Loss of power under load, revs fine in neutral

[oakback]

I haven't ever had this bike driving in normal/good running condition, so I can't say how the problem developed. I bought it a year ago and have been trying to get it running the past few months.

It'll start great, and rev fine in neutral. When I try pulling out of my driveway it bogs hard, and sounds and feels like it's running on 2 or 3 cylinders. Sometimes I can get it to drive down the street and back, not getting over 20mph, other times it won't move at all without dying. If I can get it to drive, it'll steadily get worse, then eventually won't hold idle. I'll pull into my driveway, crank it up again, and it'll run perfectly while on center stand in neutral. It's frustrating as hell.

I've cleaned gas tank and lined it, cleaned out the petcocks, replaced fuel line with new filters, cleaned the carbs several times, set the idle screws to 2 1/4 turns, verified spark on all cylinders, the pickup coil wires are not broken, I've verified continuity all the way to the coils, snipped ends of spark wires, replaced a rough-looking spark boot with new NGK, new spark plugs, replaced a float valve needle (new from mikesxs) that didn't have the spring to the bumper, replaced a valve seat (new from mikesxs) that was stuck in the carb (mangled it getting it out), replaced all float valve seat o-rings with viton ones, set float height to 1", drove with the gas cap open in case the vent was faulty, tried running it both with factory air box with new filter and pods, still runs the same.

Whenever the carbs are empty (after reinstallation), it seems like one or 2 floats always get stuck. It takes a bit of tapping and they loosen up. At least I think that's what's happening, since it'll leak out of the intake, then stop after tapping (with a soft mallet). Not sure if that's normal or if that means anything at all.

Even though I really don't want to, I'm at the point where I'm going to take it to a mechanic. But if anybody mentions something I can try, that I haven't already tried, I'll give it a shot.

[TopCatGr58]

Hey Oak,

Okay, first thing that catches my eye is your float height...too high!! The spec you quoted of 1" is very close to the 25.7mm height...which is the 78-79 spec....the 80-81 spec is 23mm...along with the newer technique of using the float bowl drain plug clear line and actual running fuel level height check=PITA IMHO. Also, the sticking float from empty is sorta common, but you can reduce that some by both shaving the inner edge of the gasket with a razor, but also adjust the float DROP tang to prevent it from dropping opening too far so that the float needle will not drop too far allowing it to get wedged/cocked diagonally causing it to stick!

Next....just to confirm....you say you've cleaned the carbs several times.... but many have stated that only to find that they did NOT disassemble them properly enough to be able to get the pilot jet and the main jet needle/emulsion tube and all of their aeration ports opened/cleaned..so that remain clogged which prevent proper fuel and air flow processes.

Along with the carbs....have you checked and verified you do not have any pinholes in the vac. slide diaphragms??

Now...even though you say you have SPARK on all 4 cylinders....you may or may not really have it under compression. What do the spark plugs look like? Any dark sooty/fouled. While running, take some water and spritz the headers and see if they ALL sizzle, or if any are cold. IF there are cold ones, and they are paired...1-4 or 2-3 then that can point to electrical problems....like a WEAK coil that can fire in AIR but not under compression!?

WHATEVER YOU DO, DO NOT TAKE IT TO A MECHANIC....that will just be good money WASTED! Your best bet is to trouble shoot HERE on the forum, WE can help you get it working much better and far cheaper than any Pro Mech/SHOP!

Back to the carbs...are you using OEM Mikuni jets/parts? You mentioned the float needle seat from Mikes....did you also get Generic jets from them? We have found/learned over and over again that our carbs do not do well with GENERIC jets...they are designed differently and just don't provide the performance of GENUINE MIKUNI pilot and main jets!

Okay, that will get you started, test and report back your findings!!!

T.C.

[oakback]

Hey Oak,

Okay, first thing that catches my eye is your float height...too high!! The spec you quoted of 1" is very close to the 25.7mm height...which is the 78-79 spec....the 80-81 spec is 23mm...along with the newer technique of using the float bowl drain plug clear line and actual running fuel level height check=PITA IMHO. Also, the sticking float from empty is sorta common, but you can reduce that some by both shaving the inner edge of the gasket with a razor, but also adjust the float DROP tang to prevent it from dropping opening too far so that the float needle will not drop too far allowing it to get wedged/cocked diagonally causing it to stick!

I'll reset the float, seems like that could be a big issue.

Next....just to confirm....you say you've cleaned the carbs several times.... but many have stated that only to find that they did NOT disassemble them properly enough to be able to get the pilot jet and the main jet needle/emulsion tube and all of their aeration ports opened/cleaned..so that remain clogged which prevent proper fuel and air flow processes.

Yeah I took those out and poked out the tiny pilot holes with a toothpick and all that.

