Air Pilot Jet

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armyofda12mnkeys

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Hey all,

Just curious, I like to have a few main/pilot jets on hand for when I eventually do a proper jetting for my bike ...
I was just curious if the 'Pilot Air' Jet would be a big factor in tuning as I need to replace mine (They got stuck in the carb body and I extracted them (aka ruined them hehe))...

My bike has #170 but MikesXS only offers the 'Small Round Type' (aka Pilot Air Jet) from #112.5 to #160 ...
Should I just get the #160 if the Pilot Air Jet isn't a big deal in getting a bike running great?
If my bike was running fine and I have to go down from #170 to #160, would I need to bump up/down any of my other jets?

Thanks!,
Ari
 
If your talking about the pilot jets in the venturi leave them alone.The only ones you want to mess with are the ones inside the carbs with black rubber plugs that cover them.If you upgraded your mains you should bump them up at least 1 size.As for the others take a needle a very small one and poke it through them to make sure they arent clogged.
 
The jets you are looking at on mikesxs are pilot fuel jets or main jets (they don't have pilot AIR jets for our carbs). The pilot AIR jet, as mentioned above, is on the opening to the mouth of the venturi.

Normally the pilot AIR jet does not need to be removed; you can spray carb cleaner through it because the opening is so large.

Finally, I don't know where you can get a replacement because I have never seen them for sale.

I attached a photo of the pilot AIR jet; notice how the Haynes manual labels the photo incorrectly. As far is I know the bs34 does not have a "starter jet." A starter jet normally enrichens the mixture when choke is on by providing fuel (not air, so it would normally be in the float bowl if there was one).
 

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Hey BCWare,
I think they do have pilot air jets for our carbs...
It was alluded to me when i first asked a similar question years ago:
http://yamahaclub.com/forums/topic/25914-xs400-air-pilot-jet/
MikesXS even mentions it on the 'Main Jets' page "Air jet on All 1980-84 XS650 Mikuni BS34 CV carbs."

Hey 1982400xs,
I know I should have removed it now :).
But now that i have and need to replace (since its stripped/drilled/extracted)... i dont see MikesXS offers a #170 Pilot Air Jet size... If i bumped it down to their largest size #160... should I bump down the Main Jet as well, or should be fine?

-Ari
 
I have never removed mine, so I cannot say if it will fit. And yes, I have only seen 160 as a max size.

If you're able to use the 160 pilot air jet you would not need to touch your main jet; the pilot air jet provides air to the pilot circuit, so you should only need to reduce your pilot fuel jet if anything. It is also possible you can tune out the difference with the pilot adjustment screws, but I cannot say. I have never tried to tune by altering the pilot air jet.
 
I have been told to leave the jets inside the venturi alone with the exception of cleaning them.Theres no need to change the size of them.
 
I must have missed something when reading about this yesterday which is very highly likely.I had some kinda seizure or something the night before that kicked my azz.Part of mind was there and part of here.
Did I read he tryed to extract them also?I hope he didnt ruin the holes they screw into.
 
I just went through a tough extraction process on my air pilots inside the fuel bowl.I also found out I had ordered the wrongs ones.The number on the jet says 142.5 but the holes at each end are very tiny.The jets I ordered were 145`s but with a large hole in the end.When i went to remove me old ones which I had out previously the one on the right carb wouldnt budge.I tryed making a new slot which didnt work.I finaly had to drill the hole on the top side larger get a small bolt bolt extractor then it finaly came out.Meanwhile Im waiting for my new jets which should be monday when i get them.So heres a bit of advice if they get stuck and ruin the slots on top.Use a small bolt extractor since the jets are brass and the housing is aluminum or pewter they will be removed easy using this method.
 
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Whoops, dont think the 'Instant thread subscription' worked. Saw these latest comments today as I had an update...

1982400xs, Luckily I didn't mess up the holes they screw into :).
esmith87, maybe I'll try to check out that website as the MikesXS jet didnt fit... Not sure what to order though (maybe that B42/55-SIZE? no online store?)...

MikesXS says the 'small round main jets' they have are used as Air Jets for the BS34 ... but maybe my 1978 XS400 BS34 carb is different than the 1980-84 XS650 BS34 Air Jets? The Air Jet screws were too small so it just went down all the way:
Here is the jets from left to right:
MikesXS Air Jet, My Stock Air Jet (ruined/stripped), Just for comparison my stock Main Jet:
8513521673_95f88ae9df_b.jpg



On a related note: MikesXS idle mixture screw (48-5011), doesn't seem to work on my XS400 BS34 carb too. Here's the comparison.
Mine is way way bigger and I guess doesn't use the pollution-control 'end-cap' which fits on mikesxs/smaller screw:
8514664124_9168ef273b_b.jpg


So curious if there is some different version of the BS34 carb I got, and where I can find those Air Jet screws hehe (and later on Idle Mixture screws should I need one).
 
Im glad you didnt ruin the holes cause your carb body would have been toast.As a side note I got my pilots in last monday and have them installed.I can notice a slightly difference is size being a bit larger I hope they workwith my main jet configuration which is 2 sizes up from stock.
 
1982400xs said:
Im glad you didnt ruin the holes cause your carb body would have been toast.As a side note I got my pilots in last monday and have them installed.I can notice a slightly difference is size being a bit larger I hope they workwith my main jet configuration which is 2 sizes up from stock.
Click to expand...

Your main jet won't have any affect. The pilot air jet will only affect idle. You may need to run a larger pilot fuel jet.

armyofda12mnkeys said:
So curious if there is some different version of the BS34 carb I got, and where I can find those Air Jet screws hehe (and later on Idle Mixture screws should I need one).
Click to expand...

The idle mixture screws you bought look like they might fit the DOHC carbs. I got a complete replacement kit including the mixture screws for my SOHC from http://www.siriusconinc.com/ (they are hard to find!).

I maintain that I have never seen a replacement pilot air jet anywhere. If someone else can prove me wrong that would be fantastic. This is why we keep telling everyone NOT to touch these things. It is completely unnecessary.
 
I got the pilot fuel jets that are inside the fuel bowl,They aretough to remove because of the small size head on them
 
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Those are pilot fuel jets. Be careful with terminology. It can be confusing talking about the pilot jets because there are two different kinds.
 
Darn, you were right bcware about MikeXS not having the appropriate Pilot Air Jet for the XS400 (and ebay and google seems to not have that part #2A2-14172-34-00 either ) ...
Well, maybe that uk company has it. That pic below of "B42/55-SIZE" looks reallly similar:

But there's no online store for this Allens Performance place? Do i have to call and give my credit card over the phone hehe (just had my credit card #'s stolen so wary of reading over the phone vs a secure web store)?...

Do the thread stuff sound correct? If so, Maybe I'll give them a call or do a 'Wanted' ad here.
"6.0mm Slot head
? Thread
9.0mm length
M6x1.1"

I think this place lists them too... but i saw in a thread they have not actually have in stock:
http://www.motorcyclecarbs.com/Mikuni_Air_Jet_B42_55_C13.cfm

or better yet googling around, i see on this forum someone mentioned this company... They have the B42/55 jet:
www.pjmotorsports.com/mikuni-jets.html

Just need confirmation I want those B42/55 and I'll order from pjmotorsports.com
 
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