This is the biggest difference between a 2-stroke and a 4-stroke carburetor. A 2-stroke has a shield at the gas needle. This is because a 2-stroke has the intake gases flowing back and forth in the carburetor. The shield ensures that the mixture does not become too rich, and the air only gets fuel when it flows towards the engine.

You also need to replace the atomizer.

If you convert your carburetor to 4 stroke.


The change from 2 to 4 stroke in the dirtbike world has of course produced very good 4 stroke carburetors, I would look for a carburetor there.
You will always have to search for the right atomizer,
but that is a relatively simple search for power.

Converting to an injection system is something I have never looked into.
But sensors capture many variables where the carburetor cannot.
Also adjusting with a laptop is of course much easier.

Think about what you can do with your laptop if you have a programmable ignition and an injection system.

Interesting comment you made Dave about the DR head not having the little bump in the center of the chamber, while the LS does.  It’s been a long time since I had a DR head in my hands, but I have no memory of noticing the difference.  But, the memory is not what it use to be either.

Oh boy Michael I can dig those heads.  Look at the size of those valves.  I bet they are at least 38mm.  And look at the angle of that intake.  That sucker is steep.  About as straight a shot as you can get.  What is the HP and redline on that badboy.

Dave, I pondered eliminating that bridge between the valves when I was trying to find more combustion chamber volume.  I was reluctant.  When you start staring at the thing, it just sort of yells at you "Don't do it".  Don't know why, can't justify my reluctance, no sound technical basis for the aversion, but it's one of those things that sort of looks like you will regret.  It just looks like it needs to be there.  It does add additional quench surface.

Zevenenergie, I am confused a bit.  Please help me understand what you are trying to share.  I want to be sure I understand exactly what you suggest.

First, I believe you are telling me that I should tighten up my quench.  Yes, or no?

Second, it sounds to me like you suggest I either leave the CR where it was, or even increase the CR.  Yes or no?

Third, I think you are suggesting that my problem lies solely in the carburetion.  Yes, or no?

If I understand correctly, you think that the sand blasting has nothing to do with detonation.  Yes, or no?

I can see how the sand blasted appearance could be the result of some sort of liquid blasting.  All sorts of stuff is going on in that crevice, and my cheap knock-off carb certainly could stand some improvement.  It wouldn't surprise me if the fuel droplets are waaaay too big for satisfactory performance in a four-stroke engine.  But any sort of blasting will require a motive force, like an explosion of some sort.  What is that motive force?  What propels the blast media?

How does this trapped fuel deform my ring land?  Why is my ring land deformed?  Why did the ring land pinch the second ring?  Wouldn't that also require tremendous force, like an explosion, like detonation?  Are you suggesting hydraulic lock?

I agree that the carburetion is less than ideal, and I agree that the carburetion could be contributing to this problem, but I am reluctant to say that detonation is not in play.  All that blasting and deformation requires a motive force.  I don't think fuel condensing and flashing off provides enough energy to deform the ring land, and corrosion certainly won't deform the ring land.  The deformation of the ring land requires BIG TIME FORCE.  Extreme pressure all at once; a hammer. Detonation.

Here is another view so that you can clearly see there is no sandblasting on the OD.

I pulled that old piston out of the junk box today.  I wanted to see if the ring land was deformed.  It is.  Just like the Wiseco the ring land is deformed .002" on the intake side.  That would require downward force, not upward force.  I don't think the tight ring gap lends itself to the deformed ring land, especially not on the intake side where things should be much cooler.

If you look at the skirt you can see it was seizing on the intake side too.

And what about all the missing aluminum?  This huge chunk of aluminum was just plain gone.  It was flame sprayed all over the place.  It was on the exhaust valves, and the intake valves, and the combustion chambers.  That sucker had to have been extremely hot.  It's a lot of aluminum.  You would think that I would have found a chunk or two, but it was all sprayed onto the surrounding parts, sorta like paint.  That thing had to have been really hot.

I appreciate your comments and suggestions regarding the carburetor.  I have been wanting to improve on the carburetion for a long time now.  I am running a Chinese knock-off PWK.  There is no emulsion tube, it's just a needle jet with an air correction port.  I have a new PWK knockoff that I have been wanting to try.  It's an upgrade.  It incorporates a bona fide emulsion tube.  That should dramatically improve atomization.  I was mainly interested in flattening out the fuel curve, but the improved atomization seems like a bonus.

Why do you feel that 2-stroke engines require the hood over the needle jet to mitigate overly rich mixtures resulting from reversion?  Shouldn't the reed valves prevent any reverse flow back through the carburetor?  BTW, don't think for a second that 4-strokes don't have the same problem.  Most Savage cams close the intake valve just after BDC, so they don't have much intake reversion.  But if you run a super-hot cam with lots of overlap and a late closing intake, you can form a little rain cloud of fuel over the mouth of the carburetor.  That charge can run back & forth through the carb several times before the intake finally closes.  It's especially problematic with drag pipes.