1979 YZ250F Carbie advice

[fred99999au]

i am talking about the small jet which is at the bottom of the inlet side of the carby it bleeds air to the main and corrects mixture at high rpm

So does it lean the mixture out or richen it?

I got one in the bellmouth of my 38mm for my IT400D and that was lean everywhere. Spoke to the Mikunioz bloke and he said leave it in there and jet around it.

Which is an excellent business strategy when you need 9 needle jets and a bucket of mains to stop the thing from cooking.

[sleepy]

i am talking about the small jet which is at the bottom of the inlet side of the carby it bleeds air to the main and corrects mixture at high rpm

So does it lean the mixture out or richen it?

I got one in the bellmouth of my 38mm for my IT400D and that was lean everywhere. Spoke to the Mikunioz bloke and he said leave it in there and jet around it.

Which is an excellent business strategy when you need 9 needle jets and a bucket of mains to stop the thing from cooking.

The bigger it is the leaner and the smaller the richer, but mainly has more of an effect at the top end. Not normally something you would change if it's the original carb.

[fred99999au]

no, it was installed in the 'miles to buggery too lean' new carb.

[Momus]

Perhaps applicable to this air corrector issue..in my Weber-carbs-on-Mazda-rotary tuning days we would use known diameter safety wire appropriately restrained in the air jets as a calibrated restriction for a quick, cheap checks.

[sleepy]

no, it was installed in the 'miles to buggery too lean' new carb.

Taking the air jet out will only make it leaner. Sounds like you need to find someone with a box full of jets to borrow till you get it correct. If the original carb was lean everywhere as well, perhapes you have a big air leak that needs fixing.

[HVA61]

www.iwt.com.au/mikunicarb.htm


Go here , sounds like you guys need to understand how to properly diagnose and set a carb.

[sleepy]

www.iwt.com.au/mikunicarb.htm


Go here , sounds like you guys need to understand how to properly diagnose and set a carb.

There is no information on that link about the main air blend jet so it is quite irrelevant to fred99999au's question.

[fred99999au]

Mine was more a rhetorical question about the function of the air bleed.

Genuine carb didnt have it replacement carb did and it was lean everywhere.

It runs Ok now and is as reliable as a woodburning stove. I was wondering what the function of the air bleed was.

[HVA61]

Leave the jet in there and jet around it.

The information is very relevant to the understanding of the operation of a carb. and setting of the same.

[sleepy]

Mine was more a rhetorical question about the function of the air bleed.

Genuine carb didnt have it replacement carb did and it was lean everywhere.

It runs Ok now and is as reliable as a woodburning stove. I was wondering what the function of the air bleed was.

The function of the air bleed? The pasage from the bell mouth through to the top of the needle jet allows air to be mixed with the fuel to aid in atomisation of the fuel as it is drawn into the air streem entering the engine. At low engine speeds there is only a small amount of air passing through this passage or jet if fitted. At high engine speeds there is a much greater flow of air which causes a pressure difference across the air jet, this in turn means more fuel is drawn out of the needle jet with less air added. If we make the air jet smaller this pressure difference is increased at high RPM making it richer but because the flow of air through the jet at low RPM is only small the smaller jet has virtualy no effect on mixtures at the lower speeds.

The size of this jet and other subtle differences in passage sizes are the main reason that fitting a new carb with stock size jets doesn't always work.

[HVA61]

www.mikuni.com/pdf/vmmanual.pdf

Attached is the Mikuni super tuning cat. which is very helpful

[Lozza]

i am talking about the small jet which is at the bottom of the inlet side of the carby it bleeds air to the main and corrects mixture at high rpm

So does it lean the mixture out or richen it?

I got one in the bellmouth of my 38mm for my IT400D and that was lean everywhere. Spoke to the Mikunioz bloke and he said leave it in there and jet around it.

Which is an excellent business strategy when you need 9 needle jets and a bucket of mains to stop the thing from cooking.

Without the air corrector the mixture would get richer with rpm the air corrector(as the name suggests) keeps that in balance. Early mid 90's 250 road bikes put solenoids on the air corrector to pass emissions tests. With modern electronics we can "rejet' without touching the float bowl.

http://www.flo-commander.com/