Concours Owners Group (COG) Forum

Concours Discussion (C10 / ZG1000 / 1000GTR) => Concours C10 / ZG1000 General Chat and Tech => Topic started by: batboy on August 14, 2019, 01:14:08 am

Title: tuning and jetting
Post by: batboy on August 14, 2019, 01:14:08 am
Briefly, I've swapped in a ZX1000A intake cam and set of 36mm carbs. I also installed a Kerker 4-2-1 header. I figured the bike would be rich and people told me it would be rich. It was at WOT. But, idle and part throttle were a little lean. I adjusted the low screw until it was 2-1/2 turns out. Still lean, so I'll try one size larger pilot jet, swapping the #35 out for a #38. The main jets in my 32mm carbs are 125 and the mains in my 36mm are 132.  I had ordered four #130 main jets from Partzilla, but they are on backorder. I tried Jets R Us and ordered a set of 128 mains. I was impressed, they shipped fast and they were a little cheaper too, bonus points that they were official Keihin jets..

So, I had planned to do one step at a time and install the 130 main jets next. But, they might be another week or two. I have 128 mains in hand and I have the 38 pilot jets from my parts carbs (Voyager). I was lurking in the Ninja forum and they said each step in jet size is approximately 1/2 of a AFR unit. If that's true, then going two sizes smaller on the main jet would be about right. So, I pulled the carbs back off today and rejetted (38 pilot and 128 main). I also zeroed the low screw and set all four carbs to 1 full turn. The carbs are back on the bike.  I have just a little bit to finish up tomorrow morning and then we'll see if I'm heading in the right direction. I'm already tired of pulling carbs off and putting them back on.
Title: Re: tuning and jetting
Post by: tdbru on August 14, 2019, 02:54:10 am
well done batboy.  i too enjoy working on my own bike.  i've always thought a 4 into 1 with mid pipe crossovers would look better on the C10.  balance out the driveshaft/final drive on the other side.  but to do it well seemed a bit beyond my present abilities and tools.  i'd have to really study whatever literature i could find on exhaust tuning a 4cyl motor.  that and get a pipe bender, etc.  so it is what it is on mine.  enjoy reading about your ups and downs, ins and outs as you fabricate your own stuff.
-tdbru
Title: Re: tuning and jetting
Post by: batboy on August 14, 2019, 11:16:24 am
Thanks tdbru, I apparently have quite a following. Several people have PMed me and told me they were following my adventures. I had to smile at the comment you made about my ups and downs--ins and outs. It has been a rollercoaster ride. Several folks have made or modified 4-2-1 exhaust systems for the C10 in the past. I found several posts and photos when I was digging around.

Dang-nab-it, I meant to bench leak test the rack of carbs again before I installed them. I have to adjust the throttle cables and get the springs rolled back in place on the air box boots. Then reinstall the gas tank, etc. Hopefully, that won't take too long. Once the tank is back on, then I can set the petcock to prime and leak test the carbs on the bike before I go any farther.

One thing I forgot to mention about the tuning, I found a jetting calculator where you click on things that might change the jetting, like slip on mufflers or full aftermarket exhaust, type of intake (I have K&N replacement filter), etc. The calculator says I need #130 main jet and #37 pilot jet (I had already decided to try 130 main and 38 pilot). If the 128 main jets are too lean (130 main jets are on back order), then I'll cancel my order with Partzilla and order from Jets R Us again. My prediction is 130 main jet would still be too rich. If the 128 jets are too rich, I still have a set of 125 main jets I can try from my 32mm carbs.

Title: Re: tuning and jetting
Post by: Steve in Sunny Fla on August 14, 2019, 11:41:20 am
you're going to need to change the fuel needle. I went through a number of needles before finding one that I liked. You can go to Factory Pro to order them. if you can get a dynojet zg1000 kit, you can use that needle, but it will be rich and effect fuel economy. In fact that's the issue with carburetion, it's not just to get it to run, but to do so efficiently. Steve
Title: Re: tuning and jetting
Post by: m in sc on August 14, 2019, 12:56:18 pm
if you are lean between 1/4 and 3/4 throttle, you can always shim the needle .020" with a thin washer. this will raise it a hair and make it slightly richer in the mid range. 
Title: Re: tuning and jetting
Post by: batboy on August 14, 2019, 02:50:59 pm
Steve, I appreciate the heads up. I'll look to see what kits and needles are available. That's new territory for me.

