Calling for some help from across the world

Hello guys

Yes this is anther one of these please help carburettor problems.

So I have a 1981 xj650 maxim non yics that I have stripped and done a custom build on.
No coin speared type of build with the attitude do it or you will regret it down the track.
Full engine rebuild
Everything vapour blasted.all bolts or worn parts replaced. Motogadget m unit ect ect.
I have put ALOT of time into this bike as it was my first build.

Now no Matter what I can’t get my head around it’s high idle problem.
So since I finished building it its just sat and got neglected. Haven’t even had it out on any back roads yet..
It has pods/uni filters

I have brought all carb parts from Len. New fuel o rings,new A/F o rings. New seals.also new diaphragms. I have stripped them so many times to see if I have a blockage but I can’t find the issue.
New genuine Yamaha intake boots.

Valves are in spec.
Floats checked.
Synced
Colourtuned
Even swapped out some bad looking carb butterfly’s
#42 pilot jet #45 made no difference.
If not rpms rose faster once warm with #45s
116 for mains.


Bike never needs choke.
Will idle great at 1000rpm straight away. Idle screw backed right out And throttle cable disconnected.

Once warmed up from a 10min ride it will sit around 1700-1800.

Now because I don’t know anyone in New Zealand with anther xj650 that is willing to let me put my carbs on there bike to see if it’s definitely a carb issue or not I can’t fase out if it possibly something else.

So what I am asking is if someone would mind me shipping my carbs to them so they can try it.
Preferably someone well known who has rebuilt plenty of Xjcarbs.

I even thought about buying some of those new FCR carbs on eBay and starting from scratch but they probably will open a whole other can of worms tuning wise.and they are very expensive.

Much appreciated for your thoughts.
I just want to ride my bike!
Marcus

 

spray starter fluid around the intake boots to see if you have a leak. you dont need a lot of fluid just a few squirts around each boot where it connects to the motor and at the carb. The high idle is most likely from running slightly lean, its either low gas or too much air. you can try color turning again and make each piston run slightly richer. while tuning blip the throttle and check the color, then hit the throttle a lil higher and see what the color is.

Depending on the environment and how moody your bike is, you might need to adjust your floats or shim the needle.

 

I have tried the starter fluid with no increased rpm when used.

When hitting the throttle it is showing orange on the colour tune.
On idle I have got most of them near blue. But they are all very different. Some end up been two turns out where anther might be 4 turns out.
My plugs are black sooty with a white tip on the electrode arm.

 

If the idle screw is backed out and it is still running, then you did not get the carbs put back together right. The bike should die when it is backed out. Does the bike have a hanging idle? If not, then I doubt you have a vacuum leak. Idling immediately after startup cold without choke at 1000RPM then I'm thinking the idle screw is not setup right. It would be normal to expect the idle to increase as it warms up.

This is normal.

Great looking build too!

 

Thanks jayrodoh
No no hanging idle very snappy.
I would think it could only go back together one way?

 

For the most part yes. When reassembling you need to make sure all the butterfly plates are closed all the way with the idle speed adjustment screw backed out. If not then you either hosed up something with the sync screws when reassembling or one of the butterfly plates were tightened down before you "aligned" it with the carb throat. Did you bench sync this prior to installing and syncing?

@hogfiddles has explained this process somewhere else on here but I cannot find it, he may be able to explain it better.

 

Y

Yup I benched synced. With all slide pistons out and bench synced best as possible I still get 1/2 mm of light shine through on some of the butterflies. I have taken them out and swapped around to get the best possible fitment.

 

Here is a decent link with the situation I was thinking of. The linkage screws (sync adjustment) were off during reassembly not allowing the idle speed adjustment to hit the pad.

https://xjbikes.com/forums/threads/82-xj650rj-carb-bench-sync-idle-adjustment.48282/

 

you HAVE TO do a running sync
the idle knob HAS TO BE IN CONTROL of all 4 butterflys
reset all the A/F screws to 2.75 out, turn the idle knob until it touches the lever then .25 turns more
start your running sync from there

 

I will try this thanks polock.
With the engine warm and the idle screw touching like you said won’t it be reving to high,giving me a false reading on the vacuum gauges ?

