Rubbermount_EVO Needle clip position & shim question

[Headly]

Could someone explain the function of using spacers above or below a needle's clip, say a dynojet kit for instance, if the retainer is on the say 3rd or 4th clip, why/how do the washers above or below work?



Is it the height of the needle for idle ? if so how will it affect reading the jet combo you use?

[rfranz1952]

On a standard needle--not a clipped needle as in the dyno-jet kit--the washers will only go under the head of the needle and serve to shim it a little higher. This will change the fuel flow characteristics (enrichen) at some throttle positions.

In the case of a clipped needle, the clip position serves that function, and I have never run across anyone that needed to put washers underneath the clip to shim it up higher. The instructions say to put the washers on top of the clip--which can only be done if the clip is not in the top position. I have two theories:

1. Its a good place to store the washers, so they don't get lost

or

2. The needle may have a tendancy to be a bit light, and perhaps float or bounce a little, which creates erratic fuel flow. The washers on top help stabilize the needle.

[milmat1]

Shimming the needle is used to Richen the Midrange Throttle Position. The Idle is mainly controlled by the Pilot (Slow)jet and screw. The needle taper controls mainly the mid range, And the main jet controlling the WOT position.
Shimming the needle up puts the midrange lower on the taper thereby richening that area...Hope that helps...

[Headly]

kinda

maybe I screwed up... I found the clip in the 3rd position with 4 shims on it, my buddy and I were taking it apart and he swore they were under, I thought they were over, so I went clip 4th position 2 over 1 under as a compromise kinda

it seems 4 over is where I oughta be, what characteristics should I be looking for?

if I were to have a dyno run, where would it show an affect of this mismanaged clip and shim combo?

btw thx guys

[milmat1]

Originally Posted by Headly

kinda

maybe I screwed up... I found the clip in the 3rd position with 4 shims on it, my buddy and I were taking it apart and he swore they were under, I thought they were over, so I went clip 4th position 2 over 1 under as a compromise kinda

it seems 4 over is where I oughta be, what characteristics should I be looking for?

if I were to have a dyno run, where would it show an affect of this mismanaged clip and shim combo?

btw thx guys

Mid throttle !!
Some have claimed that raising the needle increased the idle RPM's but I think it was just a byproduct. Raising the needle means the the tapered part of the needle comes into play sooner, Increasing the mid throttle fuel !!

[Don Burton]

The other part of the needle not mentioned above is the straight portion which regulates the mixture from just off idle through low cruise (Keep in mind that there is considerable overlap in all of the carb circuits). Almost all of our every day riding is done in this area of the needle which represents approx 1/8th throttle to 1/4 throttle. Shimming the needle just decreases the length of the straight portion that is held in the needle jet which brings on the taper more quickly as milmat has said. As milmat has also said, on a dyno sniffer the taper area mixture would show up in the mid throttle area between 1/4 and 3/4 throttle settings. Shim too much and you'll gain a richer mixture at earlier throttle opneings with poor gas mileage as a result. On the other hand, If the taper comes on too late you will not have enough fuel for optimum power when you first grab a fistful and it isn't good for the engine either. Many dyno runs are done at WOT so you'd need to ask that the operator do part throttle readings as well in order to get this reading. You might want to mark the throttle setting with tape ahead of time. The taper will briefly affect the WOT throttle mixture on the dyno as well but not significantly after the vacuum slide (and needle) is fully raised and it is running fully on the main jet.

Some needles have longer straight portions than others. I currently have a non stock needle in mine with a slightly longer (and also thinner, making it slightly richer in the off idle through cruise area) straight portion so I have shimmed it 0.020 in order to bring on the taper as quickly as the stock needle. My current setup is still conservative with Gronk mufflers and stock A/C so I didn't need an even richer needle that is available. I hope that this helps.

[Headly]

thanks Don,

seems the switch from a 45/180 to a 44/170 while leaving the needle with the wacky set up was an experiment that didn't work so well, or it was influenced by my riding style during observation of 59 miles. I had to fill 1.7 gal after riding 59 miles.

I switched the jets because I was averaging 34 mpg, viola' change the jets, stay at 34mpg. -(It was a high speed WOT mostly run to get the miles, but 80 mph feels soo smooth now compared to before, used to be 85-95 felt better,now 80 is the sweetest spot.)

It was at 2 1/2 turns out with the larger jets, I put this at 3 turns, maybe I will back it in some. I will definately get that shim from the wrong side of the needle out of there though, maybe try the 3rd clip position too.

-When I bought the bike I found the clip in the 3rd position with 4 shimms on top of the clip and the jets were 42/180- it ran nice, but I had what I thought were some lean issues/popping and deisling, that was never the jetting, it was a hole/crack in the exhaust pipe. exhaust is fixed and I am trying to undo a fix that was never needed and to see if I can do better than what I found it with.

I do alot of highway or county route riding with few stops and many miles at higher than posted speeds.

this tweaking is just for me to finally learn it myself instead of not knowing how.

thanks

[Don Burton]

Headly, Did you get things worked out yet? What changes did you make to make it happen?

[Headly]

Hey guys thanks for the information-

finally made the change today. I went for a ride yesterday, 3rd one of the year. I went out 2 up for 150 miles and was frustrated at the 2nd and 3rd gear cruising surges at minimal throttle so today I put the clip in the 3rd position and kept the 44/170 combo

feels much better at 1/8 to 1/4 throttle- then it seems just a little flat 1/2-3/4 or WOT, might be the bikes power and I am expecting too much but am thinking of trying the 180 to see if it wakes up the mid to top

my notes dont indicate if I am at 2 1/2 or 3 turns out so I will have to check that tomarrow.

feels good to ride the bike again.

-what did I do wrong- to get the top of the carb off I had to persuade the throttle cable part up a wee bit to let go of the top. the side screw didnt want to come off with pliers and the screw drivers didnt fit.

thx

[FoxsterUK]

Originally Posted by rfranz1952

In the case of a clipped needle, the clip position serves that function, and I have never run across anyone that needed to put washers underneath the clip to shim it up higher.

Funnily enough I have done just that recently. The gap between clip positions is 1mm and this can make quite a difference in air/fuel ratio. A 0.5mm washer gives additional tuning granularity.

If you are tuning by seat-o-the-pants or plug colour then it won't matter but for us anal-retentives tuning by O2 meter a clip position can be the difference between, say, an AFR of 13.5:1 and 12.5:1 and so a half clip position is needed if your target is 13.0:1.

Fox