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dt/rt yamaha vs mx yamaha

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Gday guys, i am about to enter the unreal world of vmx here in west australia and would like to know the following.....

Is there much difference in the engines on the dt/rt yammies (1970-1974) compared to the mx yammies?

I suspect they are pretty strong engines, do they take to a bit of porting and head shaving?

Parts interchangeable?

Cheers rob

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Mines a 75, but iv'e looked at a DT cylinder of the same based gear and crank lower end. WAY different porting. Don't think i could mod a DT to what my MX puts out in power. The transfer ports runways are simply too small.

70-74 could be a different story....

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cheers for that.

what @ the suspension and frame?

I'm not too hip on those years,mine was the first production year on single shock for yamaha. So...it's kinda out of the "vintage" era for racing. :smirk:

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A parts finder web site can help in finding which parts are interchangable. I have a Haynes manual for Yamaha trail bikes from 1971 up to 74. It seems that some parts can be interchanged, maybe not engine internals, but check part numbers. The manual did not have much information about my '74 MX175, so I bought a Clymer manual to supplement it. I would say that the bikes didn't change to much from '71 to '74.

On a side note. My MX is not a powerhouse, the DT's are a little less powerful. They are not in the same power class as a YZ. I'm going to tinker with the carb a bit, if that don't help I'll be looking up scale jockey for porting tips.

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I remember back in those days, Dirt Bike magazine use to praise the MX frame and hate the MX engine. Too pipey. One reader claimed to have swapped the motors and created the perfect bike for that era. Smooth motor and better suspension.

The DT is really a street bike pretending to be a dirt bike. I had a 1972 CT-175 back then.

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Well now the MX has no power. The carb had a 150 main jet installed, it calls for a 180. I went to the local shop and they didn't have any jets that small. I decided to drill the jet. I had 2 small drill bits. In hindsight I should have used the smallest bit first, but like a dummy I used the bigger one. Now the bike fouls plugs instead of running. I guess I'll just order a couple of new main jets now. I'm hoping that once I get the carb straightened out it will feel like a 175 should feel like.

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I remember back in those days, Dirt Bike magazine use to praise the MX frame and hate the MX engine. Too pipey. One reader claimed to have swapped the motors and created the perfect bike for that era. Smooth motor and better suspension.

The DT is really a street bike pretending to be a dirt bike. I had a 1972 CT-175 back then.

What? The frames were the same at least on the early ones, if you look closely both the MX and enduro they had the tabs for turn signals and the front hub on the MX even had the fitting for the speedometer cable. The MX and the RT1 had way more in common then they had differences, I think one thing people look at is that the enduro had the low front fender making it look like a street bike.

P1000022.jpg

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I think that about sums it up...back then,up until the 74 YZ everything was a striped down enduro. But with a few mods things could work out..

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What? The frames were the same at least on the early ones, if you look closely both the MX and enduro they had the tabs for turn signals and the front hub on the MX even had the fitting for the speedometer cable. The MX and the RT1 had way more in common then they had differences, I think one thing people look at is that the enduro had the low front fender making it look like a street bike.

P1000022.jpg

Well the DT/RT Enduro bikes aren't road bikes like the RD350, but they were not as dirt oriented as the European Enduro bikes. They were dual-sport bikes. Oil injection, oil tank, speedometer, and tachometer. Lots of street parts. I ran my 175 down the freeways, jumped it, and did a lot of dirt riding on it.

As you said, even the MX line was using frames with tabs for street parts. People were stripping down Enduros, so Yamaha started stripping them down at the factory and changing the motor specs. The MX line was born. I'm pretty sure the AT/CT/DT/RT line pre-dates the MX line by a few years.

I agree with the next post that not until the YZ came out did the Japanese really get serious about dirt bikes. Unfortunately, Japan rarely started with a pure dirt bike and added turn signals to it, like the modern dual-sport KTM EXC's or Huskies.

As I remember, my CT-175 was a much better dirt bike than my Honda MT250 enduro. The other bike of that era I spent time riding was my friend's 250 OSSA Pioneer. I loved riding that bike, much like my XR400. Lots of torque and lots of weight.

My first real dirt bike was my YZ125D. My old CT-175 was more fun and broke down less often.

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Rob, the MX/DT-A are the next generation from the RT/DT1 bikes - they do everything a bit better.

The reed valve RT/DT1s can still be made to work very well as a low-budget pre-75 race bike.

The DT2MX is apparently quite a good thing, and hugely under-rated as a race bike (although still not in the same league as the Ossa Phantom or VR250 etc).

If you start with a trail version, the usual two-stroke tricks apply to making the engine go better. The frame mod is well worth doing too.

Do you know about ozvmx?

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