-82 XJ650 4K0 running problems

So this is a bit of a bigger project bike, but need to start somewhere.

Found a 1982 Yamaha XJ650 that have been sitting for several years. It starts, but does not run that well and need the choke to idle at all. The seller guessed that at carb tuning would fix the problem.
I live in Sweden and this bike needs to pass a inspection before it can be road legal but when a motorcycle have passed the inspection and are more than 40 years, it is approved for life. This is the goal with the project.

A fresh battery have been installed, some wiring was fixed so the bike starts and runs, but not that great.
The idle cannot be adjusted correctly and after revving the engine, the PRM stays high and slowly settles, but sometimes not. Almost a runaway idle. If the bike is shut of and then started, it starts immediately and the idle is somewhat low, but goes up and down. When the throttle is quickly engaged, it almost stumble before it goes up in RPM.
I could also hear a "bang" or something sounding bad from the engine at idle also with white smoke from the mufflers. The sparkplugs was very black, alot of soot on them, except for the one from the No.4 cylinder. It was light grey.

Dived in on this forum and started to get a direction from where to start.

I removed the carbs and made a visual inspection inside the bowl and a small clean. I bench-synced the carbs also. But other than that, nothing replaced or changed. Put the carbs back and tested again but with no change.

The next step was to check the valve clearance, and check the shims. A stripped thread for a valvecover bolt, a cracked camshaft cap was found, this have been taken care of. Also a new valve cover seal have been ordered.
I read here on the forum that tuning the carbs without having the valves within specs would be a bad idea.
The measurements was not terrible on the intake, except for cylinder No.4. But all still out of specs. Measurements for the exhaust was all out of specs, and on the No.1 and No.4 there was no gap at all.
Here are the data:
IN
1. 0,21-0,25
2. 0,16-0,20
3. 0,16-0,20
4. <0,05
EX:
1. <0,05
2. 0,11-0,15
3. 0,06-0,10
4. <0,05

Followed the table and after changing all the shims and recheck the measurements, now they all are OK.
IN
1. 0,11-0,15
2. 0,11-0,15
3. 0,11-0,15
4. 0,11-0,15
EX
1. 0,16-0,20
2. 0,16-0,20
3. 0,16-0,20
4. 0,16-0,20

So after putting all together last night, I was hoping to tune the carbs. Have even bought a Gunson Colortune but the bike would not idle that well and it looked alright with the colortune, no big problems there. Except for the fact that it does not idle well. The same problem with the bad throttle response, runaway idle and that I could not adjust the idle made me realize that more work is needed.

I have now removed the carbs again and will be doing a "rebuild" and a ultrazonic clean of them.
Will be cleaning the carbs one by one is the plan, just so that I do not mix anything up.


When disassembling the carbs, I found that the throttle shaft seals did not look great.


But other than that, no clear issues.

Question for the forum:
Is this flow needle seat suppose to be removed? It is stuck, hard.

 

After I searched the forum, I found that this needle seat should be removed. There is a small steel mesh-filter on the bottom side.
I applied a little heat and it came loose with no problems.

The choke plunger assy was also removed, and it looked like it needed a good clean also.

The No.1 carb before ultrazonic cleaning:

And after:

I´ve run this carb 2 times in 30min with heated water. Just water and liquid kitchen handwash detergent. I have used other chemicals in this cleaner, and citronic acids but are a bit afraid to use to agressive stuff on the carbs.
Anyone with a knowledge what can be applied in the water to get a better clean?

Have used compressed air to blow any water out and then with brushes and break clean removed any dirt on the outside and inside. I will buy some carb cleaner and go over it again and then a third time in the ultrazonic cleaner.
The small parts from the carb have been on the cleaner one time so far, but will let them go several times again before assembly.

Feels good so far and really hope this will do the trick!

 

When i dissembled the carb and got to the pilot mixture screw (or the screw with several names, very confusing ) I was expecting a O-ring in the bottom of this hole.
There was the screw, a spring and a washer. But in the bottom there was no o-ring. It was a orange plastic ring. But no o-ring.
I guess that this plastic ring is instead of the o-ring, but is this really correct?
Have not taken the other three carbs apart yet so do not know if this plastic ring is on all four carbs. I will find out in the end. The ring is little rounded on the bottom, and not completely flat either.

