Performance - 1980 PE 400 vs RM 400

[yamaico]

If you haven't already, set up the squish and compression ratio before you do anything else. Quick, easy and cheap - the best bang for your buck in any two stroke.

[FourstrokeForever]

You mentioned that you advanced the ignition. In my experience, that won't help with torque, which I was you are chasing for bottom to mid grunt. Try retarding the ignition timing a couple degrees. Gary Jones put me onto this with sorting out the light switch power delivery on my old Elsinore. It made a whole world of difference and the bike actually had some bottom end grunt! And so did fattening up the pilot jet....

[80-85 husky]

a rich needle will also give a hit onto the main jet a bit harder than if its spot on.

[SON]

As Lozza said Compression is a start so fixing the combustion chamber is first,
Ignition /  Flywheel weight is second,
Expansion Chamber mods third.
PE 400s suffered from flywheel magnets separating from their epoxies
For VMX I would replace the entire ignition system with a more modern system say early 2000s 250 from a wreckers,
I can't remember exacts but it was cutting both header and mid body and the result was more mid range hit

[Barra]

Thanks all.

Carbie is next to new. I had the jetting 'fat' and gradually backed off on the pilot and needle position to find the right combo and running clean (or maybe still just a tad rich)

I've been wondering about the timing. Backing it off will be worth trying by the looks.

[Barra]

As Lozza said Compression is a start so fixing the combustion chamber is first,
Ignition /  Flywheel weight is second,
Expansion Chamber mods third.
PE 400s suffered from flywheel magnets separating from their epoxies
For VMX I would replace the entire ignition system with a more modern system say early 2000s 250 from a wreckers,
I can't remember exacts but it was cutting both header and mid body and the result was more mid range hit

Thanks Son.  On ignition, what if the original was in perfect nick? Would a modern replacement still make a difference? 

[SON]

Carburation is last,
Combustion chamber needs help, the flywheel is fine for Vinduro and most normal people but you appear to want more so a more modern ignition curve will give you that,

[Lozza]

After spending the last 8 years installing and dyno tuning programmable ignitions  I have yet to see more than 0.2hp difference in any engine by changing the ignition advance(by as much as +/- 7deg) , off the pipe. All adding advance will do is help the engine get on the pipe faster.

With that said it's of no use moving the stator around unless you know how much advance/retard your ignition currently has. You will more than likely find that the standard settings (measured with a dial gauge and strobed against the flywheel) provides the best "all round" performance and usualy 1 width of the stator mark either side of the reference mark is for fast and slow tracks. Modern DC/DC ignitions have far more voltage delivered to the plug, regardless of rpm, more accurate timing and smaller and more compact flywheels/stators. Along with 3D mapping etc etc

[FourstrokeForever]

After spending the last 8 years installing and dyno tuning programmable ignitions  I have yet to see more than 0.2hp difference in any engine by changing the ignition advance(by as much as +/- 7deg) , off the pipe. All adding advance will do is help the engine get on the pipe faster.

With that said it's of no use moving the stator around unless you know how much advance/retard your ignition currently has. You will more than likely find that the standard settings (measured with a dial gauge and strobed against the flywheel) provides the best "all round" performance and usualy 1 width of the stator mark either side of the reference mark is for fast and slow tracks. Modern DC/DC ignitions have far more voltage delivered to the plug, regardless of rpm, more accurate timing and smaller and more compact flywheels/stators. Along with 3D mapping etc etc

I agree. Modern ignitions with much smaller rotors and better pick ups/stators are so much easier to live with. And they give a much fatter spark from near zero to whoa.

Changing ignition timing won't get more power, but you can change the way the power comes on, both in 2st and 4st engines. As you say, advance makes everything happen quicker. Myself, I like having a little retard on my 2st bikes as it helps to give a bit of bottom to mid range power that doesn't come on in one big explosive burst. It actually helps to make the motor more tractable. After years of being told to advance the ignition, Gary Jones put me in the right direction.....
Personally, I'd try going bigger on the pilot jet. Put a big enough jet in there to make the bike "burble" at 1/8th throttle (just opening), then remove it and go 2 sizes smaller. This should put you in the ball park. GJ also put me onto this.
And yes, expansion chambers make a huge difference to how a 2st engine behaves. My memory of my old PE400 was that of a very tractable motor with heaps of low to mid torque. It had the stock chamber but I put an alloy silencer on it for no other reason than to save the original from battle scars.

[GMC]

As a rule of thumb all PE's, IT's and KDX's have more low end than their MX brothers.

You can talk about ignitions, combustion chambers, jetting and expansion chambers all you want but if the barrel has been wildly ported you will be forever chasing your tail trying to get the low end grunt back.

Step one; take the head off and measure down to the top of the exhaust port.
Then try to find someone with a known stock barrel to give you the stock measurement.

Raising the exhaust port is the first thing a lot of guys try when they get their first die grinder or dremmel, they don't always do it wisely.

[Simo63]

Raising the exhaust port is the first thing a lot of guys try when they get their first die grinder or dremmel, they NEVER do it wisely.

Fixed for you