What did you do to your Yamaha today?

Thank you for the heads up. I haven't had much issue with it yet. Hopefully, I complete the swap in the next week and can see how it rides.

 

Annual "wake up from hibernation" day yesterday. Oil change on the 750, wrestling the octopus on the 1100, looking forward to the extra evening daylight now. Some of you guys have been riding all winter, but just have thicker skin than me! Warmer weather is coming...

 

Yesterday I went to my son's place to work on our bass boat. He has three bikes stored under a large tarp for the winter. His Kaw, on the right side, tipped over towards the right and pulled my XJ700 on its left and his Honda to the left of the XJ, over. Broke my clutch lever off (at the base!). Took a while but got it running. Today, I think, I'll start up the Maxim X, hopefully, and take a spin. Should try to hit 70 F later today.

 

That was my Ex and the tentacles in my wallet befire I was traded in for a newer model.


Put some KM's on the SECA today, we hit a max of 49F and I really didn't feel like dealing with anything or anyone. Gotta say it stores well in that all I've had to do so far really is open the fuel, add a quarter pull to the rich lever and it fires right off. Now the cold front is blowing thru and it's going to spiral downward for the next week or so.

 

Even with a bit of wear and tear, she’s still a handsome devil, isn’t she?


Have had an eventful offseason. Replaced handlebars, replaced MC (just to get one that sits flat), added heated grips, replaced wheel bearings, rebuilt forks, replaced a valve shim, and did the performance shifter pawl upgrade.

Rides great, though apparently I’m slipping out of gear sometimes when I’m in second. I’ve heard this is a problem with worn shift dogs, but since I replaced the pawl and springs beneath the side cover, I’m somewhat suspicious that I mucked something up. Not a big deal anyways, just gotta short shift into 3rd and I’m fine.

 

I'm liking it. Nice Maxim.

 

That Maxim looks so much prettier than mine!

Where'd you get the MC? I'm still running the stock one on a set of Daytona (Japanese "standard" style) bars, and while it works OK (hasn't leaked or sucked air yet, anyway) I know I'm in for an adventure when it's time to flush the brake fluid next fall.

So the electrical system's up to handling heated grips? That's good to know.

 

I got the MC from chacal, he sells one that’s pretty close to the style of the original and sits flat on the Daytona bars. Those are exactly what I have, and I’ve been very happy with that MC.

I have had no problems at all with the grips, but I changed out the gauge cluster backlights, the tail light, and the license plate light for LEDs. These Oxford Heaterz draw 4 amps, which equates to something like 50 watts. I’m pretty sure changing the incandescents saves a good bit of power draw, so I can’t verify that these would work on a stock setup.

 

Well I do know form experience the XJ regulator won't go much higher than about 240 watts so 4 amps at 12 volts is 48 watts and going with the LED's gives you a good margin.

 

Ran the snowblower and cut a path in the 6.5" of snow, weather geek is threatening 60+ later this week so I want to be ready. Lets see if it happens.

 

Yeah, we had heavy rain all day Sunday, about an inch of snow Sunday night, then a couple days in the 20s, another inch or so of snow tonight, then 40s on Wednesday, 50s on Thursday-Friday, 60 and sunshine on Saturday. We don't really have "spring" in the midwest; it's more winter days mixed with summer days, slowly turning from mostly winter to mostly summer by the end of April... or sometimes May.

I really need a string of days when it's wet and drizzly out but warm enough to work in the garage, as I have a ton of bike projects to get done. I have a pile of parts for the Himalayan, which will get valve check and a bunch of electrical accessories that require removing the gas tank as soon as I ride it another 450 miles. The Yamaha's carbs are still sitting in the garage, waiting to be reassembled with a slight adjustment to the float limiter tab (the one that is supposed to keep the floats from dropping far enough to stick open when the carbs are empty), level-set, put back on the bike and synched, plus I have to finish the Seat Rationalization Project (raising the rider portion by about two inches so my fake knee and hip stop screaming at me).