 

measure them all first then start bringing down the higher set this will bring down the rpms untill you can use the idle knob

# 3 will be a constant as it is adjusted by the idle knob set 4 to 3 back out the idle knob

 

you can get started with just the starter turning it over, it's crude but it gets you in the ball park.
if it gets up to 2000 or even 2500, that's OK, just get it closer. then the idle knob should slow it down to something reasonable.
once your around 1500, start on the A/F screws and peak the rpm, then back to the sync and tweak it closer. lower the idle then
back and forth from sync to A/F until your happy

 

If I’m reading this comment right, I think you may be under the impression that the idle screw would not be touching when running. The idle screw will always be touching the pad on the throttle shaft assembly. As I mentioned before, backing the idle stop adjustment out should kill the motor by closing the throttle plates. If I misunderstood you can ignore.

The running sync is important but the proper bench sync first is important too. The throttle plates should snap all the way shut with the idle screw backed all the way out and then you screw it in and it should be in control of all four plates. If you did your bench sync earlier as mentioned (1/2mm light?) with the idle screw all the way out you’ll never get it adjusted right.

 

Guys I Owe you all a beers! Lots of them!

Got home from work and got straight into it.
Before Anything I made sure the idle screw was touching the plate plus a extra .25 of turn. THIS WAS THE STEP I HAD BEEN MISSING OUT
Countless times of syncing/colour tuning and that was all I needed to do.

I just thought that because it was idling so high to begin with that it didn't need the idle screw.
1&2 wore out so matching them brought the idle down. 3&4 wore okay then matched 2&3 boom nice low idle 1000rpm !
Next colour tune. Adjusted from #4 down and got to cylinder 1 to find it wasn't even firing at 2 3/4 turns out. Anyway once firing the idle was back up so I had to re sync and we wore away!

Went for a test ride which was all but a disaster. While filling up the weather decided to do a full 180 and poor down cats and dogs so I had to sit under shelter for a good 30min till it cleared. Then I noticed I had been so excited leaving home I had left the colourtune plug in...

Got home and went for round two. Bike is running great think I need to go back to a #42 from the 45 as it stumbles a tad before clearing.

Thanks to all that have helped! I never thought I would get it fixed!

 

glad this got worked out. when i first read the post i thought it was a hanging idle.

Great job on the advice, i feel like what was said here should be in a new sticky on how to adjust your carbs.

 

Me too it’s been along time.
Yes I agree definitely for those that have high idles and are leaving the idle screw out before syncing.

The ride home ended up been more eventful.
I was nearly home when the bike starting making a horrible clunking noise. I could feel it through my feed on the pegs.
It felt/sounded like somehow the Center stand had fallen down. It got worse big loud clunks and clangs.
Pulling the clutch in stopped this...
I managed to limp home. It was selecting 1/2 no problem.

If I put the bike in gear on the stand the engagement on turning the back wheel it quite a lot.(can turn the wheel lots before it engages)

Also when at a stand still in first if you let the clutch in a aggressive manor there is also a loud clunk.
Same with shifting hard when ridding

Any thoughts? I will pull the uni joint boot off today and the gear select cover.

 

Others will be able to advise better on the gear box. What i would for now is try to trouble shoot a little;

• When you go from N to 1st, after you hear the click does the wheel spin then catch or do you have to spin the wheel a bit before you can select the gear? Its normal to have to spin the wheel a bit maybe 3 to 4 inches before you can select a gear sometimes.
• Pull the joint boot off and spin the tire while in gear to see if the u-joint is spinning. If its not spinning then the issues could be in your hub but i doubt it
• drop the oil pan down just to see if there is any visible damage floating in the pan, if you see plastic then it was your guide, prep to split the case, if you see metal... prep to split the case.
• Get ready for the possibility of re splitting the case for a better look

 

It engages first gear just fine and it’s instant.

I will take a short video after work.
I have a funny feeling it’s got something to do with the middle drive gear..
I reeealy don’t want to have to re split the cases again

 

Uni joint bolts....
Ones missing other 3 are finger tight.
Pulling the swing arm as we speak to find the missing bolt.

I’m very lucky I was only going 10-15mph when it let go.
I’m very surprised there isn’t spring washers on the parts manual for this.
I am almost tempted to get some longer bolts so I can fit some. Lots of lock tight too.

 

That's great news, glad it was something simple. loctite is important!

 

those bolts are harder than Chinese algebra, any old bolt won't work.
do they have a shoulder on them?

 

Yup but I had put the wrong ones in.
Found my bag of parts I had from the build. Bag labeled drive shaft.. my mistake

 

are there any threads left in the yoke?

 

Threads didn’t get damaged in the yoke luckily

 

Yeah glad you got it sorted out. I was worried you would be miffed about the parts I sent was the problem.

 

Me to it’s been a long time.
Appreciate it mate