M, I had heard about shimming the needle valves that weren't adjustable, but again that's new territory.

I have a lot of reading to do to get up to speed on the part throttle stuff, but right now I'm concentrating on the main jet/WOT (and to a lesser extent I'm trying to get the idle a bit better). Who needs part throttle operation when you got WOT and idle? Joking.

The good news, I fired it up this morning and it still runs. I can't ride it until I get an unrelated suspension part put back together. Was working on something else while waiting for the jets.
Title: Re: tuning and jetting
Post by: Steve in Sunny Fla on August 14, 2019, 03:43:48 pm
just know that the needle choice will affect everything from off idle to wot. example, if the root of the needle is to large, it will stop fuel flow from initial discharge through the needle jet and the engine will be flat. then you try to make up for it with a pilot change, and kill the fuel economy. If the tip of the needle is to large, it will require more main jet. if the middle of the needle is to larg, it will need more main jet. then there's the emulsion tubes and air correction jets to consider. Much mre than just pilot / main / needle adjustment.
   IMO, get a WB02 and a datalogger and tune with it. That's how I did the 2 minute mod jetting - much more reliable and easier than the old "throttle chop/ plug read" method. steve
Title: Re: tuning and jetting
Post by: batboy on August 14, 2019, 05:05:30 pm
I already have a wideband installed.
Title: Re: tuning and jetting
Post by: MAN OF BLUES on August 14, 2019, 06:49:41 pm
Steve, I appreciate the heads up. I'll look to see what kits and needles are available. That's new territory for me.

M, I had heard about shimming the needle valves that weren't adjustable, but again that's new territory.

I have a lot of reading to do to get up to speed on the part throttle stuff, but right now I'm concentrating on the main jet/WOT (and to a lesser extent I'm trying to get the idle a bit better). Who needs part throttle operation when you got WOT and idle? Joking.

The good news, I fired it up this morning and it still runs. I can't ride it until I get an unrelated suspension part put back together. Was working on something else while waiting for the jets.

as Steve mentioned, the Dynojet kits, which is what I ended up installing, they have drill bits to enlarge the hole in the slide, which changes the way the actual slide lifts, and returns... also, those kits (for the 36mm used on the '86-'87 ZX1000R) have slide needles that are notched, and can be moved up and down, via location of the locking "E-Clip" location, and also contain extra spacer washers for "in between" finer adjustments.. but, as mentioned, thee "taper profile" on the needle is not really optimum.. jetting and slide springs are also included on those kits, but unfortunately i don't see the "Stage #2" kit available anymore, just the stage #1 and #3  (kit numbers 2121 and 2321)....
I used a stage #2 kit, so can't comment further on the other two. I was running the 36's with stock airbox, K&N air filter, and a set of SuperTrapp dual mufflers, from the older Ninja model.
Title: Re: tuning and jetting
Post by: batboy on August 14, 2019, 08:02:59 pm
Steve and Rich, you guys have been there and done that, so you have my full attention.

My test ride didn't go exactly as planned. I was just cruising nice and easy watching the AFR while at part throttle. I was mostly low to mid 13 (I'm shooting for 13--14). Suddenly, the AFR jumped up to 21-22 and the engine lost power. I coasted to a stop and checked everything, assuming this was carb related. I did find a coolant hose dripping a little. I tightened the hose clamp and it stopped dripping. I looked in the tank and fuel was very low. I laughed to myself and switched to reserve tank. The bike started and I headed for home. Same thing happened again. After giving it the once over, twice--I finally found the problem. Kinked fuel line. I had put on an in-line fuel filter. It had got the extra length of hose looped and when I sat the tank down, it kinked the line. It was working ok at first, but as the bike got warm, the line kinked a bit more to cut off flow. I removed the filter which fixed the problem. Glad I found a place to stash my tool kit on my bike when I relocated the coolant reservoir.

I tried the low screws at 1-1/2 turns and then at 2 turns. It ran better with 1-1/2 turns, so I'm going to change that back. Looks like the main jet is just about right. WOT settles in at mid to high 12s and then as rpm climbs up to 9k, the AFR slowly drops to the high 11s at redline. That's a little rich, but safe.
Title: Re: tuning and jetting
Post by: m in sc on August 14, 2019, 08:29:46 pm
nice. youre really close.  :beerchug: :great:
Title: Re: tuning and jetting
Post by: MAN OF BLUES on August 14, 2019, 09:37:54 pm
Steve and Rich, you guys have been there and done that, so you have my full attention.

