Classic Motorcycle Mechanics

1981 Yamaha DT175 MX

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Q:I’m hoping you can help with a running problem I have with my DT. I bought the bike unseen and have renovated it over the past two years (see before and after pictures) but it has always suffered with poor running and splutterin­g on small throttle openings. I have fitted a carb refurb kit, new air filter and checked the float heights but it still baulks down and splutters until the throttle is about a quarter opened or more when it takes off! Can you suggest any areas I should be looking at please as the bike looks great but it’s a real pig to ride around unless you go flat out everywhere! Tony Preece

A:I agree that this does sound like a carburetto­r problem, but firstly I am assuming that the crank seals and reedvalves are all okay? Also, it might be an idea to double-check ignition timing, which is supposed to be 1.8mm BTDC. If the pilot jet is correct and clean, the carburetto­r as a whole is clean and blown through (including the tiny holes in the venturi) the fuel level is correct, the fuel you are using is not too old and the air screw is set to around one turn out, I hope the engine is idling satisfacto­rily. For the next throttle position just beyond idling we rely on the throttle cutaway but unfortunat­ely I do not have a note on what the actual specificat­ion is. So you might need to check this by substituti­on if you can get hold of another DT175 MX carb, but then again, if you can and it is in reasonable order the obvious thing would be to try changing the complete carb.

 ??  ?? Yamaha DT175 after.
Yamaha DT175 after.
 ??  ?? Yamaha DT175 before.
Yamaha DT175 before.

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