hello folks
can anyone tell me if i can use a setter jet from a 74 DT360 in my 73 RT3  360
mine is missing. part # for dt360 starts with 276  and the rt3 starts with 214.
i can only find one for a 74 250/360 here in the uk.
would the thread be the same?

 

Probably not, they did have different threads and types. 

Try a Mikuni distributor in the UK. 

"Probably not, they did have different threads and types. 

Try a Mikuni distributor in the UK." 

Thanks for confirming my own thoughts, Mark.

#Gasmonkey, try contacting Motocarb or Allens for a main jet of the correct size and the same thread as the jet setter. In theory, this should work ok - I think that the only reason the main jet was originally in the bowl was so that it could be changed without removing the carb.

thanks guy's i did speak to allens, they had no info on the setter jet as the carbs were made for yamaha only , somebody on this forum thought the 6mm slotted may work , i was trying to keep it simple , the hex jet stuffed in the needle jet tube was the wrong thread just hoping the 74 jet would work .
thanks again.

A round head jet would screw directly into the needle jet , but they are calibrated differently from hex jets .
I have a graph that matches the two , which would put you in the ballpark for jetting .
Let me know what size Hex jet we are comparing , and I'll have a look .

A Mikuni Distributor might not know what Yamaha specified for your carb.  But they don't need to.  The needle jet series should tell them the threads and then you need the jet setter for those threads.  Though the way the world is going, the BOOKS that information was in may never have been copied digitally and is gone.

The standard 4/042 Mikuni hex main jet actually has standard (not metric) threads.  It is a copy of the Amal design.  The flow through the jet is measured and calibrated with fluid flowing from the threaded end to the flat end....  just like it does when threaded into the float bowl jet holder. 

When you install the hex main directly into the needle jet, the calibration is off (slightly!) as the flow is reversed from the way the 4/042 jet was designed to be installed.

The answer Mikuni used for some carbs was to use a different thread in the needle jet with a corresponding round main jet with a different thread...  the round jet was designed to flow from flat end to threaded end like it does when installed directly into the needle jet. 

At some point, Mikuni got past this nonsense and threaded the needle jets with the 4/042 main jet hex threads.

The earlier 250/360 needle jet has the metric "round jet" threads...  If you tell the distributor what needle jet series you have, hopefully they can come up with a jet setter with those threads?  If not, they may have a replacement needle jet with the correct threads? 

Obvious option is to buy the correct part...  and I've known someone who simply tapped his needle jet to the 4/042 hex threads and used the newer style jet setter.

Thanks again guy's for your information , just to let you know , my main jet is a 230 hex and my needle jet is 188 series.

so what i think i have learned , i can use a small round slotted main jet and remove the hex jet from the banjo, or use a 159 needle jet and my P-0 needle and the 276 later setter , which seems to available,

You haven't got it quite right yet .
If you ditch your current jet setter , you can use a small or large round head jet screwed directly into the bottom
of your needle jet ( 188 P-0 ) . There is a brass washer that fits between the two . A # 130 round head is a close match for a # 230 hex , but i'd probably go a size or two bigger to start with and work back from there .
The other option , as you say is to use a # 159 P-0 needle jet , and the 276- Jet Setter .
With both options you retain your current needle .
The third option , is as Mark has suggested to try and obtain a Mikuni Jet Setter that threads into a # 188 Series Needle Jet from one of the many mikuni agents throughout the world .

Thanks people. All great info worth saving & thanks for investigating plus posting it. I'll save this page!!.