mix screws

[Jethro]

I get my highest idle with the mix screws just a c-hair out from full in.

Is that normal or do I need to try some different pilots? Still having some stutter just off idle.

83 1100E, Mac 4-2-1, pods, stage III kit, 138main, e-clip on 3rd notch from top, 45 pilot, 160 air jets, screws 1/16 of a turn out. Carbs synched, valves adjusted, overall healthy (oil leak now gone! I hope...)

 

[KEITH KRAUSE]

A mixture screw that gives highest rpm with the screw turned 3/4 or less out, is usually a lean condition. (This is an edit and I apologize if reading further causes any confusion. I'm learning just like the rest of you.)
Most common reason is the pilot jet being too small. But can be a low float level, dirty carb, etc.
Also, the highest rpm method should only be used at near recommended factory idle rpm. Say around 1,000/1,100 rpm. Some people try to adjust the screws at an idle speed "they prefer", such as 1,400+. This higher rpm compromises the method and minimizes results.

 

[Jethro]

Kinda surprised that with pod filters and pipe, I have a rich condition with stock pilots (#45's). Could this be my problem with my just off idle stutter? I guess I'll throw the #40's back in, but that didn't really make a difference when they were last in. I guess the carbs could need cleaning, but I'm surprised at that too.

I was adjusting at about 1000 rpm, that's where I like to keep it.

 

[KEITH KRAUSE]

Kinda surprised that with pod filters and pipe, I have a rich condition with stock pilots (#45's). Could this be my problem with my just off idle stutter? I guess I'll throw the #40's back in, but that didn't really make a difference when they were last in. I guess the carbs could need cleaning, but I'm surprised at that too.

I was adjusting at about 1000 rpm, that's where I like to keep it.

We talked earlier about the stutter. I think that's a lean condition, at least the way you described it then. Mixture screw adjustments may be all you need for that, but the pilot circuit has to be operating right before the screws will be effective. The stutter could also suggest the needle is lean and needs to be raised 1/2 position.
If a rich condition exists such as the pilot jet being too large, you'll probably find the mixture screws have to be adjusted past two turns to achieve highest idle. There's already too much fuel to burn. Optimum mixture ratio can't be achieved. A mixture screw allows equal increased amounts of both air and fuel, but the engine really wants more air only to achieve optimum mixture and to show an rpm increase.
You always have to be sure the carbs are clean, all o-rings good, float levels correct, synched, etc, before blaming the jets.

 

[Jethro]

Yeah, when I turn the screws out, it doesn't take more than 2 turns to really want to make the bike stall. I don't get it though, I've tried a #40 pilot, #45 (stock value) and a #50. All are the same although the #40 pilot caused some surging at about 1/5 throttle. The 50's were ok, but made the exhaust sound real rough and backfired on deceleration quite a bit. The #45's are perfect, except for this off idle bucking/stutter I get. No pilot jet I have ever had in there makes a significant difference in what happens with the mix screws- they have never increased my idle at all, only decreased it and made my bike bog when I turn them- depending on what pilots I have in there

I can't move the needle either way, I've just spent months trying to get that right and it finally pulls hard and smooth to redline, with no backfiring through the carbs, and my plug reads at 2/3 throttle are great.

I don't know what to try next- could this be a timing problem? The bike finally runs perfect, except for this, which it's had since day one. Does anyone know if this is just an inherent problem with stage III kits? Maybe I just can't get pod filters to work well at just off idle? Have to live with a bucking bronco off idle?

 

[crag antler]

Geoff, not to sound stupid but have you looked at your intake boots in between the carbs and the motor?
I had a bucking issue back when I was living in NH and it turned out to be small cracks in the rubber.
Could be worth a look.

 

[Jethro]

Good call Doug, but my boots are only about 2 months old. I'm certain that I don't have intake leaks, but you are right- that would do it.

 

[KEITH KRAUSE]

There are "driveability" issues that stage 3 kits warn about. So many things can cause a problem.
With the attempts you've made to fix it, it sounds like the pilot air jet is a possible problem here. It supplies the air that mixes with the pilot jet fuel. They mix and go through passages that bypass the throttle plates at closed throttle and just off closed throttle. The mixture screw regulates one of these passages. It's for fine tuning the mixture. If air is flowing through the pilot air jet correctly, and fuel is flowing through the pilot jet correctly, the screw has to have an effective range.
Of course, everything else about the carb has to be working right too. Float level, vacuum level, clean passages...

