Great news, , the figures MEIS says are good, , your plug is a little black, In the video" it looks like thers no air filter in , ? will run better if filter installed,
My DT250D runs around 370 degree,[ uphill]

If you need side panel DC makes them in a matt finish polyethylene. Also front/rear fender. I believe you can clear them for a glossy look. www.dcvmx.com/xcart/product.php?productid=186895&cat=&page=1

Thanks frankc. I have the side panels, just didnt have them installed when I took the video

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I hadn't even thought about gearing. I'm bet this bike is geared low by the previous owner because he raced it in hairscrambles I think.

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The air filter is installed. I think you're seeing the airbox cover

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what did you have for air leaks ?

Really big leak at the bottom of the intake boot. Apparently thays really common. I should just buy a new one but I made a gasket for it and used some Yamabond. That fixed it.

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Can all three marks be aligned and timing still be off? (77dt400)

I am doing the 3.5 turns back, 1.1 turns forward thing, as well as the below method, and my flywheel which is properly on the woodruff, is about 1/2 inch before the crank mark and the stator marks (which are aligned). Using an inch (one inch divided into tenths) dual gauge.

A seemingly much simpler method than the bizarre procedure in the service manual: "you also need to "zero" your dial indicator too before attempting to read the timing. bring the engine up on top dead center and with the small hand at 5 mm and the large hand on 0, rotate the engine backwards to 2.9 mm is read on the dial indicator and check all 3 marks. they should be all aligned then."

I'm getting temperatures of around 350 degrees also at my plug. Highest temp I got was like 380 degrees 1978 dt400 

Can't go wrong with motors like that. Just put the back plate on where original screws leave a mark of having secured. Then flywheel on crank key & what can go wrong--unless something in the cdi box has gone wonky. Should be --or could be--a slight mark on the plate to align with a similar mark on the case, which in theory should align when original screw witness marks are used. That's providing someone in its life hasn't moved things all over the show & left marks everywhere. Be likely not far from center of the slots. Gives you a bit of room in the slots to play retarding or advancing if you wanted to & i guess check temperature reading which i should learn how to do.