Pilot Jet question

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WATCHMAKER

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How much overlap is there between sizes. For example 42.5, 45, 47.5, 50 If you compared lets say a 47.5 2 turns out to a 50 1.5 turn out. Assuming each size gives you the same idle quality (smoothness) and same throttle responce, is one choice better than the other? Will one yeild better acceleration when the throttle is spaped open? In other words, if you go bigger in size and it is properly adjusted will the bigger size give you that little bit of extra fuel when the throttle is snaped open from a dead stop?
 
I would like to know that to.I went from 42.5 to 45 and am wandering what it really does.It gives more fuel at the low end,but could it possibly dump to much fuel in the way that it may make the sled bog slightly when it is pinned.
 
The pilot jet with its fuel screw adjuster is no different then a nozzle on a garden hose. The size of the hose[pilot jet] will only flow as much as the nozzle[fuel screw] allows it to.
The reason we change the pilot jet to a larger size is because when the nozzle[fuel screw] is fully open[2 turns] it does not flow enough fuel because the hose[pilot jet] is too small.
This works the other way to...if the pilot circuit is too rich with the fuel screw at 1/2 turn open you need a smaller pilot jet.
Hope that makes sense.
Bob
 
so sideshow..how do you know if you are flowing to much fuel..is it when it is not snappy at low end launch,in other words the hose is putting out to much fuel..is that a possibility?? It is then loading up to much?
 
Firstly...I have remote fuel screw adjusters,
I like to set up my pilots so they have a high idle hang up around 1 turn open and then I open the fuel screw to just elliminate the high idle hang up. If I can't elliminate the high idle hang at two turns open on the fuel screws, I go up one size on the pilots.
On the other end if I can't get it to run lean[high idle hang], at 3/4 turn open on the fuel screw, I go down one size on the pilots.

Works for Me!
 
I have remote adj also.I even turn down the idle screw a bit which will help the high idle come down quicker.I guess Yamaha is famous for this issue.My SXR has that idle hang up to,I turn back idle screw also so it drops quicker,only thing when sled is cold and started..the idle is a little low for it to run steadily..so have to feather throttle a bit and semi choke a few times until it warms up a bit.
 
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bluemonster1 said:
I have remote adj also.I even turn down the idle screwe a bit which will help the high idle come down quicker.I guess Yamaha is famous for this issue.My SXR has that idle hang up to,I turn back idle screw also so it drops quicker,only thing when sled is cold and started..the idle is a little low for it to run steadily..so have to feather throttle a bit and semi choke a few times until it warms up a bit.
Click to expand...

Thats exactly how mine is right now.
 
sideshow...With the way you adjust your pilots, do you ever get a hanging idle when you are riding and then come to a stop? I had mine adjusted pretty good one day. I had 45's at 2.5 turns on a 25-28F day. It was smooth, good response and no hanging idle. But I knew I had to go bigger because of 2.5 turns and it was a warm day. I put in 47.5 and set them at 2 turns out on a 20F day and after riding I had a slight hanging idle. It would settle down on it's own after about 15-20 seconds. So now I think I need 50's. This is why I was wondering how much overlap there is between sizes. Seems like going from 45 to 47.5, though it was a little colder out, did not make much difference.
 
barometric pressure plays more of an effect then temp# , ever notice spring time its above 32 and your plugs are lean ...with wnterjetting, referring to the unxpected idle hang
 
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WATCHMAKER said:
sideshow...With the way you adjust your pilots, do you ever get a hanging idle when you are riding and then come to a stop? I had mine adjusted pretty good one day. I had 45's at 2.5 turns on a 25-28F day. It was smooth, good response and no hanging idle. But I knew I had to go bigger because of 2.5 turns and it was a warm day. I put in 47.5 and set them at 2 turns out on a 20F day and after riding I had a slight hanging idle. It would settle down on it's own after about 15-20 seconds. So now I think I need 50's. This is why I was wondering how much overlap there is between sizes. Seems like going from 45 to 47.5, though it was a little colder out, did not make much difference.
Click to expand...

Did you notice any difference in snappyness right off the line or from 0-6000 RPM with the change in the pilot?
 
02ViperMtn said:
Did you notice any difference in snappyness right off the line or from 0-6000 RPM with the change in the pilot?
Click to expand...

Different days so it was a little hard to compare but i would say the warmer day with the 45's seemed a little snappier. On the cooler day with the 47.5's I had a slight hanging idle so I guess it was still a little lean. I just expected more of a difference going from 45 to 47.5.
 
WATCHMAKER said:
sideshow...With the way you adjust your pilots, do you ever get a hanging idle when you are riding and then come to a stop? I had mine adjusted pretty good one day. I had 45's at 2.5 turns on a 25-28F day. It was smooth, good response and no hanging idle. But I knew I had to go bigger because of 2.5 turns and it was a warm day. I put in 47.5 and set them at 2 turns out on a 20F day and after riding I had a slight hanging idle. It would settle down on it's own after about 15-20 seconds. So now I think I need 50's. This is why I was wondering how much overlap there is between sizes. Seems like going from 45 to 47.5, though it was a little colder out, did not make much difference.
Click to expand...

47.5 pilots are fairly big for a stock SRX to still have an idle hang at 2 turns...maybe you have some other issues.

Check to ensure the throttle cable is adjusted to factory specs and maybe try turning the idle screw setting down slightly as some times a high idle can be because the engine RPM is still in the CDI advance curve and has to fall out of it to idle down.

Have you done any mods to your sled?
What reeds are you running?
Are your needles in the stock position?[dropped needles can cause the sled to run a bit leaner off idle as well]
Are the carbs absolutly clean?

If you still can't get this sled to idle down, start looking for air leaks, crank seals, carb boot gaslets ect...

JM.02c
 
It's a 780, case ported, 145psi, stock carbs, reeds and pipes. It was recomended to run 50's by the engine builder but they seemed a little rich. I had read so many posts of people using smaller pilots that I wanted to try it. I added fuel screw adjusters which helps a lot. Needles at 3.5
 
If 50's are to rich for a 780 motor,how come smaller sized motors like the 600 in the v-max600 comes stock with 52.5 pilots...don't understand the logic.
 
WATCHMAKER said:
It's a 780, case ported, 145psi, stock carbs, reeds and pipes. It was recomended to run 50's by the engine builder but they seemed a little rich. I had read so many posts of people using smaller pilots that I wanted to try it. I added fuel screw adjusters which helps a lot. Needles at 3.5
Click to expand...


OK! That explains things better!
Yes I think 50s should do the trick...I was running 50s last year on my ported Aaen piped 2002 SRX. Interesting though, when I removed my boost bottle, and replaced the VForce 3 reeds with Boysen rage cages I now need 42.5s to run clean. I think the cages made a big difference in my SRX's low speed jetting.
 
bluemonster1 said:
If 50's are to rich for a 780 motor,how come smaller sized motors like the 600 in the v-max600 comes stock with 52.5 pilots...don't understand the logic.
Click to expand...

vmax 600 has 36mm carbs i believe. srx and sxr is 33mm.
 
sideshowBob said:
OK! That explains things better!
Yes I think 50s should do the trick...I was running 50s last year on my ported Aaen piped 2002 SRX. Interesting though, when I removed my boost bottle, and replaced the VForce 3 reeds with Boysen rage cages I now need 42.5s to run clean. I think the cages made a big difference in my SRX's low speed jetting.
Click to expand...

bob, i think it was the boost bottle that made you need to fatten up your bottom end so much, as my buddy needed to go up to like 52.5 pilots on his 600 srx w/boost bottle.
 
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