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Carb help [Yamaha DT50MX]


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Hello, my name is Harvey and I own a 1987 Yamaha dt50mx that I am currently restoring. The old barrel on the bike was scortched and getting piston slap so I decided to buy a 70cc airsal kit. I found out that the VM20-273 mikuni carbs are recommended for my setup but was unable to find out what I should have my needel height or pilot jet set to. If anyone has any known information on this please leave a reply

   - Harvey 

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Wild foamy  did a big bore kit on these,,,, hes in the R,AF,   not been on for a while,  ,  search for his posts  on this,   in archives  ,

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Bloody hell, that's an 8mm jump for 20cc, where did you get that info from. Even the 80 only has a 16mm carb.

General practice when I was knocking about on these (when they were new sigh) was the DT50m carb was the goto choice, 16mm and good to go, bolts straight on with an inlet manifold from the same, tricky to find though now. 

I cannot understand how 20mm will do anything but make somebody money knocking out special manifolds, bigger reed blocks. 

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19 hours ago, Cynic said:

Bloody hell, that's an 8mm jump for 20cc, where did you get that info from. Even the 80 only has a 16mm carb.

its only a 5mm jump as the stock barrel is 40mm and the barrel I have is now 45mm. and the stock carb is 17.5mm bolt one one, Ive never seen or herd of people running the 70kits with stock carbs.

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No, unless something weird is mixed up. I thought the 50 had 12mm, the 80 had a 16.

The DT50m had a 16mm carb and that was designed for 60cc, went bloody well on it too, at 60cc (quality bore kit) I was clocked by an RXS100 at 70mph. Looooong time ago now though. When MX's were brand new.

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On 5/17/2018 at 4:24 PM, Cynic said:

No, unless something weird is mixed up. I thought the 50 had 12mm, the 80 had a 16.

yeah you were right i just looked at the haynes manual for the DT50M, DT50MX, DT80MX (5J2)(12X) and the 50mx is meant to have a Teikei y14p carb.

Bloddy hell sounds like great fun! I'm gonna tune mine up and hopeful get around the speed of 70mph.

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I'm out now, a dirty horrible civvie... Found my way back to the desert for some reason

The MXs either had a TK or Mikuni 14mm jetted 78 from stock. 

 

With the 60cc kit I had on mine and DEP exhaust etc I had to jet up to 88 to keep the mixture right, if a bit rich, ran just peachy on the stock carb though.

Dellorto carb kits sometimes come with a selection of jets, might be worth a try if you want to mess around with mixtures. 

 

Blew mine up atleast 3 times though. Would do 55+ flat out but you'd feel it start to pinch up, keep at 40mph all day though. 

On 5/16/2018 at 5:22 PM, blackhat250 said:

Wild foamy  did a big bore kit on these,,,, hes in the R,AF,   not been on for a while,  

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Oops fog of age I thought it was a 12. Must have been one of the other bikes with a 12.

I know several lads wanted the carb off my bike (a 50m) back then. 

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