GSF400 Pilot Air Jet Alternative

I picked up my dream bike, a 1991 GSF400, a few days ago and I'm in the middle of a needed full carb cleaning. Unfortunately, some of the jets, namely the pilot and the pilot air screw were buggered and although I was able to remove them, they are damaged enough that I want to just replace them. The question is about the pilot air jet specifically.

The pilot air jets in the carb now are stamped 1.45. According to every website I have found, these are no longer available (part number 09493-29002), unless I want to pay $10/piece plus $7 ship with no combined shipping from Germany.... Found here:

http://www.ebay.com/ulk/itm/331551854815

There ARE, however very similar jet sizes available from Partzilla. I can get a 1.5 or 1.55. They aren't much cheaper but it's a reputable source and I can get combined shipping.

Question is, will going from a 1.45 to a 1.50 make much of a difference, apart from idling a tad leaner until the choke is turned off?

Thanks and sorry for the stupidly specific question.


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Congrats on the bike, those little bandits are awesome, i got the opportunity to ride one when my friend owned one.
As for the jets, I dont know for sure, as I have never been into the carbs on them, but i dont see the jump from 1.45 to 1.5 being a problem at all, as long as they are sized on the same scale.

Good luck with it! I'd be lying if i said i wasn't a little jealous.

Thanks man! I was thinking the same. Certainly it would get me "close enough", or at least closer than a screw who's head I can't even grip with a flat head.

I've been looking for a nice 400 for a while now. I ran across one in Alabama that's just a true beauty. 3800 original miles. I about wet myself when we made a deal.




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. If they are Mikuni carbs you can probably get correct jets from Sudco, jetsR-Us, etc (I haven't worked on 400 for 10 yrs or so, can't remember the carbs.
You can also go up in size on the pilot jet to compensate for larger air jet)

Jetsrus only has the 1.4 or 1.5, but no 1.45 which prompted the question. However getting a larger pilot jet is a definite possibility. Those are plentiful in size.

I didn't think to try Sudco

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PJ, does one size up in air jet equal one size up in pilot, though? Next size up for air would be to a 1.5, and next size up for the pilot would be a 35. The pilot is a 32.5 now.


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Is than an early yzf1r?

Also, i dont think you need to worry too much about the pilot jet if youre only going up a half size on the air jet. I do also know that most bikes are lean on the pilot from the factory, so you maybe still benefit from the pilot. Eaither way i think you will be alright.

Not sure - that pic was taken by the PO - looks like a FZR to me. It's the only one I had on my phone at the time.

As long as it starts, I won't be staying on the pilot circuit for long. Not with a 14k redline that is


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Jboogie13 said:

Is than an early yzf1r?

Also, i dont think you need to worry too much about the pilot jet if youre only going up a half size on the air jet. I do also know that most bikes are lean on the pilot from the factory, so you maybe still benefit from the pilot. Eaither way i think you will be alright.

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Nope, it's a much later 'Deltabox' frame on the Yam.
The jet 'holes' are a logarithmic progression, you may need 4 sizes larger to cope with 1 size on air jet (air being around 1000 time 'thinner' than fuel)

crazypj said:

The jet 'holes' are a logarithmic progression, you may need 4 sizes larger to cope with 1 size on air jet (air being around 1000 time 'thinner' than fuel)

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CrazyPJ, I think you're going to end up spot on with this. I got the bike running with new o-rings and such. It pulls across all RPM ranges but has a little dead spot from about 3-6k. You know that the 3-6k range doesn't happen very often with a 14k redline bike so it's not that big of a deal, but it still bugs me.

I'm at 3 turns out with the fuel screw and it still idles a bit erratically and has a hanging lag coming back down to idle as well as a slow throttle blip response and gear shifts. I feel I am still too lean at idle.

I'm going to try to go up in pilot sizes now to compensate for the slightly (half size) larger than spec air jet.


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dont do it. You want all the cylinders running the same. The early advice to go ahead with the wrong air jet is ludicrous. Pretty easy to tell not many here have experimented with air bleed jetting.

Which reminds me, if you havent done it then stfu and wait for someone that has. PJ is the only one here with a clue.

Why not try to score a set of parts carbs on ebay, if this is your dream bike you will have it a while.

DohcBikes said:

dont do it. You want all the cylinders running the same. The early advice to go ahead with the wrong air jet is ludicrous.

Why not try to score a set of parts carbs on ebay, if this is your dream bike you will have it a while.

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Find me four discontinued 1.45 air jets and I'll do this. Why wouldn't all 4 be running the same? All four have the same air jet and the same pilots. I'm just shifting everything up. I never said I was replacing one carb with a different jet. I did all four. THAT would be ridiculous.

I'm not sure I follow why cylinders would be running differently (apart from by bench sync being off and me needing to buy a set of vacuum gauges to get it spot on) if all the jetting is the same across the bank.

Surely if the 1.5 air jet is stock spec for the California import, I can get this thing running right tinkering with the pilot tinkering. The air jet isn't "wrong." It's just stock for a different import state


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No i thought you were only doing one. My mistake.

But I mean a whole set of carbs, not just the airbleeds. Whatd you do break em all? Why would you need 4?

Dont mind me ive never done this stuff before.

DohcBikes said:

No i thought you were only doing one. My mistake.

But I mean a whole set of carbs, not just the airbleeds. Whatd you do break em all? Why would you need 4?

Dont mind me ive never done this stuff before.

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Ha, nah man thanks for joining in. To be honest I've always struggled with off idle conditions with tuning. Not my strong suit. Wish I had a Dyno and $$

If I had to be resourceful I could piece together a set of 4 purchasing them from overseas on eBay, spending a lot of money and adding in the couple half decent ones I have left.

But they're so old I'm afraid of messing them up if I need to ever remove them again. Which I will. As you said, I'll have this bike for a while.

I'd rather find a jetting alternative using the 1.5 air (instead of 1.45) since the 1.5 is so readily available.


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call me on this some time b4 you drive yourself nuts