I am not so sure it is a dirt or dust issue as noted previously.
you found dirt in the jets, so there was an issue and may still be one.
Once again it ran reasonably well until it was warmed up - say about twenty minutes into our ride. Pops at cruise speed were few at startup, then minimal. Then it started popping intermittantly at cruise speed, be it 2000 rpm or 3000 rpm. You can feel the engine missing when it pops - it is subtle but there..
You need to check the carbs when it is warmed up - if you are doing it only when cold, then things can change when warm. Personally, I synch them with a warm engine. I drive with a warm engine so that is most important. My car runs a bit rough until warm - then it purrs.
Then the accelerator pumps are probably set right.
Stopped the car and found a carb that was not firing. Put the syncro meter on and found it was flowing slightly less air. Slight adjustment and it was firing. Now with all four carbs balanced perfectly per the meter, took it for another ride.
Same issue. Popping intermittanly at cruise speed and low speed. Yet it idles smoothly with no popping or backfiring, even thought he mixture screws are not calibrated.
Until the carbs are near correctly adjusted - including the mixture screws, none of this matters really. What your engine is telling you is that you don't have it set up - it can be one of a few things here.
can't get the mixture screws adjusted. Most will reach the point where the idle speed drops while turning them in, but usually 2 or 3 carbs (it changes from carb to carb depening on the day of week) won't respond. I can turn in the mixture screw all the way and it makes NO difference in idle speed on those offending carbs. Obviously there is an issue. I have changed the idle jets, from 55 to 60 and back to 55. No siginficant difference.
So not being able to even get the idle mixture screws to respond, trying to fiddle with jets seems premature.
Yes, fiddling with idle jets seems premature here IMO...until you get your carbs closer together in settings (flow and mixture) it is hard to get a handle on what is changing what. You can chase your tail.
Ian, your point regarding balance of the carb as higher speeds is well taken. But how does one check balance at 3000 or 4000 rpm? Sure can't do it with that little flow meter! I guess pulling plugs is about the only way. But then what does one do? Adjust the flow to get it better at higher RPMs? That would then throw it off at idle, and then we get back to not having a cylinder fire at idle.
I would recheck it at the highest flow your sych meter will read - whatever RPM that is.
I am wondering if perhaps it is too rich. When cold that extra fuel is good, but when hot it is not. But we are already down to a 55 idle jet from 60 so . . . . . May be a larger air jet?
Despite the rising frustration level, still plan to pop the tops off the carbs check for sediment and recheck the float levels.
I would not be messing with air jets yet - you need to get the idle circuit under control - that is where you will do most of your driving. Being on the too rich side of the equation can produce some of the results you are seeing. Do you have a exhaust gas analyzer available? If not, I have one I can send you or I can show you one that costs less than about $150 that I used to determine I was way too rich on one weber installation.
Oh and one other issue. For fifteen minutes after shut down one of the forward carbs spills gas into the throat of the carb. You can see the puddle of gas just setting on the throttle plate.
Have you got the proper fuel pressure to these carbs - 2-3psi?
I am just about ready to buy an Edelbrock intake manifold and a Holley carb. But Ryan does not want to give up yet . . .
Don't do it - yet! Honestly, and please don't take this personally (I am trying to help)but fomr what I am reading, I think it could be your process. I am just trying to help, but, having gone through this during my learning curve with these carbs - and then coming out the other end - the process is critical (I think). See my post above.
Regards,
Mike