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Yamaha 1980 DT175(200) Major Problem

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Hey guys i havnt posted in this Yamaha 2 Stroke forum before so please be gentle on me and if i have posted in the wrong section could a mod please move it for me thanks.

Ok onto the problem. I own a 1980 DT175(Bored to 200cc by previous owner) and have had it running like a dream for the past 6 months or so. Sure it does suck through excess oil from the wet sump case since the seals inside are pretty much shot but once it gets down to about half on the sump stick its stops smoking pretty much all together except for the usual pre-mix oil smoke.

The problem that has occurred last time i went riding with it on my m8's farm was we were in a nice soft sandy paddock and of course my friend couldn't help but do a bit of circle work. I presume this is where the problem happened as about a minute later when he came back and stopped with the bike still running it started revving uncontrollable and wouldn't idle properly like it had been doing before. It started revving at full bore so i stopped it before it shat itself but the switch didn't work so i ended up having to put it in gear with brake on and stalling it.

This has me really confused because it started revving up and not idling down low and on top of this it wouldn't stop using the start/stop switch. What could have caused this because sure my m8 may have revved it quite a bit in first while doing some circle work but its a 2 stroke and made for that isn't it?

If anyone has any idea's please share because now the DT wont really run very well at all. The only way to get it to run so that you can actually ride it is either to run it with the choke off and basically having to continue to feather it when idling so it wont stall or to run it with the choke on and back down the idle and pretty much run it flooded. No matter what i do it wont idle but instead it will either rev up by itself for no reason or wont rev down after being revved up and also will not idle at a normal pace like it had done for the past 6 months. Also i should add that it is a shit to start but i can start it with patience and quite a bit of kicking.

I should add that although i did get this bike off a friend for $50 that it has been a great machine until this problem started. My old man and i have taken off the carby and had a close look and blown it out and it actually looks pretty much perfect and we couldn't see anything wrong with it. I am actually quite confused now as what could be causing it to not idle and rev up itself or just continue revving when revved up instead of dropping back down. As i stated the only way to stop this is the run it with the choke on and fiddle with the idle/fuel mixture screw but with choke on it runs flooded.

The only thing now i can think of is the reeds(I have no idea how these work) in between the engine and the carby. I presume for a 2 stroke they somehow stop airflow and start them but these are the only things we didn't check when we had the carby off and so i am wondering if this could be the cause of the problem? Could someone please explain to me how these reeds work and if in fact this could be the problem or is there some other thing that i may have missed as the carby looks top notch.

I really need some help with this as hopefully before Easter which is in i think 4 weeks over here that i can get this old yet great bike running again for another bush bash :smirk: Also if these reeds are the problem could this also relate to it being a bitch to start? I know it may be a wreck but for $50 bucks it had been running like a dream except for the oil being sucked out of the sump because the seals were shot which has stopped at a around half and being a little hard to start.

Any help is really and i mean really appreciated and please throw any and all your idea's at me as it really has me stumped and i do not know much about 2 strokes of have any idea's left except these reeds which i am unfamiliar about. Sorry about the long post but hopefully has a few tips on this problem or has had this problem with another 2 stroke or DT175.

Thanks Alot

Matt

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Well since it seems no one out of several people have any clue as to what my problem could be does anyone know if the head gasket or cylinder leaking could cause this problem as it also seems to have dropped some compression?

Anyone got any idea's or tips on this problem as i really do miss the smokey bugger :smirk:

Hopefully someone can help please

Thanks

Matt

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When the bikes get a stuck throttle, the kill switch does not stop them. It is a strange sensation, but pushing it does nothing. Your bike was also hot from the "circle work" and this would aggravate the problem.

Your in the right place. Most of us are from America and its been 25 years since we were allowed to buy basic two stroke offroad bikes like yours in 175-200 cc's. many of the younger people have never seen one.

The air cooled bike you have and sand have always been a bad combination. With the air cooled bikes you never got the warning signs of overheating like a puking radiator. I think your friend overheated the bike.

