Xj 550 Idle adjustment - Help!

Hello,
I just replaced the cracked carb to manifold boots on my xj550 with new ones. I also cleaned the carbs blowing compressed air and carb cleaner through every orifice i could find and knew about. I set the idle jets back to what I measured them before cleaning - 4 and 1/2 turns out. Now when I start the engine idles too high - 4000 -5000 rpm . Before it used to idle at 1200 approximately.
My question is how do you know if it is too rich or too lean? I don't know if the boots are not tight enough or my cleaning process produced a vacuum leak (causing lean) or if the unclogged idle jets are making it too rich. I am going to turn the back in to 2 and 1/2 turns tonight. Do I have to take the tank off to make these adjustments?

Hey at least its running.

thanks,
Hananiel

 

One thing at a time or it gets confusing.

Engine speed is a factor of how much gas/air it gets so if it is running fast you need to look at those issues.

1) make sure your throttle linkage is not caught on anything and that the cable is not tight at no throttle.

2) check your idle adjustment screw. If your jets were clogged it may have been turned in to get a decent idle

3)Check for air leakages

Lean/rich is a balance of gas and air. You can tell is you are lean or rich by reading the plugs. Search the forums for plug reading there are some good pictures. But once you get your idle settled you can work on the rich/lean.

 

Bill,
Thank you for your response. If it is not the throttle cable issue and assuming there are no air leaks, then for a constant amount of air coming in, does more fuel increase the rpm or decrease it or is it a curve increasing and then decreasing as you increase the fuel?

I did hear a ping and at least one back fire I think. Also the exhaust was very smoky and i think it was not just water vapor (it was very cold). I smelt smoky. I am at work right now and I am trying to be a responsible husband, father and employee or I would be at home tinkering with it instead of asking .

Also once the float bowls are primed and I remove the tank how long can i expect the engine to run before I have to hook the tank again?

thanks,
Hananiel

 

It should run a few minutes on the bowls but will lean out near the end of course.

The carbs run off of air pressure, as you open the throttle the butterflys open to allow more air, the pressure difference causes the slides to rise opening the main jets more. The gas is also sucked from the bowls into the air stream because of the pressure difference.

To answer your question for constant air I believe RPM would increase slightly until you get rich enough to actually choke the engine. But in reality that is not a normal condition. To rev at 4 to 5 k you need more air - pulling more gas.

If your jets were clogged I'll bet your idle adjuster if cranked in (which opens the butterflys), now that you have them clear it's reving up.

 

Bill, you are very helpful. Thank you. What you are saying points to an air leak i think in my case. Unless i accidentally turned the idle adjuster while cleaning the carburetor. But I just remembered something. don't know if my bike is just different. Before I did the carb cleanup and changed the boots, as I had the choke on and it warmed up, it would rev at 4-5k . How tight should you have the bolts on the rubber boots on the manifold? They were very easy to remove so when i put them back i did finger tight plus quarter to half turn till i "felt" the same amount of resistance. I do have a torque wrench but i don't know how much to set it at. I just have to play with a few things when i get back home.

 

4 to 5 k on choke sounds high but hard to say how things are set on your bike.

Which boots are you referring to? The manifolds (boots from engine to carbs) we generally warn against removing as they usually are frozen. You may have gotten lucky. Usually you remove the boots to the air box and pull the carbs out of the manifolds.

I don't have any torque specs on the 550 one of our 550 guys can help there.

 

I am talking about engine to carbs. I am pretty sure the previous owner did the hard work. I have allen head bolts and they were not frozen at all. The reason I started doing this was that it was having starting trouble - I now believe the reason was a poor battery (because it starts only when I jump it). However the engine to carb boots had a lot of cracks on them. I would spray them with silicone to plug air leaks and i thought i had better luck starting - but i am not sure. When i removed the boots, there were some cracks that were on the inside as well. However for all these problems it idled at 1200 and ran quite well. Actually I ran some left over sea foam through it and changed the oil, and i felt that it sounded much much better. I will let you know in a few hours what i find.
thanks,
Hananiel

 

Per the factory 550 book: Carburetor joint to cylinder head: 7.2 ft/lb.

 

Thanks for the torque numbers Bigfitz!
I am completely mystified.

I set the mixture screws to 2 1/2 turns
I also sprayed silicone liberally on the carb boots in the hopes of plugging air leaks.

It now races to 4-5k on full choke, and when i turn the choke off it comes down in rpms and then it seems to die unless i give it throttle.

I looked at the throttle linkage , it seemed fine.
i turned the idle adjuster and it didn't seem to be touching the throttle linkages at all. But i loosened it anyway. Why is everything so inaccessible , the japs that built it must have really small hands.

