so the compression release valve when open allows some compression to leave the cylinder and it goes into the exhaust, very simple!

I did some tests with the cylinder that had open compression release holes and saw where the hole should be and if the punch I use can go through that little hole. it can go all the way through without damaging the cylinder.

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I packed the cylinder with paper shop towel and using a hammer,I drove in the punch and it pushed out a lot of carbon from the compression release chamber.

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before this, I tried blowing it out with a rubber tipped blow gun and of course this did not work.

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I

I drove in the punch until it protruded into the cylinder.

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I used a small straight blade screwdriver to finish the cleanup.

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once this was all done and the rag was taken out with the carbon, I put it at bottom dead center and looked at the cylinder walls. it all looks fine anyway.

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to wire in the Powerdynamo system. I took the red wire from the regulator/rectifier and hooked it to the yellow wire and the white wire.

I connected the white wire to the red wire from the bike together.

the red wire from the bike goes to the key switch and it connects the red wire to the brown wire. this is the switched power for the accessories like the horn,brake light, possibly tail light and turn signals.

I need to get the accessories before I can test this and see how it works.

the headlight,instrument illumination and high beam indicator work beautiful.

the Powerdynamo has no trouble powering a 12 volt 60/55 watt H4 headlight.

Do all the ports visually seem alot larger than the DT. Glad you got that compression release flowing again. I think your idea of moding the webco 360 head with the greater cooling fins is a good idea. Some of the endures seem to have a shortfall in that department. I don't know if the factory did that for the appearance. Thanks.

I remember the Trackers with the comp-release mounted on top of the head.I don't know if it was a mod or what but seems like maybe they were mounted in the 2nd spark hole.Also you welded the stinger with the lap backwards.

they cut the fins down on the MX400B head to clear the pipe itself as the expansion chamber sits right above the head and since it was for Motocross and Scrambles work, engine cooling was not a big concern since it was designed with closed course competition in mind.

the desert racers used Webco heads to allow the engine to live in the murderous heat.

pretty sure styling was another reason for the very short cooling fins.

the European bikes like the Maico of that time had radial fins and the Japanese started catching on to this in the mid 70's and that is a possible reason there.

the ports in the MX400B cylinder are larger and have much higher port duration than the DT400 cylinder. Enduronut called my converted DT400 a race engine and rightfully so. it is mellow enough to ride like a DT400 or let the revs climb and it makes a lot of power. the power does not come on in a explosive way at all but like the smooth rush of a great performance engine with vacuum secondaries opening in a 4 barrel carb.

power reminds me of the way my 1975 CR250 comes on, not freakishly explosive or anything but in a smooth controllable way and of course much more power than that 1975 CR250 can muster in stock form.


the compression release in the spark plug hole was a aftermarket add on and I don't care for them that much.

the factory compression release was never meant to be used like the spark plug hole one as it works in a similar fashion and the spark plug hole compression release can be used as a sort of a jake brake on a 2 stroke, it kills compression some to allow more precise cornering while relying less on the brakes themselves.

the factory one is triggered via a cable and by the kick start. I wanted to go the stock approach as I want the bike to appear mostly stock.

I welded on the Stinger to how it would had been on a stock Hooker pipe. the pipe now has room to open the seat latch whereas the seat latch handle needed to be modified to clear the stock Hooker stinger. the OD on this 1 1/4" pipe is not as big and does not require the latch handle to be trimmed.

I plan on adding a elbow with another length of 1 1/4" tubing to mount the silencer.

here is a pic of this pipe mounted on my other DT400.

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here is a video with the Hooker pipe on a stock DT400.

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Thanks for all the good info BigDog. Great project!

If you have not already welded the stinger i would suggest that you experiment with length.But again I would not make it a guzinta but a guzova to keep the flow smooth.Diameter counts as well,smaller is higher velocity.Good luck tinkering!

the inside diameter is about the same as it came with the Hooker pipe stinger with the silencer installed. when I add a length of pipe to the stinger,the stinger length should be very close to original with a much more effective silencer.

I also plan to install a TTO temp gauge on it as well. right now the engine is not running too hot and when I opened the top end it appeared to be in great shape. the plug is a medium chocolate brown in color on the electrode. so far so good!

here is another video I uploaded on Youtube. I went a little easier on it in this video and the bike never missed a lick until I stalled it but it lit right off with no trouble.


the compression release cleanup work was a complete success. it feels like you are kicking over a 80 or 100 cc two stroke,almost too easy!

I also found out the other day that the clutch is really slipping very very little. I got it up on the ports the other day with it in 3rd gear and it broke the rear tire loose violently, so much so the bike actually fish tailed a bit! when I get some tires on it that will hook up, it will then be really interesting!

Ah so,I thought it was a manual engine brake but sounds more like a auto startup assist.The reason I spoke of the trackers I remembered was I thought the top hole being larger may not coke up as much.As for the stinger I remember adding at least 3 inches to it to get it into 10k as well as changing the CDI.I think 10k on that will be 120+ though.