XS1100 looses power

[xsryder]

Hi group,
I have owned, maintained and restored several XS1100s.
My current XS11 is a 1979/80 hybrid. Two years ago I bought a running 1980 bike primarily for the engine, seat and tank, and had it fully serviced, including carb overhaul and cam chain replacement before I totally dismantled it, and have spent two years building up a fully restored machine pulling together the best parts of several bikes.
The roblem is that since I finished the rebuild, the engine runs out of steam at about 110kms. The strange thing is that it goes like a scolded cat up to that speed, but then feels like it has run out of gas. The local Yamaha dealership have been working on it off and on for three months, and have thrown in the towel saying that they just can't pin-point the poblem.
I have fitted new inlet manifolds, new carb diaphragms, carbs overhauled and balanced more than once, plug caps changed and timming light shows seemingly correct advancement.
It idles nicely with good throttle response, and the drop of the clutch is as exciting as ever, especially with the sidecar attached because the home-made wheels are considerably smaller than the standard 19" alloys and the altered gearing easily lights up the tyres.
But as soon as I get to the outskirts of town and my speed increases to around 110kms, the engine loses power and I am forced to pull over and wait for revs to rebuild before I can continue. The engine doesn't miss-fire or blow smoke, and has good compression across all four pots. The engine is in good condition and set up as a sidecar has gone over 170kms/hour and has been timed at 15.5 seconds quarter mile (with out second gear). There is something very simple preventing this engine performing as it should, and the local Yamaha dealership and I have run out of ideas...can any one help?

[81xsproject]

try opening the gas cap. the vent might not be doing its job

[prometheus578]

Not to question the work of other mechanics... have no idea what they have already tried, but I'll play your game.
Bike runs fine... but then as speed builds, it dies, and then must wait for RPM to build up before continuing onward.

Reduced fuel flow from the tank, pinched or collapsed fuel line. Bike runs fine when there's lower demand for fuel. As one goes faster and drinks down more fuel, float bowls run dry as fuel can't get in fast enough to replace the loss. On the side of the road at idle waiting, bowls fill up again and off you go.
Sure, it's a long shot...
Sure, it doesn't happen often...
But it sure was what was wrong with the bike I was working on yesterday. Took me a while to catch it, too.
(Ok, not a while... rather quickly... I mean, I'm a Guru, after all)
Next time the bike loses power, shut it off. Immediately drain the float bowls and see how much, or how little, fuel you get out of there.
Clogged vent in the gas cap can do the same thing, allowing a vacuum to form in the tank, slowing or stopping fuel flow.
Maybe your bike just doesn't like having a sidecar attached. I'd explore that, too. One never knows.

[xsryder]

good comments

Thanks for comments guys.
Years ago I fitted in-line fuel filters to another XS1100, and when I took it for a test ride a similar think happened, and I quickly realised that one of the fuel lines (extended to accomodate filter) developed a kink as I lowered the tank into position. I simply rerouted the line and all was well.

On my latest XS1100, there are no kinks in the line (that was my first thought), and no, the side car doesn't make any difference. I've clocked up many thousands of Kms on several XS1100s with out without the chair. The smaller wheels alter the gearing to a point where there is very little difference in mid-range performance, but of course a decreased top-end speed.

We all agree that fuel delivery is most likely the problem, and I was even going to remove my taps from the tank to make sure there was no excess sealer reducing the flow. But I'd bet my bottom dollar that the breather is the problem.

Excuse my ignorance, but does the 'S' shaped tube which goes from the fuel cap resess to the rear of the tank serve a duel purpose? (both drain tube and breather) If this is the case, then perhaps the painters have have sprayed too much paint around the resess and it has run down and blocked the tube.

BTW-I had a lot of trouble finding a fuel tank that wasn't affected by rust. Over time the drain tube blocks in the bend; water then sits in the fuel cap resess; rusting away the resess; and if the water gets into the tank, rusts away at the inside of the tank. On my previous bike I used wire, chemicals and compressed air to clean out drain tube, and even considered having it cut out and a new one braised in.

[Ken Talbot]

The tube from the fuel cap recess has only one purpose, to drain that recess of rainwater, spilled fuel, etc. It does not vent the tank.

[TopCatGr58]

Hey Wayne,

Have you ever taken apart the gas cap, the 3 screws that hole the metal part that holds the rubber gasket that seals it? The Yamaha Exploded view for both the Standard and the Special don't show the little washer with a pinhole in it that is the vent hole in the cap. It can get clogged from rust, fuel varnish, etc.!

Also, your profile states your machine is an 81H? No matter, you shouldn't need to remove the petcocks, but just put them in PRIME mode, and see if you can reach the required speed! IF so, then the petcocks are not flowing properly, which can be due to several problems depending on what kind you have, the vacuum controlled ones of the standard, or the gravity style of special that uses the Octopus vacuum valve. With the Standard vacuum style, the vacuum plunger can be not opening due to vacuum leak to it, corrosion, a leak in the diaphragm, etc.!
Good Luck!
T.C.