Luckily, there should be plenty of these days in April... which is good because I'm hearing the clock ticking. The Slimey Crud Run weekend is less than seven weeks away, and I really hope to have the Yamaha ready for that ~600 mile trip; and I'm leaving for New Orleans on the Himalayan all of three days later. My "riding season" is all year round, but things do get a lot more intense between May and October.

 

Today i re-fitted some standard forks to my XJR which i had powder coated and removed the fashion victim USD's.

 

I'm really diggin' that XJR1200. That big boy would look great next to my SECA 750.

I'm somewhat familiar with northern Illinois weather having worked for Motorola at Schaumberg for various training and other duties. Some days were hot and other days not but the wind was a constant. Was a good gig until Google screwed it up and cut the company in half.

 

Took out the 1982 XJ750 after working on it over the winter. Went to lunch with my dad, he has a 2003 Vstar 1100. Was a good day to get the bikes out to stretch their legs.

 

Wow! Very nice SECA

 

Put some miles on the bike today bring it to just under 100 away from the magic 50,000 point. Runs great but seems to have an intermittent miss that feels like a coil is briefly dropping out so I will be addressing the connectors in the coming days.

 

I love those OEM control units, much nicer and cleaner than the ones on my 1982 XJ650. Never understood a three post killswitch when you could just do on/off

Also tell me about those grips? They're beautiful

 

Thanks. Not sure where the grips came from. They were on the bike when I bought it.

 

Almost done with the handlebar swap. Picked up a shorter clutch cable, and will fit that tomorrow. New pro grips are nice and comfy compared to the ones I took off.

 

Tank cleaning round two.. perhaps someone noted it somewhere i missed.. but it turns out it is more important to get vinegar neutralized and tank protected than it is to shake out nuts and bolts.. had to do it a second time cause i was so focused on getting agitators out the tank flash rusted on me..

 

What did I do to my Yamaha today? Well, I didn't push it off a cliff or call the Click & Clack Donation Hotline (yet). That's something, given what a frustrating day it was.

The sun came out and the temperature went up to a balmy 55º, but instead of riding one of my running motorcycles I decided to make some progress on the 650's carbs, the ones that have had this overflowing problem that at times seems to have come from a bit of rubber stuck in the float valve and other times seems inexplicable. Last fall I pulled the rack to clean things out, then moved on to taking the rack apart and going through the carbs. Today was the day to put things back together.

But first... I went through all four, polishing the float tangs with my Dremel tool and slightly bending the stops that restrict how far the floats can drop when the carb is empty. Then... back together, time to set fuel levels. I did this one at a time since I had them apart and it's a lot easier to drain one carb than four every time I need to bend a tang a tiny bit. I came up with this high-tech fixture:



This is the pesky #2 carb, which had been overflowing before I split the rack apart. Notice the level to assure things are straight.

Fuel level check:



Parallax makes it hard to photograph things well, but the when I sat with my eyes at the level of the carb and sighted down the edge of the bowl, I got them all into the 3+/-1 mm range. Each carb got checked twice to confirm no overflowing. So far, so good.

I put the rack together, using a piece of plate glass I keep around especially for this task. Then it was time to put the rack onto the bike. I set the airbox boots in the sun to let them get nice and flexible (that 46-year-old rubber is still surprisingly supple) and greased them up with a bit of No-Mar tire mounting lube, so the neighbors were exposed to a minimum of handy expletives.

Install the tank, turn the tap to "prime," and... dribble dribble dribble. Gas pouring down around #1 again. WTF? I checked that carburetor at least twice and maybe three times, and there it is dribbling gas. At that point I shoved the bike back into the garage (after turning the gas back off) and called it a day. The alternative, as I said, is to push it off the end of the pier or call the donation hotline.

I am in a very unhappy place with this bike right now. It makes no sense that the float valves would stop working as soon as I assembled the rack. I am having flashbacks to other old vehicle fiascos, in particular a British sports car that I got cheap, got going pretty well, and which then rewarded me by having everything start failing. I feel like I have spent too much money (when I stopped keeping track in the fall of 2024, I had put over two grand into this "free" motorcycle, though about $400 of that was just to get it titled by the State of Ill-Annoy) and way too much time on this bike, and been rewarded with relatively little actual use (about 4000 miles). Sigh. I am on the verge of trying to cut my loss by listing the thing on FB Marketplace as "runs but pours gas on the ground."

