Main air jets and what they do?

[Vloukole]

Can anyone please tell me what the Main Air jets do and what they influence when going larger or smaller?

My Suzuki GS550 ET has 1.6 main air jets(stock). I bought new jets and it came with 1.8. Is that a problem?

 

[tkent02]

Your terminology is wrong, that makes no sense. Main jet is a fuel thing. The pilot air jet is an air thing, but the number should be something like 150 or so.

 

[JTGS850GL]

Actually his terminology is correct. The main air jet is indeed 1.6mm for the GS550ET. It's a press fit jet opposite of the pilot air jet on the air filter side of the carb. It's usually not changed as most modifications can be done without changing it out. It's also a royal pain the but to replace.

You say that you bought new jets... What jet kit did you buy and why? What mods have you made to the bike to warrant changes to the jetting?

 

[tkent02]

Why isn't it shown in the parts diagrams?

 

[JTGS850GL]

Why isn't it shown in the parts diagrams?

Because it's not normally a replaceable part. It's press fit into the body by Mikuni. It comes with the carb body and is part of the assembly defined by the assembly number.

 

[Vloukole]

I bought new jets cause the old ones were all the wrong size. It is called a main air jet(on most sites and manual) and is not pressed in. It screws in.
It is the only jet you can remove on the intake side.

In the manual the size is 1.6 and on the jet it is 160 tkent02.

 

[tkent02]

That's a pilot air jet. Should be numbered 150 or so.

 

[JTGS850GL]

What year is the bike? If it's a pre 1980 then that would explain it. The VM carbs did come with main and pilot air jets that were defined in mm sizes.

 

[Vloukole]

My manual states it's the Main Air Jet.

Any answers to my question?

It is a 1980 model.

 

[Guest]

For clarification, which jet are we talking about?



The small orifice at 4 o'clock, or the slighter larger one at 8 o'clock?

 

[hampshirehog]

For what it's worth, I've worked on 2 SA bikes (GSX 1100 and a GSX 750 - both never fiddled with) and they were jetted a little differently to both UK and US bikes and to what the manuals say. It might be a US / UK emissions thing but both bikes ran fine with 'the wrong' jets fitted.

 

[Vloukole]

Larger one 8 o'clock.

So 180 will be fine if the stock size is 160(1.6)?

 

[tkent02]

That's the pilot air jet. Mikuni numbers them by flow rates, not diameter. Some other brand jets may be numbered by diameter.

 

[Vloukole]

Look at specs in the manual if you have one

 

[Guest]

Yep, pilot air jet. Mikuni #150 for my market. Might be a tad different for SA. As tom says, that relates to flow rate per minute, rather than physical dimensions. Presumably you're replacing the jets because they can't be cleaned?

 

[Vloukole]

I bought new jets cause the old ones were the wrong sizes. Mains were 115 , pilots were 45 with stock airbox and exhaust

 

[Guest]

Yep, sounds like some one fiddled. Mine runs 92.5 mains, and 40 pilots. I can't tell you what effect the new pilot air screws would have, because they have a different numbering system to Mikuni. Basically, a smaller jet would allow insufficient air at idle/low-range, whereas too large a jet would cause it to run lean.

 

[Vloukole]

Yes that is the sizes I bought. Lets say the stock size is 160 cause that is what the carbs had in and I change them to 180s. Will the bike run fine?

 

[Guest]

Personally I would stick with the 160s. That's already two sizes up from what I have, but as HH mentioned, that is probably something to do with local regs.

 

[Vloukole]

Is yours 140s?