Now it wont start at all. Now I did not mention that I jump the bike . However, the starter thingy i have runs out of juice quickly. So I have to wait while it charges. I could hook it up to the car , but in the past i did not have good luck with that. I dont understand because the car battery is good enough to crank the car but not the motorcycle. I suspect the cables.

Mystified - like i said.

 

Maybe pull the plugs after an idle->die?
It sounds like there is too much fuel @ idle.

 

Believe it or not I think you are making progress (I'm assuming your original post means running at 4-5 k with no choke). Once you have it started with choke (I still think 4 to 5 k is high) let it warm up a bit. Adjust the choke so you are running at 2k or so for the warm up. Now that you have loosened the idle screw you will need to turn it in until it will idle at 1050 rpm with no choke once warm. It is actually behaving properly.

The you can start checking your plugs and getting the mixture right.

Fitz is 4 to 5k normal on a 550 with choke?

 

My 82 XJ650 will rev 4-5k with full choke when the engine is warm.

 

That is right. I didn't understand that it was progress. I was suspecting that there was too much air going in through the vacuum caps or hose or something. So you think turning the idle adjuster will fix it huh. Ok I will try it tonight. It would help if it didn't snow. I feel like a complete idiot with the bike in front of my garage in snow trying to start it.

 

If you were running 4 to 5k with out choke we have progress. I would expect it to die with no choke and the idle screw all the way out.

The snow just adds to the excitement

 

With full choke I believe it would be. Mine doesn't need full choke to start (actually starts better on about 1/2-2/3 choke) and I keep backing the choke off as it warms up to hold it around 2500. (With all this talk of "choke" remember it's just a TERM not a real choke, it's actually an enrichening circuit.)

 

True but enrichment circuit is such a long thing to type

But that is an excellent point - you are adding fuel to the mix by opening the enrichment circuit so I would set it so the bike runs about 2k or so as Fritz mentioned until warm.

In regards to our earlier conversation since you are not adding air it is a very rich mixture and can foul your plugs if left to idle for a long time with full enrichment.

My 650 in the cold runs about 2500 with full choke but that increases as the engine warms up. In warmer weather I use very little choke to get it running.

 

Update:

Yesterday it ended with me turning the idle mixture screws to 2 and 1/2 and the bike wouldnt start. I didnt know if it was the battery or not.

Today with a fresh battery ,it doesnt start.
I set the mixture screws to 3 and 1/2 it starts and goes to 4-5k without choke.With chock it now goes to 6k which scares me so I turn the choke off almost immediately.
I dont think I turned the idle adjustment. Oh well!

I then turned the mixture screws in to 3 turns out. Still at 4k without choke.

So now I turn the idle adjuster all the way to the left then I unlink the throttle cable completely.

Now it comes down after the choke off but it dies. Great!
I loosen the throttle adjustment nut at the handle bar to make it lose and reconnect it and then same thing. Better.

Now I start playing with the throttle, a small blip makes the engine race to 4k and stay there after the throttle got returned back. It doesnt feel like the cable is catching.

Now I start adjusting the idle adjuster to the right. As soon as the adjuster starts lifting the butterflies, the engine shoots to 4k and stays there making it difficult to tune.

Also then idle seems very rough like one of the cylinders is working against the others or something.

So What do you guys think?

 

I think you have one or more slides hanging up. Since it's snowing anyway, might be time to pull the carbs and give 'em the once over. I'll bet one of them is miserably failing the "clunk test."

 

I think Fitz is correct time to recheck your carbs. Special attention to clunk test. you are getting some strange results but they seem to point to the carbs. Sorry. I did mine 3 times then I finally tore them completely down and rebuilt. Been very happy ever since.

 

I just did the carbs!!!
I did notice one of the carbs was sticking a little bit so I stretched that spring a little bit and it seemed to be fine. what is the clunk test? I did a google search and got some medical stuff .. so i am assuming you are talking about something else.

Btw you guys are geniuses. I had my own theory going in but what you guys said made more sense after i was done.
thanks,
Hananiel

 

Here are some useful links

Clean carbs
http://www.xjbikes.com/Forums/viewtopic/t=2908.html

Carb Sync
http://www.xjbikes.com/Forums/viewtopic/t=2132.html

Bench sync
http://www.xjbikes.com/Forums/viewtopic/t=6366.html

In Ricks clean carb link there is a description of the clunk test near the end. If you did not do that you need to. Those pistons should drop to the bottom with a resounding clunk (diaphragm not seated of course).


