tells you what to do step by step. If it doesn't idle with the plates where they should be, then it may be time to send it back
I "think" I see the throttle plate(s) above the progression holes.
The idle setting is most critical on a Weber.
Get your engine running and slow the idle down as slow as you can get it.
THEN, reset the timing, this should stablize or even increase the idle speed.
If you have a vacuum guage, put it on the vacuum advance source on the carburetor. This is to the right of the choke and down on the mounting flange.
At idle, which is absolutley no more than 1/2 turn in on the idle speed screw, you will have ZERO vacuum reading from the ported vacuum source.
THEN, you should find the "Lean Best Idle" or the "Sweer Spot" where the engine idles the best.
Re-Cap:
No more than 1/2 turn in on the Speed Screw,
ZERO vacuum at the ported vacuum source,
Re-set the timing,
Find "Lean Best Idle".
Some use a .50mm idle jets and some use .55mm idle jets.
Float height of 18mm from gasket to the top of the float. (do not depress the ball and spring inside the needle valve)
Let us know where your settings are.
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Unread 02-11-2013, 03:20 PM   #7
uptillnow
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I just noticed you are in Delaware. I guess it's pretty cold there now.
Sometimes the choke linkage does not "kick completly off" therefore keeping those throttle plates open exposing the enrichening holes when returning to idle, therefore runs bad.
Sometimes reducing some of the tension on the choke will allow it to come off a little sooner, elininating that in-between choke on, choke off action.
Just another thought for you.
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