You probably need a new piston and rings and maybe a fresh bore. I would hate to spend the money for this and leave a leaking crank seal. That should be dealt with as well.

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With is revving out of control, it is most likely an air leak, if the throttle did not wedge itself open. The reed boot could be dry, and cracked from general use. No avoiding that. A toast reed gasket or lose reed-side carb clamp could be a cause also. After riding in the sand, some could have found its way into the area where the flywheel, stator and left-side crank seal reside. If that happened, the crank seal could have been compromised, therefore, would let excess air in and cause the engine to rev like you said.

Those engines are oil-injected, correct? Its possible that the hose that leads into the intake manifold (or carb in your case?) could have dried up and cracked, or the banjo bolt (injection to the intake manifold) could have rattled lose.

Does your engine have a Boost Bottle? The tube from it, to the reed boot could have sheared off / come lose from vibration and use.

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OMG guys i cant believe it problem solved and you wont believe how.

Well tonight i went outside and started up the DT175 and again nothing i did would make it idle properly and then in a split second i saw a pipe hanging down near the ground and a little hole going into the crankcase that looked like it was meant to have something in it.

Here is a picture of the hole that i found in the crankcase

94871559zw1.th.jpg

So i grabbed the pipe that was hanging loose and pretty much just sitting tangled up in the frame that some how hadn't fallen off for the 30-40mins i had ridden the bike after this issue arose. So i got the pipe and put it back in its place and now it looks how it should as seen below.

99948385sk2.th.jpg

So after i hooked it back up properly i wound the idle in and turned the fuel mixture screw out a bit and first kick she fired up back into life and i cant believe that its now back to how it was in the first place idling like a dream. I was so happen i screamed well i better not say it on here :smirk:

Anyways i would love to thanks you guys as once i read your posts i went outside and searched around the whole bike for anything that looked out of the ordinary and i found the problem.

Thanks so much and here is the beauty now back up and running :)

16944779de8.th.jpg

Thanks Again

Matt (PS. and the $50 dollar bike lives on :ride:)

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Your in the right place. Most of us are from America and its been 25 years since we were allowed to buy basic two stroke offroad bikes like yours in 175-200 cc's. many of the younger people have never seen one.

Also just curious about this comment and what it means? Are you telling me for the past 25 years over there and up until this day in time that you havnt been able to buy a 2 stroke motorbike in that cc range? Is this true and if so is it mainly due to pollution of burning oil because over here in Aussie i feel sure you can still buy YZ 125 and 250's 2smokes.

Any info on this is new to me thanks

Once again thanks for the help in fixing my old DT175 2smoke :smirk:

Matt

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Oh no.. that little hose is the oil injection.If it has been off for a while you've got some engine damage. Unless your running pre-mix (of course)

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Ah really? So your saying that little hose is for the autolube system?

Which doesn't really bother me lol since the bike hasn't had a autolube on it since i got the bike and i just run a pre-mix instead.

Just curious if thats what it is for why didn't it idle or run properly with nothing in it(Just a bare whole)? Because the only way it would idle, run properly was when i luckily found the missing pipe hanging on the frame and connected it back up and now it runs like a charm? Whats the reason for this as now it only has a small air hole now instead of a much larger one with no pipe connected. You sure its a oil/autolube system pipe thingy cause it just has the pipe connected to it leading to the back of the bike to draw air or exhaust air or whatever it wants to do with it etc?

I presume this setup now is ok and correct as it actually runs properly again :smirk: (Although i could be wrong)

Thanks for any replies

Matt

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It's good you've been running premix. The other problem with the hose being off is that it simply was sucking air and was leaned out(fuel).So there still might of been some damage from running lean.(a little piston seize)

You could put a screw in the hole just to block it off and get rid of the hose.

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Also just curious about this comment and what it means? Are you telling me for the past 25 years over there and up until this day in time that you havnt been able to buy a 2 stroke motorbike in that cc range? Is this true and if so is it mainly due to pollution of burning oil because over here in Aussie i feel sure you can still buy YZ 125 and 250's 2smokes.

