Carburetor main jet size

I need to put the main jets size back to standard. There are numbers on the body of the jets to indicate what size they are. Does anyone know if large number is actually a smaller size jet size or large numbers means large jet size?

 

Number refers to either size of hole in hundredths of a millimeter or how much fuel will flow through hole, so yes bigger number equals bigger hole.

 

Thanks Mega.

Hummm...this will complicate things further. I bought standard needles and standard 122.5 & 125.0 main jets. When I strip the carbs, I found what looks like Dynojet needles and 057.5 main jets. Don't they normally go up in jet size rather go down, when they Dynotune?

 

They did when I had a carbed 1200 bandit Dyno'd.

 

They wouldn,t go from 122 to 57.5 mate. Could be a flow number? Are they Dynojet jets? Got any piccies?

 

Damn! Got a Haynes manual and there seems to be some differences between info in above photo from manual and the respected website below.
http://www.cmsnl.com/yamaha-yzf750rfc-1994_model10165/partslist/B-07.html#results
I've replaced what Haynes refers to as a starter jet (No 8) where the website regarded the same as a main jet. According to the manual, the main jet is next to what I've replaced and didn't need to replace Now am twice as confused! Oh well, it only cost £3 each.

 

The main jet is normally in line with the needle, part 20, and needle jet, part 22. On your diagram it is at 90 degrees to it, part12. different design of carbs than I am used to? The pilot jet is usually a lot smaller than the main jet and is screwed in or out of the carb from outside the carb body. 900 Fireblade main jets are around 120. Got any pix of the actual jets mate?

 

View attachment 1985
This is what I've took off
The carbs are Mikuni BDST38
Below is where it came out of. The hex headed one is where the needle lives

 

Hhmmm, looks like a main jet, but not big enough if it's 0.575 mm diameter.. Any chance you can get the carbs up to my place , so I can have a look at em and blast some cleaner through em and see where it comes out ?

 

Look at the carb inlet. see if there are jets screwed into it and what size they are?

 

It's 57.5. and it's same size for all 4 cylinders. Haynes manual states (which is what I've brought) is 122.5 for cyl 2 & 3 and 125 for cyl 1 & 4. Strange because if the number dictates what size they are then I would of though the 125 would of been better for cyl 2 & 3 to compensate for the extra heat being in the middle of the 4

 

It may not be the main jet or it's a flow number. Have a look at the inlets, could be jets in there?

 

Inlet has the pilot and main air jets

 

Can you take pix of carb inlets?

 

It's dark out back and not wanting to go out to fetch them again But the inlets are as what the photo of Haynes manual shows

 

Do you have a 1 mm drill? If it will go through jet, it may be 122 ? I'd like to have a look at carbs, there's a lot more jets in those than my Keihins?

 

Think I want to go back to Fi again after all this

 

What's the other writing on that jet mate?

 

"666" was the other markings!

Nah, only what I've said already. Well at least I've sorted one problem out which was to put the needles back to standard. I know that is right.

 

Did you find a 1mm drill and try it in the main jet? The blunt end obviously?