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Discussion Starter #1 (Edited)
Every FUCKING time I want to ride this piece of shit motorcycle, it's got carb problems. Soon as I can get it running right again, I'm selling it. I've spent a lot of time fixing up this bike, but what a piece of garbage that carb is!!

Here's the problem;
After it's sat for more than a week or two, when I go to start it, it will fire up fine on choke. Full choke only though. After warmed up, it will run on half choke, but there is a 'dead' spot just off idle. It acts as if the needle is not lifting out of the mid jet that it rests in when the throttle is off. If I turn it slightly past that point, just off idle, it will rev up and to the moon. Once warmed up, it really won't idle and will instantly die if I give it any throttle. Back to part choke, then rev, then take the choke off, it will run as long as I rev the throttle past that dead spot just off idle position. Also, when I chop the throttle, choke off, then rev it again, it will back fire on the throttle chop. It's pretty obvious to me that the carb is not allowing fuel in from the time I crack the throttle open until maybe 1/4" twist on the throttle, then it revs up as it should at that spot. If I slowly close the throttle, at that position just above idle, it will bog and die unless I rev it again. Every chop it backfires as it bogs. Lean condition!
I've removed the carb and inspected everything I can find. Main jet is working as that is why it will rev; I twist the throttle past mid range and the main will fuel the bike and it'll run. It's between idle and 3/4 that is the dead spot. I pulled the mid jet along with the main jet and inspected. It looks good too. I can hold the jet to the sun and see light though all the holes; 3 on opposite sides and 2 on the other opposite sides. The carb looked in perfect condition when I opened it.
In the past, it's done this and all I needed to do was rotate the carb enough to pull the top, then the rubber stack that contains the springs and needle and clean the needle and spray some carb cleaner into the needle jet. Reassemble and she runs fine. Now this time that doesn't work.
If I didn't know better, I'd say the rubber diaphram isn't sealing right or has a hole, there-by not allowing the needle to come up out of the needle jet and fuel the motor. It works on vacuum and it behaves as if it needs a ton of vacuum with the wide open throttle, for it to work right. Barely open throttle allows in air through the butterfly valve, but it's like the needle isn't coming up. Not, at least, until it's reved up with the choke providing fuel to do so. Then there seems to be enough vacuum to pull the needle up. Until I unchoke and let revs slow down. With slower revs, throttle bogs as if lean and will die without fanning and working up the revs again enough to get enough vacuum to pull the needle out of the needle jet and allow fuel in.

Needless to say, I am very disappointed in this. Nothing has changed in over 3 years; I start the bike, warms up within a minute and off I go. Last few months the carb acts up and I pull the diaphram/needle, spray a bit, wipe a bit and she's back working.

I flushed any old fuel, replaced with fresh stuff just in case that is causing any problem. Don't see how with the symptoms I'm experiencing though. It's just a for-shit carb that is way too touchy and isn't worth shit.

So, if anyone has any ideas, please let me know. I recall replacement Chinese carbs off eBay helping out and I'm ready to do that so I can get this thing running and sold. Over $5,000 into it and it feels like all I did was polish a turd.

****EDIT****
I rarely swear. Thought I'd edit out the swearing, but it really conveys how irritated I am. I mean I threw shit around in my garage, kicked shit until I think I busted my toe and damn near rolled the bike into the field where I dumped the old gas and set it on fire. This is a machine. One I understand how is supposed to work. Everything is in place and in good repair. It should run, but it won't. That pisses the hell out of me!
 

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Gee Jerry, had I known of your frustration I would have made a cash low-ball offer on what otherwise is your finely equipped camouflaged TW. Instead your baby might just deserve a new OEM carb, or sweet-talk me out of my spare carb. After that much time and effort maybe a little plug-n-play satisfaction is well deserved , especially if you are tired of wrenching to no avail. Sure, the stock carburetor may not be optimally tuned but at least you can ride your TW rather than curse it. Just leave it alone. While you are likely the "fastest carb remover in the west” that slide diaphragm might be loved to death from shim experimenting.
 

