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TOPIC: Are Carb Plugs necessary? (above pilot jet)

Are Carb Plugs necessary? (above pilot jet) 30 Jun 2020 21:00 #829482

  • chrisM
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Hi everyone,

I cleaned my cabs today ('82 Kz1100 A2) and I had to pull on of the little plugs off with pliers because it was stuck. The others almost fell out.

These are little metal plugs that go on top of the pilot jets. They have an O-ring and the O-ring on this plug looks swollen - It's a bit loose on the plug and I can't seem to get it back in.

My question is: Are these plugs necessary? If so, for what purpose?
Is there a way to shrink the O-ring somehow, so that it will fit? Or should I buy a new O-ring?

Thanks in Advance!
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Are Carb Plugs necessary? (above pilot jet) 30 Jun 2020 21:41 #829486

  • Nessism
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Those plugs are necessary. Fuel is fed though the main jet and then over to the pilot jet. Not sure why Mikuni designed the carbs that way but it's fact.
Regarding the O-ring, that looks like the wrong one.
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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 06:32 #829494

  • 650ed
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chrisM wrote "My question is: Are these plugs necessary?"

Would Mikuni or any other company spend money installing plugs and o-rings if they were not needed? I think not. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 06:45 #829496

  • chrisM
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Thank you.

I guess I'm trying to understand what would happen if there was no plug. The O-rings came from a rebuild kit I bought 2-3 years ago. Strange that the other ones fit but this one doesn't.

I look for a new O-ring then

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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 07:35 #829503

  • ckahleer
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It will run too rich and foul the spark plugs without the plugs installed, I have found some o-rings and rubber plugs swell to double there normal size in gasoline.
It seems you got a mixed set, 3 made of material that doesn't swell, and one that does. If you let it dry out for a day, it will shrink back down.
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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 09:37 #829514

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Ok, Thanks. That makes sense. I'll try drying it out or... I might have to get another rebuild kit and hope the o-ring will fit.. :-/

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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 11:35 #829524

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If your near a Harbor Freight they sell Viton O-ring kits for under $10.
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Are Carb Plugs necessary? (above pilot jet) 01 Jul 2020 14:12 #829541

  • ghostdive
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Regarding the pilot jet plugs; some carbs need them, others don't, and you can tell by looking down the bores of the jets. If there's a hole in the side of the pilot jet's bore, then you need plugs. If it's just a straight tube, no plugs. If yours has them, you probably need them!

Regarding the Harbor Freight O-ring kits - I've found mine to be very useful to have around, but now and then there's a specific diameter or thickness of ring that isn't included; so it's a good set to have, but keep in mind that OEM may be "ideal" for some situations.

Good luck!
1982 KZ750 Spectre
Dyna 2.2 coils + 8mm wires
Mikuni BS34s
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Are Carb Plugs necessary? (above pilot jet) 02 Jul 2020 18:36 #829650

  • chrisM
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Yes! I found a small pack of O-Rings at an auto parts store for $4 and it had one 0-ring that was just right. Plug slid right in.
Didn't think of that, but it was an easy solution. I know it won't be as good as a OEM O-ring but I think that O-ring was from a rebuild kit anyway.

Thanks again!

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