Hi all I have a 1978 dt 175 and I'm in need of some help with it. The bike starts however that's about all it does right. The idle is very rough and and it smokes way more then it should. Also the bike bogs out and dies when any throttle at all is given. I am unsure of why this is? I have tried a lot of different things I have cleaned the carb several time and blown it out I just found out after having the bike for a year that I have a 79 carb and was missing a I ring to seal the main jet. I ordered some "correct ones" but I also I have found one that seems to fit but no change at all has occurred. A friend has recommend me playing with the timing but I'm not sure if ican adjust it at all because it has a cdi or even how to test it.

I'd appreciate any insight you guys could provide.

Here's a video of my bike running

Ok " so it starts, is this on choke only ? you cleaned carb ? did you take out the pilot jet, ? as this is the first 1/4 throttle fuel supply.

, leave the timing , till as fuel system is fixed,

The exhaust ? take it off, and de-coke it, baffle too.

the idle is too low, screw it up a bit,,

Carb should be clean by all accounts the piolet jet is a bit big at the moment because I put the 78 jet in the 79'carb but a new one is on the way. I've had the exhaust cleaned out already as well as done it my self shouldn't be and issue. Not sure what you mean by baffle though. The bike will run off the choke but is more likely to die it will pretty much run indefinitely with it on.

Also adjusting the idle screw doesn't affect it that much nor does the air mix

sounds choked up and lots of smoke...I wonder if the crankcase has lots of oil in it ?

For awhile I was running the bike without oil in the case because i just wanted to get it idling and revving right and it behaved the same way

For awhile I was running the bike without oil in the case because i just wanted to get it idling and revving right and it behaved the same way

Nahh I'm talking of the crankcase not the transmission...dont confuse the two

Ok how how would I empty /check?

I'm afraid there isnt a drain plug so it would be cylinder off and dip something in the void to check!

a fair bit of work if i'm wrong though!

can you smell fuel in the transmission oil?

You do understand how a 2 stroke engine works.

The gearbox should have oil in it. That should not affect the engine proper at all.

Constant idling of big 2 stroke singles (175 is a big 2st cylinder very over square) they will not generate any heat in the bottom of the engine. Heat is needed here to keep the oil as a mist within the charge. Also to clear any oil left from when the engine was last run.

This is why 2st smoke so badly from cold. The mixture goes to crap and back clearing the oil. Then there happy.

What do you mean the carb "should be clean by all accounts" it was a really small amount of crap shut my 250 down at the weekend. Used a tiny copper strand to clear it.

Lastly you may not realise but the jetting differences between a 79 and a 1980 dt are HUGE like 40 points on the mains. So 2 questions.

What side is the 2st oil tank.

What size is the main jet.

Airhead I replaced the rings so I have had the bike down that far and I nor did the person who was helping notice any oil build up and we did check in case there was some sitting. The reason why I think it could be timing is it's not combusting right and not burning up all the oil. My mixture could also have to much oil but I've filled the gas tank multiple times and it's always smoked like that. Also I don't smell fuel in transmission oil

Cynic I have cleaned my carb many times however I do have a question about something if your looking at the air intake side there's the three holes the left most you can see the air screw the middle is blocked by a metal ball( not sure of technical term) and the third almost looks like some sort of jet to me. I tried to blow compressed air into while checking other ports and holes on the carb and that was the only thing I couldn't feel an outlet on. So my question is what is this is it some sort of airjet? Should I feel air coming out somewhere? Also I have a 140 main jet in the carb currently. The 2st oil tank should be on the left side but I don't have it. I have the pump disconnected and plugged at that carb.

Thanks for your input guys really appreciate it

Yeah thats the air jet, air goes into there and is regulated by the taper of the air mixture adjustment screw...normally set at around 1 1/2 turns out from gently seated (mixture adjustment)

Ok that's what I thought if I blow air through it and the air screw shouldn't it outlet somewhere?

Into the float chamber and on the other side of the slide in the venturi.

Ok and if this where blocked would the air screw have no or minimal effect on the bike as I adjust it?

yes but dont forgat its a very small hole so there wont be much volume of air passing through it

Ok I'll check it out again but the air mix screw really does nothing unless I take it out far enough and the bike just doesn't run

Ok I'll check it out again but the air mix screw really does nothing unless I take it out far enough and the bike just doesn't run

sometimes there is an o ring on the air mixture screw, check it's , look out for a groove if there isnt any o ring but bear in mind that some dont have the o ring...i suppose a groove would be a giveaway

Well looking at the diagram on a part site a 79 carb air screw should have an o ring and I know he one I have in it now doesn't another fatality of the carb mixup

Air jet should be clear had good air flow to the main jet. Still have to order correct air screw.

Here's a new video