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Discussion Starter #7
Thanks for the tips. Might be as simple as the intake having a leak. I'll check tomorrow.
When I played with shimming the needle, I got this bike purring. The throttle was smooth as silk. She would start without choke if the temps were over 60 degrees outside. Just ideal from sea level to 7K'. Then it sat for a while and that's when it started messing up. Pull the diaphram and needle, clean and reinstall, she ran as she once did. Until this time. Now it will only run on full or half choke and has a bad lean bog from throttle opening to about 1/4" or so of throttle movement. Past that, if I'm fast at fanning the throttle, she'll rev.
It's got to be the needle and needle jet circuit, but dang if I can find it.
Now that it is suggested to check for other potential lean issues, the intake boot for example, maybe it's not the carb.

Up until a few months ago, this bike would sit for months and start on half a crank, idle like silk. It really frosts me that the bike was parked perfect and next time I go to ride it, won't run. Nothing in between slowly failing, just bam!
 

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There's a hole which runs through the bottom of the carb throat. I believe fuel flows through it as air passes over it. I can't remember but I think it is part of the pilot circuit. I ran a wire, oh no, or tip of a long needle through it. You have to access the hole from inside the carb. Just look inside the throat where the hole is and you will see what to remove to access it. Mine worked great after that. Mine would start and idle but giving it gas would chug, jump or die. I was trying to run it through by driving it like a tractor and the choke was my throttle, that didn't work. I use only ethanol gas. It's still running good. OEM carb parts seem to be most helpful on these carbs also. Aftermarket carb parts give issues on these carbs. That is my experience anyway.
 

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If you had the old style carb I would say you had a plugged pilot jet. The teeny hole the runs the long ways through the jet. My suggestion would be to buy a new pilot jet, maybe one size richer.

I have played with old jets in carbs trying to get them to work right. What cured the problem was new jets and dang if I could see a difference between the old and new.

Old style jets can be bought on AliExpress for $10 for 12 of them -- both high speed and pilot -- and they work great! Get a variety of sizes and experiment to your hearts content.
 

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Really sounds like the pilot circuit has ingested some crud.

Seafoam and/or take it apart and dump it into someone's Ultrasonic tank.

And I understand how you feel. All I do is work on bikes when I have time. I had a BMW sit for over a year because of a pain in the ass issue. And I should know better, but I threw parts at it and used the excuse that it was all part of the "refurbishment". Turned out to be a 13 dollar hose.

Stay calm. You will not be beaten by the machine if you relax, take a step back, and the rationally think it through.

Or, to put it the way I do...
Some motherfucker built this, And I'm the motherfucker that damn sure as hell can fix it.
 

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My bike was in mint condition with super low miles when I bought it for $1,400. The guy was sick of it. He told me he had just spent over $200 on the carb and it still runs terrible. I took it home and when I went to take the carb off it was already loose....on both ends of the intake boot!! I tightened it up and it ran like a champ. Fast forward a year and we are riding in an off-road event and it starts running bad again. When I went to take the carb off this time I took the intake off and could see the crack on the underside of it. One other thing, I don't like just looking or blowing through jets. I use a piece of the small size guitar string to poke through them. You will get it figured out, worst case scenario is buy the jet kit. Best of luck. (Wait....worst case scenario, I'll give you $1,400 for it.)
 

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Discussion Starter #12 (Edited)
O.K. couldn't wait til tomorrow. I fired it back up and it will high idle on full choke, idle on mid choke and, IF I adjust the idle, it will idle with the choke off veerrry slowly. If I try to turn the idle screw up more, in essence opening the throttle, it will stutter and eventually die, just as if I were slowly rotating the throttle. I don't think it's the idle circuit/pilot, or it wouldn't idle if I find that sweet spot on the adjustment screw. I can then adjust the pilot mix screw and set it up for best idle at this time as well, with a negative effect if I go to far either direction. Happy about 2 turns out and unhappy at only one turn or 3 turns out. 2 is it's happy spot. This was true when the bike ran fine as well.

