Idle (Pilot) Air Jets

[Vin]

Hi Guy's,

I have been talking with Allens and they are saying that the idle (Pilot) jet is only available starting @ 1.5

If I have my facts correct the standard size for the jet is 1.1 (47X) and Martin Kietsch tuning book suggests leaning things up a little especially for the 1GE model that I am currently building and go for a 1.4

My question is have anyone tried a 1.5 and or know of anyone that can supply smaller sizes?

Any help much appreciated.

[Rick Lance]

Pilot jet and air jet are two different things. You are looking for air jets that are m4 x .7 pitch thread and are commonly available in a range of .5 to 2.0.
They are not pilot jets.
The pilot jet range starts at 15, not 1.5 and go up to 40 in 2.5 increments.

Pilot jets flow fuel. Air jets meter air.

[Linx]

Hi Vin,
I bought some from
http://www.allensperformance.co.uk/shop/
They are the Mikuni BS30/97 jets £4.58 each.


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[Vin]

Thank you for the explanation.

However l am aware of the difference, l put pilot in brackets due to these jets being called several names ( valve seat, pilot air jet) this is from the Yamaha service manual.

I had hoped stating such a small size that it was self explanatory really?

You say readily available but Yamaha do not supply them and my next call Allens as my thread says only start at 1.5.

So saying a place that could supply them would be more helpful!


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[Vin]

Hi Vin,
I bought some from
http://www.allensperformance.co.uk/shop/
They are the Mikuni BS30/97 jets £4.58 each.


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Thanks Linx l may be talking to the wrong person at Allens then? What size did you get? Regards Vin


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[Linx]

I tried changing my 1.1s for 1.4s. Seemed fine in the hot weather but one it got down to 20 ° again, there was a definite hesitation at low revs. So went back to the originals [emoji849].

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[phildu31]

You have four jets in one carburettor.
Main jet ( for fuel ) and main air jet ( for air ) for the main circuit.
Pilot jet ( for fuel ) and pilot air jet ( for air ) for the pilot circuit.
In the RD/RZ 500 carburettors, main air jets are not removable : values are 1.8 for the upper carbs and 1.6 for the lower carbs. These values are the same for 47X and 1GE bikes. The jets starting at 1.5 that you talk about are probably these ones.
Pilot air jets are removeable, value is 1.1 for 47X bikes and 1.4 for 1GE bikes.
Valve seat is used for the input of fuel in the float chamber. What made confusion is an error in the service manual scheme. In the carburettor scheme, pilot air jet, valve seat and float are inverted.
8 -> float
9 -> pilot air jet
10 -> valve seat

[MK]

If a 1.4 was too lean at lower temperature, why not using 1.3 instead of the definitely too rich 1.1?

I always got mine here:
http://www.mikuni-topham.de
They speak English and ship worldwide.

Another way to get the appropriate size is to buy 1.1 or 1.4 directly from Yamaha.
Or if you need intermediate sizes, buy a 1.1 and drill it to 1.3 mm. The number on the jet is the inner diameter in mm.
If you only have 1.4's and want them smaller, solder first and then drill appropriately.
If you don't have matching tools : see your friendly jewelry next door. They'll be glad to help with those tiny bores.