There is one more possibility I intend to check tomorrow: I noticed the carb-to-carb fuel connectors turned really, really easily, and I wonder if the o-rings on them have given up the ghost and are leaking. I figure that I can do an approximate fuel level check tomorrow to see if the carbs in fact are not overflowing but gas it dribbling from the fuel lines. While it looks like they're overflowing, gas moves in mysterious ways on metal surfaces. It is a thing I can check without too much work. Of course, if the o-rings are shot, then the rack has to come off and come apart... again...

 

Yeah... been down this road a few times. If you can pull the level tube as close to the mouth as possible so this way you can get the best idea of the level with the parallax error. As for the dribble... you will have time as I'm sending some of our cold your way, just thought I'd share.

 

@ScottFree, the fuel rail o-rings. It must be an epidemic or pandemic or some such as in the last 2 weeks I have had similar issues with the racks of carburetors from my Kawasaki Concours and a Honda Nighthawk 550 for a friend. Some new o-rings and neither is currently appearing to dribble fuel. Good Luck, at least the XJ carbs are easier off and on that either of these 2 beasts.

 

I had this exact problem with my bike when I bought it, so that’s my bet too. Especially if fuel is dribbling out “around” one of the carburetors as described. I think if the carb overflows from a stuck float, it’ll flow into the airbox instead of out around the carbs.

I also experienced the exact same “too easy” movement of the fuel rails that @ScottFree described above when I first split the rack. Just a thought of “hmm those came apart really easily for parts that are supposed to be watertight…”. With proper o-rings installed, they are a very snug fit.

 

Lately I've run my carbs dry at season end. In the Spring I set the petcock on Prime and get ready for some overflow from a sticky float. Rapping on the bowls tends to release the floats if stuck and I am good for the season (after throwing absorbent litter on the spilled gas).

Edit: Forgot to mention, the fuel overflow is out one or the other overflow lines, not the connecting tubes or bowl gaskets. I did have to replace the supply tube on one bike with a new brass one with actual o rings because the original was too loose.

 

"April is the cruelest time..." —Deep Purple (back when they were still good)

The average high for the second week of April in the Chicago area is 62º F. Today's high will be 48º (14 below average); tomorrow will be 42º (20 below average). Both days will, of course, be sunny. We get a warm-up starting on Wednesday, eventually reaching 70º on Sunday, but (of course) heavy rain. There is a window of potentially nice riding weather on Wednesday (mix of clouds and sun and 64º) before the rain moves in, but given that's two days out I wouldn't trust the weather prediction. That's the basic rule of spring in the midwest: if it's sunny, it's cold; if it's warm, it's raining... though rainy and cold is always an option as well.

Anyway, back to carbs: this afternoon I intend to pull the tank, hook up the extension hose I use when synchronizing the carbs, turn on the gas and see if I can spot the fuel rail leaking. And check the fuel level in the carbs--may not be able to do it with perfect accuracy, but should be able to verify that the carbs themselves aren't overflowing.

Hadn't thought of that, but it would make a great deal of sense. When mine dribble gas, it always seems to appear on the joint between bowl and body--so either the gaskets aren't doing their job, or the gas is coming from somewhere else... outside the carburetor itself. Sigh. I just spent a lot of time this winter searching for a leak in my house plumbing; of course the deposit of corrosion was a couple feet from the actual leak...

Good to know. Mine required approximately zero force to slip into place, and the one I could grab between thumb and forefinger (the longer one between carbs 2 and 3) could be easily spun.

One of the rebuild kits I bought included what may have been replacement o-rings, but they did not seem to fit: a bit loose on the pipe itself, but didn't want to go into the holes in the carbs (kept walking out of the groove on the pipes). Typical Chinese stuff--"it's close enough for Amazon!" If I do conclude that mine are leaking, I'll be ordering the Viton ones from Len.