My test ride didn't go exactly as planned. I was just cruising nice and easy watching the AFR while at part throttle. I was mostly low to mid 13 (I'm shooting for 13--14). Suddenly, the AFR jumped up to 21-22 and the engine lost power. I coasted to a stop and checked everything, assuming this was carb related. I did find a coolant hose dripping a little. I tightened the hose clamp and it stopped dripping. I looked in the tank and fuel was very low. I laughed to myself and switched to reserve tank. The bike started and I headed for home. Same thing happened again. After giving it the once over, twice--I finally found the problem. Kinked fuel line. I had put on an in-line fuel filter. It had got the extra length of hose looped and when I sat the tank down, it kinked the line. It was working ok at first, but as the bike got warm, the line kinked a bit more to cut off flow. I removed the filter which fixed the problem. Glad I found a place to stash my tool kit on my bike when I relocated the coolant reservoir.

I tried the low screws at 1-1/2 turns and then at 2 turns. It ran better with 1-1/2 turns, so I'm going to change that back. Looks like the main jet is just about right. WOT settles in at mid to high 12s and then as rpm climbs up to 9k, the AFR slowly drops to the high 11s at redline. That's a little rich, but safe.

Having a clean tank, full of GOOD fuel, is a big factor when doing this tuning, as you note, we paid the prices to maximize the "bang".. in reality, after i played with a dozen or more sets of custom drilled emulsion tubes, I did find some better responses, and reliability, but at the price I tossed for the ones I drilled, some i enlarged a pair of holes, some had 2 pairs, some had 3 pairs..(which works better...? drilling the upper ones vs the lower ones? etc..) etc, and then re-drilling with a hand held bit the size of a gnat's leg, over and over, I settled on one universal size.. I spent probably $200 on emulsion tubes, for experimenting..(this, in effect, is what Steve is trying to say to you.. main, and secondaries, are crude adjustments.. the way the "fuel is emulsified" and drawn thru that main needle, is the real source...) and the pilot air screw, for idle and low rpm, plays a part in everything from idle, to 3k rpm.. so return that to 2-2 1/2 turns out.. and work on the other areas.. rich at idle goes away really fast, but it effects rpm "rise/response" all throughout the process..  so as i noted wayyyy back, get used to pulling the carbs.. you will be a pro at it shortly.. and use a lot of band aides in the process...  :rotflmao: :rotflmao:

I think Steve would agree with me on one thing, when someone watches us pull a set of carbs off a bike.... they shriek like a scared little girl, because we "rip them right off..and hand them to the owner".. there ain't any gentle way to do it..  :rotflmao: :rotflmao: :rotflmao:  It looks really violent when we do it.. but we know it's just part of the job. :rotflmao: :rotflmao:

keep up the good work, you seem to have enough tenacity for this, so carry on. :great: :great: :great:
Title: Re: tuning and jetting
Post by: tdbru on August 15, 2019, 01:48:49 am
batboy,
i tend to agree with SISF that needles are a good place to investigate too.  my zr7s was a bit lean mid range, due to epa tuning i suppose.  after studying how these variable venturi carbs work, it appeared that the low to mid range A/F was mainly controlled by the needle diameter in the straight section of the needle due to the "clearance" with the emulsion tube, if i recall, while only the WOT A/F was controlled by the main jet size.  those factory needles had a long straight section.  the dynojet kit i ordered had tapered needles the whole way.  and they recommended smaller main jets, typically.  so it looked like the dynojet kit meant to increase the fuel ratio continuously as the needle got lifted.  i wasn't sure that's what i wanted.  so i found a machine shop that would turn the factory needles in the straight section down 0.001" in diameter.  i thought that would richen up the low/mid range just a scooch and leave the WOT unaltered.  the zr7s has non-equal length needles from the factory.  inside 2 are different length than the outside two.  those guys at the machine shop freaked out when i asked, but eventually thought they could pull off and they did.  low to mid range is now just a little more "perky" on my zr7s.  that's all i ended up changing.  Reading through SISF's posts on variable venturi carbs, and the C10 induction system, it appears that the intake (inlet) hole size on the airbox (plenum?) that holds the airfilter also has a big effect on the carbs performance and the machine's driveability.  based upon how much (Sisyphean effort really) work it was to try to "improve" the fueling on the zr7s, and the fact that i'm so buried at work all the time now that i don't have the hours to fuss with the Connie, so far i have elected to leave my C10 stock when it comes to fueling.  lazy i guess.  but i really cheer and encourage folks like you and SISF and others that have put in the hours & sweat to improve things.  well done.  my hat's off to you guys.
-tdbru