But have anyone seen this plastic ring in this position before?
And does this need to be plastic, or is it better to change to a proper viton o-ring?

 

No, not at all.

Use the proper-sized Buna (or Viton) o-ring.

 

So.
A few weeks later and time for a update.

I´ve now cleaned all carbs with a lot of carb cleaner and also put all of them in ultrazonic bath. All jets and all small screws and springs have been individually cleaned.
When disassembly the remaning 3 carbs, there was indeed a o-ring in the bottom of the hole for the pilot mixture screw. So I guess that someone have lost one o-ring and replaced it with the plastic ring I´ve posted earlier.
I have put new o-ring in when assembly them so this is now corrected.
When cleaning the carbs, I really did not find any big concerns but if feels nice that I have done this cleaning and "rebuild" correct so that I can eliminate any issues due to not given them a good clean.
Everything is back together and no loose or left over bits or pieces.

Here is the carbs assembled and I´ve done the bench sync at this point.

The carbs have been put back into the bike and I´ve started it up to continue with a color tuning with the Gunson kit.
But I still have problems with the bike running well at idle. And I´ve looked into the forum and I have the same issues as others.
When the bike is warm, it is a bit problematic to get the idle really low and the lower I get it, the idle is very unstable. When I twist the throttle the idle hangs up at 2000-3000 rpm and then slowly goes down, but not completely down. I have not done a vacuum tuning, but I will. But it feels that I need this idle problem sorted first.

What I think is the problem is the throttle shaft seals.
They were in bad shape on all carbs and they needed to be replaced. I´ve have had problems finding the correct ones so I have tried the alternative O-ring option that I´ve read about here at the forum.
But even if I have the right size O-ring, it feels that the throttle does not close the way it needs. I´ve tried to put more tension on the springs for the throttle on each carb, but this does not solve the problem.
I´ve tried one #11 O-ring, combined with a thinner one, but this got it worse and the idle was running free. Changed back to 2pcs of O-ring, but then the idle does not come down completely.

And yes, I understand that I need the correct seals. And I know where I can find them and I ´ve been in contact with XJ4ever.
The problem is that I live in Sweden, and since this is a country in the EU, regulations for shipping and deliveries to Sweden have it´s problems.
I´ve have some more testing with different O-ring that I can do, but not really sure it will work. At least have I got a good workflow to remove and take the carbs apart at this point .

I´m under a deadline also since I need to have the bike running for mandatory road inspection by Swedish law before I can use the bike on the street. So if I can´t get this working well, then this bike will sit in the garage until spring 2024. And if that will be the case, then I have a lot more time to get all the things that I need.

 

Do the vacuum synch! You might find that it cures the problems that you are experiencing.

 

Aha!
That would be a relief if that would work. Thought that there was no idea to to the vacuum sync unless the bike run better. But that might be just the problem.
I will check with a friend if I can do the vacuum sync done.

That will probably confirm if the seals needs to be changed, or not.

 

Throttle shaft seals get blamed for all sorts, but one thing they can give you is an erratic, maybe unstable idle. However, without vacuum synching first you are wasting your time. The extent of throttle seals leaking really depends on the condition of the spindles and bores...
Let us know?

 

Will do for sure!
Just talked with my friend and I will be able to do the vacuum sync tonight.
I´ve read a lot of info regarding the usage of the YICS-tool when a vaccum sync is preformed. And from what I have read is this both a must, and on the other hand not needed.
In the Haynes-manual that I have, this tool is used if I´m not mistaken. Do not have the manual with me to check at the moment.

I´m still under a little tight deadline and found some pictures and measurements for a home made tool that might work.
I like to make stuff my self, and this tool was a perfect little project.
So I made one from some pictures and measurements found on Google, here is the tool.