Anyway, thanks for the input. Further reports when I find the smoking--or dripping--gun.

 

After adjusting, polishing and still getting caught by overflows, this has become standard practice for me as well. Turn to prime and then play whack-a-mole on all 4.

 

Well, the weirdness continues...

The good news is that I got the bike running and took it for a nice (if short) ride this afternoon. The bad news is that I'm still not entirely sure what the problem is/was.

This morning I pulled the tank and inspected for any signs of fuel around the carbs. None to be seen. Next thing I did was perched the tank on the back fender, hooked up an extended fuel line, and turned it on, hoping to catch what was leaking.

Nothing, that's what. No leakage around the fuel rail, no leakage around the float bowl gaskets, no nothing. I hooked up a hose to the drain on #1 and found that the fuel level looked (within the limits of what I could see) correct. WTF is going on here? I have heard that the o-rings swell after exposure to gas, so perhaps sitting overnight did something. Or perhaps... I installed an inline filter last fall. It's pretty crowded there, and it is not entirely outside the realm of possibility that I did not get it fully hooked up to the petcock and it was leaking from there. Maybe.

So I cut a new, longer piece of fuel line (without a filter for now) and installed it. Made sure the hose was all the way on the petcock. Then I turned the key, hit the switch... and she fired right up. Went straight to 4000 rpm, which turned out to be nothing more than where I had set the idle speed knob when I assembled the rack. I went for a little ride, across the river, down the other side, back, about 10 miles. Got it warmed up and got the idle speed down. It was still having problems with idling; the speed kept going up as I rode. When I got home, I got out the vacuum gauges and went through the synch procedure. It was a little frustrating because the thing never wanted to simply idle. Often, a small adjustment to one of the synch screws caused it to either stall or slowly run away to 2 or 3000 rpm. The screw on #2 is particularly hard to reach, too. I need one of those Harbor Freight carburetor adjustment tools, the long and flexible tube with the speedo cable screwdriver on the inside...

Anyway, I got it to about where it was last fall: it runs pretty well, drops back to 1050-1100 quickly after I shut the throttle, but then slowly loses speed and stalls after about 30 seconds. Sigh. I need a Carb Whisperer™.

I still plan to get new o-rings; even if they have swelled up a bit and are now sealing, they are marginal at best. But at least the thing runs, and it is still fun to ride.

 

Handlebar swap looks great. New flatter master cylinder was very quick to bleed, which makes me feel it was too easy. The brake handle is very firm, no sponginess. Went to a single line instead of the two line. Ended up with a custom HEL line. The challenge I'm encountering is finding mirrors that don't hit the windscreen on the fairing when turning. I'm going to be stubborn and keep the fairing, and may end up with bar end mirrors as a compromise for now.

I drained the tank to clean it, and put in a new fuel filter. The amazon fuel line is hard as a rock, so I'll change that to a better line, and will pull the bowls off of the carbs to see how gunked up they are, and if they're bad, I'll pull the carbs and clean them without breaking the rack. Ran fine last time I cranked it, so we'll see what the bike has in store this weekend.

 

Small question, not sure where else to ask: those cool roll stands like this:


Is there a way to make those work with the XJ? I'd like to get a pair of them, and yes, there's the center stand, but I'd really like both tires lifted off the ground during winter storage. I wasn't sure if there was a safe spot to rest on one of these on the front or back.

 

