Cleaned the carbs twice but bike dies at warm idle

I own an '81 XJ650 and have had the carbs apart twice in the last two days. The first carb clean revealed a decades worth of gummy gas that took me hours to clean up with carb cleaner. I reinstalled the carbs and the bike seemed to be acting fine so I figured all was well until it started to die when it warmed up and would only start with the choke on.

I decided to pull the carbs again and disassemble all four so that they were separated from each other and I soaked each one in boiling lemon juice for a half hour. This got them clean on the inside and out. I even cleaned the brass parts and they came out looking like new. I was confident that these carbs would run flawlessly. I was wrong. I reinstalled the carbs, set the pitcock to prime and the bike fired up after I gave it some gas. It seemed to be doing fine, so I switched the pitcock to the on position and let it idle for a bit until it warmed up. I set the idle to about 1200 rpm after the initial warm up, but then I noticed that the bike started to bog, so I gave it some gas, but it still died. I switched the pitcock back to prime (while noticing that one of the carbs would drip fuel when I did so) and it fired back up. I then turned the pitcock to the reserve position and it seemed to run fine...for a bit...then it died.

Now, the only way I can keep the bike running is if I keep my hand on the gas and don't let it die. It seems to rev up fine with no hesitation through the powerband, which is comforting, but the thing simply won't idle. I've screwed the idle adjustment screw in until the bike idles on its own, but that occurs around 3000 rpm...too high. If I lower the adjustment screw, it dies. In addition to all of this, I'm getting a lot of white smoke out of the right tailpipe. It doesn't have the burning oil smell to it, but it certainly looks the part.

The only thing I can think of is that maybe my pitcock is bad? When it's in the on position, it doesn't seem to flow and gasoline and I'm assuming the bike just stays running because of the fuel left in the float bowl. I've heard that a bad pitcock can lead to fuel being sucked through the vacuum line, causing a rich condition in the cylinder it's attached to. I will pull that spark plug and report back on its condition. Are there any easy ways to inspect the pitcock? What about disassembling it? Is this the type of part that can be easily clean and fixed or does it need to be rebuilt/replaced?

Anyone else have any other insight as to what may be my problem as to why I'm puking white smoke and why I can't get the bike to idle?

 

test petcock.
put a clear tube from petcock into a gas can, take the vacuum line from the carb boot & suck, with the petcock "on" you should get flow but no taste of fuel.

 

The plug in cylinder 4 was black...and I mean black! I'm thinking the pitcock is sucking fuel through the vacuum line and right into the cylinder. Cylinders 1 and 3 didn't look too bad, but didn't look great either. Cylinder 2 was also pretty black, but not nearly as bad as 4.

I'm sure the decade of gas sitting in the pitcock wasn't easy on it so I think I may take it apart and have a look inside. Maybe boil it in lemon juice! Seemed to work for the carbs! Ha.

 

But with a bad pitcock, I'll get a mouthful! Yum. This test sounds fun

 

Petcock cleaned and tested and it seems to be working. I was an idiot when I tested it the first time and thought no fuel was flowing when it was in the on position....turns out I just didn't have enough gas in the tank. Dumped another gallon in and from what I can tell, when the bike it on and running, the fuel is flowing!

So, I've got this thing now where the bike won't stay running unless I keep it above 3000 rpm or so...OR...if I cut off the fuel to the engine. If I cut the fuel, I can adjust the idle to wherever I please and the bike stays running, but I imagine it's just burning off the leftover fuel in the float bowls and will eventually die. The second I introduce new fuel to the carbs via the petcock, the bike will bog down and die unless I roll the throttle and keep it to 3000 rpm. I can adjust the idle screw such that the bike will stay running without my assistance, but then the engine races and doesn't sound natural.

I've been doing some searches and some post suggest that my throttle cable might be holding the butterfly valves open. Nope, when the throttle is at rest, there is visible slack in the cable. Overly rich idle adjustment screws? Possibly. I turned all of them in as far as I could and backed them off about two turns. Was that too much? Too little? I removed the plugs after a solid 10 minutes of 3000 rpm idling and the once black plugs are beginning to look like they're leaning out some, but they don't look great.

I intend to get some new plugs so I can get a better idea of the mixture in each cylinder as these old carbon fouled plugs make it hard to tell. Some other ideas I've been throwing around are the possibility of a clogged air cleaner or weak ignition system. When I originally tested for spark, I noticed that it didn't look as strong as I thought it should, so I'm going to remove the coils, clean the electrical connections on them, especially the ground wire. I'll also see if I can find some resistance values for the plug wires, which look like the originals, by the way.

