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burton500

DT 175 MX main jets

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Hi

Re: 1981 DT175MX - can anyone confirm the standard main jet size please?

Many thanks

Lee

Mikuni VM24SS, Number 3U500

Standard Set up with factory porting, standard exhaust and air filter

Throttle Slide cutaway 1.5

Needle, 4j6 Clip position 3 from top

Needle Jet, 267 0-8

Main Jet, 160

Pilot Jet, 20

Reed side diameter, 35mm

Filter side diameter, 43mm

Length, 85mm

Float Height, 21mm

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Can any one suggest what the jetting ought to be if running pre-mix?

+ Pre-Mix ratio?

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Mike jetting size depends on which model,I would go up 5 points on the main jet (whatever is in now) and premix 35/1 would be enough although myself I prefer pumped oil

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Mike jetting size depends on which model,I would go up 5 points on the main jet (whatever is in now) and premix 35/1 would be enough although myself I prefer pumped oil

Engine's 78 MX points ignition; it was running pre-mix when I got it. TBH I Haven't checked behind cover to see if lube pump is even there. 2T res isn't. ... would prefer to run the pump, but 'for now' it's not a priority... it was 'running' which for the moment is 'good enough'; need to sort suspension, steering & brakes before I do anything! Tearing it down, there is an odd mix of work 'done' to it. Some stuff is very neat, very contientiouse, like it was prepped for enduro, cables neatly cable tied, bullet connectors chopped & solder spliced, that sort of thing you would do for 'reliability'... then there is shear botchery, twisted wires & insulation tape, oversize nuts uised as spacers over stripped threads, etc..... suggestion being, at some point in its life, bike was much loved, and well cared for by some-one who had some pretty good ideas about how to do 'stuff', but later fell into the hands of your average field-bike bother! IF auto-Lube was removed by the chap that knew what he was about; might already be upjetted for pre-mix. If simply dumped by bodgers later, probably not! Hence interested to know what ought to be in the emulsion tube and idle jet, and what, other folk running petroil, use.....

If the pump is there, when I have a look, and if it pumps, I'm tempted to jury rig an old battery acid bottle or something as 2T res 'for now', (just 'lost' res on e-bay, that went far too high for my pocket! But only one I have spotted to come up in the last eight months or so) If I cant run the pump, then down to pre-mix until I can sort it out; and if I can use a 'tried and trusted' formula for pre-mix ratio and jetting, so much the better..... idea of starting from scratch with a box of jets, three or four spark plugs, and a bunch of pop bottles with a measured litre of petrol & oil at ratio's from 30:1 down to 50:1, running the thing up, doing a plug chop, swapping a jet, trying again, then draining tank, swapping fuel, trying again, adjusting timing between runs etc..... Hmmmm lots of 'fun' to be had.... but I'd rather not, if I don't have to!

Ta for advice anyway.

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two points

1 if you do look to but a 2T res make sure you buy one for the later model with square swing arm, that one would mount on the right of the bike with air filter on the left

2 so the later DT175MX engine would have a carb with an id number 3U500

these are the original specs for that carb

Mikuni VM24SS, Number 3U500

Standard Set up with factory porting, standard exhaust and air filter

Throttle Slide cutaway 1.5

Needle, 4j6 Clip position 3 from top

Needle Jet, 267 0-8

Main Jet, 160

Pilot Jet, 20

Reed side diameter, 35mm

Filter side diameter, 43mm

Length, 85mm

Float Height, 21mm

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two points

1 if you do look to but a 2T res make sure you buy one for the later model with square swing arm, that one would mount on the right of the bike with air filter on the left

100_0428.jpg

Right?

The 'hole' I presume the res should go is on the left? Under exhaust.

If I got one that mounted on the right, presumeably I would have to swap out the air box, battery box and took box assembly?

What would be the advantage?

But good heads up, is tank is swapped on later models! One I didn't 'win' might not have fitted!

{Haynes manual is on shopping list, but waiting for Yambits to get back to me about some of the bits on it, berfore placing order!)

2 so the later DT175MX engine would have a carb with an id number 3U500

these are the original specs for that carb

Mikuni VM24SS, Number 3U500

Standard Set up with factory porting, standard exhaust and air filter

Throttle Slide cutaway 1.5

Needle, 4j6 Clip position 3 from top

Needle Jet, 267 0-8

Main Jet, 160

Pilot Jet, 20

Reed side diameter, 35mm

Filter side diameter, 43mm

Length, 85mm

Float Height, 21mm

Only markings I can see on outside of carb body are: "Mikuni - Japan" next to choke knob; then on other side on boss just above auto-lube nipple; "2H5" and onder "00"

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so you posted incorrect info in you original post thats why i gave you info for a 1981 bike!

ok then for the earlier version

Mikuni VM24SS, Number 2H500

Standard Set up with factory porting, standard exhaust and air filter

Throttle Slide cutaway, 2.0

Needle, 4j13 Clip position 3 from top

Needle Jet, 249 0-2

Main Jet, 130

Pilot Jet, 25

Reed side diameter, 35mm

Filter side diameter, 43mm

Length, 85mm

Float Height, 21mm

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Just to confirm then, I have a 1981 DT175MX but the carb on it is a 2H501. Should I really have a 3U500?

If so it will go a long way to explain why I'm still trying to get the jetting sorted considering the 3U500 has a 160 MJ and the 2H501 has a 130MJ.

Cheers

Lee

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Damnn yes Lee your bike will be running lean. if your aibox is the more modern one accessed from the left of the bike you need a 3U500 carb...and its not just the main jet!! also the needle and needle jet, pilot jet and the throttle slide cutaway are different. This is because the later air filter box is a less restrictive one as compared to the early version.

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Damnn yes Lee your bike will be running lean. if your aibox is the more modern one accessed from the left of the bike you need a 3U500 carb...and its not just the main jet!! also the needle and needle jet, pilot jet and the throttle slide cutaway are different. This is because the later air filter box is a less restrictive one as compared to the early version.

Hmm very odd. I do have the correct left hand air filter for my model. However, it looks like my bike has the early carb on it then, but with a main 160 jet fitted. I best double check what the other jets/needles/slide etc are!

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Ah, my 79 bike has the old air filter box, newer carb with a 160 jet, and possibly an older style cutaway. This is because I had a spare carb in my box of bits, could only source a rebuild kit for the newer carb, but didnt have a cutaway or carb top for the newer carb. It all got screwed back together in the folly of youth and has run ever since.

Any ideas if a proper cutaway would be better? And I " probably" have a later oil tank, so could do a swap oved,but dont think i.have a later air box. Aaaaarrrrrggggghhhhh. Too many options. Help. Someone decide for me.

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Ah, my 79 bike has the old air filter box, newer carb with a 160 jet, and possibly an older style cutaway. This is because I had a spare carb in my box of bits, could only source a rebuild kit for the newer carb, but didnt have a cutaway or carb top for the newer carb. It all got screwed back together in the folly of youth and has run ever since.

Any ideas if a proper cutaway would be better? And I " probably" have a later oil tank, so could do a swap oved,but dont think i.have a later air box. Aaaaarrrrrggggghhhhh. Too many options. Help. Someone decide for me.

wow a 160 jet with an old type filter, has the filter cover been butchered drilled in the usual way ?

is there a problem with how it runs then?

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No butchery that I know of. It runs. And to be honest I have nothing to compare it to. Its a horrible old 2 stroke trail bike to anyone else I know so there opinions will be biased. I sold my rxs a while ago too. But that was a very low mileage minter.

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