[xsryder]

Thanks for good feedback

I phoned the bike shop this morning and told them about the suggestion of opening the fuel cap. They phoned me half an hour later to say that made no difference.
I picked up my bike this afternoon and brought it home, and tomorrow I'll ride to Morrinsville about 30 minutes away to see a freind who has the same model XS, and hopefully we can swap fuel tanks and lines.
However, riding my bike home today through town, one wouldn't think that there was any problem at all because it goes so well. But we all know that XS11s aren't designed to putt around town at 50kms per hour.
If the fuel tank swap makes no difference, then I will start swapping other parts. I have a spare set of coils and 5 spare CDI units (4 have been modified for a speedway bike. Not sure if the mods are to limit revs or accomodate the 'lumpy' cams though).
So far the mechanics have tried;
new inlet manifolds
new diaphragms
new plugs
new plug caps
carb overhaul and balance
removal of air intake rubber
removal of seat.......and engine still loses power over 110kms (without sidecar).
I still feel it is running out of gas, and I might just buy a couple of feet of new fuel line tomorrow. It has taken me two years to finish the restoration, and I reckon it would only take a spider web in one line to affect fuel delivery enough to cause such a problem.

[81xsproject]

Swapping tanks sounds like a lot of work as opposed to just riding it, and opening the cap. You should tell us what the number stamped on the motor is too. Like TC eluded to, the 81SH did not have the tank with the recessed cap. Standard tanks have those, not specials. Then, we can help you, help us, help you by figuring out just what year/model you have so you can post it in your signature. Lastly, enough people here have experienced the vent problem first hand that, at least on this issue, the folks down at your shop are full of it.

[prometheus578]

81xsproject,
I think XSRyder meant that he phoned the bike shop, they tried it, and phoned back later saying that it didn't change anything.
Oh, I feel sorry for those guys... every once in a while, ya run across machines like this.

[DiverRay]

Don't forget the VENT LINES if you have the '79 carbs. I would also check the seat for the needle on the carbs. If you have the screen on them, and junk in the tank, that could be a problem that would NOT be found, as the carbs have been "cleaned".

[81xsproject]

I think, after a re-read, you are correct, Prom. Was trying to make that not to offensive for you . I have never had my bike in a shop. But, my truck has. And being moderately knowledgable about it, I have been extremely offended a couple times when I was treated like an idiot for trying to give useful background info. It is just like medicine. Good docs listen very carefully to what patients say. On first read, it sounded like they just blew him off. My bad

[pggg]

Ryder, must be fuel starvation with those symptoms, should be easy and simple to fix. Dunno what that Hamilton bikeshop crowd have been smoking, try with the petcocks on 'prime' and ride it. Any change? If not, tear off both petcocks, strip em' and check things out in there. Are they 'standard' or 'special' petcocks? Octopus or not? The 2 breather hoses from carbs to airbox, not kinked or blocked somehow? Not running pod filters? If yes, they could be blocking the air jets if they're not a perfect fit. Getting to the electrical side, the pick-up coils and their wires can be dodgy, but it sounds like fuel starvation to me, but keep posting as to what's happening. Cheers.

[xsryder]

chequered history

I bought my second XS in 1994, but although its papers stated 1979 XS1100F, and Engine and chassis numbers both 2H9-110424, it had been modified heaps with a sidecar, leading link forks, home-made wheels, many parts missing, and even the wiring loom appeared to be from an H rather than F model. The previous owner had also experimented with a twin carb set-up, so I wasn’t even sure if the mukini carbs were original items.

Then in late 1998 I ran into the back of a car in town and bent the frame at the steering head. The replacement frame was from a 1980 XS1100G with the number 8X1-000628. There appeared to be no difference at all with the frames, and in fact the only difference I could find overall, other than cosmetics, was the fact that the G model wasn’t fitted with a kick starter and shaft.

Once I got the F bike reassembled around the new G frame, I had perhaps the best bike I’ve ever owned. I had fitted new 0.5 over sized pistons, rings and gudgeons, new primary drive chain, under-cut 2nd gear and new 4-into-1. Then in 2001 my partner’s X-husband poured some engine-destroying substance into the oil reservoir while I was parked at her house over night. So then I needed another running engine. *#!%*

In late 2004 I bought a complete running bike for $1,600, with the engine number 8X1-000611 (very close to my G frame number). The steering head was dangerously out of alignment and it was running rich, so I took straight to my Yamaha dealer to have the engine serviced, including new cam chain and inlet manifolds. Then once I got it home I completely dismantled the bike, and built a whole new bike from the ground up using the G frame that I already had, and the engine, tank and seat from the new one. I'm never really sure what model to asign to my bike, because it's assembled from F, G and H parts.
To be honest, I’m not sure if the carbs are from my original F model or the 8X1-000611 G model I bought in 2004. I didn’t think there was any difference. If you want to check out large images of my bike(s) check out xsryder.spaces.live.com