 

[Anonymous]

Mix Screws

Mix Screws

Jethro,
I just installed the stage 3 dj kit. I run pods, V&H sidewinder(no baffle). I followed the directions exactly, exept the part about the air jets included in the kit. I shouldnt have put them in. They caused the same symtoms you have(off idle stutter and bucking). Put the stock air jets in and no more problems. As for pilot jets, Im running 47.5 . 50's were just to fat and bike would'nt idle. The bike runs great , "going by dynojet instructions" dj138 mains, stock air jets, screws out 2.5 turns, slides drilled, mikuni 47.5 pilot, needles 3rd groove from top. You can only get so much out of theese carbs, no matter how good you can tune them. I see RS flatslides in my future.

 

[Jethro]

You can only get so much out of theese carbs, no matter how good you can tune them. I see RS flatslides in my future.

Amen. I agree with that statement 100%. I think it's about as good as it gets for me, I'm just gonna have to learn to ride with it. I hate having to wind it up off the line, but that's the facts.

ANYONE HAVE A STOCK AIRBOX FOR SALE???? PLEASE!!!!

 

[Hoomgar]

Hey Geoff, I just instally my Dynajet stage III kit last night. My instructions say in big bold letters "MAKE SURE YOUR PILOT CIRCUIT IS COMPLETELY STOCK BEFORE CONTINUING!" Now that is for my bike and maybe yours is diff but I was thinking that maybe what MAVERICK82E said holds some weight? Did you use the air jets that came with the kit or are yours stock?


MAVERICK82E, what's this about drilling the slides? My kit came with a drill bit that I don't know what it is for and didn't read anything about what it is for either? Am I missing a step? Bike is 78 GS1000 with stock vm26ss carbs.

 

[Anonymous]

slide drilling

slide drilling

Hoomgar,
The Dynojet kit that I have is for 80-86 GS1100-1150 16valve. On the34mm cv carbs, the slide where your needle is on the bottom and rubber diaphram on top. The small hole next to the needle hole on the underside of the slide has to be drilled out. The drillbit went off center on all four, others have experienced this too. They still work fine. The purpose of this modification is to increase the speed the slide travels in the carb. The faster the needles come up the better the throtle response. Dynojet does not tell you the size of the drill bit, its a 7/64 I measured. I was hoping to walk the front wheel a little on hard acceleration, but it stays down,"bummer". I'm running a 180 on a gsxr wheel, and 14/45 gear ratio for street and strip. Are any 1100E riders getting there somwhat stock bikes lift the front wheel on hard acceleration. Am I doing somthing wrong?

 

[Jethro]

On really freakin' hard acceleration my front wheel gets light, thats for sure. But I need to be near 9k rpms between shifts to feel that.

Hey Geoff, I just instally my Dynajet stage III kit last night. My instructions say in big bold letters "MAKE SURE YOUR PILOT CIRCUIT IS COMPLETELY STOCK BEFORE CONTINUING!"

Yeah, I've had the stock one in to start, I've got 4 other air jet sizes I've tried, I've tried 5 different sizes of pilot jets, all needle positions (including some half positions with shims), 6 different sizes of main jets, stock slides as opposed to drilled slides, anywhere between 1/32 of a turn to 6 turns out on the mixture screws, at least 20 different float heights, the carbs have been dipped twice, hand cleaned, and they get synched an average of once a month. Nothing has improved my stutter off idle. Sucks.

Just have to get used to revving up to 3 grand on every take-off. I don't like that. I want a smooth, quiet bike that can haul when I need it. But if wishes were horses...

 

[KEITH KRAUSE]

Mark, do you really think there's ANYTHING I wouldn't tell you that was necessary to do with your re-jet?
Drilling out the vacuum ports to the diaphragm chamber is just for the CV carbs. The drill bit you have in your kit is for removing any factory caps that cover the pilot fuel and air screw heads.

