Are you having a stroke ? You sound like Yoda

When we raced a long distance event when pinned in 5th we'd hit the kill button for a couple to help keep it cooler.

I liked the choke hooked up to a 4 stroke decompression lever to enrichen it when WFO.

I think running a large bore two stroke at a set rpm for long times leads to detonation and possibly other problems. I could be wrong here, but i think i remember jerry hall telling me this once. That this is part of what led to the demise of the 2 stroke streetbikes.
Something about sustained high rpm running being an issue with detonation.
Maybe J.H. Could chime in about this?
If i was to set up a zilla for high speed riding. I.e.  running 60-80 mph for miles and miles, i would think that gearing the bike to run lower rpms could help.
I dont think spinning a zilla to 9k+ for extended times is a recipe for reliability

I'd try to keep the RPM's as low as possible, target your final drive ratio to your expected top speed (the speed you'll be running most often) so the engine is just barely getting on the pipe.
That'll give you the power to continue accelerating if need be, the ability to downshift and bring it way up into the powerband, while allowing the engine to cruise at a lower and healthier RPM.
The engine is put under much less stress when you're not peaking it out on the pipe, so wherever possible keep it down low and make use of the 500's torque instead.
If you're thinking that it's ridiculous to never get it way up on the pipe and push those high HP numbers...just keep in mind that endurance isn't about power output, it's about being able to cross the finish line.

Lowering compression will help longevity of an engine in demanding conditions.
Using a less restrictive stinger will also help to scavenge more heat out of the engine, at the expense of your pipe's state of tune.
A larger radiator would be a good idea, bring the temps even lower than what they're normally at.
Stock porting (or a mild port) that keeps as much of the sleeve intact will help with ring life.
All of these things traditionally lower the HP output of an engine, but that's the tradeoff between power and longevity.
Be sure to do all of the reliability mods like the RM bearing and thrust washers, welded ears, heavier clutch springs, etc. as well.


One of the most important things that I'm saving for last...oil ratio.
If you're going to be running for an extended time with lots of throttle, you need a lot of oil.
Consider going down to a 20:1 or 25:1 ratio to keep everything happy in there.

The performance we were shooting for was for maximum reliability. The only modifications that I recall were a custom pipe &silencer, head mods, cyl stud upgrade, custom airbox with a trx250r filter. 19 hours 47 minutes the engine ran continuously. But this was 1991 so there wasn't special thrust washers/rm brg available yet.

I just noticed that you are attempting to use a power jet carburetor.  DO NOT USE THEM ON THE LT 500.  The power jet feature on the TM 38 makes the carburetor next to impossible to accurately tune at partial throttle.

Adding another head or base gasket to lower the compression is the WRONG approach!!!!!   The proper  piston to head clearance and squish shape is essential in preventing detonation REGARDLESS of the compression ratio, exhaust, or other engine specifications.

Below is my response I made to Frank in a Private Message.  Maybe others can benefit that have the same questions.




High performance 500cc single cylinder engine are most reliable when operated for brief periods of full throttle with a properly designed engine, with the correct exhaust system and a properly jetted carburetor.

Large two stroke cylinders do not scavenge properly at high RPM and partial throttle like when cruising down the Autobahn at 100 kph.  As the state of tune of the ports and exhaust system progresses in the direction for higher power levels, the possibility of detonation occurring at partial throttle increases dramatically. 

Carburetors can be jetted excessively rich for throttle positions below 1/2 throttle opening to minimize detonation occurring but increases fuel consumption, spark plug fouling and makes the engines run very rough when operating the engine in the RPM range and throttle position where the incomplete scavenging process and resulting detonation occurs.

I have had a lot of trouble with Paul Turner pipes and silencers burning pistons under wide open throttle operation.  The inside diameter of the outlet pipe on the tail cone of the main pipe body is too small and the aluminum muffler's inside diameter is also too small if the engine has been ported to the level of 55 to 60 HP or more. 

A Power Valve that is stuck in the open position can also contribute to burning pistons.

One of the symptoms of an exhaust system that has too small of an outlet is it will need to use a smaller main jets to prevent the engine from miss-firing at wide open throttle but will also increase piston crown temperatures to an unacceptable level.

Our HPR 19 pipe uses a larger outlet pipe and silencer inside diameter.


What year LT 500 is the TM 38 from?

If your TM 38 is from a 1987, there are modification that are required to make the carburetor work properly.

If you have a TM 38 from a 1988 to 1990 LT 500 I would use the following jets as a starting point if you are using the air box with the lid removed. 

420 to 450 main jet
If the lid is installed:   350 to 450 main jet depending on the exhaust used
22.5 to 27.5 pilot jet
389   R2 to R8 needle jet
6DK3  clip in 3rd or 4th position from the top
air screw 1 to 1 1/2 turns
4.0 slide.
air correction jet removed
3.5float valve

If you have the air box removed with a large high flow air filter set up you may need to go as large as a 660 main jet when running our exhaust system.

thanks God for jerry...and all the brothers here in the forum.
your willingness to help and the passion did exists in the forum.
 there is nothing in the world any other.

Ihave reinstalled the Powerjet,
and the main jet i change with 420
must drive with airbox lead,
Is just too loud without.
 For me and for all other neighborous and for the police :-)
I installed this at 7 clock in the Morning and take a ride aroud the Frankfurt city.
When the most Streets are empty.
My zilla runs a lot better.
but if I in gear disengagement the engine turns on ...
and I have to slow him down again with the clutch.
It isnt the trottle cable .
I must check the ignition system ?
Or the powervalve has any scratch ?

Thanks for the baja article  are very intrest for me.
More of this kind of stuff please i love the vintage of the zilla.
I like the stoey of people that have glory with thisold 2stroker quad...

El diablo must say i have 15 in Front and in the rear 35 teeth sprocket maybe i build me one wit
32 or 30 teeth. Or any body knows on this sprocket was installed on a other bike ?
My target is to drive in healthy rpm's 140 kmh on the Autobahn ;-)
FRANK....

Hey Buckeye !
For the memories....

Than you very mutch...
This saying makes the leak down test needles.
Ok give me on Day
And im back with good or bad news...

Ooh i so sorry
I ve never seen tis gunny people
Hahaha

I start the sesrch for the needle 6DK3
 look in the mikuni shops around and all what i found is a 6DH3?
Is this rename the needle ?
Can i use this as the same ?



In my mikuni is a 6DH2 allready installed.
Usefull?
Iwill take tomorrow a Testride .

You will have to order the needle from a Suzuki dealer.  It is a proprietary needle that Mikuni makes for Suzuki and is not available through any other source but Suzuki.  The 6DK3 is the stock needle for the 1988 to 1990 LT 500.  It is the best needle I have found for the TM 38 on the LT 500.

Honestly, your best option is to get the head o-ringed and eliminate the problem.