Suzuki 2 Strokes

Pistons are in the right way, I did lift a head. Standard air box and everything else. I’m going to strip and clean the carbs again and put it all back to standard settings and start again. I’m pretty sure the cases are well sealed. Rebuilt with new crank seals.

High speed coil winding on the alternator?

OK, I haven't read all the way back through this thread, but an idea came to me. So you may have already answered it.

What size Main Jet is in the carburetors?

The early carbs ('72 and older) require a 150 Main Jet.
The later carbs ('73 and newer) require a 97.5 Main Jet.

Putting a 150 jet in the newer carb will definitely be super rich, and cause the motor to "Bog down" (Personally, I hate that term, as it doesn't exactly explain what is happening. It either loses power, as it want to go but it can't, or it starts 4-stroking, where it doesn't seem to fire on every revolution).

The 1975 T500M would certainly have the newer carbs (identifiable by having overflow/vent hoses attached to the carbs). However, if an aftermarket rebuild kit was used, there can be an issue. many kits are sold stating "Fits 1969-75 T500". This is completely untrue, as there were two totally different Main Jets during those years! And many times, the Main Jet supplied isn't a correct match for either one.

I would:
1. Confirm which carb is installed (Early/Late, as who knows what someone did before you)
2. Confirm there are genuine Mikuni Main Jets installed
3. Replace the Main Jets with the proper Mikuni Main Jets if in doubt

See Service Bulletin General-9 for info on main jet types Suzuki used. The main jet #s 97.5 & 150 are for different types of jets so the #s aren’t really comparable.
http://www.ozebook.com/compendium/techb ... %201-9.pdf

Look for the partial part number stamped on the carbs.
For example, my T500 carbs have 15313 stamped near the intake pipe location. The corresponding RH carb full part # is 13201-15313, which was used on GT500s & later T500s.

As others have often said, if you have jets from carb kits then that is likely a problem. But not necessarily the only problem.


If the motor “hits a brick wall” at 3k rpm regardless of load & throttle position, then I would suspect the ignition system. The amount of time to charge a coil decreases with increasing rpm. If you are getting good voltage at the coils & the points look good, then the coils and/or capacitors are likely culprits. Given that you already spend big $$$ on the motor, personally rather than do battle with this issue I would install new capacitors & new aftermarket coils.

Also make sure you have a good battery that is fully charged up.

jabcb wrote:See Service Bulletin General-9 for info on main jet types Suzuki used. The main jet #s 97.5 & 150 are for different types of jets so the #s aren’t really comparable.
http://www.ozebook.com/compendium/techb ... %201-9.pdf

I disagree that the 97.5 and 150 jets are different types. Both are Large Round type Main Jets.

From 1969 through the last GT500 model, the part number for the P-4 Needle Jet is 09494-00051, the 188 Series, which takes the Large Round Main Jet. The large difference in the metering of these Main Jets is due to the method of venting the float bowl (homopressure carbs are internally vented, newer carbs were externally vented to ATM). As the ATM pressure is higher than that found in the internally vented carbs, a smaller orifice is needed, as there is a higher pressure on the input side of the jet.

It is not due to the difference in measuring Round vs Hex style jets.

Interesting, I stand corrected.

so what was causing the issue in the end?
I"ve had my bike for 6 years and ran into this issue on the way back from a trip, had to ride under 3000rpm the rest of the way home!
I am currently rebuilding and want to make sure I address this issue!