I took my XJ for a ride of about 80 or so miles on Wednesday. Things started out good enough; the first 25 or so miles it ran like a champ, except that it seemed I had to turn down the idle speed at every stop sign--I'd set it to about 1100 by the tach, ride a few miles to the next stop sign, and it'd be up around 2000; turn it down 10 1100, ride a few more miles, it's back up at 2000; repeat. After about 25 miles it started sputtering as if it were running out of gas--possible because I had "borrowed" a gallon or so to run the snow blower over the winter--so I switched to reserve... which made it run considerably worse, especially at lower engine speeds (below about 4000 rpm). I switched back to main and it ran a little better. Tried the "Italian tune-up," and it did run quite nicely at speed, though I detected a change in the exhaust note--it went from a smooth purr to something lumpier, more like a triple. Hmm... pulled into the gas station just as it stalled out. It took 2.8 gallons, which is exactly what I would expect if it had just emptied the main tank. Filled it up, had an ice cream cone (the "Pete's Castle" Marathon station has this Wisconsin Chocolate Shoppe dark chocolate ice cream that is to die for--or perhaps to die from, as their slogan is "if you want nutrition, eat carrots"), continued on. It seemed to run better, and I had a fun time wicking it up to 70 mph (against a 20-gusting-to-30 mph wind) and going around what few corners are found in this part of IL (pro tip: roundabouts are your friend)... but the exhaust note was still... off. Still sounded more like a triple than a four. Made a stop at the Royal Enfield dealer (I was looking at a fantastic deal: a 2024 Interceptor 650 with all of 44 miles on the odo--65 after my test ride--and 32 months left in the warranty, for the princely sum of $5300 out the door), rode home. On the way back it started running a lot worse, missing badly and sputtering with no power at all below about 4000 rpm. Just past 5000 it would seem to clear its throat and make good power, but there was still the "triple" exhaust note.

When I got home, I checked plugs, expecting to find some carbon fouling on #4 as I did the last time it acted like this. Nope, #4 was just fine, as were #1 and #3. Maybe a little darker shade of tan than I'd prefer, but nothing that would explain the bike's bad behavior. This time, it was #2 that had a coat of fluffy soot and smelled like unburnt gasoline. Hmm...

Yesterday I had some time to fool with it. First thing I did was check for any signs of carbs overflowing. Nope. Then I went through the four idle screws to make sure they were where they had previously been (1-3/8, 1-1/2, 2-1/3, 3/4). They were. I decided to install a fresh plug in #2 and see if that corrected the problem (even temporarily). Nope. Soon as I took it off enrichener (about a block from home), it behaved exactly as it had on Wednesday. I did a quick turn around through a subdivision and came home after going all of four miles. Coming down the fairly steep hill using engine braking, I noticed a lot of popping out the pipes, which is not typical. When I pulled the #2 plug, it already had a layer of soot.

So... now what? It appears something is dumping enormous amounts of gas into #2. I't's not the mixture screw. Far as I can determine, it's not an overflowing carb (I intend to pull the boots later today and see if I find any signs of gas overflowing out the carb's intake). What's left? Vacuum piston sticking (far as I can tell, this won't affect air flow but will, by lifting the needle, affect fuel delivery)? I'm a bit baffled. Worse, I have a lot of stuff going on the next few weeks and it's not clear how much time I'll have to fiddle with this bike. It's looking highly doubtful that I'll be able to ride it to the Crud Run on May 3rd...

Any thoughts?

 

If I were trying to get the wheels off the ground for winter storage (something I don't do anymore; about thirty years ago I read that modern tires don't suffer from being in contact with the floor like older ones did), I'd just put the bike on the center stand, have somebody lean on the back seat to get the front wheel up in the air, and stack a couple two-by-fours under the pipes up front. They're pretty solidly mounted and aren't going anywhere.

 

Finished the handlebar swap. Had to go with bar end mirrors, but I can now turn the bike without the mirrors or brake/clutch handles touching the windscreen. I had to play Russian roulette with some mirrors on Amazon to figure which worked. Ended up with some Kemimoto mirrors. Trimmed the ends of the grips, and the throttle assembly so I could install them. Throttle doesn't drag, and they look pretty good.

 

I don’t suppose you replaced the #2 carb body, by any chance? I had this exact problem (even in the same cylinder as you) after I replaced that carb body. The previous owner had broken one of the float posts and reconnected it with epoxy. Fun little surprise for me the first time I opened the carbs up.

Anyways, the problem wound up being that the hole that the #2 enrichment plunger sat in was cast slightly deeper in the replacement carb body. The other enrichment plungers would bottom out, but #2 would still be open. Was running mega rich and pretty much drowning that cylinder. I fixed the problem by bending the “fork” that holds the enrichment plunger on #2 so that it naturally sits a bit lower than the others.

