WobblyHand may be onto something. Even though you've flushed the system there may still be some contaminants, or misplaced sealant that could be causing a problem. His comment reminded me of a problem I encountered back in the 1970's. While the details are far different the concept is the same.
I had an older (1954) International R190 truck I used for business. After about a year of ownership it developed a problem where it would occasionally die when driving down the road. For all the world it felt like it was running out of gas. However it happened randomly no matter the amount of gas in the tank. I checked all the usual suspects, carb, fuel pump, fuel lined fuel filter, etc. to no avail. Sometimes it would happen several times in a day. Other times it wouldn't happen for months.
The weird thing was that when it died, I could pull over to the side of the road, let it set for a minute or less and it would start right up and continue on its way. After months of frustration, I finally decided to lower the gas tank and see what was going on inside. That's when I found the problem.
When the truck was built the tank fuel pickup/sending unit was installed with the paper part number tag still wired to the down tube. After 20+ years of being exposed to the fuel and air the wire finally rusted through. The paper was free to float wherever it wanted to. From time to time, it would find its way under the pick-up tube and be sucked against the bottom of it. The gas would no longer flow, and the engine would die. As soon as the suction was released by the fuel pump the tag would be released and once again float away. After the tag was removed the problem was solved. I had the truck another 5 years and never again had a problem with it stalling out while driving.
In your case the problem could be a misplaced piece of Teflon tape or pipe sealant, swarf or grit from assembly that's too big or heavy to be expelled when flushing. Another problem could be a damaged or partially blocked needle valve.
As for my Startrite saw it does have a spring at the pivot end of the head, but no counterweight. The spring has multiple mounting points to control the amount of down pressure the head can exert on the down feed dampener cylinder.
Wow, I wouldn't want to be troubleshooting that issue with the truck
With my issue being caused by clogging I can't exclude that possibility, but if it is indeed clogging it must be with something that is pretty evenly dispersed through the liquid and very small (on the order of 300nm). Stuff that small is not just invisible to naked eye. It can't be seen with an optical microscope because it is smaller than the wavelength of light. So one would need an electron microscope to see it...
It is quite possible that all 3 liquids I tried, gear oil, hydraulic oil and diesel ended up with some particulates like this. However, I did not just flush it. Every time I changed the liquid. I disassembled the cylinder and valves. I blowed compressed air through everything. The first two times I did it I also removed the needle from the needle valve, I replaced o-rings in the needle valve. On the second fluid change I polished the needle (first with 1000,then 2000 grit car paint sandpaper, finally with a "mirror shine" paste for aluminium so the needle had a mirror polish after the second fluid change). I then cleaned it very well in lots of petrol, and compressed air hoping not to introduce any of this abrasive grit into the system.
With regard to there being sealant or tape, or any other macroscopic stuff I think it would clog even at higher settings(as the gap is still well under half a thou even at fast settings) and it would happen at random, but it is very predictable. The lower the downfeed setting the sooner it happens. There are certain very low settings like let's say 2 thou per second where you can sit there and see it stop every single time within 30 seconds. This repeatability in my opinion points against any macroscopic stuff that could clog it and towards something that is evenly dispersed throughout.
As for there being microscopic particulates, that is possible, but rather than coming from the liquids (this is quite unlikely) they must have been present in the cylinder and the cleaning hasn't removed it. Perhaps honing grit from the manufacturing process embedded in cylinder walls that falls into the liquid slowly?
Perhaps I'll try disassembling everything again and running it through an ultrasonic cleaner. Then I could perhaps try distilled water as liquid (I can't think of anything cleaner that's easily available).
Looking at another angle of this. Wow, what a difference flood coolant makes on this saw. I set up flood coolant and I tried cutting the same tool steel block again today. I only had an hour of time and in that time it did approximately 60% of the cut.
and I haven't pushed it to the full yet. This is with the 6/10 blade.
That's how far it got in an hour. The motor slowly got to 55C again.
Some chips suggest that perhaps it could be fed even faster.
At this fairly high setting I didn't even had the stoppage issue. So unexpectedly, is flood coolant the solution? This is O1 tool steel BTW.
