Compression and/or fuel problem

[stay948]

82 XJ100J, 39652 miles, last rode 2 years ago.
I've been working on getting her running again. Took her to a local Yamaha shop when I had no success. They got her running, but low range power weak until 3k rpm. Determined I had an octopus issue; cleaned it up, installed new fuel lines. With gas in all float bowls, she ran good for about 20 minutes. I was unable to get her started after that.

So, I checked and readjusted valve clearances, and checked compression. Here are the results
#1 intake .005 exhaust .008 compression 160
#2 intake .006 exhaust .009 compression 150
#3 intake .004 exhaust .010 compression 130 (with added oil 150)
#4 intake .006 exhaust .008 compression 165 (fluctuates 165 - 170)

#1 plug carbon from running with choke on.
#2 plug the same
#3 plug clean
#4 plug clean

When I did have her running, #1 & #2 exhaust gases were warm-hot, #3 & #4 exhaust gases were cool-warm.

I've synched the carbs as best I could--can't keep her running long enough to get to temp and hold idle. Float levels are too low, but once I get her running steady I'll clean that up. The shop pulled and cleaned the carbs. I did it again when I determined I had a fuel problem.

The shop put in new plugs. I've tested and I'm getting spark to all cylinders.

She runs like she's firing on #1, #2, most of the time #4, and #3 if I can get the rpm up.

I'm thinking valves and/or rings, but I'm hoping I'm wrong.

1. What have I missed?
2. I live near Chattanooga TN. Anybody nearby, or know of a good mechanic/shop in the area?

Scott

[donebysunday]

Try draining the float bowls into a clean cup to see what is in there.
I suspect little specs of rust and or little bubbles of heavier than fuel water globules in the fuel at the bottom of the cup ?
I check mine occasionally but I should check more often, been lucky, so far. When putting a long sitting bike back into service the new fresh fuel slowly dissolves the residue and can cause problems for weeks or longer. This can go on simply because even cleaners take out just the surface and seem to have cleaned things fine but the problems persist until the old fuel is gone.
Not to be funny, I use a small can't believe it's not butter container cut down to about a inch and a half tall so that it fits under the carb/s and one at time drain into this, check what comes out.
If you have debris in that fuel pull the bowl and if need be get a auto vanity mirror so you can see to pull pilot jets and clean them. Pull the paper/plastic off a bread bag tie wire and use it to carefully push the plug of debris out of the jets orifice.
Put a bottle of Techron in the tank with fresh fuel and leave it to dissolve the crap in the tank for a couple weeks or as long as you can stand to wait. Drain contaminated fuel into a container for disposal.
LUCK TO YOU ! PATIENCE TOO !

[TopCatGr58]

Hey Stay,

The comps aren't bad at all, and could partly be due to 2 years sitting, stuck rings and possibly just needing running a while to RESEAT THEM, #3 intake is a smidge tight, but that shouldn't keep you from getting the bike running. But clogged carbs WILL, and even though the bike shop cleaned them....the pilot circuits are very small and easily clogged, and your poor throttle response below 3K points to them still not being clean.

Secondly, unless you have the YICS block off tool, you won't be able to get the carbs synced anyways, and just having them staticly bench synced again should be all that's needed to get it running.

When you cleaned them, did you put in new jets, and if so...did you get jets from a K&L Kit or such? These bikes/carbs don't like GENERIC jets, they are sized/metered incorrectly, and can easily cause excessive rich conditions=black sooty plugs. Ensure you are using GENUINE MIKUNI jets.

T.C.

[stay948]

Compression and/or fuel problem--follow-up

My thanks to both TopCatGr58 and donebysunday.
I finally got back to working on Lucille last weekend. I pulled the carbs, did a complete teardown and soaked all the jets in injector cleaner for about 4 hours. I took those disposable dental picks (soft rubber or brush tips) to every thing. Once I reassembled and reinstalled the carb, I fired her up. Took a little patience,perseverance and priming, but when she did kick over and warmed up a bit, she ran good. She was firing on all four and I was getting hot exhaust out of 3 & 4 cylinders.

Then she died. I still seem to have a fuel problem. I've checked the petcocks and fuel flows freely from both. I had installed new clear fuel line, and could see fuel filling #1 & #2 tubes to the octopus. Lines #3 & #4 have inline filters installed, and I could see fuel flowing through #3, but not through #4. Took the octopus apart, cleaned it, backlit the diaphrams to check for pinholes and tears -- they looked good, compressed air through all ports--no blockage that I could find. Reassembled and reinstalled; still not showing fuel getting to #3 & #4 carbs. Priming works to fill the carb bowls because I've crossfed the priming ports--left petcock feeds # 4 line while right petcock feeds #3 line (I didn't like the way the lines kinked when connected IAW manual). I re-primed the bowls. Must have left the prime open too long because I began to leak fuel out of the airbox. Shut off the fuel flow, cleaned everything up, and called it a day.

