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.

 

[salty_monk]

Take the shim off & replace it with a stack of washers to new height (or source the Canadian ones, they have 4 grooves).

There is a "electrical" washer that is exactly the right dimension, they used to sell at Radioshack but you must be able to find them on Amazon or somewhere.

 

[danny01975]

I have not done a plug chop. The issue is mostly "transient" and difficult to reproduce in a way that I can reliably keep in that state. It's possible sometimes, but not always.

The main reason I think it's lean is that the condition is greatly amplified anytime I try to lean out the mix. The exact opposite it true of enrichening the mix however. Each time I make the mix richer, the condition gets markedly better. It doesn't go away, but the window of occurrence shrinks and the severity is reduced.

Lastly, coincidentally, I happened to run out of gas on a ride this morning. I didn't check the fuel level before heading out. Before switching to reserve, the bike started to stutter when applying the throttle. Exactly like it does in these transient passing moments, except it was at all throttle positions. I've read much conflicting advice on what a lean condition sounds and feels like. Some say a lean condition surges like yourself, some say it causes a stutter. I can definitively say that it's been my experience on more than one occasion, including today, that the bike stutters when it runs out of fuel and it does not surge. I've run out of gas a couple of times now and it's been the same each time. That's how I know to switch to reserve.

I have tried the tuning method you suggested and it always returns to idle normally except at the most extreme ends of the pilot adjustment range. To rich and it falls below idle, too lean and the RPMs float a while before returning. But the adjustments in between those two settings are quite wide. I also have done the fastest-lean-idle method to make adjustments. That's a little more granular. But the problem still persists even when using that method.

 

[dgates1]

I'd go back to the pilot jets... either clogged (running out of gas can send the gritty bits through the carb) or you need to go back to the stock size since you are running a stock airbox.

 

[rphillips]

Monk, we were thinking a lot alike back then. We thought about going to the trouble of sourcing the adjustable ones from Canada, but back then without computer access we have today, it was a lot harder to do. Like you we found the washers from Radio Shack that the fit made it appear they were designed just for raising the needles in our carbs. Worked great.

 

[danny01975]

I'd go back to the pilot jets... either clogged (running out of gas can send the gritty bits through the carb) or you need to go back to the stock size since you are running a stock airbox.

The larger pilots are brand new. The bowls are spotless each time I take them off. And each time I go back and forth with the different pilots, I've inspected them and they're perfect. But I go ahead and soak and clean them anyway just in case. I understand pilots can get dirty and clogged but I don't think that's what's going on here.

I also understand that I "shouldn't" need the larger pilot jets. But when I go back to the stock jets the problem is way worse. Until I turn the stock jets out to 3.5 - 3.75 turns out. Then it gets better. Also, anecdotally, I read allot about how these bikes are set up to run lean from the factory, and upping one size on the pilots / mains make them run better. I can't say if that's accurate or not, but I can say mine runs way better with slightly larger jets. The previous owner upped the mains one size, probably because he thought it would make it faster. I don't have the stock mains to put back, but it doesn't seem to have any issues at WOT anyway. I upped the pilots while troubleshooting and have gone back and forth several times. The result is always the same.

 

[zed1015]

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.

What size is the stock main jet ?
Is it 115 ?

 

[danny01975]

What size is the stock main jet ?
Is it 115 ?

The stock size should be 115. This bike has 120 for the mains.

 

[zed1015]

The stock size should be 115. This bike has 120 for the mains.

Your issue is likely a lean spot on the transition from the pilot jet to the jet needle.

Normally this off idle hesitation is a result of removing the airbox and running open stacks / pods or modifying the airbox to significantly increase airflow .
The cure for this on your machine would be to fit air correctors for the hesitation and 145 mains for the increase air flow at midrange and top end .

All other jets and settings remain STOCK..

Removing the snorkel may have introduced enough extra airflow to initiate the hesitation but not enough to warrant the 145 main.

Personally i would fit air correctors and go with a 120/125 main if a top end plug chop doesn't show a lean mix.

Fitting bigger pilots and lifting needles blanket bombs the entire fueling slope which only serves to mask the hesitation whilst killing power and increasing fuel consumption.

 

[danny01975]

Your issue is likely a lean spot on the transition from the pilot jet to the jet needle.

This is what I have suspected all along. Which is why I was attempting to raise the needle.

Personally i would fit air correctors and go with a 120/125 main if a top end plug chop doesn't show a lean mix.

What is this "air corrector" you speak of? Are you suggesting bigger air jets and then a larger main to compensate? It's already got 120 mains.

Also, I have a replacement snorkel on order. Had to buy an entire airbox assy and have it shipped here from GB just to get the snorkel. We'll see if that changes anything at all.

 

[Nessism]

This is what I have suspected all along. Which is why I was attempting to raise the needle.



What is this "air corrector" you speak of? Are you suggesting bigger air jets and then a larger main to compensate? It's already got 120 mains.

Also, I have a replacement snorkel on order. Had to buy an entire airbox assy and have it shipped here from GB just to get the snorkel. We'll see if that changes anything at all.

zed has a link to the air correction jets in his signature. Turn on view signatures in your profile if you can't see the link