Another 18hp Vanguard question

[garretttpe]

Hi All
I have a issue with my 18hp Vanguard and I will try my best to put all info in the post.
1. year 2000 vanguard 18hp
2. year 2000 max II
3. Exhaust Restrictor plugs removed. stock exhaust
4. High Rev kit, stock flywheel
5. Carb main jet drilled 1 size up. I believe .016 or .020 , been a year since I drilled it
6. Gov. disconnected and new linkage installed using another members schematic.
7. Valves set to proper gap.

The above was what was done to the engine a year ago. I have a tiny tach and the past 38 hrs of drive time the engine ran perfect, idled great, revved up great. I was extremely happy with the power and performance, I rarely went above 4400 RPM due to not having a Billet flywheel,

Now it has been 2 months since I have driven it and yesterday lots of issues.
I put fresh gas in the machine and the engine started right up as usual but it went to aprox 3k RPM and stayed there. I tried turning the idle down and a slight CCW turn and poof the engine died. Started it back up with no issue and back to 2700-3200 PM. then it would backfire like freaking crazy when I would snap the throttle to try to get it to idle. The engine will either die or stay at high RPM, I took it out in the woods near my house and under load it worked great as long as I was on the throttle, Under load it would die if I came off the throttle. No load high rpm. and of course when the few times I could snap the throttle and the rpm did come down it would back fire like crazy, sometimes once sometimes rapid backfiring.

Sorry for the long post I wanted to try to get all the info I could think of. Any clue what could have happend? went from good to not good due to sitting.
Thanks
Larry

[Nubs]

Reformulated gas problem would be my first guess, ethanol separation. if no ethanol in the fuel then maybe water.

http://www.lcbamarketing.com/phase_separation_in_ethanol_blen.htm

[garretttpe]

Thanks Nubs

The fuel here in Maine is 10 percent ethanol, I have 2 qrt cans of 93 octane with no ethanol that I use on my chain saws and weed Wacker, I will feed my engine direct from that fuel and see what happens. It will be a few days, I will get back and let everyone know what the outcome is.

Thanks
Larry

[Nubs]

I would gravity feed the good fuel from a another tank right to the carb for testing, it can take a bit of run time to work the crap through the carb. the ethanol can lay in the low sections of the fuel lines, fuel pump, tank etc.

[garretttpe]

Problem Fixed, There were a couple of issues,
1. gravity feed fuel and no difference
2. Removed carb and found a small piece of crap in the secondary jet, acting as a flapper it appeared. making it stall when off the throttle
3. removed low idle/air mixture screw and put carb in my ultrasonic cleaner, air blew dry all looks good and clean
4. found the screw holding my return spring bracket a little loose and it prevented the linkage to come back to full idle., keeping me at high RPM
5. adjusted low idle/air mixture screw all the way in and out 1 turn.
6. Clean fuel, 87 octane with 10% ethanol, I will start using 100LL for a while as I am not able to get fuel with NO ETHANOL.
7. Fuel filter was full of dirt and crap after 29 hrs so I installed 2 new ones to insure no more crap gets in my carb

After all the above was found and fixed the engine runs like new and idles at 900 RPM and has instant throttle response,

Thanks All
Larry