I fired it up waited about 15 seconds, then took the chole down to about 30% on to test for vacuum leaks.
I got an RPM increase when I put the propane nozzle at the carb inlet, but nowhere else. I pulled and blocked the two vacuum lines with no effect. Based on that, I am reasonably confident I don't have a vacuum leak.
At this point (2 min later?) I finished taking the choke off and left it all the way off for the rest of the tests.
I let it idle for a couple minutes here while I tinkered with the charging system and warm up a bit more. At this point the heat riser started to open.
I revved it up as high as it would go before starting to stumble (maybe 1500RPM) and slapped my hand on it. When I tried revving it again, it went higher before stumbling so I tried that 2 more times before it stopped making a difference.
It pulled hard enough that the air cleaner stud hole left decent marks on my hand. Of potential note: my hand was wet with fuel after each attempt.
Now if I ease into the throttle, it revs to about 2k, then hesitates for a moment before jumping up and continuing to rev.
If I snap the throttle, it gets to about 2k rpm, stumbles just enough to hear (with that same hissing sound I mentioned before), then continues revving fine.
I adjusted the idle mixture screw at that point to see if it would smooth out the transition, but it did not seem to have any effect.
Watching the heat riser when I was doing the throttle snaps and such, it was open maybe 1/4 at idle and would swing open most of the way as I revved the engine.
I did try holding it all the way open when doing a throttle snap to see if the riser spring was just too stiff, but that also did not do anything.
At this point I have a couple theories:
1. The bracket shown below holds a rubber stopper in the top of the carb that looks like it should open when I get on the throttle, but both the linkage side and the carb side are bent. Based on the position, I am wondering if that is part of the power piston circuit and it should be opening more/faster with the throttle?
2. Based on the lack of a tag, the carb has almost certainly been tinkered with and might have incorrect pieces in it. If so, maybe that is contributing the to dead-ish spot in the middle.
3. There is still some amount of yuck in the carb that need cleaned out as part of a rebuild. The fuel filter I took off was the gravel sized glass ones that were popular in the 90s. It had a decent amount of debris in it, but I have no concept how long it had been there. The new paper element type I put in does not have any visible gunk in it yet, so the tank might or might not be filthy. Cleaning that is a project for another day.
4. There is evidence of seepage most of the way around the airhorn. That gasket could be messed up/leaking inside as well. That would be a rebuild fix as well.
Any other suggestions, (on-topic) comments, or thoughts? At this point I am inclined to move on to other projects until I can get a kit for it.
