Wonneber, I have always bypassed the tank filter so there is less dilution for the purge. I like to use it full strength. Sorry, but I did not mention it... I agree, the use of a small in-line filter on the hose coming out of the purge can, going to the tandem pump is a necessary. We often see debris coming back to the purge can from the return line. So, 1. You know the purge is doing job and 2. you don't want any debris going back into the injectors.
Another thing we have incorporated, is the use of two cans of purge, separated by a complete engine cool-down between cans. The thought is that giving the engine some time to let the parts cool allows the purge to crack some more crap off of the parts.
As for the vibration, It was never clear to me, and I asked, was the rpm related to the miles per hour to make the vibration, or was it only engine speed. I certainly agree, if it's related to road speed, it's something to do with the axle, wheel or tire.
I have a notion to check the balance of a dual mass flywheel (DMF), as we do occasionally install those against DSG transmissions. It's not something we will ever do for a DMF on manual transmissions. I think the Single Mass Flywheel (SMF) discs with the larger springs and Exedy hub are better and longer lasting when attached to a SMF that is balanced and properly surfaced, than any DMF. Driving style and purpose have a lot to do with it.
The reason we find great flywheel balance important is not that it will make the clutch feel smoother. Most of the times, you can hardly detect the flywheel's out-of-balance (OOB), but it will protect the main bearings from the oscillation created by an OOB flywheel. The deeper studies are considering Noise Vibration Harshness (NVH), and everything from imbalanced pistons/ rods/crank/ crank distortion/ torsion loading, etc., etc. will make cylinder head flow calculations look easy. We aren't trying to balance a V-12 Bentley engine with it's double throw V-90 dual VR6 piston pattern. I have considered that insanity and wonder if they even got close; counterbalances and all.
At an early age, I had a 396 Ford that the machinist told me the flywheel was 3 oz OOB. Considering the size of the flywheel, I said,"That's not much." If looks could kill... The machinist said,"That 3 oz. turns into 3 pounds at 2,000 rpm!" The physics of dynamics. At the 8,000rpm we were wanting to turn, and you can imagine, the OOB weight exponentially compounds to ridiculous numbers; sometimes hundreds of pounds of OOB. When you start down the rabbit hole of balance, things get insane, even calculating ring drag and rod rotation circle.
Fortunately, with the lower engine speed and the simplicity of a 4 cylinder engine we generally work with, balancing can be simplified to some basic roots. Reciprocating mass. Overall balance. No counter-balance weighting to contend with. What we generally contend with is very basic and simple. We always balance our flywheels. We always balance our pistons and rods. And I can tell you.. When it came to piston/ rod weighting as VW did it, they did not care. As Sachs and many others have done flywheels, 1/4oz on a 21lb flywheel is way too much, especially if you expect to run over 5000 rpm.
If you do want to check your flywheel, I can do so. Matter of fact, our balanced flywheels are cheaper than what many price for 'off the shelf', 'untested' components. And if you ever see a flywheel that is cast and has no drill marks, you are looking at one of the very cheap flywheels; not balanced at all.
