What do pilot jets do

[Dusky 13]

Just wondering if they are effecting my idle speed from wrong setting

[rodbolt17]

man I could have fun with this.

however I will tell you.
pilot jets are fixed and allow a certain A/F mix.

or they fly cropdusters.

[boscoe99]

Effect on idle rpm speed, not so much. Effect on fuel/air ratio, yes. Which might in turn affect the idle speed.

Why do the japs call them pilot jets in the first place?

Now in a cropdusters piston engine airplane, if it has a carburetor, the idle mixture will be adjustable. Two ways in fact.

[TownsendsFJR1300]

If the idle jets are clogged, as noted above, it will affect the slow speed A/F mixture and will indeed affect your idle (rough or lack of idle).

Its easy enough to clean, I would pull them, inspect/clean and make sure you can see light thru them.

[rodbolt17]

many Yamaha carbs use fixed pilot air and pilot fuel jets.
I guess idle got translated as pilot.
if your carb has a fixed air orifice or a pilot air jet and a pilot fuel jet then A/F ratio is fixed at the factory.

[99yam40]

Just wondering if they are effecting my idle speed from wrong setting

Never, I repeat NEVER post without the motor's model #

Could you possibly be trying to say pilot adjustment screws instead of jets

[Dusky 13]

Never, I repeat NEVER post without the motor's model #

Could you possibly be trying to say pilot adjustment screws instead of jets

Yep that's what I am trying to satin thanks for that new to this outboard stuff 70hp tlrr

[TownsendsFJR1300]

A year would help too..

Up above, in red, is the purchase Yamaha parts. You can put in your information, eventually click to the carb and see a break down of it. If you look at the parts list below that, it'll show jets, adjustment screws, etc.

[99yam40]

A year would help too..

The last R says it is a 1993

Most people get the year wrong when they post, that is why a Model # is needed

[DennisG01]

Yep that's what I am trying to satin thanks for that new to this outboard stuff 70hp tlrr

Auto-correct is not a substitute for proof reading. (forgot the smilie with my original post)

Guys, before we go too much further with this, we found out in another of his threads about this issue that he's running the engine on muffs. Although limited, my experience with OB's is that you really can't figure out idle problems unless you're in the water (or at least a bucket) due to the lack of backpressure on the exhaust when on a hose.

[rodbolt17]

wrong.
will work for some antique jhonny rude and merc stuff but for the most part, if a Yamaha idlers well on the flusher, it idles about the same speed in the water.

[DennisG01]

wrong.
will work for some antique jhonny rude and merc stuff but for the most part, if a Yamaha idlers well on the flusher, it idles about the same speed in the water.

Interesting. And not at all to say you're wrong - far from it as you have much more experience with these engines than I do. But my '00 250HP OX66 never calms down to a normal idle on the muffs - maybe about 1,100 - and doesn't stay "constant", either. But it's absolutely perfect in the water. It acts the same as some of my older stuff (all the brands you mentioned) - anywhere from mid-70's to mid-90's.

[TownsendsFJR1300]

My F150 idles fine on muffs BUT, when out of the water, generally (7 times out of 10) has a slight hesitation if you blip the throttle slow to med speed (right off of idle ((700)) to maybe 1,200 RPM's).


In the water, NO hesitation, no matter what the speed you blip....

[rodbolt17]

some folk are just to thick to deal with.
oh its a freaking motor, it musty run just like grandpappys 3 hp ev light twin.

[DennisG01]

some folk are just to thick to deal with.
oh its a freaking motor, it musty run just like grandpappys 3 hp ev light twin.

Now, THAT is wrong. I'm not so thin-skinned that it bothers me, but quite honestly, it's a little on the rude side and rather unprofessional. If that was said with some sarcasm, well, it wasn't obvious.