So... I have a can of starting fluid and with the choke off, the idle and pilot screws set so it will idle, I squirt some around the boots. No effect. I blip the throttle ever so slightly and it dies as expected. Start the bike again and this time, with the seat off, I squirt some starter fluid into the air intake. Idle stays the same. I blip the throttle a little and it responds perfectly. I do this a few times and as the starter fluid wears off, it bogs and dies again. So I start over and this time I keep burping starter fluid in the air intake. Bike runs as it should through the whole throttle range as I do this. If I stop squirting, the symptoms return. Evidence that there is a lack of fuel when the throttle is just coming off idle to the 1/2 to 3/4 throttle range where the primary fuel circuit is the main jet. Now... Why is the needle/needle jet circuit all of a sudden acting up? Either the needle isn't lifting as the throttle is applied, or fuel isn't making it's way up past the main jet, though the needle jet, past the needle that IS rising. What would cause this on the midrange throttle to do this? A CV diaphragm pin hole perhaps? A leak past the cap that holds down the diaphragm? I don't SEE any flaws with the diaphragm but then I'm not stretching it either to find out. Those things are something like $35 or so from a dealer. But nothing else explains why there isn't fuel when I move the throttle off idle until the 1/2 way to 3/4 throttle that I can think of.
I will test every idea you fine folks throw out there as well. So keep 'em coming!
For background, I have rebuilt more motorcycles than I can ever try to remember. I've dialed in this carb using shims and have given away my extras here, so I know it wasn't just a fluke. Shimming the needle raises it so more fuel is fed through out the range of operation for the needle. Off road bikes have clip positions on their needles, something that isn't legal on street bikes, hence the shims. If anyone wants to shim their needle, getting rid of the cold blooded nature of their TW, here's a link to buying a bunch;
https://www.amazon.com/gp/product/B006U20G5Q/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Right now, I'm thinking I'll remove the carb again. (BTW, it's a piece of cake and I can have mine off in as little as 2 minutes if the tank is already off, and back on again just as fast. If anyone wants the steps to do so, let me know, I'll post up a new thread on how.) I'll check out all the tips and suggestions y'all throw my way and if none of those work, I'll order a diaphragm. Any suggestions where to get one cheap? Probably a new bowl gasket while I'm at it too... I already have stainless steel allen head bowl hardware.
 

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These damned CV (constant velocity) carbs are a bitch. Most of us are accustomed to "pumper" carbs. Ya, twist the throttle and it shoots a jet of gas in the carb and off you go. CV's? Not the same. Ya gotta have air blasting through the carb throat to "suck" the gas through the jets and out of the bowl. Very different.

I was lucky, I got my '95 TW and immediately took the carb apart and soaked the parts in old fashioned carb cleaner. Very toxic. Nasty stuff. Reamed the jets, blew them out, and reassembled it. I paid special attention to the "diaphragm". I still do not know what it does but if it is cracked or, even, too "flabby" from age it needs to be replaced (not part of a normal rebuild kit).

I did not REALLY understand this issue until I met a guy with a '94 Suzuki DR350. He could not get it started. Period. He had just got it back from the shop and was tired of spending $'s on it. I saw it was a CV carb and knew what to do. I bought it for $350 (5700 miles). We cleaned the carb as per the previous TW experience and she started on the second crank. Lesson?

CV carbs suck. Even a new CV carb will have a brief hesitation if the throttle is opened fast. It needs air first and THEN gas. All us old hot rodders know this is BS.

