If it runs like its lean, but its not

Hi all,
Back again with another issue (read:a real head scratcher).
Lets start with what the issue is;
The bike runs good, but the idle will stick at 3000 when the bike warms up. I can force it back down by ridding the clutch and it will eventually run at 900 (my normal preset).
Now this makes me think its an air leak, but i cant find it. The bike was not starting in the fall and i was push starting it a lot.
Here is what i have done so far:
*Valves checked (within spec)
*Compression checked (within spec)
*Spark plugs changed and gapped to .028 (all 4 look the same color)
*Timing checked (within tolerance)
*Carbs zestfully clean pistons drop with a nice thud sound.
*Carbs synced with manometer and port blocker.
*Air mixture screws set to 2.5 out.
*Sprayed WD-40 on all rubber parts with no change to high idle. (Worked when one carb boot had a crack in it 10 years ago).
*Airbox checked, filter looks good.
*No change in enviroment or altitude.
*Temp probe on 4 exhaust pipes and found that 3/4 run cooler than 1/2 and 2 is hotter than 1. I dont know if this is normal spec.
*Issue was not present when YICS port blocker tool was inserted. (checked for air leak here after sync).

Seriously cannot figure out where this is coming from. Im worried i have a crack in the engine, but i cant see and oil leak anywhere.
Ive had the bike for 10 years and getting to my whits end.

If anyone is in the LA area, or knows someone i could really use help. No shop will take a bike this old, or they want $600 just to clean my carbs.

 

That the problem went away with the YICS ports blocked tells me that the crush washers for the YICS gallery bolts need to be replaced, or that there is a crack in the casting.

Also note that WD-40 is not the same all across the country. There is a non-flammable version, and I think that's the only version sold in California now.

 

The butterfly seals on the throttle shaft is most likely source of air leak , you do not state carbs have been rebuilt , to replace you have to "break the rack" and pull the butterfly plate , there is an inner and outer seal . Xj4ever has the seals , when I did my carbs the old seals were rock hard . The other thing is the carb boot gasket , and are your boots weather cracked? A smear if RTV can help if you get real creative a bicycle inner tube attached over boot makes a good repair.

 

re-sync without that yics tool

 

If the WD-40 is flamable or not wouldnt it still block up minor air leaks for a moment to let me know where the leak is?
The washers seem to be intact but i will check again.

 

Honestly have never broke the carbs apart, ill check those seals with my WD-40 trick.

 

Nope.

The crush washers are meant to be a one-time use thing, thouhg they can be reused a few times without issue. The thing is that you don't know how many times they have been used. There have been a few cases of a PO overtightening the plug and cracking the casting. Inspect carefully.

If all is well there then the throttle shaft seals are the next (and honestly most likely) candidate for the cause of a vacuum leak. The trouble is that the seals might be fine at idle, but leak as the throttle plates are moved. You might not find the leak by using a spray cleaner or propane, which is why I tend to reccomend replacing the throttle shaft seals as a matter of course. The seals are cheap, and having the carbs apart more than once is a real bother.

 

I thought that was counter to how the bike us meant to be tuned.

 

Hardly anybody uses the tool. There is so little difference between using it and not using it that it's probably only necessary if you were ever to need to pass an emissions test.

 

way back here

exhaust pipe temps are ok but there's too many variables to really be useful.
the tool changed something, but, you don't have it going down the road. you want it to be right while your riding so you tune it that way

 

I recently had the same issue . I replaced /installed new [chacal], 4 mixture screw o-rings, 4 mixture screws, 4 mixture screw springs, 8 throttle shaft seals, and fuel rail o rings while I was at it. and poof my my problems went away.

 

https://www.xjbikes.com/forums/threads/yikes-all-about-the-yics-system.14757

Executive Summary/important points to consider:

An Insight From One Who Knows:

To review:

According to Yamaha, the function of YICS is to promote more complete combustion at low to mid-range rpm by swirling the mixture around the combustion chamber. They never made any direct power claims -- the system was promoted as increasing mileage up to 10 percent and promoting lower emissions through a cleaner burning charge. The increase in mileage was not through leaning out the mixture -- the increase in mileage and reduction in emissions was because less throttle was required to maintain cruising speed. They could use the same cam timing, jetting, etc. (for performance) and still meet EPA regulations. Yamaha stated that the greatest effect was while cruising at 50 to 60 mph.

The swirling accomplishes two tasks: first, it assists mechanically in atomization of the fuel and second it speeds and distributes the flame front (and therefore combustion pressure wave) more evenly throughout the cylinder. The later "Genesis" (water-cooled "X" engines) design accomplished this even more effectively through the 5-valve design, which accomplishes the same task through a wider rpm range.


To blank or not to blank (during engine synch), that is the question: Ok, what is the function of synchronizing? Manufacturing tolerances and wear. Multiple carbs offer the advantage of increased power and performance over the single carb configuration for reasons beyond the scope of this discussion. But at a cost.....

As each carb is dealing with a fraction of the total air and fuel flow requirement, each carb must meter things in fractions of the total. That makes for some very tiny tolerances. In effect, we have 4 separate engines -- and if one is fighting the others, then we are wasting power and fuel and are worse off than we would be with a single-carb setup! So it is crucial that each one be perfectly adjusted and that all 4 then be synchronized to work in perfect harmony.

So, how can we reliably adjust an individual carb based on the results of the adjustments, if it's companions are contributing to the results? Now, to be fair-----if the bike has been reasonably well maintained and the cylinders are all fairly close to begin with, you can usually get away without blanking the YICS passage and still achieve a reasonable state of tune. At the opposite end of the maintenance spectrum, the YICS passages are often already plugged up with years worth of accumulated grunge and grime, so the bike is effectively being tuned with the YICS system disabled and the presence of the tool is irrelevant. But we have seen some examples of carbs where one cylinder was effectively relying on it's neighbors to supply most of the mixture through the YICS system, and this most certainly affects performance, especially the top end.

So, my recommendation: for an engine with approximately equal compression across the cylinders and valve clearances in spec, make sure the YICS passages are clean and use the blanking tool to tune the carbs.

 

Bump, bump bump.

Ok boys and girls. Two weekends to change the throttle seals. And Guess what..... The throttle still hangs.
I swear the carbs could not be more clean, the rubber manifolds are near perfect. Valves are great, spark plugs new
Im at the end of my rope here. About to part out the bike and go buy a royal Enfield.
Someone please talk me down off the ledge.

 

Oh sorry, also replaced the feul mixture o rings while i was at it.
So i ask again, if it runs like its lean but its snot.

 

Remove the throttle and choke cables. Work the throttle linkage by hand.
Does the idle still hang?

 

Yes sir. I have discovered a strange one though. If i i keep the RPM below 3000 when its warm it wont hang.
Now one would think this is a faulty (sticking) float piston. But all i can say to that is the clunk test passed on all 4 without issue.
And yes all 4 butterflys swing back nice and quick.

 

So it hangs when you first start it......you choke it to start ....after warm up......you back off choke and it is hanging at 3k ????

We need more info

 

Yep,
Read the initial post.
Bike acts fine, all typical items have been checked verified or replaced.
It does not hang at 3000, the throttle in general hangs as if the bike is running lean, but only if and when I am riding it and i pass the 3000rpm threshold.
Outside of that i have the idle set at 900rpm (ish).

 

Check the fuel levels in the bowls.

 

Hmm, i did a bench level check. I could do a drain tube level check in the morning.
Are you thinking the feul is being restricted?