 

Have you checked your float heights? It sounds like a problem I was having after I cleaned my carbs the first time. It took a few attempts to get them all just right, but the bike idles great now.

 

I just pulled the carbs and checked all of the float heights. All of them were way out of whack so I bent the little tab and got them all within 17.5mm +/- 1mm. Reinstalled the carbs, started the bike, closed the choke, adjusted idle and it seems to be running better. I've pulled the plugs a few times and I'm actually able to see the electrodes! I guess my next step is to adjust the idle mixture screws? I feel like I'll need to buy new plugs before I can do that as the old ones will just make it too hard to tell.

Also, I noticed some discoloration on the exhaust pipes, which if I'm not mistaken, indicates a lean burn.

 

A lean burn!
That's what I think, too.

Anytime the bike won't Idle unless the Idle Adjustment Rod is turned-in to have the bike make 2,000 rms ... or not run ... the Pilot Mixture Screws aren't giving you enough Air-Fuel to Idle and sustain Ignition Off-Idle.

The first thing you have to do is get the bike to Idle on its own without opening the Butterflys with the Idle Adjustment Rod.

You have to shift into the Tweak Mode for doing that.

Understanding that the Pilot Mixture Screws need to be moved in a minuscule amount AFTER you find the setting best to sustain Idle to provide additional richness to sustain ignition until the Main Jet Supply kicks-in.

Tweak it.
Plug Chop it.
Adjust individual Cylinders as needed to achieve the best coloration on the Plugs.

 

I now have it at a point where I need to choke it ever so slightly to get it running and it will idle around 1500 rpm with the choke completely off. I still need to pick up a set of new spark plugs for it so I can adjust the individual cylinders, but for the time being, I backed the pilot mixture screws out two full turns. The bike idles decent with a slight hiccup when revving it from 1500rpm on up. It cruises decently, but I haven't had a chance to open it up. If you've seen my other thread, the bike has no title and I'm figuring out the hoops I need to jump through to obtain one. I've just been riding it around in first gear, partial throttle around my yard.

Did I mention there are no front or rear brakes at the moment? It makes for an interesting ride!

 

Great!
No brakes!

Let's not get the bike all tuned up without being able to control the thing.
Now that you have a good idea that the engine is going to be a good runner once you do some fine-tuning ... how about if we get the binders working so you are able to bring the thing to a halt if you need too.

I'm sure you are having a good time with it. But, don't put the cart before the horse. Get some brakes working on that bike before to wind-up having to lay it down if it were to suddenly get away from you!

Let's concentrate on getting some brakes then we'll work on the finer points of interest!

 

Ha! Working on it. The rear brake lever appears to be seized so I'll have to remove the rear wheel to correct that. I took the front brake fluid reservoir off since it it was more of a solid inside, rather than liquid. I cleaned that all up and just need to put it back together, which I'll work on today. I had to drill out one of the reservoir cap screws so I need to run to the hardware store and pick up another.

 

Front brake fixed and it works a lot better now! I swapped out the plugs for new ones and have just been cruising around in my yard for a little bit to get an idea of how the bike is running. I'm noticing a decent hesitation between 1200-1800 rpm right when I give it a little bit of gas. After the bike overcomes that little hiccup, it's smooth sailing from there on out. I can't really open it up for obvious reasons, but it seems to be running fairly well. I haven't pulled the new plugs yet to see how they look, but I'll do that now and report back.

I also replaced the main fuse box in hopes that it would give me some stronger spark, but it still looks really weak...starting to think that's just how the ignition coils were designed.

 

You'll know more about how that engine is performing when you do a Plug Chop on a new set of Plugs.

Then, you'll be getting into some tuning and more than likely will get the hesitation you have in it worked-out.

 

I have the same problem. When I suck on the vacuum hose only a tiny amount of fuel flows out the fuel line. Should it flow quickly or slowly if working correctly?

 

i had a simliar problem. it went away when i changed the orientation of my inline fuel filter. i kept getting air bubbles which were restricting fuel flow.

if you have a fuel filter. it may be worth a quick 5 second peek.

 

Whoohoo. I pulled apart the petcock and it looked fine. Tried sucking the vacuum hose again and still nothing. Then tried switching to reserve and fuel flowed! Tried switching back and forth and now am convinced that I have it working. All I have to do is carry a small "reserve" of fuel and I am good to go.