Jet Sizes

[78yamahaman]

I have looked and cant seem to find it on here. I am wondering what the standard jets sizes are for a 78e. I have pulled my carbs and checked. My pilot jets are 45. The main jets are 13.75. My air jets are 2.10. I also have a 79sf but the jets in that are different. The mains are 13.75 but the pilot is 42.5 and the air jet 1.85. I have heard several people say the 78 and the 79 are the same carbs but the difference in the jet sizes has me confused. Does anyone know where I might find what the standard jet sizes were or should be? As always thanks for the help.

[egsols]

Clymer says...

Main 137.5
Pilot 42.5
Air jet 180


Haynes says.....

Main 140
Pilot 42.5
Air 180

Both specs are for e and sf

Yamaha Fische says for 1100e.....

Main 140 behind part number /137.5 at top right corner of fische
Pilot 45 behind part no. /42.5 at top right corner of fische
Air 210

[thewiz]

Well ....

there is a Tech Tip here that says that a shows a that a 78 PJ is 45. Hmmmm......

[dbeardslee]

Yamahaman - the stock mains I took out of my 79F were 137.5 (reading it directly off the jet). As the carbs are setup the same as the 78E I'm sure it's the same with your carbs. Pilots were 42.5, but as they have no external markings I have to take yamaha's word for it (fiche).

[prometheus578]

Pilot jets for the "E" are #45.
For the "F" and later, #42.5.
(Such a small difference, "it wouldn't make me no never-mind".)
Yamaha messed with the jets a little from year to year; even putting different sized main jets in carbs #2 and 3#.
Oh, sure, it'll make a difference... if'n you're tryin' to shave off a few fractions of a second at the drag strip.
But for normal people like me, who's riding just consists of trips to the liquor store and the free clinic... you won't notice the difference.

[Crazcnuk]

So you don't think the 45 PJs (over 42.5's) will affect mid range cruise economy?

[prometheus578]

Nope.
Simply put....
The pilot jet meters the fuel for the idle circuit.
The # affects how much fuel gets drawn up, which then gets mixed with air through those little holes in it, which then... get's metered into the engine, by how the pilot screw is set.
Fuel drawn up through the pilot jet comes out the hole in the carb throat that the pilot screw works for, and also those three little holes right behind the throttle plate.
This is for idle... and for transitioning to mid-range.
Mid-range, is controlled by the rising of the tapered needle in the "emulsion tube", due to changes in vacuum on the slide diaphram thingie...
(Mid-range get's it's fuel through the main jet.)

[psycoreefer]

Originally posted by prometheus578
Nope.
Simply put....
The pilot jet meters the fuel for the idle circuit.
The # affects how much fuel gets drawn up, which then gets mixed with air through those little holes in it, which then... get's metered into the engine, by how the pilot screw is set.
Fuel drawn up through the pilot jet comes out the hole in the carb throat that the pilot screw works for, and also those three little holes right behind the throttle plate.
This is for idle... and for transitioning to mid-range.
Mid-range, is controlled by the rising of the tapered needle in the "emulsion tube", due to changes in vacuum on the slide diaphram thingie...
(Mid-range get's it's fuel through the main jet.)

True but the pilots don't shut down when your in the "midrange". So using a bigger pilot jet will add more gas all the time - granted its effect on total mixture is small but I'd think a larger jet would mean less mileage because its always adding a bit more gas then the smaller jet would..

[prometheus578]

"Think I'm stupid, or somethin'?"

Note how I started my essay with... "Simply put".
(I don't write anything here... unless I leave myself a way to weasle out of it later)
Technically, Psycoreefer, you are correct.
But, as you also stated...

granted its effect on total mixture is small

That was the point I was trying to make.
Jetting questions here usually rotate around trying to get more power, not better mileage.

Here's a mental game to play...
(Again, simply put)
Joe Blow(a new member) puts in a smaller pilot jet for economy's sake. Of course, the idle starts to stumble 'cause the mixture is then lean.
So, what does he do?
He opens up the pilot screw another turn. This now lets more of that lean mixture in.
So, really, what has he accomplished?
He's about back where he started.

One may be able to detect a difference on a dyno or with an exhaust gas analyser... but you won't notice anything different on your daily ride to buy donuts... either in performance or economy. (simply put)

And yes, I also realize that those little holes by the throttle plate are not controlled by the pilot screw.

[Crazcnuk]

Yes, but my point is that the carbs for my bike were built a certain way. They were designed to give max performance with minimum emissions and around 43mpg(US).

My bike was getting 25-28mpg(US) and the only variations from stock are the larger pilot jets and wierd needles.

I also have no power above 6krpm in 4th and 5th gear, and I can't get it to idle right. It's either dieing or idling at 2-3000rpm.

Changing mains had no effect on this problem. I am trying to figure out how my carbs should be set up.

I would be ecstatic with 95bhp and 40+mpg!!

My method, at this point, would be to set them back to complete stock setup, THEN try and tune the damn thing.

[Da-Bubble]

Crazcnuk,

You mentioned weird needles? I was ready to pull my hair out trying to get my carbs right when I finally sent them to another member for analysis. He thought they looked good too until about the third time through them he noticed that two of the needles were a different size. He swapped them for a matching set and all is well. I think you're on the right track of trying to get as close to stock as a starting point.

Good Luck,
Scott

[Crazcnuk]

Well, all my needles are the same, but some off number that was never used for xs1100's (at least according to any KNOWN setup, as they seemed to use whatever was laying around).

I need a set of 42.5 pilot jets and 5GL16 needles, and I could put them back to where the manual (Yamaha's, not 3rd party) says they should be.

[78yamahaman]

Here is a spot to find pilot jets.

http://www.sudco.com/cat32/60.pdf

http://www.mrcycles.com/eshopprod_ca...TS_N151067.htm

or you could try these guys
http://www.crc2onlinecatalog.com/mis...tm#Main%20Jets

The main reason I was asking about jets sizes is that I get a small cough from my carbs. It is mainly at low rpms. I know my main jets are 150 because I went up 5 sizes like what was recommended for the changes that were made to my bike. (4 and 1 jardine header pipe and pod filters) What had me confused was the air and pilot jets. So If I turn my pilot jet out a turn this will allow more fuel? And does any one know what could be causing the cough? I have been told that it is because that lack of fuel at the lower rpms. As always thanks for your time and the advice Lords knows I need it. I have a clymers manual too but no where in it does it have jet sizes. I have looked and looked but I am an idiot and could be over looking it I guess.

[psycoreefer]

Yamahaman - If you turn your idle mixture screw out it will allow more fuel - not the jet itself but the screw on the top engine side of the carb body. That screw is a fine adjustment and may not make enough difference to get your bike running right. I think I read somewhere that if you need to turn it out more then 3 turns you should up your pilot jet.

If you did go up 5 sizes on your mains you'll need to go up on the pilots as well. The jetting recommendations are here and they recommend going up 4 sizes for 4 to 1 and pods. Read carefully as it says add up the changes and then subtract one. Also it recommends going up one pilot size for each main increase of 3.

You can find the stock jetting of your bike Here

If you follow the recommended increases you would have 147.5 mains and 47.5 pilots. But remember each bike/location/rider is different so that would be a good starting point but maybe not perfect for you.