i think you are doing the right thing with the WBO2 sensor.  wish they had them back when i was futzing with the zr7s carbs. 
Title: Re: tuning and jetting
Post by: batboy on August 15, 2019, 01:52:07 pm
As for gasoline, I'm running Phillips 66 premium (only way to get no alcohol around here is to buy 91 octane). The gas tank is amazingly clean considering it's 31 years old.

Once I got the fuel line kink fixed, I went for a longer test drive yesterday evening. While I have a Innovate wideband, I'm also trying to do old school tuning too as a double check. The idle AFR is 12.8-13.5 and part throttle cruise is 13-14 which is spot on according to my guide I'm using. But, it acts too rich.

Quote
If the throttle is only partially opened such as in a trailing throttle situation and the bike tends to load up and emits a deep tone when the throttle is returned to full open it is usually sign of a rich slow jet.

NOTE: The above quote taken from the Keihin website.

As near as I can tell, the 35 pilot jet is too small and the 38 pilot jet is too big. Of course, there's nothing in between. From what I'm reading, low screw adjustment should be in the range of 1 to 2-1/2 turns. With the 35 pilot jet, I had it at the full 2-1/2 turns and it felt like I needed to go another half turn. With the 38 pilot jet, I have it at 1 turn and it feels soggy (I tried 1-1/2 turns). Throttle response off idle does not feel as "snappy" with the 38 pilot jet. It's hard to explain, but the bike seems happier with the 35 pilot jet.

Ok, I checked the spark plugs (more old school stuff). You're supposed to use new plugs and chop the throttle then kill the engine immediately after a run (which I didn't do). The plug looked fairly normal, tan/grey, but also had a fine layer of black soot on it. Any interpretation must be viewed as inconclusive, but it does look like the plug was normal and then very recently (maybe when I changed the jetting), it shows possible signs of running rich.

I need to digest this info and decide what to do next. I feel good about the main jets. Not so much with the pilot jets. Maybe I need to go back to the 35 pilot jets and play with needles to fattening it up a little? My gut feeling is the 35 pilot jets worked better than the 38s.

Perhaps the first thing to do is to recalibrate the wideband sensor. I also need to adjust the throttle cable, it started binding a little on that last test ride. I might have left them too loose.
Title: Re: tuning and jetting
Post by: m in sc on August 15, 2019, 02:40:07 pm
thats what i would do. 35s, maybe go 1/2 turn leaner as long as idle is maintained and richen the needle a hair.
Title: Re: tuning and jetting
Post by: batboy on August 16, 2019, 03:09:31 pm
I ordered a set of #35 pilot jets and a needle shim kit from Jets R Us. I decided to get new pilot jets even though I have the original #35 pilot jets. The old ones were a little chewed up (screwdriver marks), plus you never know if the previous owner drilled the jets out or not. I was notified the order had shipped. I should have the parts Monday since it's coming from an adjacent state.

I got the throttle cable adjusted and did a free air calibration on the wideband sensor. Think I'll ride the bike a bit more this coming weekend, I want to do a couple more third gear WOT pulls up to 9k rpm (my safety redline). Power falls off like a rock after 9.5k rpm anyway.

So, no more work on the bike until I get the parts. I need a wrenching break for a couple of days.
Title: Re: tuning and jetting
Post by: Steve in Sunny Fla on August 16, 2019, 04:49:05 pm
make sure the pair valve is blocked completely or it will skew your readings. Steve
Title: Re: tuning and jetting
Post by: batboy on August 16, 2019, 06:29:02 pm
Yep, all gone. I made a couple block-off plates for the valve cover and plugged the hole in the air box.
Title: Re: tuning and jetting
Post by: MAN OF BLUES on August 16, 2019, 06:54:08 pm
Yep, all gone. I made a couple block-off plates for the valve cover and plugged the hole in the air box.

