leakdown questions

[98blaster+4]

So I have almost all the parts for the tester I am making.
My question is...
When you do it everybody disconnects the carb and hooks the tester to the intake, why not connect it to the filter side of the carb?
If there was a leak in the carb but not anywheres else couldnt it still set off the jetting?

 

[blasterdemon7]

It would leak out past the jets and give a false reading. It would push the gas back to the tank and give you more volume making you reading drop quickly.

 

[Blaner]

i also have thought about it and came to the same conclusion! i suppose if your carb is sucking air, its a bit of a loophole in the leaktest system

 

[98blaster+4]

okay, if the gas liine was capped off, and hopefully not leaking, then the extra volume would not matter as the unit as a whole would be pressurized to the 7psi. its not like a compression tester where if the adapter has too short of threads to allow more volume for an inaccurate reading.
any builders thoughts on this?

 

[cole454]

Pretty sure thats what happened with mine. The rubber plug came of the oil nipple and ran it lean. Melted the piston.

 

[98blaster+4]

one thing to add i have a 28 pwk carb , no oil injection.

 

[Blaner]

well why not try it... one thing to remember is to hold the throttle open, mabey cable tie it open

 

[blasterdemon7]

You would have to block off the over flow line and vent lines to.

 

[blasterdemon7]

It's worth the try. If it don't hold threw the carb then di it threw the boot to double check it.

 

[sicivicdude]

The throttle cable leaks around it, the carb cap usually isn't PERFECTLY sealed, and the float bowl vent leaks.

As long as carb isn't worn totally out the carburetor's leaks are accounted for in the jetting.

It's the inconsistent big leaks which cause lean jetting and siezed pistons.

 

[98blaster+4]

The throttle cable leaks around it, the carb cap usually isn't PERFECTLY sealed, and the float bowl vent leaks.

As long as carb isn't worn totally out the carburetor's leaks are accounted for in the jetting.

It's the inconsistent big leaks which cause lean jetting and siezed pistons.

thats the kind of answer i was looking for....thanks bud

 

[sicivicdude]

No problem man. Really, you don't want to include the carburetor in your leakcheck. In reality the carburetor is a major leak (one that changes it's leak rate depending on how hard you push with your right thumb) but it's also letting in all the fuel... hopefully both at a known rate that doesn't change unless you change jetting.

Just leakcheck from the intake boot to the exhaust port. As long as you've got all that sealed up, you can fiddle with the carb jets to get it right.

 

[98blaster+4]

did my leak test last night, all is well inside the blaster i guess. was having trouble with the area around the exhaust leaking a little by the end of the tests. had a bunch of leaks at the intake manifold . using genuine yamaha gasket, still was leaking....but im good for some jetting if the weather clears up

 

[sicivicdude]

Those silly intake gaskets always leak. Use a light film of silicone on both sides and then a light film of silicone on the intake boot itself and it'll take care of that problem right off.