What is the difference between the twin shock and the later, for example 400e in terms of what makes the early ones much better performance? I mean I know there will be more aggressive porting on the b and c, but is it also the magneto/cdi? I know they are different, but I am having problems with my powerdynamo which someone else installed and it looks as though I may have to buy the whole kit over again as they say it will cost about as much just to buy the magneto unit by its self, in which case I would prefer to go back to original except that I cannot find the twin shock era magneto complete at all and judging by several forums on the subject neither can anyone else. So for example what I`m asking is if I am able to piece together the later magneto setup will it still run like the twin shock or what combination of parts will work? I have had two of the 400e models and they`re gutless. Obviously set up for a low fuel consumption, low emission, torquey motor, whereas this time I`m wanting the powerband the twin shock is renouned for (and I still am yet to experience)

The ignition won't be the difference between one model year being a rocket compared to a slug in later models. But i know your not saying that. Probably a lot of things, porting & pipe etc air filter restriction, all sorts. But in saying that they shouldn't be too different. Just looked up the specs & there's a definite loss in HP on later ones if i'm reading it right. With yours, any 'complete' system from "75 to the last model should fit. That includes points ignition magnetos as well. "74" Dt360A cdi & DT250A magneto too. Trouble is to find a good one. What the problem with your Powerdynamo System?. Bit out my expertise but plenty on here have used them.

See if you can find magazine articles where they dyno tested both models independently.

I'd bet the drop in advertised power is due to a switch to a new "SAE net" standard versus the "gross" horsepower methods previously used. Apples and oranges.

I think it was in 1972 that cars in the US went to the new SAE net horsepower standard... many models lost over 100 horsepower... not in real life... just on paper. There was another change in 1975 or so and the test got even more demanding. It's even more demanding today. That's why a 200 HP car today is much quicker than a 1960's 200 HP car of the same weight.

I've never found documentation on what standards were used for motorcycle testing over the years... I can say that Yamaha rated the early DT1 at 21 HP. Magazine test dyno charts show 16 HP. Curiously enough, the later DT250 was also rated at 16 HP.

Top speed is also a good indicator of horsepower if aerodynamics are similar. Especially since I doubt the aerodynamics are significantly better on a later model... might be worse as later bikes are taller. And the early and late bikes have very similar top speeds.

A 250 might have lost 5 HP on paper over the years... but in real life the difference is probably minor.

The twin shock DT400 Engines have very very mild porting but has a much more free flowing exhaust than the later DT400 D and E. the silencer is the culprit of the restriction, this can be remedied by modding the stock silencer or go to a aftermarket silencer but the lean jetting will get in the way of the aftermarket silencer. I think a Member here has modded a stock later model DT400 silencer with good results and he also owns a 1975-76 DT400. he can tell you the difference between the later DT400 and the 1975-76 DT400 power wise. I think it is Makotosun if I am not mistaken.

The Magneto on the 1977-78 is much better than the very fragile 1975-76 magneto on the DT400. Pulsar failure and CDI box failure is pretty common on the 1975-76 400s.