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QFT 735 lean surging

If there's a leak under the manifold the pcv won't suck it all out, you'll still get it in the chambers. You'll have to at least pull the carb, but with some imagination you can rig up a way to see into the chambers, or what I've done is (securely) tape a cotton ball or piece of a rag to a small solid wire or coat hanger, and feed it down the intake runners...it will soak up some oil if there's any in there you just have to be certain you got the swab all the way in to the valve. Or just yank the intake at that point, then you have to deal with new gasket/sealing..

I just thougt a bit about the issue mentioned by you guys and I totally agree with you. In theory, I could remove the PCV valve from the valve cover and insert a propane burner nozzle. When one of the intake runners does not seal right, it should suck the propane right in and I should be able to see an rpm change. What do you guys think about that test method?
 
I asked because it turned out I had a leak that drew from below the valley pan. The plugs had an oily appearance. If you don't have that, I think you can rule out this possibility. You still might have something on the manifold side of the valley pan gasket, but let's assume you don't for now since you think these symptoms might have been there all along.

I do not think a leak would necessarily cause the idle to cycle back and forth. For this I would look to the ignition. Someone else may have a different idea.

I also asked about the MSD and coil because I had an issue with the coil (and possibly MSD) that caused more of a rhythmic idling quality (up and down) after the engine heated up. That was solved with a new coil and I also swapped the MSD at the time. The problem went away at that point.

I asked about the ignition cutting out because I had a situation where I had an intermittent miss that was related to power making it to the MSD. This was also seen in the tach. I saw this in mild acceleration and it only happened when hot. It was the connection to the fusible link that was loose.

You may know more than me and as you can see I have made lots of problems for myself, but generally have solved them. I would be careful about spraying brake cleaner into the intake because some brake cleaners combust to form bad products. I spent a lot of time trying to figure out things with an A/F gauge and it will help. I suspect the bouncing around is not directly linked to a vacuum leak because the leak should not necessarily bounce around, but be a constant addition of fuel free air. The idle will run well rich for a wile and then foul plugs so that is not the solution.

I would check out the coil using an ohm meter (I had to look online to do it). If it comes out at spec, then I think you are OK, but it is not out of the realm of possibility that the coil could do something different when hot. I would also check all connections between the key and the coil to rule out something that was intermittently cutting out, but I think you would see that in the tach. Assuming it is not the MSD (if you are flush, you could buy (or borrow) another to try, but for now assume it is OK).

It sounds like your main metering circuit (jets) are good so I would leave those. I think you have done this, but I would disconnect the vacuum advance and set the distributor to the idle setting that gave the highest RPM. I would then curve the distributor to make sure the max advance was not too high. Then I would use a vacuum gauge to set the idle mixture screws for the carburetor (I think you have done this already too). Then I would make the idle mixture screw setting a little rich (maybe 1/4 turn more open). After that I would take some Air fuel readings. They should be pretty stable at a any given RPM. If you are making traces (logging), you will see some oscillations. I wouldn't worry too much about those. They will go up and down by a lot if you are on or off the gas, but if the pedal is steady, I would assume they should sit +/- 0.5 to 1 unit of A/F. I would take A/F readings at 1500, 2000, 2500 and 3000 with a very steady pedal and see where it sits. If you are at 15 -16, you might be too lean and this might give the surging.

I have written way too much to digest and apologize.
 
Please excuse my very late response! I finally found the problem!!!
I performed some more testing as per your suggestion. When I wanted to remove the ignition cable boots, I ripped one apart. I thougt I was too stupid to do that, but when I took a closer look at the cable, I found a burnt spot right where it ripped apart. I then checked all cables and found some burnt spots hidden underneath the spark plug heat boots I specifically installed to avoid that problem. Apparently during cam break-in I melted some of my ignition cables despite having heat shields installed, which caused arcs on the headers :BangHead:
So in the end you were totally right suspecting the ignition! Thank you all so much for your help!!!
 
I could remove the PCV valve from the valve cover and insert a propane burner nozzle
I know you found the problem, but propane in the valve cover could get sucked into various parts of the motor from pumping action.
I have had people suggest using propane gas through a focused tip to check for vacuum leaks, and this guy has been a gearhead for decades
 
I am sceptical about the propane in the valve cover, too. I cannot imagine though, how I should get under the valley pan with anything. The suspected leak of the intake gasket mentioned by beanhead, could be underneath the valley pan and therefore inside the engine.
 
could be underneath the valley pan and therefore inside the engine
Did you silicone all the way around your intake ports? Someone I know who ran a 440 for 30 years and now runs a 426 Hemi told me to ALWAYS run a bead all the way around every intake port where it meets the metal head+valley pan gasket combo.
 
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