My question relates to how fuel gets to the idle circuit.
All the diagrams I've seen suggest a straight channel up from the fuel bowl to the bottom of the idle jets but on these the bottom of the drilling for the idle jets is blanked off. I've checked thoroughly with a scope and it's not a blockage.
If I shine a light into the main jet drillings I can see that this light spills into the idle jet drillings somewhere near the bottom so it seems that the idle jets are actually fed at the bottom via the main jet channels.
Can anyone shed any light on this? I just want to make sure all is as it should be before I put them back. In particular as the main jets are much longer does fuel have to go via them somehow to the idle jets???
I rebuilt them because I had an idle adjustment problem on one cylinder and having checked absolutely everything else I suspected a possible lack of fuel delivery to that idle jet.
My question relates to how fuel gets to the idle circuit.
All the diagrams I've seen suggest a straight channel up from the fuel bowl to the bottom of the idle jets but on these the bottom of the drilling for the idle jets is blanked off. I've checked thoroughly with a scope and it's not a blockage.
If I shine a light into the main jet drillings I can see that this light spills into the idle jet drillings somewhere near the bottom so it seems that the idle jets are actually fed at the bottom via the main jet channels.
Hi and thanks - I had read that thread and many others on here but the channels under the carb that get blocked don't feed the idle circuit at all; they are just for the starter and pump circuits. I've blown those through and all clear.
What I'm looking for is a diagram or description of the bottoms of the main and idle jet drillings (where they screw in) to see how fuel gets to the bottom of the idle jet. It doesn't come straight up from below on these variants.
Martin
OK so I just injected some fuel into the idle jet drillings and can confirm that it trickles out into the corresponding main jet drilling about half way down. So on these the idle circuit is fed from the main well via the main jet and NOT from the float chamber directly.
This is interesting because in the Weber tuning manual both possibilities are described but it specifically says that for DCOE it is drawn from the float chamber. I guess they changed that for the Emissions ones??? Or is it the case on all DCOE's but the diagrams are over-simplified?
There has been much discussion about "emissions" Webers in other threads. My definition of them is that the idle circuit is fed from the well and not the float chamber. These Webers require type 2 idle jets that have larger air orifices and they also require F34 or F41 emulsion tubes. They have some other features that are different from early Italian Webers but they may be shared with late type Webers that have the idle circuit fed from the bowl.
Ahhhhhhh.... yes, thanks Ed yes I do remember reading that, I think it was late and I'm rapidly absorbing all the terms - well, bowl, float chamber and which means which. A picture says a thousand words and here's my interpretation of what's going on [adapted picture I found online].
Please correct me if I'm wrong. In particular I'm guessing how far down the crossover actually is.
Doesn't explain my lack of fuel to one cylinder on idle as I reckon those were clear but they're going back on shortly, fingers crossed.
... I rebuilt them because I had an idle adjustment problem on one cylinder and having checked absolutely everything else I suspected a possible lack of fuel delivery to that idle jet...
Just a thought but could the lack of fuel delivery actually be a vacuum leak that skews your Air/Fuel ratio lean? My experience is that a vacuum leak affects idle and throttle tip in and can be at one or multiple cylinders.
My other thought would be a bent throttle plate or the throttle plate rod. This would have the same affect as a vacuum leak.
Pretty sure I ruled those out as the carbtune was showing exactly the same vacuum across all 4 cylinders. I'd have thought a vacuum leak would have increased revs as I opened the mixture screw letting more mixture through (enough air from the leak to burn it). Instead on one cylinder I could get just enough from the mixture screw to get a leanish idle but no more. Even opened right out it wouldn't run rich on that cylinder.
Anyway all fun and games.
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