Anyway, here’s a test you can do to see if this is your problem: operate the enrichment lever while looking at the carbs and see if any of the plungers don’t bottom out. You can also see if manually pressing downward on the enrichment plungers makes it run better. If that happens, you know the enrichment circuit is the culprit.

 

Nope. All four carbs are original, and nobody epoxied anything together.

However, it's funny you mentioned the enrichener, because I noticed something a bit weird about mine: when I move the "choke" lever to the full-off position, the cable goes slack but the little forks don't go all the way down (that is, I can push on the bell crank and move them down about 1 mm further). On #1, #3 and #4 this does not matter as it seems the plungers are bottomed, but on #2 I can actually push the plunger down another 1-1.5mm. Makes me wonder if this fork is not quite bent the same as the others, or if the hole is a tiny bit deeper, or something. When I had the rack apart over the winter, I of course had the linkage off, and I did not key the forks to the carbs (I did not expect them to be any different from one another). So, I guess the rack is coming off this week for a little closer inspection and a check to see if that silly millimeter is enough to make #2 run massively richer.

 

Yes it can, speaking from experience with mine. Had to tweak the lifting fork slightly to get it to seat and everything smoothed out..

So my XJ is officially out of the garage for the summer, got some miles on today despite the gusty wind. Just under 50 miles and it turns 50,000, maybe later this week we can roll the digits.

 

One more question about the enrichment system: is there supposed to be a return spring on the linkage? I know there are springs on the plunger, but mine does not have a spring on the linkage and I notice that after the cable goes completely slack (even has a bit of a bend in it), I can still move the linkage a couple millimeters further in the “off” direction. This does not appear to affect carbs 1, 3, and 4, but it does seem to be what leaves carb 2’s enrichener a little bit “on.”

 

Springs are on the plunger valves to hold them shut. If your linkage doesn't completely return after the cable slacks out then you might want to look for the reason why. All the valves need to seat completely and there should be a little gap between them and the forks, if the #2 doesn't have the gap it might be from a slight variation in how the carburetor rack was assembled or maybe something got bumped along the way and the fork was tweaked slightly. Regardless of the reasons everything must slack out when the rich lever is at rest.

 

Progress? Maybe. I seem to have found what was making the #2 (and #1 to a lesser extent) enricheners stay on. It was in the linkage. The bell crank that translates a pull on the cable to rotating the shaft that lifts the plungers uses the hat of the #3 carb as a full-open stop. Which is all well and good, unless the little tab bent out of the bell crank (which is itself just bent thin flat stock) happens to strike the edge of the screw holding that corner of the hat on the carb:



Hard to see, but there's just enough friction at the point of contact for the stop to not go all the way down... and it's just enough to hold the #2 carb's enrichener a bit open. Snap the shaft or give it a push and it goes down properly.

A few seconds with the pliers fixed this problem:



And the sun came out, so I put the carbs back on the bike and went for a ride.

And found that nothing had changed. Didn't even get out of the neighborhood this time.

And when I got back and looked, #2 was peeing gasoline from the joint between the carb inlet and the rubber airbox boot. Tapping didn't help, and I did not want to escalate to hitting the carb as hard as I would have liked to under the circumstances.

Sigh. I parked the bike, got out one of my other bikes, and went for a nice ride before the rain returned. What I did not do, and should have, is tried riding the bike with the gas turned off to see if the engine in fact ran well when the carb wasn't overflowing (this is how I got home last fall after one of the carbs started overflowing). That might at least tell me I'm down to only one problem.

I am getting close to losing my patience with this bike.

 

Well, crap. I guess the #2 enrichment plunger was a problem, but not the problem. Something is definitely up with the fuel system on that carb if it’s puking gas out the airbox. Kinda seems like the float is still getting stuck, but I don’t know how that could still be the case after all you’ve done.