So, what could be preventing fuel from getting to #3 & #4 carbs? Any thoughts or recommendations?

Thanks,
Scott

[tcoop]

I had a set of carbs that had white chalky build up in the fuel inlet "T" that prevented fuel from getting to the carbs. I had clean the carbs several times (Didn't separate the rack) then finally noticed it.

Else it could be your floats are stuck, rubbing on a gasket.

[DiverRay]

Going on what tcoop said, take your dental pick on the 3/4 pair, pull the needle/seat from the carbs, and reach up with the pick and push, scrub, and clean as far as you can reach on each carb. Then try going from the "T" and push the pick into each carb to clean it. You can also take a ziptie and do the same, see if you can push it through into each carb body. That should take out any buildup in the "T" area. Rinse by spraying carb cleaner and you should be good to go.

[stay948]

Lucille lives--sort of

My thanks to all for their suggestions and advice.
Updated status: I've lost track of the number of times I've pulled, cleaned, and reinstalled the carbs. At one point I removed a piece of 'damned if I know' from the fuel T to #3 & #4 carbs. Then I had fuel leaking through the airbox all over the place. I replaced all floats (plastic), new needle valves and seats, and all jets with new Mikuni parts. The new octopus was not shutting off the fuel flow with the motor off, reinstalled the old octopus and that seemed to fix that.

Now: Lucille starts on full choke with #1, #2, #3 cylinders firing and airmix adjusted blue with colortune. Stabilized idle at 1100-1200 rpm, no choke. Colortune showed #4 cylinder sparkplug firing, but no gas at idle (spark against black). Increase rev's to 2k-3k rpm, #4 starts firing, color blue, with intermittent yellow/white flash and backfiring. More revs = more backfiring.

Let Lucille run at 2k rpm for about 20-30 minutes. At the end, colortune was blue with less yellow/white flash and less backfiring. Now seeing blue with intermittent black and occasional yellow/white flash.

FYI, I do have the YICS tool installed but haven't attempted to re-sync the carbs as yet.

My immediate plan is to run Lucille again tomorrow to see if any further improvement is generated.

My question is--what else am I missing?

Thanks,
Scott/stay948

[DiverRay]

Throw out the colortune!
Install the YICS tool and do the sync BEFORE trying to do anything else. Carb #3 is the carb everyone else syncs to. Hook up your vacuum gauges/sync tool. If you are using a 4 gauge system like I do, put a "T" between gauges and verify that they all read the same. If they don't, and there is no adjustment, note what gauge is off, and by how far. PUT A FAN IN FRONT OF THE ENGINE TO KEEP IT COOL WHILE WORKING ON THE SYNC!
Adjust 1&2, then 3&4 together, then adjust 2 to 3 and recheck all 4. When close, you then need to adjust idle mixtures. Pry all 4 plastic caps off, if they are on, set the idle for about 900-1000rpm, and starting at #4 S_L_O_W_L_Y turn the mixture screw about 1/8 turn, watching the idle speed. You want to have the idle speed go up as much as possible. It will start to drop once you get too rich. Re-adjust the idle speed down and go to #3, then #2, and #1. When you are done and it idles at about 1K, re-check the sync on all 4, as it may have changed.

[TopCatGr58]

Hey Stay,

Sorry, but #4 isn't getting fuel from pilot circuit, that's why no color until you open it up to 2K+ rpm, then it starts sucking on the mains, then you get it warmed up, so it needs less fuel to keep running, but still isn't getting enough fuel from the pilot circuit.

Could be a vacuum leak, but thinking pilot circuit is clogged in #4 carb. The higher rpms generate more vacuum than idle and pulls the vac slide up some letting some fuel get in from the main jet.

T.C.

[motoman]

Throw out the colortune!
Install the YICS tool and do the sync BEFORE trying to do anything else. Carb #3 is the carb everyone else syncs to. Hook up your vacuum gauges/sync tool. If you are using a 4 gauge system like I do, put a "T" between gauges and verify that they all read the same. If they don't, and there is no adjustment, note what gauge is off, and by how far. PUT A FAN IN FRONT OF THE ENGINE TO KEEP IT COOL WHILE WORKING ON THE SYNC!
Adjust 1&2, then 3&4 together, then adjust 2 to 3 and recheck all 4. When close, you then need to adjust idle mixtures. Pry all 4 plastic caps off, if they are on, set the idle for about 900-1000rpm, and starting at #4 S_L_O_W_L_Y turn the mixture screw about 1/8 turn, watching the idle speed. You want to have the idle speed go up as much as possible. It will start to drop once you get too rich. Re-adjust the idle speed down and go to #3, then #2, and #1. When you are done and it idles at about 1K, re-check the sync on all 4, as it may have changed.

As Ray stated, toss that colortune and set idle mixtures 'lean-drop' method. From mixture screw being out a ways, start in till sound changes and stop. Back screw out 1/8th and no more than 1/4 turn. Do other three the same with re-setting idle each time to 800-1000rpm. THEN sync the carbs......and done.