Any info on this is new to me thanks

Once again thanks for the help in fixing my old DT175 2smoke :smirk:

Matt

We have been able to get the yz 125 and yz 250. The pw 50 na d80 has also been available.

However, the 125, 175 and 250 trail bikes are gone and have been for years.

We cannot get these http://www.yamaha-motor.com.au/motor/index.htm?motor.asp

I would love to have one of the ag bikes just for terrorizing the neighborhood.

The last fun (2 stroke) trail bike we could get here was the rt 180, but its been gone for a while. Really a shame that a cheap and long lasting two stroke offroad fun bike is just not available to us. That woudl probably the most recent bike available to us that was similar to what you ride.

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Now that you say that before i put the plug/hose back in its spot i had a rubber plug totally blocking it off and i could still barley get it to idle because the idle screw was in its maximum position and wouldn't go any further so luckily i then found the original plug/house and stuck it back in and off it went :smirk:

Any reason or this? as its got me stumped but im glad its back working properly now :)

Also in reply to Rcannon bad luck that you cant get some of the 2-strokes in your state/country and also i wouldn't really say i ride the DT175 much its for my dad mainly cause im on my HONDA XR250 thats road legal over here and im on my L plates and i love the solid 4-stroke grunt and don't like revving the shit outta the yammie even though it seems to love it lol

Thanks Again

Matt

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G'day mate

I have a 1997 DT 175 and im currently thinking about getting it bored out to a 200cc. WOuld u recommend this? How fast does urs go?

Cheers Tom

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Haha well tmcdoual considering i bought this Yammie DT175(200cc) for $50 and it was already bored and is pretty much a wreck i would have to say that it goes quite good even though the whole engine on it needs a rebuild because the owner before me didn't care about it what so ever but i have a Honda XR250 and this Yammie is pretty much just a muck around bike now or my old man rides it when we go out to our m8's farm so it running is all i care about.

I cant really say if it would be worth it since i didn't know the power it had before at stock but it can lift the front wheel when it hits power band if the rider lets it :confused: and is still good fun for a 2 smoke.

EDIT: With what ever gearing it has on it which i don't really know because its to dirty to see the numbers it goes about 100km/h according to when i was riding next to it with my XR250 speedo.

Hope this helps

Matt

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Now that you say that before i put the plug/hose back in its spot i had a rubber plug totally blocking it off and i could still barley get it to idle because the idle screw was in its maximum position and wouldn't go any further so luckily i then found the original plug/house and stuck it back in and off it went :prof:

Any reason or this? as its got me stumped but im glad its back working properly now :bonk:

Also in reply to Rcannon bad luck that you cant get some of the 2-strokes in your state/country and also i wouldn't really say i ride the DT175 much its for my dad mainly cause im on my HONDA XR250 thats road legal over here and im on my L plates and i love the solid 4-stroke grunt and don't like revving the shit outta the yammie even though it seems to love it lol

Thanks Again

Matt

funny, I have a 1980 IT125 with the same hose and "hole" in the crankcase. My IT, however runs strictly on pre-mix (as they all have from the factory). Turns out that on mine anyway, it's just a crankcase breather as the hose goes up under the tank and vents at the headstock.

The DT's and IT's share some parts, and Yamaha in their wisdom found another purpose for this hole.

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That hose should have nothing to do with your over revving problem.....I can't believe putting it back on fixed it?

If your throttle was NOT sticking open when that happened, then it sounds to me like the crank seals, one or both, are going bad. That will allow enough air to leak in just like as if you were holding the throttle open.

And don't ask me why, but once that happens and the motor runs away with itself, the kill switch won't kill it!!!

I don't know why but I have experienced this on several bikes.

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my dt200 was like that because of the wrong spark plug, it had heated up so much that it kept igniting even after kill switch and spark plug cable pulled off etc... talk about confusion!!! call BS if you like, you werent there to see it lol.

had to block exhaust with hand to eventually choke itself out.

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