So? Buy retrofit a pumper carb. On TWs? Almost impossible. On my "new" DR350? A kit with ALL the necessary cables, carb, and other stuff? $420.00! Shit! That's more than I paid for the bike. And, so it goes.​

 

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I don’t think the pilot circuit can be ruled out of hand. If it’s air passageway is occluded it won’t matter if the jet itself is clean or not. Too bad no Dial-a-Jet installed then you could add fuel through a new circuit.
 

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Hope you don't mind if I kick the dead horse some more.

I recently bought two 2013 TW200's; a matching pair with around 50 miles each. They'd been sitting for a couple years. They had the EXACT symptoms you're describing - Throttle up and it would want to die, but it would keep idleing slowly, forever. I knew that there was probably nothing wrong with the carbs, because, I mean, how could there be, with them only being 50 miles old?

I decided the place to start was with the gas. I emptied the tanks and filled them up with E-0 (non ethanol) gas, and then put a healthy dose of Berryman B12 Chemtool (Seafoam equivalent) in the gas and ran it. Immediately, I could tell it was running better, but would still cut-out when I throttled up. Nevertheless, I wanted to run this gas through it a while, so I babied the throttle and kept it going for a while. I decided to let that gas sit in the carb overnight, and the next day, It ran good enough to take it for a little ride. After the ride, the symptom was gone. I suggest you kick the horse again and give it a try.

Now, I'm not sure if it was the good gas, or if it was the Chemtool loosening up some build-up, but whatever it was is gone now.
 

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Discussion Starter #16
Fred; When I had the carb off, I pulled the pilot jet and inspected it. Looked good. Flushed it with aerosol cleaner and blew out the passages. I didn't pull the pilot mixture screw, but it was having an effect, so I figured it was working good enough. I'll pull it tomorrow and blow out that as well. Anything else on the pilot I need to check?

imlost; I changed the fuel out but didn't add any flush to it. I think I have a can of Seafoam. If not, I'll get some AND another batch of fresh fuel. BTW, both bikes had the same symptoms and were brought back to life without anything more than fresh fuel and a cleaner mixed with the fuel? Awesome!
 

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My very first TW was a 1991 that had 671 miles on it and was in showroom condition. It had the exact problem with the carb you describe. In the process of locating the offending issue I could feel gray hairs growing and I got nothing but totally pissed with all the one and off crap with the carb, rebuilding, cleaning and reinstalling only to have it not run smooth. I finally just bit the bullet and bought a brand new OEM carb for $263. I also bought the new boot from the carb to the air box. Right out of the box the new carb ran like a charm, fixed the problem and only needed the air mix screw turned out a full turn from the factory setting. I still don't know what was/is wrong with the original carb but the $263 I spent on the new carb was the best money I ever spent. I am also a staunch opponent to the use of any ethanol fuel in a TW especially ones with the old style carbs. They were never designed to burn garbage fuel. You can spend way too many hours chasing the ghost in your carb which brings you to the point of frustration I know so well. IMO I would scrap the POS old carb, buy a new OEM one and go ride your bike. If the boot is as hard as a rock get a fresh one at the same time.

GaryL
 

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I fully understood that SkiPro did a great job cleaning and confirming the pilot jet itself was clean. My point, and thus the linked video, was that the pilot jet is just but one part of the pilot circuit. If the through body air passage is even partially blocked there won’t be the required pressure differential generated via the Bernoulli principle to pull fuel through the pilot jet itself. I believe this is what Ken was explaining when he spoke in post #8 of running a thin wire all the way through the air passages in the aluminum carb body itself, not just the jets themselves. While this may not be the issue for SkiPro the point is if one cannot open up this airway then the carb will never function correctly. Confirming the pilot jet air passageway, not just the fuel passageway, is clear can allow diagnosis to move on to other possible causes. Good luck.Time to break out the guitar strings?Correct airflow and the resultant pressure differentials are just as important as fuel flow in these CVs as witnessed by how quickly the engine will stall if water even temporarily blocks the vent tubes access to atmospheric pressure
 
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