Minds Needed For A Question

[Winterhawk]

For the last 2 weeks since I've been riding and working on my 1978 XS1100 with 36,000 miles. I've been stumped. I've spent about 40 hours on the XS1100 trying to figure out why the number 4 plug is dark and pretty much dry black. I've replaced the choke valve even. I pulled the exhaust hoping to find the exhaust port plugged. Nope. The decided to once again pull the carbs for the 15th time probably. What I found was the sync tube has slipped into the intake about 1 inch. Would this cause it to want to suck in extra fuel or restrict air? Bernoulli's Principle? A 1/4 inch tube 1 inch into the intake would have what effect? Can't ride it yet and need to bead blast the plug off first to see if this fixed it. It would also cut out and sputter at a 4 to 5 thousand rpm band with some throttle opening up. I think that this is the result of to much fuel gong into the 4 cylinder. Carbs are perfect. Compression is 160 warm. pickups good. fuel visible at 3 mm before joining surface with the float height set at 25mm. The other 3 plugs are clean. Even traded the 1 for 4 plugs wires so ruled this out. This bike was built at Merriam Cycle about 6 years ago and has performed great till now.

If this fixed it then we all could learn from this as it could happen to others. I think my tube pulled out a while back and I pushed it back in without comparing the height against the other 3

[renegade_xs11g]

Sound to me like

you should consider replacing those intakes.....JAT

[petejw]

if anything that would probably cause it to run lean,
as it would want to suck in air, id pull it back up and put
some sealant around it.
Is the engine blowing smoke or burning oil?, im running
my parts engine atm which has worn rings, either 1 or 4 would foul, if i had it running on the rich side.

[DGXSER]

Needle position? I had a similar issue with one a while ago. Mine are the 81 models with non adjustable needles. I had put the needle back in the wrong order (spring and washer on wrong side). Corrected that and the issue went away.

[thewiz]

Hmmmm ...

Seems unlikely that the needle position could have changed unless you've had that slide assy. apart and if so; recheck it.

But ... jet needles do wear ... that may cause it to run slightly rich.

[Winterhawk]

I was wondering if the tube in the intake could increase the velocity thus pulling the slide up sooner and or farther then the other 3 at given RPM and maybe coloring the plug. It's not the rings and it passed the leakage test with the same as the other 3 which are white. New jets and swapped the needle in #4 to be sure. Raining to hard to test ride it and will for the next 3 days.

[thewiz]

seems unlikely to me that ...

the loose tube could do that... I think it might cause a lean condition instead.

I think you could try to fire it without the airbox while watching the slides though, if you thought they were not all lifting equally.

Are the float valves all new or have you swapped any of them out yet?... and no chance of a slightly fuel-loaded float, right?

A few of us have had loaded floats before.

[Winterhawk]

I did run it with thhe airbox off on the lift. They all moved fine. The tube is very tite. I had to sqeeze pretty had with channel locks to get it back into the hieght it should be. It runs awsome on the lift. Just the black dry coating on #4. No leakage at the tube.

I think the mixture going around the 1/4 inch tube causes an increase in vellocity. Like more fuel mixture. Maybe it affects the slide diaphram height pulling more fuel from thhe needles some how. We will find out when ever I get to ride it.

[Winterhawk]

It's the best set of carbs I've ever built. I even check the fuel level height on the outside using see through tubing. New needles and seats. All jets, floats and other parts are mostly new Mikuni. The compression on number 4 was somewhat higher then the other 3. Hot, I got a reading of 168psi. I thought it was carbon build up causing higher compression level over 158psi that the other 3 registered at.

[thewiz]

see what you're sayin about the tube now ...

Maybe it is carbon ... while you're waiting for the rain to stop, maybe pour an oz of MMO down that hole and let is soak for a few days ??? That stuff eats built up carbon good.

[SFerinTEXAS]

Put clean plugs in 1 and 4, switch plug wires and see if it switches problem to no 1. May not be a fuel problem

[79XS11F]

It might be ... Dry carbon Fouling This is from NKGs site on plug conditions.

They show a photo of a plug covered in dry carbon and say ... Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.

Link
http://www.ngksparkplugs.com/tech_su...qs/faqread.asp

Rob

[Winterhawk]

Put clean plugs in 1 and 4, switch plug wires and see if it switches problem to no 1. May not be a fuel problem

I did this and 4 still reads the same. I am hoping it was the sync tube. Carbon, my high compression? We will see if the monsoon ever lets up. I need accell coils. 6 ohms with a resitor? I forgot?

[skids]

Would the sunk synch tube cause a rich condition of the plug? I say no. That tube should have nothing to do with richness. Maybe a sinking float, a leaking fuel valve seat, the need to vacuum synch the carbs, if it is a problem at low rpms then maybe an adjustment of the pilot screw, or problems with the exhaust ststem.

[Winterhawk]

I used a set of the K@L gages ( The cost a bunch)and used a vacuum pump to check calibration. Picked up that trick from this site. The mixture was set using Brady's from Merriam Cycles way of lean best idle setting. Turn them in till RPM drops, back it out slowly until the engine sounds like it's the smoothest. Then turn it in a little until there is no difference. Seems to work great. Wished I had an EGA machine to check hydrocarbons and co% of each individual cylinder.

Still frigging pouring out