I think Steve was referring to "insure those plates are really sealed up..." like gasket sealer etc., or more.
Title: Re: tuning and jetting
Post by: Bud on August 16, 2019, 11:16:50 pm
Someone has also suggested tapping the hole and screwing a plug in there.  Who could it be? ;)
Title: Re: tuning and jetting
Post by: batboy on August 17, 2019, 03:36:40 am
I made gaskets for the block-off plates. They're sealed up good.
Title: Re: tuning and jetting
Post by: batboy on August 19, 2019, 05:42:37 pm
Jets R Us came through for me again, I got the carb parts delivered today. I removed the carb rack from the bike and noticed I was sweating a lot. I just had to pick a day with a heat advisory. It's getting brutally hot out there in my pole barn with a tin roof. I'm bringing the carbs into my mancave (den), so I can rejet in the comfort of air conditioning.

36mm carbs phase 1: pilot jets #35, main jets #132, low screw 2-1/2 turns. [first installation]
36mm carbs phase 2: pilot jets #38, main jets #128, low screw 1-1/2 turns [second installation]
36mm carbs phase 3: pilot jets #35, main jets #125, low screw 2 turns, shimmed needles [currently being installed]

After riding the bike a bit more over the weekend, I decided the 128 mains were a tad too rich at WOT, especially in the upper rpm range. It's good that AFR keeps getting richer as you go from 8k to 9k rpm. But, I'm seeing low 11s and a couple times high 10s (which is getting really rich). I decided to be thorough  and try the next smaller main jet. I might end up going back to the 128 main, but won't know for sure unless I try the 125 first.
Title: Re: tuning and jetting
Post by: m in sc on August 19, 2019, 05:48:01 pm
out of curiosity, whats the afrs at 1/4, 1/2, and 3/4 throttle ?

Im aware rpm plays into it as well. but what are you seeing under wot?

 :motonoises:
Title: Re: tuning and jetting
Post by: batboy on August 19, 2019, 06:06:41 pm
Part throttle acceleration averaged mid 12s to low 13s with the 38 pilots. With the 35s it was low 13s to about 14. I'd like to see high 12s to mid 13s for part throttle. I'm hoping shimming the needles will give me something in between pilot jets 35 and 38. I just don't know how much to expect from shimming.
Title: Re: tuning and jetting
Post by: m in sc on August 19, 2019, 06:12:42 pm
thats why i suggested it.. should help for sure. (id imagine). very cool, hope it does.  :beerchug:
Title: Re: tuning and jetting
Post by: batboy on August 20, 2019, 05:50:46 pm
Shimming the needle worked, maybe too well. Part throttles are plenty rich usually in the 12s AFR. Idle is mid to high 13s. I only did one short WOT and that started out in the 12s and richened up in the high 11s at 8k rpm when I let up. So, the 125 main jet was not too small after all. Oddly enough, I have the same 125 main jets and 35 pilot jets in my 32mm carb rack (OEM ZG1000). The cool thing is there is no flat spots or bogging anywhere I could tell throughout the rpm  range at part throttle.

Here is what I also learned. Not sure it the ZG1000 is like this, I thought all the needles were the same. But, I looked at the numbers on the needles in the 36mm carbs and there are two different part numbers: N36D in carbs 1 & 4 (outer) and N36E in carbs 2 & 3 (inner). I looked on a parts website with exploded diagram and it shows up there too on the ZX1000A list. One part number must be leaner than the other. But, which is which? The needles looked a little banged up. I might buy new ones if I knew which part number flows better.

What to do? The shims are 0.5mm thick. Are there thinner shims? Think I need to remove the needle shims or find some that are only half as thick. Also, I need to figure out what the difference is on the needle part numbers. Guess I should check to see if those needle are even available.

Unrelated to tuning, I finally got my Soupy adjustable lowering links to play nice with my ZZR1200 rear shock.

