well,this post is on installing the fuel tank,rebuilding the petcock and installing the Hooker pipe.
these 2 wires is what runs the headlight and powers the rest of the electrical system. I have not installed the regulator/rectifier assembly just yet.

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I removed this exhaust collar from the cylinder.the Hooker pipe has a flange to bolt to the cylinder.

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I used the tank off the other DT400,now is a great time to put in a new valve in the petcock. this petcock needed rebuilding as it leaked and would drain fuel into the engine parked overnight.

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now to install the Hooker pipe.
the pipe fits like a glove despite no fin relief on the head to clear the pipe.

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put on a fuel line and mixed up a 1 gallon batch of 32:1 with Yamalube 2S and fuel with no ethanol in it.

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she is ready to go for a test run of the fresh engine.

here is the video. I had the idle speed screw out too far and I probably flooded it but she lit off and sounds pretty good!
this thing will rip once the engine is broke in and tuned!

ignition timing is roughly at 2.4 to 2.5 mm BTDC. engine never kicked back at all. the timing spec on a MX400B is 2.7 mm BTDC.

the idle mixture is not exactly ideal like it has the mixture screw in a little too far. despite this the engine runs smoothly and has pretty snappy throttle response. the stock DT400 throttle and cable only opens the throttle at about 3/4 the way open at full throttle.

I have a few things to take care of but it shows lots of potential. I need to strip it down back to a bare frame and get the frame and swing arm for paint. fix the brakes to where they don't stick and put a set of sprockets and chain on and put on the missing pieces.

need to get all new cables and 1 foot peg and put a good silencer on the pipe.

I have 2 heat cycles on the top end,the second start from a cold engine started in 2 swift kicks. I am hoping the stock DT400 clutch will handle the power. it has snappier response than my other DT400 does. this should be 1 very fun bike to ride!

the engine does not vibrate any more than a bone stock DT400. all in all we are off to a strong start.

the engine even runs cooler than I expected.

Seems like you are the only one who has a Super DT400. Congratulations!

the MX400B top end and 38 mm carb can be done by anyone on a DT400B or DT400C. it is all bolt on stuff.

I got in touch with Dave Meis and he says he can build a DT400 sleeper pipe to match the MX400B cylinder's RPM range and all that.

a MX400B can rev out to 8,000 to 8500 rpm. I think the 38 HP a MX400B made it's power peak at 8,000 RPM.

a stock DT400 was all done by 5500 rpm all bone stock. it would rev to 6500 rpm but it was futile to spin it that high.

a schizophrenic DT400B that thinks it is a MX400B could be a very entertaining bike to ride to say the least! the MX400B is also known for a excellent torque band and lots of torque from the bottom to peak revs. I suspect if you limited yourself to 1/4 throttle it would mimic a stock DT400 pretty well.

but where is the fun in that?!?!

my mind is made up,I will put a Sleeper pipe on this bike! I will still use a aftermarket silencer on it,probably a FMF Turbine core II 1 1/4" universal silencer. I am pleased with that silencer on my 1978 DT175 and I think this bike will receive one too.

this video performance wise is what I am aiming for.

I think you already have that bike beat all to hell BigD. .Yours sounds very nice to me.With the sleeper pipe and a good flowing air filter it should rip.I doubt you will ever need to wind it to 8500 unless my ears fail me.

BigDog. I am porting my cylinder for my 78. I hope it gets on half as good as the MX400. I added 2 boyesen auxillary intake ports, lowered the intake 3/16 inch-flat bottom. Cutaway the separate boost port so as to incorporate it with intake, reangle to 10mm before spark plug and widen , widen exaust port to 65percent only above transfer opening, widen all transfers 1mm, raise transfers approx. 1/2 mm, lower verticle angle of rear transfers to about same angle of piston crown, which is less than the above 40 degrees that they were, reangle rear transfer wall to back toward intake. I have just 1 side bank of transfers left to do and the cylinder will be complete. I am using no port map or timing figures so I hope I did not screw up the cylinder. Also I will cut a rectangular hole in the piston 5mm or so below the lower ring land for under piston crown cooling-evacuation. Next after I get it running a oval bore to carb to 35.5 mm, adjustment of squish, and much later pipe mods by dtmeis when he wants to make a run of sleeper pipes for 77-78. It will be worth waiting FOR. I have never ridden a yz or moto cross bike, so do you think the bike will be more exciting to ride after the mods.

If I interpreted your mods correctly, it sounds like you are on the right track . . . you will definitely pick up some power throughout the power curve ... esp. mid range, and maybe a little more top end . . . The stock exhaust pipe will be holding it back from showing the true potential of your porting work.

I would be interested in seeing you start another thread on your own bike . . . . including pictures & the outcome of your port work.

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sounds like you are on the right track!


thanks!

Good work gents, I would upgrade the clutch, the IT 465 is the same amount of tangs . [ fitted my DT250D & dt400 engine] the MITAKA kits are good, stronger spring in kit.