Confirming my check....

[81gs1100]

OK, I think I know the problem but before I start on it I wanted to bounce some other opinions around.

The bike is a Yamaha XS1100, 1981 I think, anyways, year don't matter. This bike has been a nightmare ever since it came into our shop. If anyone has worked on this fuel piping they will understand what I mean. Anyways, I had dipped and cleaned the carbs, new jets and needle/seats, new boots. However the air box isn't exactly where it should be yet, air leaks here I know, but hasn't effected the idle or throttle that I have noticed. The bike accepts throttle pretty smooth till 6k or so, would rev higher maybe but its a customers bike and no reason to test the bottom end. Anyways....

Ok, bike is cold, temp outside about 45 to 50. Pull choke about half way, bike starts clean and quick. After a few minutes, choke off the bike idles around 1000 - 1200 rpm. Snap the throttle, bike revs and comes down quickly. Shut the bike off, put on gear for a test ride. Bike starts quickly without choke, idles good. Take off for a test ride. bike seems to run good, no bogging down, maybe a slight miss. (New Plugs) Bike does smoke but compression was pretty even in all 4 cyls. After about 3 miles or so at 45 MPH about 3.5 - 4k RPM I accelerate to near 6k RPM and the bike bucks and seems as tho the valves are floating, if anyone has floated the valves in a chevy 350 they know what i mean. 3.5 to 4k RPM and its pretty tame again sounds good throttles up and down. below 2.5k RPM the bike seems to fall a bit off with power. I went to the end of the road and turned around and the bike didn't want to idle, idle was about 700 RPM and kicks like it wants to die if you don't feather the throttle. Rode back to the shop again flawless between 3.5 to 4k RPM. I get to the shop take off me helmet as the bike was running to listen to the bike and it was quiet, no valve sound, no ticking, very quiet from when the bike was cold. The bike died as I tried to let it idle. I tried to start it and nothing, messed around and got it running but I had to slowly open the throttle while cranking as it was firing and trying to run till it finally did. Again let the bike idle and it died. I called the owner told him about the progress or lack of. About an hour later I started the bike, no choke and it started quickly again and idles fine around 1100RPM. And I could here the valves clicking faintly.

I recommended a valve adjustment...

I think the valves are too tight and when the bike warms up the valves arn't closing.

Is there anything I might be missing or overlooking?

Normally I would just check them anyways, but this customer flew off the handle when he got the first bill after replacing all the boots and carb kits. Now its like walking on thin ice. If he happens to pay for anything that doesn't improve the running of this bike he may shoot me.

Again the bike in the story is an 81 XS1100. A ton of miles, barn find, the bikes needs alot of work yet, we just want to make him satisfied so we can wash our hands and get his bad taste out of his mouth.

Thanks

[tom203]

Might just be erratic fuel delivery to carbs. Maybe bad petcock or a gas tank cap that's holding a vacuum with a plugged up relief hole. Barn find? the owner has to expect this kind of stuff. Lots of folks would just strip it and skip figuring it out.

[BassCliff]

Hi,

A barn find probably needs everything done to it. The customer should know that having a repair shop return every system to nominal condition can quickly cost more than the bike is worth. You might want to explain this to him. Sure, you can get it "running" well enough, but a couple months down the road will he be back screaming and yelling that your repairs didn't work?

Could it be a thermally intermittent ignition component, igniter (CDI?) or coils? Have you gone through the wiring under the fuel tank? Maybe a connector is melted and losing its connection when it gets warm. The valves should probably be checked, but I don't think it's causing your problem.


Thank you for your indulgence,

BassCliff

[81gs1100]

I have explained to him when he brought it in that it was not going to be cheep to fix and the chain of weak links are going to rob your savings account. but he said that he picked it up cheep enough that sticking money into it was ok. And he was ok untill after each repair the next in a chain of weaknesses shows up.

As far as the wiring goes the wires all look good, no brittle connections or wires. Al coverings are bright colored yet. I didn't see any signs of the wires to have been getting hot.

As far as fuel goes, this dual outlet, dual petcock, and all 4 pipes running to a transfer block to fill the 2 inlets to the 4 carbs all seem to be functioning properly. The gas cap could be clogged but that wouldn't matter as it does not make a tight seal. The idle never climbs as you would suspect with low fuel levels, or leanning out.

Like i mentioned the bike does run good in a wide RPM range, just after warming up in 3 or so miles at 45MPH the bike will not hold idle, will start very hard and feels like the valves float at over 6k RPM. Other then that is runs like it was when it was cold. I will be checking valves as soon as he can come in and give the ok to move ahead or if he is going to feel it is satisfactory to him and leave it alone.

I have had a ton of Grizzly 660s atvs come in that start hard and once started takes a while to clean up and idle, only to find the valves tight. Set the valves and they start quickly again. Thats what is bringing this idea into my head. I will also pull the plugs and see what kinda shape they are in. I'll let you all know what i found with the valves if and when that time comes. Untill then I love the ideas you all have.

[simon kuether]

Just as a little aside , there's a bloke down here that makes a chain drive conversion for them .

Cheers , Simon .

[koolaid_kid]

It is interesting that the RPM you mention is where that bike "comes on the cam" and should take off like a scalded rabbit.