 

[Anonymous]

jethro, I've been having a very similar issue as the one you're having, with a very similar setup, (4-1, pod filters, '83 1100 [though I have stage 1 cams in my bike as well])

I was just at my Suzuki shop asking about carb tunings and the mechanic there said he could never get bikes tuned properly with a stage III kit and then he started changing the float levels a mm or two:

if you're having trouble with a lean condition richen the mixture by adjusting the floats 1mm closer to the carb body - visa versa for a rich mixture - floats closer to the carb body richens the mixture further away leans the mixture.

He said this works best for bikes experiencing problems at lower throttle positions, I haven't tried it myself yet as I have a ways to go as far as tuning my carbs but I'm certainly gonna try it soon.

 

[Carter Turk]

Fast 7

How's your ground clearance with all those mods? Does the thing corner like a champ?

Jethro, I had to lean my floats way out to work with my used jet kit and pods.

The Mac is probably mostly to blame.. The compromise is probably showing up right where your problem is.

I have a stock airbox if you want it.

 

[Anonymous]

hey Carter,

not much ground clearance, I scrape my pipe a bit over speed bumps, I do have my triple clamps down about an inch on my forks though. I could get a little more clearance if I was to raise it.

Corners pretty tight, I do need to get my forks rebuilt/set up though, the seals are leaking presently, it'll probably handle nicely once I do that.

Hey I see you're in Bellingham, I'm in Vancouver, BC, I've been meaning to get down and take a ride on Chukanut drive, we should hook up and go for a ride sometime.

take 'er easy

M.

 

[Jethro]

The Mac is probably mostly to blame.. The compromise is probably showing up right where your problem is.

For the record, this is not one of the late generation (read: crappy) MAC pipes. This is one of the last true performance MAC pipes when they were as high quality as anything out there. It's a true 4/2/1, ceramic coated, free flowing performance pipe. But it may still be the problem.

About richening up the floats, I don't know about that. The problem I am having is that I can't seem to find a pilot or air jet that makes my mixture screws do a damn thing. Here is what I have done- stock is a 45 pilot, I have tried a 40, 47.5 and a 50, but nothing affects how my mixture screws work- no matter what pilot or air jet I have in, the highest and cleanest idle I have is at 1/32 of a turn out from bottom. Even a 1/4 turn out makes the bike begin to stumble. So it would seem I have way to rich of a jet already, but when I tried the smaller than stock #40 the stumble seems a little smoother, only becasue the mix is a little thinner. When I had the bigger #50 pilot jets in there, the exhaust note was nasty, like it was burbleing. It just sounded rougher, so I assume it's too fat.

Tonight I am going a different route in an effort to aleviate the problem. I am gonna service the advance unit and I am buying a timing light. Anyone wanna tell me how to use the friggin' thing? I know nothing about the ignition system.

I still think I have a jetting problem, becasue my mix screws never make my idle increase, no matter what jets I have in there.

 

[KEITH KRAUSE]

Like I said before Jethro, your mixture screws are telling you it's lean.
If you check out jetting websites...or study a diagram of your carbs...then you'll see it must be the pilot circuit that's causing this IF the rest of the bike is adjusted correctly, such as valves, carb synch, clean carbs...
If you've tried many different pilot jets, then it's probably what I said in my first reply. The float levels.
This should come down to 3 things. Float level, pilot jet, and clean passage for the pilot air jet.
Sometimes you just can't get it right because of a particular set up. You may even have more than 1 problem. There's some jet needle overlap at small throttle openings too. That could cause a stutter taking off. But the needle wouldn't cause your screws to fail a highest rpm check at 1,000 rpm idle.
Have you tried any testing, such as partially bagging your pods, about 2/3 bagged, just to see the results? Use electrical tape to adjust the baggie. "Stuttering" can be taken both ways (rich/lean) and a positive test may help you figure things out.

 

[Jethro]

Have you tried any testing, such as partially bagging your pods, about 2/3 bagged, just to see the results? Use electrical tape to adjust the baggie. "Stuttering" can be taken both ways (rich/lean) and a positive test may help you figure things out.

I've been thinking of doing this, maybe tonight will be a good night to do that.

Tomorrow I have the whole day to try and get this taken care of. New chain and sprockets going on tonight, and tomorrow is a another carb tuning day.

I set the floats recently using the hose attached to the bowl drain, it was really close to the level specified in the manual. Is it possible that with my modified setup that I may need to alter the float heights from stock?