I have a 99 scrambler 4X4 and all last yr after I put it back together I got 10 mpg. I don't ride hard either. I have had to screw the idle way up too. I have been checking it out here lately to try and get it ready to ride (just got done sledding on Memorial Day weekend!) and was hoping on finding out what was not right with this thing. I have read many threads on this all along and most claim 14 - 19 mpg.

I have checked my carb and it is exactly what I was told last week was baseline for a 99 400. I did have my screw out to 3 turns instead of the 1.5 that he told me his was at, but.....

I also turned my reeds around. I put them in new last yr (not many miles/aftermarket brand name - don't remember which one tho) and they seemed to be unseated. Is this normall? After turning them around they are now seated. Seems to run the same around the yard quick.

I tried to use a timing light to check the timeing, but I couldn't get the light to work? I thought that maybe the bat on the Pol was too low (which it likely was) so I pulled it up to the truck and still couldn't get anything useable. It would flash occasionally, but nothing worthwhile. So I tore it down to check for the timing "mark" on the ..... well the moveable pc that you bolt on. Given the poor milage and lack (in my mind) of top end perf I thought that it might be retarded, but it seemed to be slightly advanced, so I am assuming that my timing must be pretty close to possibly advanced?

Maybe these 14-19 mpg Sc's are all 2WD's? Maybe the 4X4's are supposed to get 10 mpg?

The fact that I had to screw the idle up a bunch from what it was set at originally (before it sucked a piston skirt - and then I bought it and rebuilt it) tells me SOMETHING aint right with it!

Suggestions? Or should it doo this bad?

 

what oil are you using? check for proper oil ratio (32.1 or 40.1),
no engine is the same,if you get told to screw out the carb screw it cannot be the same on YOUR machine,also if you got aftermarkets reeds,mostly can be tuned for low or top end performance gains,so maybe yours are in low end setting,if the engine is stock you might keep the stock timing setting wich is 23.5.yes,the 4x4 400 scrambler eat more gas than the 2x4 as well...
check carb setting (pilot jet,needle,main) and air filter,make a carb/engine cleaning sometime also help.

 

I didn't actually check my oil usage, but it never seemed high at all. Plug is dark yes, but not fouled.

I had the carb all torn down last yr and again today.

Seems like they may have been Boysons. But they weren't anything fancy. Just replacements b/c the stockers seemed in need of replacement at the time.

 

if you got boyesen reeds,it is very possible they can be tuned for low
end or top end setting,but what KIND of oil do you run? run on regular or 92 octane fuel pump?if timing has been advanced,you must fill some
more octane in the gas (octane booster).is the clutching setup alright
to pull the engine on gas like that?
i'm just try to help,mine is a 400 '99 too,but i take off the 4x4 system completly (running 2x4 tranny) and it is full modded...

 

and my last guess,do you tried to fill some carbon cleaner in the gas tank to clean the fuel system completly?