Yes

Yesterday I worked on a Tillotson off an engine that would not idle. Pop-off check always is the first thing I do on a carb, and this one was extremely high, without clear pop and reseat.
Took off the diaphragm which had a hook-in pin, and compressed the lever spring using a little heat. Pop-off without the diaphragm fitted was 25 lbs, and seating a solid 15 lbs.
Now the funny part. After refitting the diaphragm, pop-off rose to about 40 lbs again, as if the hooked in diaphragm held the lever up. So I snipped off the collar part of the diaphragm pin, and refitted. Problem solved, and the carb pressure dropped with every piston bump, which indicated proper function. No feedback yet of how the engine will now run.
(Engine old 3W75, with cracked intake manifold, which needs to be replaced first.)

Saw that once myslef..The groove in the pin was so narrow it didn't allow free movement...

Hey, why did I not think of that.
Thanks Ralph.

Yeah that's interesting. Gotta remember that one.

The shape of the lever has to be just right...If the forked end is not almost parallel to the groove it can bind...

Ralph, allow me to pick your brain.
Do some carbs need the diaphragm to pull up the regulating lever and thus prevent fuel pressure in the plenum chamber?
Belts and braces maybe, because the spring should shut off fuel flow. Maybe that is why some can get away with very low pop-off pressures.
What's your opinion on this?

I don't know why the lever is forked..I'll cal Luis Salas at Walbro today, he will know...
Just called Luis...Way back years ago some of the chainsaw companies thought the fork would stabilize the idle...Walbro did some tests, and disagreed...However, the customer is always right...Walbro made a TON of carbs that way...When all the forked levers are used up there will be no more...End of story, the fork has NO function..There are diaphragms made with no groove in the lever, they work just fine with the forked lever....From Luis Salas at Walbro..any "expert' out there who thinks otherwise is WRONG....
I asked him about the Tillotson carbs, he just laughed...
It's always best to ask a REAL expert

Does Salas still have the same 989 prefix number?

Yes

Originally Posted by rcign

I don't know why the lever is forked..I'll cal Luis Salas at Walbro today, he will know...
Just called Luis...Way back years ago some of the chainsaw companies thought the fork would stabilize the idle...Walbro did some tests, and disagreed...However, the customer is always right...Walbro made a TON of carbs that way...When all the forked levers are used up there will be no more...End of story, the fork has NO function..There are diaphragms made with no groove in the lever, they work just fine with the forked lever....From Luis Salas at Walbro..any "expert' out there who thinks otherwise is WRONG....
I asked him about the Tillotson carbs, he just laughed...
It's always best to ask a REAL expert

Thanks Ralph. It is nice to be so close to the source.
Did he laugh or just chuckle?
In the future, I'll just snip off the part on all carbs I serve. One less problem to raise it's head.

He just chuckled...

Regarding fuel injection for model airplane engines:

I'm at AUVSI in Denver, CO. this entire week.

3W has real fuel injection systems on engines from 30cc and up - yes only 30cc with a fuel injection system. They had some giant behemoth 4-cylinder engine in a glass case with a fuel injection system too. Purdy cool stuff. I asked the rep if they would ever do this for the RC hobby industry. I shouldn't quote the guy directly, because I don't know who he is - except that he was a 3W rep from Germany.

Basically, it's too expensive for hobby use.

Lots of heavy fuel aircraft on display. Fun place to spend a week walking around, taking pics and chatting to people in various niches of the industry. But no fuel injection for gasoline 2-strokes in our near future. There was a new 2-stroke engine manufacturer though. Very unique way of lubricating a 2-stroke engine with a closed crankcase and a traditional exhaust valve on top of the cylinder - the kind of exhaust valve you'd expect to find in a 350 chevy motor. It has an intake valve dead center in the middle of the piston. It works on crankcase pressure. He had an animated slow-motion video of the engine in operation. 500cc engine - 35 pounds. None of the "usual" 2-stroke emissions, but all the power of a big 2-stroke. Friggin wild!!!

This is what the early rotaries had as well. Reed valve in piston, exhaust valve in cylinder top, cam operated.
The ship diesel engines I worked with had blowers and full piston controlled porting in the lower cylinder part for gas entry, and exhaust valves, which were cam operated. Scavenging and combustion is very efficient with little pollutant quantities. Pressure charging is also possible with this design.

So No Fuel injection in our future Right?
Too Bad.

Now back to cutting the spring pressure issue.
You guys are all saying that cutting the spring is of no use to your engine situation?
If so then you guys must fire up and go from the pits.
And do your engines have to come down from a High idle to normal only after waiting 10-20 seconds?
Please give detailed responces please.

Thank you
Tim