OS 50 Hyper losing power at half-tank

[cclasen]

I tried to search for this. I'm sure it's been answered before, but here is my problem. I have a Raptor 50 with an OS 50 Hyper engine on it. It has been properly broken in and has about 5 gallons of fuel through it (CoolPower 20%). From a full tank to about the halfway point, it runs great. The power this engine produces just continues to amaze me. At about the half-full point on the fuel tank, it loses a significant amount of its power. This continues until the tank runs out. It behaves to me like its too rich during the last half, with a more feeble puttering engine sound. When it's out of fuel, it runs much faster for 5 seconds then dies. I have never run it too hot/lean. A fingertip on the rear of the crankcase at the end of a run can be easily kept there. It does this losing power business sporadically, and during the times it doesn't do this, when it runs out of fuel, it doesn't rev up right at the end and die, it just dies. I had the engine tuned by someone who knows what he's doing; before then I had it a bit rich. I have the stock header tank and fuel lines. Any advice will be much appreciated.

[Mr-C]

The number one reason for an engine to lose power is overheating. You're confident it's not but do keep this in mind and know that either one of the needles can cause this, along with various loose engine parts.

After the five gallons you've burned, it wouldn't hurt to check and replace your clunk line in the main tank. Maybe it's collapsing. At the same time, make sure there is no crud in the tank and examine the rest of the fuel system.

[BarracudaHockey]

My bet is clunk lines, if its the stock stuff that came with the kit replace it with Aerotrend medium or Hayes clunk line. If you use Hayes cut them both a few MM shorter than you think you need, they will swell a bit for a few tanks. If you don't cut it short enough the clunk will stick to the back of the tank and flame you out.

Replace both the main and header tank clunk lines every few months. Also most of us replace the plug after breakin.

[cclasen]

Thanks to both of you for the tips. I changed the clunk lines today and put a new glow plug in. This time I didn't experience a drop in power until maybe 1/4" of fuel was left in the main tank. All my fuel lines were clean and i used a pipe cleaner to make sure the muffler pressure fitting wasn't clogged. Thanks again. I guess this is why people have gone to pumps instead of relying on muffler pressure.

[BarracudaHockey]

One other thing to check is the nipples on the sides of the fuel tank can get worn by the frames. I sand the sharp edges on the frames before I install tanks on new Raptors, take a peek at that.

That should run fine through the whole main tank with muffler pressure.