No pop off

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Mikuni Carb won't pop off. Just holds air until the plugs fly off

 

[burtshaver2021]

Mikuni Carb won't pop off. Just holds air until the plugs fly off

What is the carburetor off of, what pressure do you make it up to before the plugs come off

 

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Off of a 99 yamaha ls200. They fly off around 60psi

 

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I tried different spring. Heard a lil hiss but no pop

 

[burtshaver2021]

What carb is it? Are you putting it on a Seadoo, did you wet the needle and seat with WD-40? Yeah, 60 pounds is the highest I’ve ever heard of a pop off being. My XP and HX pop off at 45 I believe. Are you sure you are putting the air to the intake fitting? And not the pulse line

 

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Its on a jet boat yamaha. Needle seat wet. Line on intake fitting

 

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They say should pop at 55psi

 

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Super bn 44

 

[burtshaver2021]

The spring affects the pop off pressure, do you know what the pop off should be with the old and new spring? I’m not familiar with Yamaha but that seems awfully high. Why did you change from the original spring?

 

[burtshaver2021]

Maybe try taking it apart and cleaning it? And maybe a new needle and seat? I’m thinking maybe the circuits/passages are partially blocked causing the super high pop off? Not really sure though

 

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Ok. I try cleaning it again. Thanks.
Needle and seat appear to be ok

 

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The spring affects the pop off pressure, do you know what the pop off should be with the old and new spring? I’m not familiar with Yamaha but that seems awfully high. Why did you change from the original spring?

Thinking it was the problem

 

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The original spring is longer

 

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The spring affects the pop off pressure, do you know what the pop off should be with the old and new spring? I’m not familiar with Yamaha but that seems awfully high. Why did you change from the original spring?

Should be 55psi

 

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I have 2 carbs, both doing the same thing

 

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Cleaned it, tried different springs, still no pop

 

[burtshaver2021]

Cleaned it, tried different springs, still no pop

Wish I could help, but I can’t think why, hopefully someone else like @mikidymac might have an idea

 

[burtshaver2021]

Just came to mind is the lever that pulls the needle out flush with the top of the carb body

 

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Yes

 

[mikidymac]

What plug is popping off?

The only thing that pop-off tests is the spring pressure and seat size.

If it will not pop then you don't have enough pressure or air leaking around the fuel pump.

 

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Pressure was 60 psi. No leaks. The plugs i used to close off fuel outlets

 

[mikidymac]

Then you need to verify you have the correct OEM springs and needle/seat size. Both will change pop-off pressure.

 

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Put in new needle and seat, original spring and now it hisses at 25psi, no pop

 

[burtshaver2021]

Put in new needle and seat, original spring and now it hisses at 25psi, no pop

Where is it hissing from? Have a look at Mikidymac’s carb rebuild thread, you can find it in his profile. Maybe send a picture of your set up for the pop off test,

 

[mikidymac]

You have to wet the seat with WD-40 every time you test it. Will not work dry.