xj550 valves need adjusted?

hey, im new here so bare with me.
My buddy dropped off his '84 xj550 to work on (ive rebuilt an xs650 and a harley so he thinks i can do anything. eye roll)
but he was having trouble with it "losing power when it gets hot". which i was guessing it was a valve issue
im going thru it and checking most easy things off the bat. cleaning carbs, setting cam tension, new plugs, etc
the bike is showing decent compression. 125, 125, 113, 112 psi.
but the valves are slightly tighter than the recommended range:
cylinder 1: exh=.13 int=.12
cylinder 2: exh=.14 int=.12
cylinder 1: exh=.15 int=.10
cylinder 1: exh=.14 int=.08
(book says exh=.16-.2 int=.11-.15, correct?)
my question is: since the bike has decent compression, and the clearance isnt TERRIBLY far off, do you think its fine to leave the valve clearance alone? or do i have to change shims slightly on all valves.
yes, i realize im being lazy/cheap.
thank you for any help

 

Welcome to the forum, you found the right place.

You’re either in spec or you’re not. No grey area there. Get them in spec and report back. Valve clearance is number one before you start any other tuning. Shims are cheap and even cheaper when you trade in on the pool.

 

Compression looks low to me - I'd expect 140-150 I think.

 

cylinder 1 and cylinder 2 intake clearances are in spec.
i assume its a typo, for cylinders 3 and 4, saying cylinder 1 and cylinder 1

 

Yup, my mistake.

Ok. Took out the shims, wrote down what size they are, put em back. The clearances are now reading within spec or .02-.01 mm tight. I think I'm guna run with it and change them next year. Or once I get this thing running
But changed out the valve cover bolt washers, put clean carbs back on and bolted down the valve cover to ~7 nm.
Now the compression is reading 55, 80, 120 and 80.
What would cause the compression to drop so much by only reading the shims? I didn't trade the shims or replace them and they're showing decent valve clearance.

 

How are you doing your compression check?

 

With my harbor freight compression tester. Throttle wide open. All plugs out, ignition module unplugged. Crank it till the needle stops moving. Yea its a cheap tester, but it gives repeatable/constant results
I did put a little oil in 2 holes. Compression raised ~20 psi.
But it was giving decent numbers 2 weeks ago, so I was thinking rings were fine. They can't cause a problem without it even starting, can it? Was thinking maybe a lack of oil in the cylinder from not running in a while would give low numbers?

 

tighter the shim the longer the valve stays open which would lead to low compresion
"losing power when it gets hot". which i was guessing it was a valve issue
when shims get hot they expand making them tighter

valve clearances are the first thing to correct as it affects the the compresion and tuning. if you do the shims after tuning you have to tune again.
you should be able to swap around some shims to correct clearances and get the ones you have to replace,

cylinder 1: exh=.13 int=.12
cylinder 2: exh=.14 int=.12
cylinder 1: exh=.15 int=.10
cylinder 1: exh=.14 int=.08
(book says exh=.16-.2 int=.11-.15, correct?)
all your exhaust are tight and 2 intake are tight

125, 125, 113, 112 psi.
55, 80, 120 and 80.

shims may not be seated correctly

 

Nope it was relling you you had low compression 2 weeks ago, now after you played with the shims its worse.That tell me you need to go back and check your work.
note that stuck rings can cause low compression too so get it running and see if they 'unstick'. Failing that it's a top end strip.

 

Okay. So buttoned it back up. Compression is 130-145 on all 4, so looking good there.
Put some fuel in it and started her up. Adjusted the idle screw to ~1000 rpm.
So I'm doing this with the tank off, funnel on the fuel line and my thumb plugging the vacuum line. Itll idle perfectly and sound real good. I give it a blip of gas, idle increases, hangs a second, then drops back to 1k. Give it a little more throttle and it revs to 3k rpm and doesn't drop until I take my thumb off the vacuum, then it drops back down to 1k. Whys it reving all the way to 3k and getting stuck there? Throttle butterfly valves out of sync?
Taking these 4 carbs off to resync is a pita