Along with the carbs....have you checked and verified you do not have any pinholes in the vac. slide diaphragms??

Yes, the diaphragms looked brand new. Nice and supple and no light shining through. The guy I got the bike from said he bought it from a mechanic, who supposedly had worked on the carbs. I'm guessing they were replaced during that time.

Now...even though you say you have SPARK on all 4 cylinders....you may or may not really have it under compression. What do the spark plugs look like? Any dark sooty/fouled. While running, take some water and spritz the headers and see if they ALL sizzle, or if any are cold. IF there are cold ones, and they are paired...1-4 or 2-3 then that can point to electrical problems....like a WEAK coil that can fire in AIR but not under compression!?

I did the spritz test the last time I rode it before posting, and all 4 sizzled. I have a multimeter that has a temp probe, I haven't used it before but I can get some temp measurements next time. I'll pull the plugs too and take a look at those.

Back to the carbs...are you using OEM Mikuni jets/parts? You mentioned the float needle seat from Mikes....did you also get Generic jets from them? We have found/learned over and over again that our carbs do not do well with GENERIC jets...they are designed differently and just don't provide the performance of GENUINE MIKUNI pilot and main jets!

The only other parts I've replaced are 2 main jets, and those were Mikuni.

[BA80]

The bogging and dying when put in gear sure sounds like a pickup coil wire issue. The pickup wires and the neutral light wire all run in the same loom up to where they plug in behind the fuse panel on the right side. sometimes the insulation will deteriorate and the wires can contact each other inside the sheathing.

Just for giggles disconnect the neutral light wire from it's switch, the switch is located on the bottom left of the engine between the frame rail and the oil pan, and try it just loose and with it grounded and see if it makes a difference.

Some say ground it and some say just leave it loose, I think it probably depends on which pickup it may be contacting as to which will work.

Worth a try. 15 minute simple test.

[3Phase]

Oakback,

I have an '80G too, do you have a shop manual?

Have you checked the compression, cam chain tension, camshaft timing and valve clearances? You'll drive yourself crazy trying to tune an engine that has bad or uneven compression, is mechanically out of time, has loose/tight valve clearances or all three.

Are you still using the original Fuse Block? It's over thirty years old, maybe your carburetors are having electrical problems!

Have you tested the Ignition supply circuit voltage?
Check the voltage at the 10 Amp Ignition fuse.
Check the voltage at the Red/White wire on the Start Solenoid.
The two voltages should be the within half a volt of one another.

Keep the voltmeter probe on the Red/White wire and toggle the Start/Run (kill) Switch. The voltage should drop and come back smoothly and completely as you move the switch.

If the Ignition supply voltage is good then check the Ignition Primary circuit voltage.

If the Primary is good, check the TCI.

Happy troubleshooting!

.

[oakback]

I set all the floats very carefully, 23mm. I also adjusted the float tabs so they don't drop so low, but I wasn't sure how far I could go with them. At least one seemed to have been stuck.

It still runs exactly the same. Idles alright, then if I try driving up my driveway (up hill) it bogs hard then dies.

Just for giggles disconnect the neutral light wire from it's switch, the switch is located on the bottom left of the engine between the frame rail and the oil pan, and try it just loose and with it grounded and see if it makes a difference.

Some say ground it and some say just leave it loose, I think it probably depends on which pickup it may be contacting as to which will work.

Worth a try. 15 minute simple test.

I can't seem to find the neutral light wire. Do you have a pic of what it looks like?

[oakback]

Found the neutral switch, disconnected it, no difference. Grounding it will have to wait till another day, the area around the switch is super grimy and I don't have any time left today to clean it, ground it, and try again. Will update with my next failed attempt later this weekend. I'll give you a preview though:

"tried a bunch of stuff, still runs the same, super frustrated"

[Bonz]

Hmmm... What year is your XS? Is it a rich bog or a lean bog? Like you smell gas after it dies possibly? Good job on trying the gas cap open.

Few things not mentioned yet...

-Are the boots from the airbox to carbs sealed and boots from carbs to engine sealed, no leaks? Would make it go lean as soon as you gave it a load if enough of a leak(s). Reason I ask is if it does the same thing with stock airbox and filter and also with pods, pods would make it lean with stock jetting and would happen with airbox if boots are not sealed. Also, are the manifolds (boots from carbs to engine) cracked (aged) to the point they could be letting air in?

-Had previous owner been in the carbs? Do you know what size main jets are in it, 78-79 carbs are very different jet-wise than 80+ models. If it has adjustable needles, what position is the clip in (78-79 had adjustable needles I believe).

I know, lots of questions, but could help out moving forward with suggestions.

