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General Category >> Rubber Side Down! >> Pilot jets
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Message started by bobdog on 06/06/17 at 22:46:39

Title: Pilot jets
Post by bobdog on 06/06/17 at 22:46:39

Can anyone give me the lowdown on bleed holes in a pilot jet,what do they equil in a regular solid pilot jet ?

Title: Re: Pilot jets
Post by IslandRoad on 06/07/17 at 01:30:15

I think I recall reading on the forum that the holes make no difference in the Savage/S40. Someone with more knowledge will surely correct me or add more info.

Title: Re: Pilot jets
Post by Dave on 06/07/17 at 01:46:35

The bleed holes in the Pilot Jets are for carbs that have an "air mixture screw" like the Mikuni VM carbs. When you adjust the idle fuel mixture on those carbs, it adjusts the amount of air that goes through the bleed holes, and that is how the richness of the fuel mix is adjusted (more air - less fuel).

The bleed screws in the pilot jets don't do anything in the Savage CV carb. The pilot jet fits into a hole that doesn't have any passages for the bleed holes to do anything - therefore no air or fuel can get to them and they don't do anything. The CV carb has a fuel mixture screw, when you adjust it you control how much fuel flows (not air).

An easy way you can tell if the carb is a "fuel" or "air" mixture screw is to look and see where the adjustment screw is located in relation to the slide. If the screw is on the cylinder side of the carb slide - it adjusts the fuel.....if the screw is on the air cleaner side of the carb slide - it adjusts the air flow.

You can use any pilot jet in the Savage carb (with or without holes), and it will work fine.

Title: Re: Pilot jets
Post by justin_o_guy2 on 06/07/17 at 19:43:36

An easy way you can tell if the carb is a "fuel" or "air" mixture screw is to look and see where the adjustment screw is located in relation to the slide. If the screw is on the cylinder side of the carb slide - it adjusts the fuel.....if the screw is on the air cleaner side of the carb slide - it adjusts the air flow.

A Nugget.

Title: Re: Pilot jets
Post by piedmontbuckeye on 06/08/17 at 16:07:40

I haven't taken this carb apart yet, but my experience on other carbs, is that the side holes in the jet actually enhance the mixturing process by helping to "atomize" the fuel/air mixture.

I know this is the case on main jets (so called on some carbs) or needle jet as it was known on Bings. (do not confuse this with the designation of "jet needle" which refers to the actual needle-like jet going through the needle jet).

Title: Re: Pilot jets
Post by Dave on 06/08/17 at 18:38:47

78616D6C6567667C6A7D6B636D716D080 wrote:

I haven't taken this carb apart yet, but my experience on other carbs, is that the side holes in the jet actually enhance the mixturing process by helping to "atomize" the fuel/air mixture.

That is true when there is air that goes through those holes, and on carbs that have the air screw the air enters through the holes in the side of the pilot jet and the atomization of fuel does begin in the pilot jet - but on the Savage CV carb there is no air that enters the pilot jet (not from the bottom and not from the sides)....the threaded hole that the pilot jet screws into does not have any air passages on the side (the VM carb does...and the holes in the pilot jet do serve a purpose on that carb.....and there may be some CV carbs that use the side holes - but not on the Savage CV carb). In the Savage CV carb all the mixing of air and fuel happens in the passages after the fuel leaves the pilot jet. I am at home and can't post the image that show this....I will post it tomorrow.

If I could sit in the same room with you and show you how the Savage CV carb and the VM carb are different....I am sure I could convince you that the holes in the side of the pilot jet are meaningless on the Savage CV carb.

Title: Re: Pilot jets
Post by Dave on 06/09/17 at 06:41:52

Here is a photo that shows how the Savage CV pilot circuit works - is has an "idle fuel mixture screw" and when you move the screw your are adjusting the amount of fuel that flows at idle. The air enters at the arrow marked (1), there is an air correction jet in the chamber under the slide diaphragm. This chamber gets filtered air from the oval hole at the top of the inlet to the carb. After the air goes through the jet it flows down a passage to an area just above the pilot jet, and the fuel coming up through the pilot jet combines in this passage with the air, and the air begins to atomize the fuel - the air/fuel mix then goes up to a passage that has holes into the inlet side of the throttle butterfly shown in the area of arrow (2). One or more of these holes goes directly into the inlet and supplies some of the fuel/air mix to the engine - the rest of it goes through the idle fuel mixture screw and it provides additional fuel/air and the amount is controlled by the setting of the screw. You will notice that the pilot jet is screwed into a threaded hole and it seats against the carb body at the top - there are no fuel or air passages on the side of the pilot jet....so no additional fuel and no air can enter the sides of the pilot jet.
http://i67.tinypic.com/o5uckl.jpg

The VM carb has an "air mixture screw" and you are adjusting the amount of air that mixes with the fuel coming though the pilot jet. The filters air enters at arrow (1), and some of the air flows to the holes in the needle jet to mix with the fuel coming from the man jet, the other path for air goes downward in the photograph to a passage that goes to the idle air screw shown by arrow (2). Fuel flows up through the pilot jet from the float bowl, and it mixes with air that is coming through the bleed holes in the side of the pilot jet. When you make and adjustment of the air screw you are controlling how much air can mix with the fuel - when you turn the screw in less air flows and the mixture becomes richer as the vacuum pulls more fuel and less air. You can see that the threaded hole for the pilot jet has an air passage around the sides of the pilot jet and the holes pass this air into the jet....fine tuning can be done by using jets with different size bleed holes or more or less bleed holes.
http://i64.tinypic.com/r8wh95.jpg

The stock Savage CV carb come with a pilot jet without any bleed holes - as there is no reason to have holes since no fuel or air can enter through these holes. You can use pilot jets with bleed holes in the Savage CV carb and it will operate the same is it would without them - as the holes can' t do anything. On the VM carb you have to use a pilot jet with bleed holes so the idle circuit can get air - you can change the size and number of holes to fine tune the operation of the pilot circuit.