Off Roading Forums banner
1 - 6 of 6 Posts

Discussion Starter · #1 · (Edited)
I think I have a '81 Yamaha DT 175, apparently there are 3 versions of the 175. Mine is a 2 stroke. It was given to me after sitting for about a year. I think it is a DT because it has lights and turn signals and I had to buy a part and the DT stock list IPB had the part I needed. One of the other two models also had the same part number, but I forget which. Another reason is the only book I could find was combo Clymer’s for the DX and XT and although similar, does not look like either. Any way to determine which I have?

Now for the real questions. After getting it running, I have a couple if issues.

1. The Oil indicator light stays on. It has a separate reservoir for 2 cycle oil. Since I don’t know the proper term for it, I’ll call it the ‘Oil Controller’ basically, it is a mechanical driven pump that has fresh oil line coming into it from the reservoir and is shaft driven by the engine. The oil amount is controlled when the throttle is rolled. A single throttle cable goes into a box on one side, comes out as two cables on the other - one connects to the carburetor and the other to the oil controller.

As best I can tell, oil is getting to the engine side of the oil controller because I removed the oil controller and raw oil was present, by raw I mean it was just as clean as from the oil reservoir.

How can I confirm oil is getting into the cylinder? After running the engine for about 5 minutes, I took the plug out and it looked pretty ‘dry’, I was expecting it to appear a bit wet if oil was getting into the cylinder. Does it take a while for the oil to circulate? I am afraid to run it too long for fear of causing damage. Of course the oil reservoir was empty when I got it.

2. I am having trouble with setting the idle. I think it may be related to the float level. After about 5 minute warm up It will only idle if the choke is part way on which makes me suspect the float level is set too low. Another reason I suspect it is too low is because if I shake the bike from side-to-side or bounce on the seat it will die (as in not getting fuel). I took the carb apart before I got it running and it was surprisingly clean. No sticking parts or ‘varnish’ from old fuel. The fuel flows out of the tank in a steady stream when disconnected from the carb. The bike also starts really easy even when cold (1 or 2 kicks).

I can’t determine the location of the idle adjust screw because the resolution of the picture in the book isn’t good enough to figure out what the arrow is pointing too. There are two candidates; one is a knurled bolt with a tensioning spring on the bolt that I can adjust without any tools. This is about center of the carburetor, on the top half of the carb (bottom half being the float bowl). It looks as though if it adjusted all the way in, would keep the throttle from closing completely. I think this is air mix only. There is also a small set-screw to the right of that at a slight angle. I think is the idle screw. I cranked it all the way, both directions, which was only about 4 turns, but did not notice much of a difference.

Any suggestion?

Thanks in advance!


Discussion Starter · #2 ·
'81 Dt175

Hi Sans1,
I purchased a 1981 DT175 last year for my son at school. It came with the small owners manual clearly identifying it and so I'm sure what it is. Describing mine a bit may help you know what yours is. It has a bright red tank with white plastic fenders. It says enduro on the sides in black. It has all the lights including turn signals.
If these bikes are running well tuned I wouldn't expect to see the plug really oily looking because the fire in there would be pretty intense each time it fires.
Regarding the carb I'm having some trouble also, especially since I don't have a shop manual. I believe the big spring knob is for the idle mixture (probably needs about 1 & 3/4 turns).
Our's has now developed too weak of acceleration until up in higher gears and rpm. Took carb apart and found rust, from tank I believe, was holding up the main needle in the main jet and flooding it. I saw that the float was also obviously messed with by an amateur probably to compensate for dirty carb.
Can you tell me the correct float setting from your manual?

Discussion Starter · #3 ·
Float setting

The way it said to set the float was to warm it up and then connect a clear hose to the fuel drain (that can handle gas). Loop the hose and rest it against the side of the carb. Open the fuel drain, look at the level where the fuel is in the tube will tell you the bowl level (I took the book back to the library, but think it said at least 3/4 of the bowl).

I have not tried it, mine was actually set too high and the fuel was never shutting off (ran out the overflow). I adjusted the float until I was sure it shut off the fuel, but did not change the symptoms. Best I can tell, it does not seem to matter too much.

As far as where the oil dumps into the carb, it is right at the exit of the carb/ entrance to the cylinder. When I disconnect the hose and roll the throttle, oil oozes out a bit. Not real excessive, but since it mixes with the fuel at this point, makes sense it would not be a lot. The oil light stays on, I'll need to figure out where it senses it and check it there.

Sounds like mine is a DT 175, same as you described. However, it turns out it is a 1980, not 81 as the guy that gave it to me thought. I did get a chance to ride it at my friends, (30 acres) got it up to a little over 50 on the washboard driveway before I slowed down, worked great at speed, but still does not want to idle.

I sprayed carb cleaner all around the engine looking for air leaks, but didn't find any.

Discussion Starter · #4 ·
Thanks Sans1,
I was thinking that I may have had the float such that the level was below the idle circuit because it kept quiting after a few seconds but it was because the plug was bad. Bought a new plug and like new bike.
A good thing about concentrating so hard on the carb though was that I found that the tube or jet the main needle goes up and down in was able to push out of the carb body and had small holes in it that were plugged up. I used a chop stick and tapped that brass jet deal out and cleaned with a piece of fine wire...
Doing that may benefit you if you haven't already.

Discussion Starter · #5 · (Edited)
Wish I had correct float height though.
Idling great, but stuttering too much below power band, because rich now I'm betting, from one forum comment I saw.

· Registered
4 Posts

Lost my account credentials for a while and moved on to other bikes. Wanted to give an update just in case someone comes across this old thread.

My issue turned out to be a clogged air hole where the air screw goes into the carb. I had sprayed it many times with carb cleaner, but finally I removed the screw completely and worked the straw on the carb cleaner in and out of the air hole going deeper each time until it was all the way in. Turned out there was quite a bit of dirt completely clogging the hole which also explained why the screw did not seem to have any effect on the engine performance up to that point. Put it back together and now idles fine and runs great.

As for the oil, I disconnected the oil injector and use a mix of 32:1. This was the bike my daughter learned on and she has since graduated to an Honda XR250. I keep this one for guest riders - it has served me well and running strong.

@ Motoguy - As for the float level - paraphrased from Clymer M412
1. Remove the carburetor.
2. Remove the float bowl from the main body.
3. Measure the height of the float above the carburetor body. Hold the carburetor so the float tang is just touching the float needle-not pushing it down. For all DT 175 Models (77-83) the book says 21.0 mm
4. Adjust by carefully bending the tang on the float arm. If the float level is set too high, the result will be a rich fuel/air mixture. If it is set too low the mixture will be too lean.
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.