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yamaha mx360 engine

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I have a 1976 yamaha dt250.I am wondering about building a 1973 yamaha mx360 engine for it.Does anyone have any advice for me before I commit to this?I am thinking about using a powerdynamo ignition and was wondering if anyone has experience with this system?Its kinda expensive and would like some feedback.Also thinking of using a pwk 35 keihin carburetor.Any advice would be greatly appreciated.

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I would try to stick with a stock ignition as much as possible, they are still available on the internet and they are more than adequate for 95% of anyone's needs for the engine.  If you are looking to build it for serious power (45-50 HP??) then you would probably want to go aftermarket.  But if you are just looking at a mild build, no sense in spending money on an aftermarket ignition.

 

A 35mm carb would be a good choice for the engine (believe 34mm was stock), possibly a little overkill depending on what you are planning on doing.

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I want to insure this bike for road and dirt riding.I don't think the stock ignition would have the lighting coils,would they?Is this a good engine to rebuild,or would a dt400 engine be better?The 250 engine is a little gutless.Also would a rt360 piston work in the mx engine?The mx piston only has one ring and the rt has two.

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I doubt that the stock MX360 coils would support running lights, but you would have to do more investigation on that front.  It was common way back when for the OEM to use the same coil backing plates in several models that would span the street and dirt worlds.  So, it is possible that you could just swap in the ignition from a DT400 into the MX360 and get a working lighting coil.  But again, you need to do some more leg work and research on that front.  Checking the online parts fiche's would be a good place to begin.

 

Same thing with the piston.  You need to verify the bore, stroke and wrist pin to crown measurements.  Also need to check the piston crown shape to ensure that it is compatible as well.  I would just stick with the correct piston to alleviate any headaches.

 

The MX360 was a great engine for the day, but it is technology that is now 40 years in the rear view mirror, and it was designed as an MX bike to begin with.  If you are looking for something that you can ride legally on the streets and take on the trails from time to time, and you are in love with the idea of 6" suspension travel, and the very real possibility of having to push your bike out of the woods once it quits on you, I would start with the newest RT360/400 that I could find.  You would get more enjoyment out of a bike that was street legal from the factory than spending all of your time and money trying to make a frankenbike run right and be reliable.

 

Of course, you would be happier still with the newest dual sport bike that you can afford as you would have better parts support, better suspension, more performance, etc, etc, etc.

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Thanks for your advice.I have had my dt250 for a couple years and its been nothing but reliable.I am a fabricator and enjoy a good project so I am building my parts bike that's already street legal.

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Just my opinion.  I really wouldn't believe a cdi based ignition would offer any more performance than a points system, in fact possibly less. The short, but higher voltage cdi spark does nothing to ignite more of the fuel air mixture - but it will fire an oil fouled plug or support high reving race engines. Also, no more points to clean. But, the points system offers high duration spark that helps to insure more complete combustion, as long as your not reving to the moon, or running high boost pressures. Higher fuel air density means more resistance to the plug. I would save that money for other upgrades.

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My dad has 3 360's and 2 250's between 71-73. I've ridden them and honestly the 360 didn't wow me very much. I prefer the 250 that is running good to the more chuggy 360.

Regarding the ignition, why not just use an enduro ignition from a dt instead of the MX? How different are those motors anyway? I didn't think it was very much.

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Does anyone know if a dt250 points ignition work with a mx360?I know they are slightly different.I am starting to think this might not be a good idea.I was originally looking for a rd350 or 400 engine for my dt.I thought a 2 cylinder two stroke enduro would be cool,but this engine fell into my hands cheap.I do appreciate the input from you guys.

Andrew

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That would be great.Also,would a piston from a rt 360 with 2 rings work in the mx 360 that only has 1 ring?I am still trying to decide if this is worth it.Its starting to look like a expensive and risky project.Once again,thanks.

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Alright, sorry I'm a bit late, but I spoke with my dad about it. Basically he said it depends on what year frame, and what year MX engine you have. Like if you had a 70-73 DT, and wanted to put a 70-71 MX engine in it you could, as they were basically the same exact engine. 72 the MX saw changes in engine and are closer to the 74 DT. Then in 75 the MX engine saw even more changes and pushed farther from the DT engines.

 

Sorry if I'm not that helpful, but I'm going off memory from the conversation. He has a few books with all of the serial number ranges for these bikes as well as many parts books for them. If you want to shoot him an email send me a pm and I'll give it to you as he and his friends are very knowledgeable on these bikes.

 

Here are 4 of his enduros (2 250's and 2 360's) and his KZ900 He also has a 175 and another 360

 

23B0230D-A4B5-4BB6-BF64-A50DE90DBEFB_zps

Edited by MXRider72
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Wow,Nice!They look like the rts.I really like the kz too.I know I can make the engine fit,I am a welder fabricator.What I need to know is if the 1973 mx 360 is a motor worth while rebuilding.I have been told its prone to back-firing really bad.

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Yeah I have heard that quite a bit.I think I am going to forget this idea and see if I can trade this engine for something else.I am 43 and don't want to hurt myself when it back fires.

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Need help of mx250 stator and flywheel on a 74 dt250 runs to mid range but then won't pull running a vm32 200 main 45 pilot stock jets,

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it could be how you set your timing,a 32 mm carburetor is kinda big for a dt engine.My 75 dt 250 has a 28mm carburetor with a 160 main jet.The mx is probably ported out more.Did you set the timing for a dt or mx?

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