How to raise the needle?

[danny01975]

82 GS1100. Stock air box (missing snorkel if that matters), 4-into-1 delkevic exhaust with baffle, one size up main jets and pilot, valve clearances all within spec.

I've been chasing down a stutter at 1/8th throttle for a while now and it seems to be right at the transition between the pilot and the needle transition. I raised the float height to 3mm and while that helped some, it's still there. I read that raising the needle can help with that handoff by making the midrange just a bit richer, sooner. I understand this bike does not have clip positions on the needed and instead has a nylon washer. Adding spacers lowers the needle, but how do I raise the needle? Are there special thinner washers I can get? Do I slowly sand them down to a given thickness?

Honestly, I would much rather have it be reversable so I can return to stock if I need to. What is the right way to accomplish this?

[chuck hahn]

someone will have a link to shimming washers. Sounds like youll only need a few thousands to get it close. Place shim washers between the clip and the slide
I used to have a place bookmarked but after scrubbing the laptop i lost the favorites and i cant remember the name.
Also i wonder if maybe opening the mixture screws 1/2 turn would add a bit more fuel into the transition. This may be worth a try and its g\fast and easy to do.

[danny01975]

someone will have a link to shimming washers. Sounds like youll only need a few thousands to get it close. Place shim washers between the clip and the slide
I used to have a place bookmarked but after scrubbing the laptop i lost the favorites and i cant remember the name.
Also i wonder if maybe opening the mixture screws 1/2 turn would add a bit more fuel into the transition. This may be worth a try and its g\fast and easy to do.

I thought that adding washers lowers the needle. Not raises it. No?

And I don't disagree about adjusting the pilot. I've been everywhere from 2.5 turns on the stock pilots, to 3 turns out on larger pilots. It runs great at all of those settings, but the hiccup at the transition is always there.

[chuck hahn]

if you put a shim BELOW the E clip it raises the needle. So as for the screws. General wisdom says two turns out to start. Then go out 1/4 turns at a time a see how it rides. The stutter could actually be too much fuel and its not easily ignited. I would reset at 2 out, clean the plugs really good and start all over I also would start with 1 over pilot and 1 over mains. Gotta play Chinese jets game to find right combo

[danny01975]

Ah.. ok. There’s an e-clip in the mix. I understand now.

I already have 1 over pilot and mains. Last I settled on 2 1/4 turns out and I’ve been riding like that for a while. As it is now, it’s 2 turns out with the fuel level at 2.5 - 3 mm. I reduced the pilot because increasing the fuel height made it start without the choke.

FWIW, I checked the plugs at the same time I did the float adjustments and they looked a little bit lean.

maybe I should just go back to 5mm fuel height and start playing with the pilot again. Then focus on the needle. The damned float height is such a pain in the ass to adjust.

[Nessism]

if you put a shim BELOW the E clip it raises the needle. So as for the screws. General wisdom says two turns out to start. Then go out 1/4 turns at a time a see how it rides. The stutter could actually be too much fuel and its not easily ignited. I would reset at 2 out, clean the plugs really good and start all over I also would start with 1 over pilot and 1 over mains. Gotta play Chinese jets game to find right combo

Sorry chuck, but this is wrong.

To lift the needle on the Mikuni BS CV carbs, you must reduce the thickness of the shim on TOP of the E clip. Please check my rebuild tutorial, this is covered in detail there. Or, search the forum, for countless similar posts.

[danny01975]

Sorry chuck, but this is wrong.

To lift the needle on the Mikuni BS CV carbs, you must reduce the thickness of the shim on TOP of the E clip. Please check my rebuild tutorial, this is covered in detail there. Or, search the forum, for countless similar posts.

Thanks Nessism! This is what I was looking for! So the way to reduce the thickness, if I want to keep it reversable, is to use a stack of washers. Any suggestions on step size? I understand that it depends on what the bike needs, but should I just go in .5mm or .25mm increments each time until I find something that works?

Additionally, I see the picture you use demonstrating the wet method for checking the fuel height shows 2.8mm. That's right about where I'm at now. Even though the spec is 4.5 - 5.5 mm. Should I bother adjusting it back to that range?

[Nessism]

Thanks Nessism! This is what I was looking for! So the way to reduce the thickness, if I want to keep it reversable, is to use a stack of washers. Any suggestions on step size? I understand that it depends on what the bike needs, but should I just go in .5mm or .25mm increments each time until I find something that works?

Additionally, I see the picture you use demonstrating the wet method for checking the fuel height shows 2.8mm. That's right about where I'm at now. Even though the spec is 4.5 - 5.5 mm. Should I bother adjusting it back to that range?

Getting the fuel level perfect is not worth the effort. Main thing is that it's a few mm below the gasket surface. Get it there, and call it done.

Regarding lifting the needle, I usually sand down the plastic spacer a couple mm and call that done also. If that doesn't clear up your running issues, the problem is not the needle.

[danny01975]

Effort indeed! I’m glad to hear that. Trying to get the fuel level spot on is an exercise in frustration and a real test to one’s patience.

Will try sanding down the needle spacers next and report back.

[KiwiAlfa156]

May be it's too rich? Have you plug chopped with fresh plugs while it's 'farting' around to ascertain what the combustion is like at this point? Stutter is usually a descriptor of a rich mix. Lean mixes surge, like your starting to run out of gas (because you are). As Nessism says in his signature "To measure is to know"

I say this because I run a large foam air filter in place of the airbox and a four into one and the pilot mixture and needle position is stock. The bike carburates beautifully. In fact the only re-jetting required was the main jet that is up 4 sizes.





Which makes sense if you think about it. Jetting is about adding the correct amount of fuel to the airflow inducted into the engine across the rpm range. Correct AFR = best combustion = best running/best power.

Air flows through the carburetor because the pressure the engine side of the carburetor is lower than atmospheric outside the air filter. At small throttle openings at which the pilot circuit is boss, the volume of air flowing through the air filter medium is small and slow, and the interference offered to that air flow by either the stock or an aftermarket air filter is negligible. So if airflow is the same, why would you need to add fuel?

Air flow through the induction system is limited by some form of restriction or another. Most of the time that restriction is the throttle. That's why its called a throttle. It throttles the air-flow. Where the exposed foam air filter pictured above flows more air than stock air box is at WFO throttle, when it offer less restriction than the the stock arrangement, and more fuel has to be added by way of larger main jets to attain the correct AFR. Ditto legal four-into-ones they only increase air flow at small rpm band/resonant frequency. Reduction of back pressure in an unbaffled pipe may require pilot circuit tuning, but generally its an adjustment of the fuel (pilot) screws.

Finally, the last bit of tuning head-scratching I had on the 750 above was pilot mixture screw. I had stutter/hiccup at about 1/8 throttle which was annoying as hell, especially when feeding in throttle from closed mid-corner. Because I hadn't found a reliable feedback process to judge the difference my screw adjustments were making -you can't practically adjust the screws when your riding. I was flying a bit blind. I followed numerous advice/tools and found that 'blip testing' worked. Essentially set all your pilot screws the same, warm the engine (go for a ride), set a steady idle with the idle stop screw and blip the throttle letting it snap shut under its springs. If the idle hangs or slowly returns its lean, if the revs drop below the idle you've set before stabilizing, or it stalls its rich. Adjust all screws in equal increments until the revs drop quickly to your set idle speed without deviation.

I discovered that i was way rich in the pilot mixture at 1.5 turns. The bike is now joy to ride and the screws are at about 7/8th of a turn from seated.