Now. I have no idea if this actually will work, or if it is done correctly since the info on this home made tool was not that great.
I have tried it on the bike and it functions and gets stuck when the wingnut is tightened.
Either way, it was a little side-project and if it works (or if it is needed at all) might be revealed during the vacuum sync later today.
My plan is to do the sync without this tool and see how that will turn out. And if things go as planned, I will maybe try to use this tool and see if I get any change on the sync-equipment, or the bike.

 

i can,t find any referance to wet setting the floats, have you done this ?, if not, all other settings are irrelevant

 

Have not wet set or checked the fuel level in the floats, so no reference to that being done. You are correct.
Maybe I´ve overlooked and missed that this is a crucial step?

The carbs have not been rebuilt completely I might add.
I have not touched the floats, needle or seat. Or changed any of the jets or washers in the float bowl. Yes, I have touched them in the cleaning, but they have not been altered or changed in any way that I know of.

 

have you watched mezzmo engineering on you tube? he guided me on carbys and i have had no issues, his vids are superb imho.

 

Yes!
Have looked at some of his videos, very informative.
The work he does is far more correct and complete than my own...

 

My friend lend me a "Carbtune Pro" for the vacuum sync.

Removed the seat and tank and installed a auxiliary tank and then the hoses from the carbtune.
Here it is installed before i started the bike:


The vacuume was too low so I needed to turn the carbtune around to get a good view before I started to change any screws. The Haynes book was also good to have so that I could understand how to do this tune right.
I managed to get the carbs tuned quite right and the idle down to about 1500 RPM. But it still was a bit rough and when I turn the throttle it hesitated before the RPM went up, and then slowly returned down to about 1500 RPM, but sometimes settled at 2000 RPM. It was a lot better than before that was for sure. But it did not feel right. Especially when revving the engine and the response was hesitant and the slow return to idle.
The other issue was that if I tried to lower the idle with the center adjustment knob and go lower the bike, lets say around 1000-1100 RPM, it would hold there for a short time and then slowly, slowly get lower and lower until the bike died. Still very hesitant on the throttle.

I called my friend and gave him the report and he told me: "More fuel!"

I have previous done the color tune and the flame was "bunsen blue" with all the pilot mixture screws out 2,5turns. Since the color tune gave a blue flame, I did not change anything with the screws.
I did now another color tune and backed the screw out until I got the yellow flame on each cylinder and then screwed them back in until I got a blue flame again. And this was about 2 more full turns...
I could hear the engine running better already and when I turned the throttle, the bike responded directly!
After the color tune, I did a vacuum sync again, very small changed needed. And the carbs were again in sync, and the idle very stable at just over 1000 RPM. I could now turn the throttle and no hesitation at all, and then back down to idle.
Here a picture during the sync, bike is running in this picture.


Also, I needed to turn the carbtune back around since the vacuum increased now so the reading did not work upside down.
I mounted the seat and gas tank back on the bike and went out on the street. And the bike runs great!!
The throttle response is direct, and the idle goes down perfect every time.
I´m actually very happy with this at this point and I think some of you guys know the feeling when it just suddenly works. It is a great feeling and I´m really exited to might get this bike back on the road again. It have been sitting since 2008. Have almost been givning up the last weeks since I could not get the changes that I was hoping. But now, a halleluja moment for sure!

So the conclusion was probably several things. But I´ve checked and done the valve clearance. I´ve taken the carbs completely apart and cleaned them. Found a plastic ring on one of the pilot mixture screws, changed that and on all the others after cleaning. The throttle shaft seals did not looked great so I changed them, but with O-rings. Float bowl seal also replaced. Other than that, just cleaned carbs and put them back together and back on the bike. And a new air filter also.
And I do not know if the big change on the pilot screws from "baseline" 2,5 turns out to in the end over 5 turns out is a indication for something that needs to be looked at. Maybe it gets too much fuel now, but I rund great so do not really want to change anything. But maybe someone have insight on what to look at when I do the complete rebuilt in the future.
The carbs have not been completely rebuilt at this point, and I think this will be something I will be doing.

So what was the conclusion? The valve clearance, cleaning and seal changes on the carbs was necessary I think, but also the color tune so that I could adjust the fuel and air. And then of course the vacuum sync.
So right now, no running problems!

 

That is great news!