[oakback]

Hmmm... What year is your XS? Is it a rich bog or a lean bog? Like you smell gas after it dies possibly? Good job on trying the gas cap open.

Few things not mentioned yet...

-Are the boots from the airbox to carbs sealed and boots from carbs to engine sealed, no leaks? Would make it go lean as soon as you gave it a load if enough of a leak(s). Reason I ask is if it does the same thing with stock airbox and filter and also with pods, pods would make it lean with stock jetting and would happen with airbox if boots are not sealed. Also, are the manifolds (boots from carbs to engine) cracked (aged) to the point they could be letting air in?

-Had previous owner been in the carbs? Do you know what size main jets are in it, 78-79 carbs are very different jet-wise than 80+ models. If it has adjustable needles, what position is the clip in (78-79 had adjustable needles I believe). Not in brand new shape, but no cracks or tears.

I know, lots of questions, but could help out moving forward with suggestions.

Seems rich, it blows some of that yummy rich fuel smoke and stinks up the place.

Boots from carbs to engine have been covered with something, I remember reading about it on where somewhere. Some kind of rubbery sealant. Boots from carbs to airbox are in good shape as well (these "pods" are just uni sock filters clamped over stock carb-to-airbox boots).

Someone's definitely been in the carbs, and everywhere else on this bike. Rewired fuses, visible wiring repairs, kreem was in tank, but the carbs looked improved. The boots look brand new, very supple and no light passing through anywhere. The first time I took the carbs apart there was very little residue, and it looked like it hadn't run much (if at all) since someone cleaned it, I could see scrape marks at the bottom of the bowls.

If the needles are adjustable, I've never been able to see where. I couldn't see any sort of clip or anything anywhere for that. The main jets are now all 120 (2 new, 2 unknown age but in good shape). Two of the main jets were soft and broke easily the first time I took them out, I asked somewhere on xs11.com about replacement sizes and was told I can put in 120 jets all across.

[mack]

Plugs

Your plugs may hold the answer, they can tell you a great deal. Please plull your plugs and describe them in as much detail as you can. Colour, wet, dry, sooty, particles on the bridge, get a good light and shine it into the electrode cavity and tell us what you see alone the wall and at the base.

[Bonz]

Gotcha. Sorry I missed the "80G" in the signature line. That would mean non-adj needles, and 120 mains should work fine.

I am more of a carb guy than electrical, interested to see what other ideas are shared.

[oakback]

Your plugs may hold the answer, they can tell you a great deal. Please plull your plugs and describe them in as much detail as you can. Colour, wet, dry, sooty, particles on the bridge, get a good light and shine it into the electrode cavity and tell us what you see alone the wall and at the base.

Is it best to pull them right after idling the engine, or when cool, or does it matter?

[mack]

Actually

put new plugs in it and take it for a scoot after warm up and as soon as it dies, read the new plugs.

[TopCatGr58]

Hey again,

Okay, The 80 carbs don't have adjustable vac. slide needles.
Next question....did your carbs come with the rubber pilot jet tower plugs on them on the bottom of the carbs under the bowls?? The reason I ask is that Yamaha had some bastardized carb bodies during the early 80 production line, and even though they used the 110/120 main jets...they also had the fuel SHARING TUNNEL between the main jet tower and the pilot jet tower...
and so they put VITON RUBBER pilot jet tower caps on the pilot jets to prevent them from getting fuel directly from the bowl....but to get it via the sharing tunnel and the main jet's access to the fuel.

However...with carb kits....they almost always come with the rubber pilot jet tower caps....but the later 80 models, and the 81's pilot jets are supposed to get their fuel directly from the float bowl because they do NOT have the sharing tunnel anymore....and so the rubber caps are NOT required, but if they are put in....then the bike/carbs won't work right because the pilot circuit can't get much/any fuel at all!

Now, you say you've been able to ride the bike, but only up to ~20 mph or so. SO...now some other "stupid" questions. Can you easily spin the rear wheel in neutral while on the center stand? The rear brake can seize up and cause considerable drag which can greatly affect throttle performance!?

IF the rear wheel actually doesn't turn easily in neutral, first remove the caliper and then recheck....if it then moves easily, then the brake was severely dragging. IF it still turns very hard after the brake removed, then the middle gear may be at fault...see below!

Also, if the middle drive has been run without gear lube, or drained and forgottne to refill, or just unknowingly leaked and allowed to run low/dry, the bearings can get burned up, and again can cause severe DRAG/Resistance to spinning...which can also translate to very poor throttle response when in gear! Just throwing out other ideas and things to check/rule out for us!?

You'll need to pull back the rubber swingarm boot, disconnect the driveshaft and again feel if the rear wheel will spin/turn easily. If it then does....then it points to the middle drive as damaged.....prone to failure and you'll need to replace it.

T.C.