get some long fuel hose and run the hoses from the tank of the running 80 to the carb of the non running 80 and see if she fires lol. or just swap tanks/cap ect.

the only thing i can possibly think of is the petcock or fuel cap or something then

 

Would letting it run with the carb, fuel supply line and clear pancake fuel filter all full of fuel not connected to the tank be the same. I did that let the pancake filter empty before taking the choke off to ensure fuel was in bowl it slowly died

 

yes and no, there may be a supply of fuel, but is it enough to KEEP the bowl full? thats what im wondering. also, is the pancake filter directional? is it the right way. not trying to question your mechanical ability, its just that something doesnt make sense

did you test compression AFTER you pulled apart and sanded the score marks from the cylinder? maybe you lost compression somewhere. did you test the spark. i had one where the boot for the spark plug screwed on, and the wire broke and wasnt making contact all the time, pulled the boot off, cut a fresh section of plug wire, re screwed the boot, and it fixed it

 

Can't remember if its directional but sure I checked the others I use on my banshee are directional didn't check compression but just put it on cold 112psi. trust me this one is driving me I had less trouble synchronizing the carbs on my banshee 10 years ago with a lot less knowledge. Something I thought about the injector oil smelt alittle funny like it was a mix of two stroke oil and gear oil u know that smell gear oil has I eliminated that and premix 36/1 castor 927 and 93 octane actually have 100 octane in it right now, anyway does oil collect quite a bit in bottom of crankcase the crank throws could actually pick up oil off bottom of case every revolution while I had top end off tried putting hose in and sucking all that I could out

 

i have taken two apart where the crankcase was full of premix, and they were running great before the teardown, the other times the crankcase was empty. i dont have any particular knowledge in that situation to be honest. i've wondered it myself.

 

Took front clutch out today to check crank seal,noticed a little up/down play in the crank should there even be the slightest play,it might be distorting the seal when running causing my what seems like vacuum problem, but sitting still the crank seal looks good. Also there is the o' so slightest movement back/forth is that normal.

 

I don't recall any play up and down or side to side.I'll check a bottom end.
The seal will "look" good.

 

i never had play of any kind. you may need crank bearings, and since the seal is mounted in the case, and the crank is moving up and down, you probably are experiencing an air leak, that will cause your engine to run very, very lean

 

I didn't figure there should be any play just wasn't wanting to pull engine and split the cases, how much trouble to replace the big end rod bearing while apart figured I should while I'm in there. This wll be the 1st bottom end I'm getting into!

 

I was thinking and I too agree that there should be no motion in the crankshaft.
First bottom eh..Study up. It's no small feat getting it back together with the crank still straight.
Rod bearings: I recommend a new crankshaft if the bearing is bad. The pin and crank 1/2's are very small/thin thus weaker (so to speak) making it tough to get them together and straight.
ie: a 250R crank/pin is so big that they go toether in minutes and able to be straightened in a cpl bumps. Not usually the case w/LT80 cranks.
Sure it can be done tho.
If the rod bearing is OK, I'd leave it alone. You can check for side to side play and up down motoin in the rod. Thay all have a slight amount of side to side. To much and it's obvious that it'll pull up and down.
If interested, I do this work. Seems I got good at it. LOL