Suzuki 2 Strokes

I,m having issues with my T500R. Stock airbox and jetting. 150 mains, #30 pilots, stock needles with the clip in the middle position. It runs well in the lower throttle setting range, however, upon larger throttle openings, the engine does not pull. If you back off the throttle, it will pull better. I just dropped the needle 1 notch and it runs much better. However it will still not pull at wide open throttle. The needle is now at the second groove from the top. Should I try and drop the needle another notch or try a 147.5 main jet. The plugs are tan colored and the exhaust pipes are greyish inside. The plug color came after a longish highway run although I did leave it in 4th due to high headwinds and the fact that it wouldn't pull 5th. Thanks for your input.

Have you checked for inner seal leakage? The seals could be at an early stage of failure. Do you hear any detonation?

Stock exhaust? Are the baffles clean or have they started to clog with old oil and carbon?

How clean is the air filter?

Have you checked plugs, points and ignition timing?

Thanks for the replies. I've installed new plugs and points, set the timing (with timing light). Also cleaned the exhaust baffles. Virtually no buildup in the mufflers. Since my original post, I've dropped 2 main jet sizes. I'm now on 145's. It seems to be getting better with each size drop. Plugs still a tan color after highway riding. Can't do a full throttle plug chop because it still won't quite pull full throttle. I'm also using 91 octane non-ox pump gas and using the stock airbox and clean filter. Is gas different today than in 1971? The way it was jetted stock, it was nearly unrideable. I,ve got smaller main jets on order. Also, the low and mid-range seem to be fine. Hoping I don't melt a piston. No, I don't hear any detonation, and I,ve been keeping a close eye on the plugs. Thanks in advance for any input.

It is getting harder to get REAL GAS these days. Most States require 10% Ethonol

Ethanol has a lower energy content that gasoline and burns at a much richer A:F ratio so 10% ethanol usually causes motors to run lean.

The next wrinkle is that unleaded fuel tends to burn with more soot than leaded fuels. I'm no chemist but it's something to do with the carbon atom linking or something. So a bike running on unleaded that previously ran on leaded will tend to have black plugs. For example when we run leaded race gas we run colder (harder) plugs than we do with unleaded or else it looks like it's running lean.

But since leaded gas for the street has not been available for years, I doubt that the problem lies there.

Did it always run like this or is a recent change in performance if if so what else changed? Were the jets changed from original to jet kit or to a different style of jet?

What about the main air jets and passageways? Are they completely clean and flowing OK. A blocked air jet will cause it to run rich.

If it runs better with the throtle closed a bit, that is usually a lean condition. You might have gone the wrong way with the needle.......