- Thread starter
- #21
So you don’t think that is an issue for me at the moment? You were correct on the fast idle screw holding the plates open initially. I have since corrected
Weber 38 DGAS needle valve size
- Thread starter MTCO60
- Start date
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On a synchronous carb, the primary and secondary butterflies don't start off closed. Air needs to pass somehow at idle. If you can stall the engine by closing the idle mix screws, or the idle speed screw, you have achieved your baseline.
A bigger problem is using too small or too big an idle jet, and compensating for that by getting the idle mix screws dialed-in outside of Weber spec. The reason why is because you will create a lean or rich spot when you start throttle. It would only be evident by burning out valves, or wasting gas, or if you are actually measuring your exhaust.
A bigger problem is using too small or too big an idle jet, and compensating for that by getting the idle mix screws dialed-in outside of Weber spec. The reason why is because you will create a lean or rich spot when you start throttle. It would only be evident by burning out valves, or wasting gas, or if you are actually measuring your exhaust.
- Thread starter
- #23
Okay that makes sense on the baseline. In what scenario is the progression port covered then? I’m reading through a Haynes carb book that has been helpful. Still learning though
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@ 10:45
I don't know about all carbs, but my DGEV 32/36 has no visual on the progression holes, at minimal or maximum idle speed screw settings. Because a carb works on the Venturi principle, it really depends on where the air is flowing to get the negative pressure, not that there is necessarily more negative pressure on the manifold side of the throttle butterfly.
This is a bad photo, but the bottom plate is the primary throttle bore, and there are no progression holes exposed. It is a brand new carb, and there is no wear on the throttle shaft, or throttle bore. Being in spec means that there is a little hole that is right in line with the thickness of the butterfly (but, I can't see it here), and it would contribute fuel/air mix even if the mix screw is closed completely (even though it isn't enough to keep even my 2.4L Z24 motor at idle. The challenge is getting enough air thru these carbs while observing their specification for idle settings - jets can be changed, a hole can be made in the throttle butterfly. The goal is to have a correct air fuel mix, at high altitude, across the full range of throttle.
I get a big kick out of these things, because bit of carb skill, and knowledge, is worth a small fortune in equipment for fuel injection.
I don't know about all carbs, but my DGEV 32/36 has no visual on the progression holes, at minimal or maximum idle speed screw settings. Because a carb works on the Venturi principle, it really depends on where the air is flowing to get the negative pressure, not that there is necessarily more negative pressure on the manifold side of the throttle butterfly.
This is a bad photo, but the bottom plate is the primary throttle bore, and there are no progression holes exposed. It is a brand new carb, and there is no wear on the throttle shaft, or throttle bore. Being in spec means that there is a little hole that is right in line with the thickness of the butterfly (but, I can't see it here), and it would contribute fuel/air mix even if the mix screw is closed completely (even though it isn't enough to keep even my 2.4L Z24 motor at idle. The challenge is getting enough air thru these carbs while observing their specification for idle settings - jets can be changed, a hole can be made in the throttle butterfly. The goal is to have a correct air fuel mix, at high altitude, across the full range of throttle.
I get a big kick out of these things, because bit of carb skill, and knowledge, is worth a small fortune in equipment for fuel injection.
- Thread starter
- #25
Great video. Thanks for the info. I’ll update most likely in a few days
- Thread starter
- #26
Alright so check this out. My manifold is cracked and PO changed the stock setup to fluid heat riser on the manifold. Could I be pulling coolant into the motor through the crack? I am getting white smoke out the exhaust. This is in addition to multiple vac leaks that I found.
trying to decide if I purchase a new manifold or take it to a welder.
trying to decide if I purchase a new manifold or take it to a welder.
Use the fluid heat riser as a block-off plate. Cap the water lines with pipe plugs, and use RTV to form a seal under the manifold. Every 2F intake manifold has that crack, even the one that came with my rig that was welded - the crack runs thru the weld.
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The original intake as I found it. I wish I had that aluminum plate for the water heater, but I'll fabricate one instead.
- Thread starter
- #29
Got it. So since I have headers I don’t need any cooling method for the manifold? I guess if I block off the heat riser correctly, the crack in the manifold won’t make a difference, as long as the crack doesn’t spread to the side wall of the manifold.
The headers keep the intake manifold almost too cold, in the winter. The crack likely won't spread, it is simply the weak spot from when it used to take on the heat from the exhaust. The area surrounding on the manifold is really robust.