I am currently in the process of restoring an 1981 'X' Plate DT125MX. I have opted to change the piston, barrel & head with a DT175MX, and have rebuilt the engine, and reinstated the 2 stroke autolube with a DT175MX oil pump, shaft etc.

I am now ready to refurb the carb, which is currently dismantled for cleaning. I understand that I need to change the main jet in the carb as it will now run as a '175', and the '125' jet will not be sufficient and may cause the engine to run lean, and seize.

The main jain in the carb is currently a 140. I've checked the good old Haynes manual, as well as the part manual, but can't make a lot of sense. The Haynes manual refers to anything from a 150 to a 200 jet.

I intend to keep the stock airfilter box, and air filter. I went to the local bike shop in the village, and the guy at the shop suggested a 160 to start with, and if needs be switch to a 180.

Does sound correct and what size jet would have been fitted to a DT175MX when it left the factory.

Appreciate it can differ for different countries and climates, but I am referring to a UK spec model.

Look forward to hearing from anyone who can help.

Thank you

all depends on the airbox

acces from the right was 130 standard

access from the left was 160 standard

The two carbs had other spec differences along with the main jet to cater for these different airboxes

You've got me thinking now. I think mine had access from the right, so a 160 will be OK. I couldn't read the number on the original jet very well, but it looked like a 140 to me.

Ok will give it a go with the 160.

Thanks for your response.

Cheers

You've got me thinking now. I think mine had access from the right, so a 160 will be OK. I couldn't read the number on the original jet very well, but it looked like a 140 to me.

Ok will give it a go with the 160.

Thanks for your response.

Cheers

access from the right is 130 standard, thats why 140 may be ok but 160 will drown it!

I need to dig the airbox out. Its sat in a stacker box awaiting cleaning etc.. I'm a bit concerned now as I wasn't aware that there were different airboxes. I bought the bike as a field bike, and the air box, 2 stroke tank etc where all missing. I've managed to pick the bits I need up, but it would just be my luck that I have the wrong one... will check tonight when I get home. #

Thank you

Early bike

Round sect swing arm

airbox on right

oil tank on left

carb main jet 130

Later bike

square sect swing arm

airbox on left

oil tank on right

carb main jet 160

Great ! You've just answered my 2nd question. Dug the airbox out, and the air box cover is on the left. The battery sits on the right.

I bought the bike from someone who had used it as a field bike, and the airbox and oil tank were missing. Thought I'd bought the wrong airbox as the carb inlet from the airbox seems to be very tight. Will use a bit of fairy liquid to get them to fit together. The carb is a mikuni, and '4J3 00' stamped into it. Have fitted the 160 jet so hopefully this should be enough in its '175' guise.

I've bought the carb repair kit but it looks like I've bought the wrong one. The rubber O rings in the kit look nothing like the carb I have assuming that I should get a float chamber gasket with the kit.

Just refurbed the genuine headlamp I bought on EBAY.... next job the front forks.

Thanks for your response.

Great ! You've just answered my 2nd question. Dug the airbox out, and the air box cover is on the left. The battery sits on the right.

I bought the bike from someone who had used it as a field bike, and the airbox and oil tank were missing. Thought I'd bought the wrong airbox as the carb inlet from the airbox seems to be very tight. Will use a bit of fairy liquid to get them to fit together. The carb is a mikuni, and '4J3 00' stamped into it. Have fitted the 160 jet so hopefully this should be enough in its '175' guise.

I've bought the carb repair kit but it looks like I've bought the wrong one. The rubber O rings in the kit look nothing like the carb I have assuming that I should get a float chamber gasket with the kit.

Just refurbed the genuine headlamp I bought on EBAY.... next job the front forks.

Thanks for your response.

The 3J300 carb is for a 125 bike, the throttle slide cutaway is vastly different to the 175, it is 2.5 where the 175 is 1.5 for a later model. if it were me i'd be getting a 3U500 id carb

Will it not work if I just jet the carb up with a bigger jet?

Just had a quick look on good ole ebay and there's no carbs to be had!

Hi there.

Maybe this might be of assistance:http://www.ebay.com/itm/NEW-CARBURETOR-YAMAHA-RT180-RT-180-DIRT-BIKE-CARB-CA30-/230653474348?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item35b404b62c