piolet air jet

[Guest]

Hey would any one be able to tell me if the piolet air jets get fully seated or do they get a few turns out? The bike is an 85 GS700ES.

[mike_of_bbg]

Jets are seated and do not get backed out - regardless of whether they're the pilot jets or the air jets (which are different). The mixture screw gets backed out various amounts from 1.5-3 turns usually (as an initial guesstimate) depending on the model.

Air Jet:



Pilot Jet:



Mixture screw - this one gets backed off after being lightly seated:

[Steve]

Yep, there are only three items that don't get fully seated on your carbs:
1. the idle mixture adjustment screw
2. the carb sync screw
3. the idle speed screw

All other screws, jets, fasteners, etc. will be snugly seated.

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[mike_of_bbg]

Yep, there are only three items that don't get fully seated on your carbs:
1. the idle mixture adjustment screw

Oh, and Steve's post reminds me...

In that picture the idle mixture screw is called an "air screw", which is not correct - it controls flow of fuel in the idle circuit, not air. But it's a lot easier to link to JPEGs in the original carb cleanup series than to grab them out of Ed's PDF. Ed's PDF is going to be the most up-to-date guide to go by:

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Ed refers to that as the "pilot screw", which I still don't care too much for (knowing Ed that's probably the official name) but it's a much better description than the "air screw", as it really has nothing to do with air at all.

[Steve]

In that picture the idle mixture screw is called an "air screw", which is not correct - it controls flow of fuel in the idle circuit, not air. ... Ed refers to that as the "pilot screw", which I still don't care too much for (knowing Ed that's probably the official name) but it's a much better description than the "air screw", as it really has nothing to do with air at all.

If you want to get down to the really nitty-gritty technical stuff, you are still not quite right.

Yes, I call it "idle mixture screw", but the name that is used in the factory service manual is, as Ed says, "pilot screw".

Where you are technically still not quite correct is that the screw actually controls a MIXTURE, not just fuel and not just air. The pilot air jet is in the intake throat, the pilot fuel jet is in the float bowl, near the main jet. Together, they produce the pilot mixture, which is then sent to several holes in the top of the carb outlet. One is just downstream of the throttle butterfly and is open all the time. A second (and sometimes there is a third) hole is hidden by the butterfly and is uncovered just as soon as it starts moving. These are "transition" ports. At idle, that first pilot mixture port is not quite enough to allow the engine to run, so there is a second port, but this one has an adjustment screw to control how much more mixture is admitted.

On the older VM-series carbs, there were "fuel screws" and "air screws" because that's what each one controlled. With our BS-series carbs (sometimes called CV carbs, but "CV" is a type of carb, not the series name), the only adjustment is to the mixture.

This picture from the manual shows those passages and ports quite well. By the way, THESE are the passages and ports that typically get plugged up when the bike is not used. You can see how inaccessible they are to simply spritzing some carb cleaner spray in there, this is why they HAVE to be soaked.


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[mike_of_bbg]

And Steve cuts through every layer of over-simplification

My objection to the name of "air screw" is that first it's, well, wrong and that it confuses the effective mixture changes arising from the tightening/loosening thereof. As I said, Ed would probably not have used "pilot screw" unless it was the absolute technically correct term (like our bikes have a "cylinder head cover" and "head cover gasket", not a "valve cover gasket" - but 98% of the time the former term is used ). My only issue with the name really is that it can cause confusion with the "pilot jet". Though I understand they're both part of the pilot fuel delivery system.

Let's not even get started on the "choke" or "CDI"

[Steve]

And Steve cuts through every layer of over-simplification

Dang it, I did it again.

Let's not even get started on the "choke" or "CDI"

Even though the knob or lever on the bike is clearly labelled "CHOKE".

Yeah, it bugs me, too, but every time I use the term, I use quote marks, like you did. Somewhere in the post I will explain that it is an "enrichment system", but "choke" is so much easier to type.



"CDI" is just plainly wrong, but hey, it's electronic and the hot item for cars at the time was a CDI system, so they must be the same. Right?

Unfortunately, Suzuki's term for the box, "Ignitor" wasn't much better, as it didn't really ignite anything. It's just a few transistors that are replacing the older mechanical points.

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[Danaconda7]

Well then... fully seated. good. Thank you.