I am problably overlooking the obvious but here goes.....2 engines 1 Toro 25, 1 Mac 25 both behave the same, on the test
stand they run great, haven't tached them, don't care, they idle great throttle up and scream with a 16x8. Here's the problem,
as soon as I mount them in a plane they won't run for $#%! hard to start, hard to keep running, won't idle, won't throttle up.
Both on mag, same fuel, any ideas? I've been spinning my tires for a few days now, can't figure it out, 'bout ready to list'em
on e-bay, but they run so sweet on the test stand.........maybe I should just put wings on my test stand !! HELP !! thanks , Craig

Either you have the lines reversed on the tank,vent hooked up instead of fuel line.Or your line with the clunk fell off inside the tank.
What ever it is,its a tank issue i believe.
You do have the tank vented,right.

theres a thought ! I'll try that, I'll take the tank setup off the test stand and put it in the plane, BOY! I'll feel like the south end
of a horse walking due north if that's the problem ! thanks for the idea

It happens to the best of us.

I had one that wouldn't draw fuel. I had a Tee in the fuel line for a filler line with a wooden dowel stuck in the fill tube.

The wood in the dowel was porous and you could suck air through it like it was a soda straw.

When I flew the plane some, I was getting hits on the radio. Found a old non resistor spark plug in the engine where one of the kids had traded with me for their weed whacker, blower, or chain saw?

update: I took the tank and lines off the test stand and installed in the plane set both needles at 1-1/2 and started it up
runs....ok but still won't idle, well, it idles, but high, as soon as I try to trim down the idle it revs up and then dies...
I screwed around with the needles but no change. Craig

Got a picture of the installation?

no unfortunately I don't,

How is the airflow around the carb while mounted to the plane, as compared to the test stand? I can't imagine reference pressure being an issue while sitting still on the ground....but, something was missed here.

on the plane I tried it with and without a velosity stack, this one I'm playing with now is the Mac 25 out
of a hand held leaf blower has a wabro 324 carb on it, as I said earlier sweet running engine on the stand
and couldn't wait to put it in a plane. Thought I had it with the gas tank idea Craig

well I found the problem with the mac 25, the head bolts were loose ! tightened them up and it runs fine! Now
back to the toro....it idles fine but as soon as I throttle up it dies. Tried messing with the needles...no go. I'll
try a different carb....Craig

I tried a different carb and that did it ! WHEW ! What a couple of days screwing around with these!
thank you for your thoughts and ideas...Craig