Weber mixture screws Options

[dumbjim]

Hi all, I spent yesterday fooling around with my weber idf 40's. by following mrbubbleheads instructions. With my snail, I got all four barrels pulling the same by adjusting the air bleed screws. I then moved on to the mixture screw. The mixture screws have absolutely no effect on how the engine is running. I can back them out or screw them in and there's not change in the idle. Is there something else going on here? In general, after adjusting the bleed screws, the engine is running pretty smooth. Any ideas? Thanks for reading.

[dumbjim]

Thanks for your comment Ansbacher. How am I gonna learn if I don't try and do it myself. If I screw it up, I can always pay an "expert".

[Charles Freeborn]

Thanks for your comment Ansbacher. How am I gonna learn if I don't try and do it myself. If I screw it up, I can always pay an "expert".

Okay, here's an "expert" sequence. Do each of these in sequence or all bets are off.

1. Fully understand the design of a Weber carbeurator. I suggest this book:
https://vwparts.aircooled.net/Weber-Tech-Ma...tech-manual.htm . It is by no means the last word, but it is a good starting point. There are 3 basic circuits in a Weber. Idle, mid and WOT (wide open throttle). Each of them has jets to control the fuel mixture in each stage. They overlap and must be in synch or the system does not work to spec.

2. Confirm top end health (that's rings, valves, etc) with a leak down and compression test. (as said in my previous post ). Much more important than compression is leak down as it can inform you of where ( rings, valves) the problem is.

3. Confirm you don't have vacuum leaks anywhere else such as intake manifolds, carburetor gaskets to manifold gaskets, etc (as said in my previous post )

4. Make sure the carburetors are properly clean and adjusted - jets clean, fuel pump pressure correct, etc .(as said in my previous post ).

5. If the problem (idle mixture still non-op) persists then go back through the previous steps and find the fault.

6. If you still can't find the problem you need to consult someone who has more knowledge than you. If your idle mixture screws have no effect then there is a problem. In a healthy engine /carb set up if you seat the idle mixture screws (all the way in) the engine will not run. Period.

I can't sugar coat it any more than that. If you have tried all of the above steps, I applaud you for trying, but maybe you're lacking sufficient understanding to trouble shoot this issue.