Title: Re: tuning and jetting
Post by: m in sc on August 20, 2019, 06:06:17 pm
if you have a hole punch kit (a real one) you can make shims out of shim stock any thickness you want. Also try turning the fuel screws IN 1/4 turn. or buy actual needle shims in varying sizes.

 http://www.wahlracing.com/Needle-Shim-Kit.html (http://www.wahlracing.com/Needle-Shim-Kit.html)

Title: Re: tuning and jetting
Post by: MAN OF BLUES on August 20, 2019, 08:14:08 pm
THE "E" needles are the "inner" ones, the "D" ones are the outers...
Inners run leaner, and you may find the actual jet sizes are smaller on some bikes.. not all, but some...
https://www.kawasakimotorcycle.org/forum/vintage-motorcyle-info/101237-86-zx1000r-a1-keihin-cvk-36-question.html (https://www.kawasakimotorcycle.org/forum/vintage-motorcyle-info/101237-86-zx1000r-a1-keihin-cvk-36-question.html)

I used the Dyna ones, with "slots" and  "E" shaped clips, which allow up/down locations/adjustments... the fixed position like you have, are segregated by D/E to accomplish this. Hope this helps.
Title: Re: tuning and jetting
Post by: batboy on August 20, 2019, 08:48:17 pm
Ok, the inner N36E is the leaner of the two. That's what I was trying to figure out.

The throttle started binding up and I think the sync is messed up again. I had static bench synchronized these carbs before I put them on the first time. Yesterday afternoon I spent a long time redoing the bench sync and now it's way out of whack again. Either I'm doing something wrong or there are loose or worn parts. I'm done for the day, we have another heat advisory.

Top priority, figure out why the carbs won't stay in sync and decide which needles to use.

[UPDATE: feels like there's extra play in the butterfly of carb #1. It's definitely out of sync again.]
Title: Re: tuning and jetting
Post by: Steve in Sunny Fla on August 20, 2019, 09:16:13 pm
 ahhh, from a guy who now tunes on a Laptop and doesn't get dirt under his nails anymore, I can tell you I don't miss the "old days"  :nananana: :nananana: :nananana:  :rotflmao: :motonoises: :motonoises: ;)  Steve
Title: Re: tuning and jetting
Post by: MAN OF BLUES on August 20, 2019, 11:44:26 pm
ahhh, from a guy who now tunes on a Laptop and doesn't get dirt under his nails anymore, I can tell you I don't miss the "old days"  :nananana: :nananana: :nananana:  :rotflmao: :motonoises: :motonoises: ;)  Steve


we certainly don't "miss"them, but we remember every single thing.. and make a point of saying "Ya really don't wanna do...."  but it's all a good learning curve.. and one worth (i don't know why, but say yes.. worth) doing.. remaining a bit humble, and reflecting is what matters.. I hate seeing people slam a thumb with a hammer..
 :rotflmao: :great: :great: :great: :great: :great:
Title: Re: tuning and jetting
Post by: Lee on August 21, 2019, 09:39:59 am
Do not have a dog in this one. Do enjoy the read though.

Curious as well, What is the logic in leaning the hotter inner cylinders? Would seem jetting richer would be required to utilize cooling effect of fuel.

Seem to remember my v-twin is richer on rear cylinder for such reason. Am I missing or misunderstanding a technical point or theorem of some kind?
Title: Re: tuning and jetting
Post by: batboy on August 21, 2019, 11:15:17 am
When the inner carbs are jetted different than the outer carbs, it's called staggered jetting (according to my google skills). Sometimes it's due to the head design and the flow characteristics. The outer two cylinders tend to run a little cooler, but I'm not sure what the logic is for running the outer richer unless it has something to due with air density. Staggered carb settings were more common back in the air cooled days.

I plan to go with all the same jetting (same needles too), because my wideband would read the AFR more accurately. With staggered jets, at best, you're seeing average AFR. I'm not sure I fully understand the logic either. Now on the ZG1000 32mm carbs, all the jets and needles are the same.

The real issue is that I'm having trouble finding new needles for the 36mm carbs. If I do find some, I hope to put the N36D needles in all four carbs without shims or use four shimmed N36E needles. I have N36H needles from a voyager (one is bent), but I have no idea if these are leaner or richer.
Title: Re: tuning and jetting
Post by: batboy on August 24, 2019, 06:35:07 pm
Update: I have parts ordered. While waiting for them, I will probably need to pull the 36mm carbs back off to examine the throttle shafts. I can't keep the carbs in sync. The #1 carb  (left outer) seems like has a throttle shaft that is too loose (presumably worn out). I actually found a throttle shaft and butterfly for the left outer carb on eBay, so I bought it since it was cheap. But, I know it's more likely the bushing in the carb is worn, not the shaft. I want to repair this if possible.