 

use a golf tee to plug your vacuum hose.
start by checking the routing of your throttle cable and that it is properly lubed routed and adjusted.
are you using the choke lever ? with that on rpms will go to 3 k as motor warms. up

to set idle motor has to be fully warmed up. setting idle cold will result in idle climb as it warms up

get your self a lawn mower tank to use as an ax fuel tank not a funnel

 

when you bench sync carbs and install you will find that your idle will be high.
start bike with choke and as rpm riseslowly back off the choke keeping rpms around 1200 untill you can completly shut off choke . then if needed adjust idle knob.
during this process do not touch the throttle

 

good idea on the golf tee, ill have to try that.
throttle cable is smooth and operates just fine.
i start out with the choke, but it doesnt take long before i need to unchoke it. My last post was when it was warm, and unchoked
next time its all together, ill set the cold choked idle at low rpm and turn it down as i start unchoking it. but, there wasnt much room to lower the idle, the butterflies were basically closed.

last night i took the carbs off and broke them down again.
i didnt replace the throttle valve seals earlier, so im planning to do that this time around. Thinking that might be an issue as theyre decently crusty. It seems like all the screws/bolts on the carbs are welded on. (yes im using a jis screwdriver) i stripped half the bolts on the rails, an air screw, and some of the screws holding the butterfly valves on. I need to figure out how to remove those butterfly valve screws... i can tell that wont be easy.
and i need to order throttle valve seals and butterfly valve screws.
this has turned into quite a headache for just helping a friend out.

 

Not unusual for a hanging idle if the carbs are out of sync. The mechanical sync will get you close but you have to do a running sync with a vac sync tool to get it dialed in right and proper return to idle. You can literally hear the engine sigh and settle down when you finalize that process.

 

the 550 butterfly screws are peened so you have to file the ends down a little so they will come out

 

update: got the butterfly valves off, changed out the throttle shaft seals, and got it all back together with new screws.
put it together, fuel line and carb was leaking.
take carbs off again to put in a new fuel line with fuel filter.
put it together. after letting it warm up, and setting the idle, it ran great. probably put 15 miles on it last night.
check it out this morning, there a small seeping fuel leak dripping off the connection between carb and airbox.
floats not set right? im so close....

 

I suspect you're missing an important step - the wet set of the float bowls.
This is done before you mount the carbs back on the bike.
It verifies 2 things, float bowl fuel level and that the carbs are shutting off when full.

Make certain the fuel has not contaminated the engine oil.

yep.
but you are close, keep at it.

 

Update: broke it down again, took off the carbs, dry set the carbs based off one that i knew was correct, then wet set them. carb #4 was still reading way high (top of the intake mani). so after beating my head against a wall, I broke it down and switched out the o-ring on the intake seat thing. seemed to do the trick, so i changed the other 3 orings. rebuilt the fuel line with a new inline fuel filter, new line and new clamps.
there was still some rust in the tank, so broke that down, and gave it a second 3 hour soak in muratic acid, flushed it good, then coated it in wd40. got most of the rust out.
slapped her back together.
she fired right up and ran PERFECTLY. rode it 25ish miles around town. did a final oil change, fresh tank of 91 ethanol free gas, and even took her to the car wash.

took her to the grocery store, came outside and that new tank of gas was all over the parking lot... F*CK.

took the fuel line off and the petcock was just pouring fuel with no stopping.
whoever designed a petcock with no OFF feature is a real dipsh*t.
took the airbox off and could see that carb #1 was leaking fuel out of the intake, into the airbox and onto the ground.
im assuming a little rust blocked the petcock open, and carb #1 seat.
any advice on preventing rust from ruining my day, again?

 

Get an inline sintered filter to help prevent that. You should probably think about rebuilding the petcock so it doesn't leak gas to the carbs too. The last rebuild I did, I reassembled to petcock on the tank, put gas in, attached a hose to the vac nipple and a fuel line to the gas output and ran it to a gas can. By sucking on the vacuum line I would get fuel flow, stopping suction would stop fuel. That is the final test.

 

If the tank is full of garb, you might want to address that too.