DT 175 mx revival

[oak framer]

Hi everyone, after a long time without a bike 18 years!! I recently got given a DT 175 MX that runs but needs work. Unfortunately It didn't come with a V5 or registration number. I would like to try and put it back on the road one day. The frame and engine numbers match but I don't know the year of it. I know it is a later model because of the box section swing -arm I learnt to ride on a DT175 mx with a tubular swing -arm my first bike! Is it possible to date the bike ? Can someone point me in the right direction please thanks AD

[blackhat250]

Hi , welcome ,,, The best thing to do is join The Vintage Japanese M.C. they can help date and register your , DT,

Plenty of DT fans on here,

[Airhead]

Hello and welcome oak framer, given it wow thats lucky whereare you? an intro would be good

...Paul

[oak framer]

Hi and thanks Black hat I will try vintage Jap club.Hi Paul I am in Welsh Borders.

[Airhead]

I read something on here once that the dealer may have registered the bike at point of sale and that you may be able to retriever the reg number from yamaha uk

or if that fails,I Have also read that... using your frame number yamaha uk will write a letter stating the age of the bike in question for a nominal fee, this can then be used to get an age related number from DVLA

[oak framer]

Morning all, Thank you Paul I will make some enquiries. I was just reading another thread on here where Cynic says this "You have the bike listed on your profile as a 2k4 thats just a chassis number prefix common to DT Mx's, if its a 1981 bike its a 4J4 chassis number 2k4-020101 onwards.

If it is an early bike then it would be a 2X2 with a chassis number 2K4-010101 onwards". My bikes frame and engine number start 2k4-0262.... and it has a 3u500 carb with a 160 main jet so I presume it is a 1981.

Also I was reading somewhere on here about later DT175s having a different type of spark plug but cant find the thread to read again. My bike picks up ok in lower gears but seems to lack top end and splutters at higher revs and at full throttle almost like its restricted. I am wondering if this is the reason why. I have a BR8E1X plug fitted in it.

Adam

[Airhead]

Morning all, Thank you Paul I will make some enquiries. I was just reading another thread on here where Cynic says this "You have the bike listed on your profile as a 2k4 thats just a chassis number prefix common to DT Mx's, if its a 1981 bike its a 4J4 chassis number 2k4-020101 onwards.

If it is an early bike then it would be a 2X2 with a chassis number 2K4-010101 onwards". My bikes frame and engine number start 2k4-0262.... and it has a 3u500 carb with a 160 main jet so I presume it is a 1981.

Also I was reading somewhere on here about later DT175s having a different type of spark plug but cant find the thread to read again. My bike picks up ok in lower gears but seems to lack top end and splutters at higher revs and at full throttle almost like its restricted. I am wondering if this is the reason why. I have a BR8E1X plug fitted in it.

Adam

Yours is a later one and will give you good service / reliability and heaps of fun when you sort it out (lucky git ), spares can be expensive though and there is usually a lot of competition for them on ebay

As far as I know they all used the same spark plug an NGK B8ES, not a BR8... as you quoted.

They had a B8ES and also a resistor type plug cap (5000 ohms)...so if yours has a resistor plug cap and also a resistor plug (BR8..) you are in effect doubling the resistance and it wasnt designed for that. However if your plug cap is not a resistor (aka suppressor) type it should be ok with said resitor type plug.

Lack of top end and spluttering can be a hard one to find so I hope you're a patient sort who has a multimeter, start with sorting the plug and cap.

[oak framer]

Hello all, still trying to sort out lack of top end on the DT, tried new plug as you suggested Old git but did not improve performance. I have been through the carb and cleaned it but for some reason it keeps pi**ing fuel out of the overflow pipe, checked float height and set at 21mm but still no joy.

I also would like to check the electrics with a multimeter, I saw a good thread here with photos that went through the whole fault finding process but I cant find it now, any one remember the title of it?

Adam

[blackhat250]

Aye oakfrmr" if the fuel still pisses out overflow pipe, then the float valve [ small pin that pushes up ] must be leaking , you can sourse mikuni parts easily,

& try a search for that post on DT"s

[oak framer]

Hi Black hat, I replaced the valve a while back as it was leaking then, but it made no difference.

[Airhead]

The fuel leaking is either the valve and seat or the float adjustment or the float is leaking.

[blackhat250]

The fuel leaking is either the valve and seat or the float adjustment or the float is leaking.

Yeh auld een , i forgot that, float itself could be taking fuel into it , and not floating .

[Airhead]

..........I also would like to check the electrics with a multimeter, I saw a good thread here with photos that went through the whole fault finding process but I cant find it now, any one remember the title of it?

Adam

is this the one?

[oak framer]

Hi guys. the float was also replaced with a new one at the same time as the valve along with the mixture screw.

Old git in the thread on cdi / multimeter etc the chap ended up converting his DT to a 12 volt system using parts from a honda C90? it showed all the wire colours and ohm readings/values.

[Airhead]

yes i remember the thread in question

did you replace the valve and seat or just the valve. I must say i've had this trouble too with new valves passing.

Also there is a gasket under the seat it needs to be there to revent fuel coming down through the threads but this would cause a leak as bad as p1$$ing out

[Airhead]

Hi guys. the float was also replaced with a new one at the same time as the valve along with the mixture screw.

Old git in the thread on cdi / multimeter etc the chap ended up converting his DT to a 12 volt system using parts from a honda C90? it showed all the wire colours and ohm readings/values.

[oak framer]

Thats the thread Old git thank you very much couldn't find it ! , the other thread is very good too. Regarding the carb I will check to see if there is a gasket there.

Thank you again

Adam.

[Airhead]

DT175MX Ignition checks

There were two versions of ignition systems on DT175MX bikes. The mk1 version from the earlier bike had a 7 wire CDI the early bikes had a round section swing arm.

The mk2 version had a 6 wire CDI, the red wire is absent on these. These bikes have a square section swing arm.

The HT cap (AKA spark plug cap)

unscrew it off the HT lead, it is supposed to be a resistor cap so should be around 5K Ohms

The ignition coil secondary...HT lead to battery neg should be 5900 Ohms +- 20%

If the readings are much higher, check the ignition coil has a clean ground connection.

Yes and the ignition coil mounting is a wiring harness ground point too, so check its clean and bright there.

Disconnect all the wires from the CDI.

Then using your multimeter on the loom side of the connectors.

Black probe on a clean part of HT coil ground point

Red probe on......

Orange, Meter to 200 Ohms, expect 1 Ohm (HT coil primary)

Brown, Meter to 2k Ohms, expect 420 Ohms for mk1 and 300 Ohms for mk2 (Magneto charge coil)

White/Red, Meter to 200 Ohms, expect 12.4 Ohms for mk1 and 10 Ohms for mk2 (Magneto pulser coil)

Red, Meter to 200 Ohms, expect 13.6 Ohms for mk1 only. (Source coil 2 or high speed coil)

Black female connector, Meter to 200 Ohms, expect dead short

Black male connector...as above

Any difference in the results for the two black wires may possibly be rectified by cleaning the front engine mounting bolt and a little of the frame behind the bolt head, then tighten to torque spec.

Black/White, Meter to 20K Ohms, with ignition off expect dead short, with key on expect open circuit, with kill operated expect dead short (Engine kill operation)

If all these tests are good you would be well advised to try another CDI.

If they are not good...reading higher...disconnect and clean any plugs/sockets you find along the way, if the magneto coils are reading lower, new ones needed if more than 10%...or so the book says