 

Continuing the carb saga… yesterday I tried an experiment, replacing the needle and seat on that pesky #2. Didn’t have a new part, but I did still have the 46-year-old original, which I replaced during the cleaning and rebuilding three years ago, and which was not leaking at the time. Bench test showed no overflow and fuel level OK, so I stuck the rack on the engine for a two-hour soak test while I rode one of my other bikes to the shop to arrange a new tire. Didn’t want to come back and find the gas tank had emptied onto the garage floor, so instead I rigged up a 60cc syringe above the fuel line. Poured gas into it until the carbs were full. No leaks. Topped the syringe off to 40cc and put a plastic bag over the top.

Two hours later, the syringe was down to 10cc and a small amount of gas was oozing out of #2’s intake. Hooked up a hose for a level check, and the level was just a bit above the throat.

So… what would cause this? Things seemed tight for about a half hour, but eventually the carb is overflowing. I’m pretty mystified.

 

I'm not intimate with the carbs you have, but do you have a brass float that may be "sinking", maybe on one half ?

 

I've never done it, so it may be a ridiculous idea, but maybe the top of the #2 carb body and float could be set on a glass or clear plastic cup with a fuel supply rigged to it so the float would still close normally. Then maybe you could see if the fuel is leaking through the needle, or around the seat washer, or from some unseen crack in the casting. Throw some food coloring in the gas for extra clarity?

 

The floats are plastic, and I believe they are blocks of foam dipped in some sort of coating. The #2 float does have a suspicious-looking "bite mark" on its underside, but I did the David Letterman "Will It Float?" test by floating it in a container of gas for a half hour or so. It did not seem to misbehave. Perhaps I should swap floats between carbs 1 and 2 and see if the problem moves with the float or stays with the carb. Or I could weigh the float and compare it to one from a carb that is not overflowing...

 

Honestly I'd weigh all four of the floats as I'm not sure how accurately those nitrile floats are made. At one point I did see a seller with some clear plastic float bowls for the HSC32 on eBay, don't know how good they are but it might work for diagnostics.

 

My thought as well. I had some time this morning (I'm cleaning beer kegs, which means I filling them with cleaning solution and waiting for it to work, perfect for running out to the garage to fiddle with bikes), so I weighed the four floats. They are all 6.7g. I couldn't find any spec for float weight, but since they are all the same and three of the four carbs are just fine, I assume it's correct. I then swapped out needle and seat in #2 with yet another spare from the original ones, just as a test. A quick bench check indicated no leakage, but also showed the level in #2 as exactly level with the underside of the carb body, or about 3mm high. Well, that can be adjusted...

Side note: I notice the manual says the procedure for checking float levels is done with carbs on the bike, bike on center stand with front wheel blocked up so that the carbs are level, after starting the bike and running it a bit. This would make setting levels almost impossibly time-consuming, not to mention potentially dangerous as you're now working with gasoline around a hot engine. Does anybody actually do it this way? I have done my level checks on the workbench. And honestly, I don't see what running the bike a bit before doing the check would accomplish that tapping the carbs a few times and maybe running a bit of fuel through that clear hose before taking the measurement wouldn't. I have a strong suspicion that even Yamaha didn't do this; I think the carbs came from Hitachi pre-set for the correct level and at most they did a quick final check as the bike came off the assembly line.

I have been thinking a bit: just how perfectly is a carburetor float valve supposed to seal? The carb is a dynamic system and the function of the float valve is to assure that fuel enters the carb at the same rate that the engine sucks it out. The 30 cc of fuel that leaked in the space of two hours during Thursday afternoon's soak test might be well within the acceptable spec for the carb. It's certainly not much compared with the amount of fuel the bike consumes when it's running (about 3800-5000 cc per hour). I may have been simulating a situation that isn't "supposed" to occur in the real world, effectively leaving the carbs sitting for two hours with the fuel turned on. This is not supposed to happen in real life, as the vacuum petcock shuts off fuel when the engine's not running. Last week, I clearly had a real problem, as the carb was overflowing when the engine was running. But I realize that if I had skipped the soak test, hooked up the carbs and gone riding, I never would have noticed that #2's float valve didn't have a perfect seal. Hmm...

Any thoughts about this? Is the float valve supposed to be a perfect seal, or is some minimal leakage (far, far less than the amount of fuel the engine uses when running) acceptable?