Are Main Jets and Pilot Air jets the Same Size

[Guest]

Are pilot air jets and main jets for CV mikunis interchangeable. I am looking for some 175 pilot air jets and cannot obtain them. Can I fit main jets of the same type. Do they physically both pass the same amount of air (in my case)?

[jwhelan65]

I will say no, but there will be an expert along here shortly with details.

[TheCafeKid]

I don't think they have the same diameter on the threads. I might be wrong but why are you looking for a specific size like that? What is in the carbs should generally work with whatever mods you've done. Otherwise they come in full sizes (160-170-180) and you adjust the mix screws accordingly. If you're trying to get rid of back pop, it's not always they pilot circuit that causes it. Sometimes you need to move the needle clip to cure it, and sometimes it simply can't be cured. Listen to a GP bike... Those are the tunedest (yes i know thats not a word.. ) of the tuned. They still pop like a son of a gun on decel from high revs.

[Suzuki_Don]

Josh the carbs I purchased for my conversion were from a GS650G which had #150 pilot air jets in them even though as standard they were supposed to be #160s. The GS650E requires #175 pilot air jets. And as my motor was running extremely rich at idle my plan was to replace the #150s with the #175s to weaken the idle mixture. The combustion chambers, spark plugs were extremely sooty with a strong smell of fuel about the bike coming from the exhaust.

Apparently according to STEVE's comments the idle mixture is regulated by the combination of the pilot fuel jet and the pilot air jet, not by adjusting the idle mixture screw left or right.

See STEVE's comments below:

"By they way, Mac and Jknapp, carb screws will let more of whatever they are adjusting when you turn them LEFT and less when you turn them RIGHT. The trick is to know what they are adjusting . . . On the BS carbs, the mixture is pre-set by the pilot air jet in the carb intake and the pilot fuel jet beside the main jet, under the rubber plug. How much of that MIXTURE is allowed into the engine at idle and low throttle openings is what the idle mixture adjustment screw does."

So where can I get the #175 pilot air jets from. ANYBODY.

[midnightcafe]

my
79 GS750 pops like a mofo under heavy engine braking in the midrange. I changed main's to size 125 and raised the needles two notches, vacuum synced... the guy at the local vintage bike shop told me that's indicative of incorrect pilot jets.

Do the stock mikuni's allow for pilot jet interchangeability? It's been too long since I've rebiult my carbs so I'm unsure

[waterman]

So where can I get the #175 pilot air jets from. ANYBODY.

Don, I don't know if they ship to your area, but maybe these guys will have what you need.

http://www.motorcyclecarbs.com/Mikuni_Air_Jet_B42_55_C13.cfm

Let me check in my garage, I am pretty sure I had a 650E rack of carbs, I will see what air jets are in them. If you can use them, I will ship them your way.

[oldgrumpy]

cv carbs...

i only just recently stripped and cleaned my cv carbs on my 1980 gs1000e in aust. and no they are not the same at all ,,and z1 in the states do sell the jets at a good price,,, they are also a different thread size as well hope this helps you regards david

[Suzuki_Don]

Don, I don't know if they ship to your area, but maybe these guys will have what you need.

http://www.motorcyclecarbs.com/Mikuni_Air_Jet_B42_55_C13.cfm

Let me check in my garage, I am pretty sure I had a 650E rack of carbs, I will see what air jets are in them. If you can use them, I will ship them your way.

Thanks Ed that would be terrific.

[waterman]

Sent you a pm, found my (your) air jets. I am surprised that it was that carboned up in that few of miles.

[Suzuki_Don]

Sent you a pm, found my (your) air jets. I am surprised that it was that carboned up in that few of miles.

Yes I was surprised when I pulled the motor apart again to see how bad it was. But considering it has #150 pilot air jets and they should be #175 which amounts to 10 jets sizes too small then I can see the pilot system was not getting enough air and too much fuel. Alas an extremely SOOTY motor.





That is with just 100 miles on the motor and a fair bit of idling in the garage.

.