Airbusboy

Now the spark plug cap is something that I hadn't thought of....I'll check that tomorrow. As for the other ideas....3 different carbs...problem still persists so it can't be a slide, diaphragm or air cut off issue. I thought it might be a float level issue, thinking maybe I'd bumped it wrong when changing carbs, but 3 different carbs yield the same problem. I read on one sight that a crack in the intake boot could cause my symptoms, which is why I replaced THAT too...but no help.

yep, forgot to mention. Tried TWO filters. No change.

I thought of that, which is why I'm going to try completely replacing the line from the petcock to the carb. Someone said you can see the filter/sock on the inside of the tank when the fuel level is low...anyone able to verify that?

It's odd...it acts just like the main jet is clogged and not giving fuel for the 3/4 throttle and up range, yet 3 different carbs don't help! I don't get it.

Here's what I thought I'd try next.....1) adjust the valves AGAIN to verify the correct .006 setting. 2) replace the entire fuel line from the tank petcock to the carb inlet. 3) double check compression and 4th, try loosening the fuel tank cap while the issue surfaces IN CASE she isn't venting properly while running. I already drained the tank and put in fresh, premium fuel. I'm running out of ideas. SURELY the valves aren't set properly since it WAS running fine till I decided to do the valves yet I've set them multiple times! I'm reaching for that stick of dynamite!

Admittedly, it was running fine before I adjusted the valves. I had decided to adjust the valves purely because of age and a VERY slight valve clatter. I had recently installed a 'Silent Rider' secondary muffler but pulled that off thinking that might be restricting the exhaust...no change. I had been negligent on the air filter for quite some time and when I checked, I noticed some deterioration of the old filter, which is why I replaced it. Before reinstalling the box I inspected the inside of the metal can that the new filter slides over and it appears clear with no clogging. Plus, running the ATV without any filter box/restriction doesn't change the issue of low power so I think it has nothing to do with air intake. With two rebuilds on the original carb (again, age reason not mileage), a Chinese knockoff AND a brand new Honda carb, PLUS removing the fuel filter (possible restriction?), I don't feel like it is a carb/fuel flow issue. Could the original fuel line be restricting due to leaded fuel over the years? I thought about trying to re-adjust the valves SLIGHTLY loose (like .008 instead of .006) but not sure on that. How can I check the exhaust for possible blockage? Oh and thanks for your ideas! Oh and no, I was at BDC on the first valve adjustment but on the second, third and fourth valve adjustment I'd watch for the intake rocker to close THEN go look through the window for the 'T' mark and also physically verify that BOTH rockers were slightly loose so I KNOW I was at TDC. I'm ready to blow it up!

Hey guys...newbie here...and I need some ideas. My issue. Original owner. 2003 Rancher ES. 100% factory. No mods. 900 miles on the clock, not 9000, only 900. I decided I would adjust the valves due to some slight clatter and the ATV being 17 years old. I also installed new air filter. Now she has very low power, especially at high rpm. Will run fine at mid-range and down...about 3/4 throttle and up...not so much. Compression checks at about 145psi. Backfiring and sputtering through carb above 3/4 throttle. Tried new proper plug...no change. I've tried a knock-off new Chinese carb, the original Keihin factory carb rebuilt TWICE and finally a brand new factory carb, with all adjustments left from factory build...no change. I tried a NEW CDI box...no change. I've rechecked the valves and both are set right at .006...cold. I even tried a brand new factory intake manifold...no change. I've tried SLOWLY pulling out the choke knob when she starts sputtering at higher rpm and it only dies, not improves. I have NOT tried pumping the primer knob while it's running badly. I've tried running it with and without the airbox...no change. I also added a clear-bodied fuel filter, which I thought might be impeding the fuel flow at higher rpm so I removed it...no change. I'm out of ideas....anybody got any suggestions? Thanks in advance for your thoughts!