Can I quote you to my wife about the genius part? She has a differing opinion :lol:

 

I do have a problem with the hypothesis though. The butterflies control air flow through the carburetor primarily. The function of the slides is to make sure the air flow does not increase suddenly leaning out the mixture due to a sudden jerk on the throttle grip. But in my case, the opposite is true. When coming from a wide open butterfly to shut, the airflow is completely shutoff. The slide's position shouldn't make a difference anymore except the next time i open it up, if the slide were still stuck up, I would miss the benefit of the slide. That's not what I am seeing, after I shut the throttle down, the engine keeps going. That is why I am still suspecting a vacuum leak meaning extra air is coming in from somewhere. like the vacuum caps , the tube, the new boots or just didn't tighten bolts and screws properly.So I am a little confused by your analysis. But a little experience is better than a ton of theory. So if you are very sure i have to pull the carbs, i will.

 

are you talking you stretched a DIAPHRAGM spring? If so, you made it so that carburetor (and not the others) would have to have MORE vacuum to pull its slide up (has more spring tension to overcome now) than the others. That might just be your problem. It really sounds as though the carbs aren't acting in unison.

 

Guilty as charged but I did not stretch it that much. But I seem to be having multiple issues here. Have to sort them all out one by one. It was working great before I "fixed" it. I will sort it out eventually with yall's help of course.

 

Weellll...step one is going to be to locate an unstretched diaphragm spring...

 

I am planning on scrunching it back. I believe since the material of the spring did not change a given length of a spring should have the same spring constant. I will measure it to make sure they are the same length. BUT I did find something new this morning. I believe it will explain everything i am seeing. My float pins or float pins assemblies are leaking. How do i know? This morning I tried to start it wouldn't crank. I removed the spark plug and its full of fuel. That explains whats happening. I don't think its vacuum leaks because the plugs always pointed to rich. so if there is too much fuel behind the butterflies, when i open the butterflies this is exactly what it will do.

 

Hmm - check for gas in the oil and also check you petcock is working properly.

Make sure you change the oil and filter if as has gotten in there.

 

Why do you mention the petcock? I left it on prime. My understanding was, even in prime, the float pins should do their job?

 

Yes but if they fail (as yours appeared to) that allows the entire tank to empty by siphon action. The petcock is designed to turn off the gas flow when the engine is not running. It is not good practice to leave it on prime.

 

Ah I see what you are saying. But I wouldn't have found that my problem was with the float pins. I just want to ride my bike already (

 

I fully understand - I have an oil leak I thought I fixed but it is back. There is always something.

 

update:
I got more disciplined with doing what i was supposed to and spending time with kids etc. So it took me forever to clean the carbs, but i took my time. Since the problem I guessed was with carbs flooding because of stuck float pins, I cleaned the inside the of the brass fittings with a nylon brush on a dremel. I sometimes use salt for abrasion. Salt is softer than brass but harder then the crud (at least that's my theory). I wipe down the corners of the float pins with 440 grit sandpaper. I test the float levels by setting them on the bench with the tank on an elevated support and now one was still stuck open. I opened to examine the float assembly and found the "stop tang" the thing that keeps the floats from falling to the bottom was too far so the float was coming too much down and the pin was getting stuck open. I remember I had a lot of trouble while removing the pin on this carb so i must have bent it accidentally. anyway i bent it back and then measured the fuel level was too low. so i bent the "pin tang" down to allow more fuel and it seemed right. I couldnt adjust this more correctly without getting the carbs on the bike. so with this I fired the bike up. After a few starts and back fires (from the fuel in the exhaust i assume) it started idling at 4k with choke. Turning the choke off cuts down the rpms and i still have to adjust the idle screw but I am pretty sure i solved my problem.

 

after spending a frustrating 3 hours setting float levels, I think that bending the tang up & down is the most primitive idea ever, why can't there be some sort of grub screw for adjustment. :evil:

 

Probably because the THEORY was "set it and forget it" if we set it at the factory it should never need to change. Remember, the people who designed and built these things had no intention of them being truly serviceable. The Japanese didn't build motorcycles to last forever, so why would that ever need to be adjusted again? Oh, and from a guy who started his "IT" career on Olivetti mechanical calculators, you don't bend the tang. You FORM it.

 

Yeh, right, "factory set" like the mixture screws, how many of us have removed those sealed caps to find the screws set anything from 1 to 4 turns out? I guess we should'nt be tinkering with these "obsolete" machines.

 

We're not TINKERING my friend we are preserving. Somebody has to do it, we wouldn't want to lose a piece of motorcycling history now, would we? Besides, "tinkering" implies a certain casual attitude; we're way too involved to be mere tinkerers. A "tinkerer" would have given up after an hour.

 

Today I finally took the bike out for a ride. Its like 10 times smoother than before and my electrics are now working. I do have to shut the turn signal manually off but it doesn't bother me . I will later need some help colortune ing and carb tuning. But I am relieved that it finally works. Thanks for everyone who helped me diagnose and fix my problem.