1979 YZ250F Carbie advice

[Ozadvntr]

Hi, just making sure I buy the correct Mikuni Carbie for a 1979 YZ250F - 38mm or 36mm?
thanks,
Mick

[shelpi]

from memory only will check the manual after but 36mm
get 2 manuals 1 for the YZ250F
and 1 for the carby SUDCO mikuni tuning manual 5th edition, GOD wrote it, its all I have to say about that!

[Viper666]

36mm

Basically any carby from yz250\400\465-E\F\G\H will do but you will need to rejet to suit.

Number #3 slide

50 pilot

Q-0 needle jet

F-16 needle (I think)

390-410 main

Obviously location heat altitude will all be determining factors.

I can double check the jetting but they are the starting point.

[Hoony]

Bloody hell Perko how do you remember this detail after all those Beers 

[oldyzman]

Ant comments on the air correction bleed jet guys?

[Viper666]

Bloody hell Perko how do you remember this detail after all those Beers

I don't.

Just guessing

Ant comments on the air correction bleed jet guys?

? ? ? ? ? ? ? ?

Do you mean the air mixture screw? Or the needle jet mixture? I will double check that one too but I thought it was Q-0 & needle F-16 but as I said "Off memory"

[Viper666]

Number #3 slide

50 pilot

Q-0 needle jet

6F16-4 (4 is clip position)

390-410 main

[oldyzman]

i am talking about the small jet which is at the bottom of the inlet side of the carby it bleeds air to the main and corrects mixture at high rpm. from memory it should be approx 1mm dia id, some people just take it out on bigger bores.

[Viper666]

Still not sure what you mean but there is an air bleed jet on the 32mm. The larger ones dont have the jet just the hole where it would go.
Once you drill something out it's a bit of a pain to go back. Have to make a very small bush.

YZ125 No 4 jet

http://www.boats.net/parts/search/Yamaha/Motorcycle/1978/YZ125E/CARBURETOR%20YZ125E%20-%20F/parts.html

YZ250 no air jet

http://www.boats.net/parts/search/Yamaha/Motorcycle/1979/YZ250F/CARBURETOR/parts.html

[oldyzman]

yep, thats the one i meant...

[Ozadvntr]

I just checked an old test and everything I read suggests a 38mm Carbie.

I also understand that 36mm will give an increase in torque. Is this correct?

[oldyzman]

 Definitely 38mm according to my info and samples.

[motomaniac]

36 mm carby on the 77 yz 250 d , 38 mm on the E and F , 400 had 38 mm from the D model on

[Ozadvntr]

thanks, Just ordered a new 38mm. Just over $200 delivered to me with all the correct jetting in a separate kit.
thanks for the advice.

[Viper666]

38mm

Stand corrected