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Discussion Starter #1 (Edited)
Hi,
I know this is not a Honda but my other bike is an RD04 and i know you know a lot about bikes so can i pick your brains???. im currently in the states and have been riding around on a beautiful old 1974 two stroke Yamaha DT 175 (the girlfriend hates the smell of a 2 stroke but i think it rekindles my youth so she will have to learn to love it!!! :D)
the problem with it is that its fine up through the gears until it gets to 5th then at 4000 revs it splutters and wont pick up.
the carb set up is as it should be, points are good and there are new reed valves- but the spark plug is slightly wet and oily, i have checked the oil injecter and it leaks small drips of oil that builds up in in the crank case which i need to empty every once in a while. can i bypass the injecter by premixing the oil/fuel (30:1 mix ratio i think) would this damage this old classic bike and would this malfunction cause the plug to become fouled.
Any ideas
Many thanks
Ian
 

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2 bikes = twice as happy
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I had what was probably the later model with a single shock -a DT175MX. I had continual problems with the alternator windings mostly manifesting as a weak spark, with misfires and very difficult starting. A weak spark plus a heavy load on the engine in a high gear tends to result in a misfire. A rewind of the alternator was the cure. I think the alternator is shared with air colled RD yamahas of the era.

Other than that it's a two stroke so as I am sure you know, very sensitive to carburation, air filter, reed valves and exhaust. A build up of 2 stroke in the crank doesn't sound good to me either. Running rich and or to much oil or someone has been playing with something in an attempt to tune it.

Not much help this really and it's over 25 years since I had mine. I would love another if a good one came up at the right price. Not sure they are proper classics but were bloody good bikes.
 

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my sons old feild bike was the watercooled version and that.. ran fine on a 25/1 oil in Tank mix, as the oil injection was removed, ( along with most of the stuff not needed to thrash around a field )

great wee bike, smoked like a 1930 french whore :D
 

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The Angry Pasty Muncher
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6,170 Posts
Hi,
I know this is not a Honda but my other bike is an RD04 and i know you know a lot about bikes so can i pick your brains???. im currently in the states and have been riding around on a beautiful old 1974 two stroke Yamaha DT 175 (the girlfriend hates the smell of a 2 stroke but i think it rekindles my youth so she will have to learn to love it!!! :D)
the problem with it is that its fine up through the gears until it gets to 5th then at 4000 revs it splutters and wont pick up.
the carb set up is as it should be, points are good and there are new reed valves- but the spark plug is slightly wet and oily, i have checked the oil injecter and it leaks small drips of oil that builds up in in the crank case which i need to empty every once in a while. can i bypass the injecter by premixing the oil/fuel (30:1 mix ratio i think) would this damage this old classic bike and would this malfunction cause the plug to become fouled.
Any ideas
Many thanks
Ian
One of these you mean



you can do away with the injector side of it and go to pre-mix. This one also seems to be suffering at the moment from being way too rich
 

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Try the premix, but if I recall, the setup for premix carbs is slightly different; possibly down to jet sizes. You can't break it, but you might need to clean the carbs.
 

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It is possible that the injector is worn meaning it gets the wrong mix for the power. I have known of the bikes having the injector system removed and premix being used with great success.
 

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Stone Crazy
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5,310 Posts
i think you can rebuild the pumps you know . my view is the old fart about of mixing oil and petrol is long gone, injectors give you a bigger shot of oil at high revs and less at low speed which helps it too run more efficiently, my Rd250 does like you say drip a bit of oil into the crankcases i think, it is very smokey after standing for a while, but i look at it as a good thing as it means i know it has oil in the engine when the engine is cold

also you can shut the carb down to stop the engine when the throttle is right off and the engine still gets oil on the overun,

f You must go ahead and do away with the oil system either remove the pump and blank off the hole or run a pipe from the inlet to the outlet and fill it with oil so it circulates it,

if you want some more specific help with the DT 175 there are a few guys on the Yamaha Motorcycle Owners Club Forum that own one has had his for20/ 30 years or so from new and knows more abut them than me so if you want too join us there please do
merv
 

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No one has mentioned a clogged exhaust, all strokers rely on a clean carbon free exhaust. I used to compare the weight of a new one to a used one, sometimes the difference is staggering indicating the weight of carbon build up. My DT175MX was spot on, did motocross and trials on it (both different set ups) and green laneing. In my opinion first place to look is the exhaust.
 
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