XS11 bogs down on acceleration

[wmengers]

Hi,

This is my first time on, don't mind hearing if I'm not doing something correct.

I have a 1980 XS11 I bought last year with 7,500 original miles on it. I think I can believe that, it is in very good condition. The problem I have is that at fairly low RPM's, when I accelerate, it acts as sounds like what might be the carburator slides are not raising up and it has no power. If I down shif to get the RPM's up it gets through this and will accelerate fine. I recently rebuilt the carburators. I replaced the needle valves and made sure they didn't leak, set the float levels at the 1980 carb prescribed levels, replaced o-rings and the bowel gaskets. I coated the cracks in the manifolds which didn't go all the way through. The idle adjustment screws had been tampered with so I set them at 1 1/4 turns out. To check the diaphrams I removed the needles, reassembled the diaphrams into the carburators and pushed them all the way up to the top and, while holding them in this position, I taped the holes on the bottom of each slide and marked a line to where they slightly desended, and let them side for a couple of hours. None moved at all, which told me they didn't leak. Then I removed the tape and of course they came right down under spring pressure.

My latest theory is that maybe the slides don't go up unless you really rev it up is because the compression is low. I checked the compression and it ranged between 110 and 120 in all cylinders. I realize this is low. I squirted oil in and it whent up into the good range, about 140.

Does anybody know if low compression would produce the symptom of the slides not moving up at lower RPM's? I'm sort of baffled. I don't think I have any vacuum leaks, but I will thoroughly check that before I run out of ideas. Thanks for any help you can give.

Bill

[natemoen]

To check for vacuum leaks spray the whole area around the carbs, intake boots, and the airbox boots with carb cleaner when when bike is running. If the RPMs increase there is a vacuum leak there. (have a fire extinguisher nearby just in case, and no a garden hose really should be avoided for this...)

Was the compression checked on a warm motor or cold? Did you hold the throttle open when you turned the engine over of was the throttle closed? How much has it been ridden since you got it? The compression numbers are not really a problem at this point it seems and they numbers do have a tendency to increase after being ridden if the bike sat for a long time.

You never mentioned doing a carb sync. Did you do one? If not you have to sync the carbs and that could be a HUGE part of your problem.

These bikes seem to also have a nagging lag somewhere around 2500 RPM. It seems to plague lots of these bikes. You can get rid of it but it seems to be very individualized to each bike and it takes a lot of work and tuning

[Larrym]

Slides Show-n-Tell from TC...

Hi,

This is my first time on, don't mind hearing if I'm not doing something correct.

The problem I have is that at fairly low RPM's, when I accelerate, it acts as sounds like what might be the carburator slides are not raising up and it has no power.

My latest theory is that maybe the slides don't go up unless you really rev it up is because the compression is low. I checked the compression and it ranged between 110 and 120 in all cylinders. I realize this is low. I squirted oil in and it whent up into the good range, about 140.

Does anybody know if low compression would produce the symptom of the slides not moving up at lower RPM's? I'm sort of baffled. I don't think I have any vacuum leaks, but I will thoroughly check that before I run out of ideas. Thanks for any help you can give.

Bill

Bill,

Here's a video of the slides doing what they're s'posed to to and when they're s'posed to do it:

Slides Under Load
(Courtesy TopCatGr58)

Slides No Load
(Courtesy TopCatGr58)

Both videos have sound as well so I'd say that if your carbs look and act like the ones on the videos then they really are doing what they should. Just pointing out that the slides in a Constant Velocity Carburetor are sometimes misunderstood as far as what they really do versus how we would expect them to behave.

I'd say that if you had no compression at all then the carbs wouldn't have any air drawn through them on the intake stroke. No air flow would mean the slides wouldn't lift in order to do their "constant velocity" function. But as long as they're getting a good flow (higher rpms=more air flow...) the slides will sense the flow and respond. The engine is just one big air pump after all.

These bikes are definitely NOT s'posed to Bog or stumble. They wouldn't have left the dealership that-a-way. I'd say keep looking for something "Non-standard" like the wrong jets installed, something still plugged up in the carbs, or a bee's nest in your airbox. I mean someone ELSE has been in there before you, right? You might be trying to fix something the PO caused, was unable to diagnose, and then threw in the towel.

HTH...

[TopCatGr58]

Hey there Wmengers,

First off, I'm no carb guru, just had fun doing the videos!

Secondly, you said YOU rebuilt the carbs...so I/We can only assume that you really meant you, and not that you had somebody else do the work!?!?

The 80 carbs were during a transition time with Yamaha, from the earlier model 78-79 with smaller slides, shared pilot and main jet towers...a little tunnel between them, so they used larger mains as part of the feeding of the pilot jets.

In 80, they still had some of the older styles....sharing tunnel...but still different, so they capped the pilot towers with rubber caps, even though they used smaller jets..until they ran out of carb bodies with the tunnels, then they opened the pilot tower to draw fuel directly from the bowl. Just some info to check when you're back in there.

Also, what gear are you trying to accelerate in from below 2k? I'm amazed at the # of folks that want to ride/drive these machines like they are harleys!
Yes, they do have strong power and torque, but doing a just off idle roll on in 4th or 5th is tough!

Also, when you cleaned the carbs, did you SOAK them in cleaner? If so, then you could have damaged the throttle shaft seals, as others were alluding to checking with the vacuum leak carb spray technique!?

Also, did you remove the pilot jets and the main jet emulsion tubes during your cleaning...they have very small ports that clog easily from fuel gum from sitting.

IS the bike otherwise stock, OEM air box and exhaust or any mods?

You said idle adjustment screws....these are on the TOP FRONT of the carbs down in little tunnels.....and are capped off with brass caps from the factory, but can be removed. The screws between the carb bodies and part of the throttle plate assembly are the balancing/synch screws. No aspersions on your abilities or such, just that we can't assume what you know or don't know at this point.....until we get to know you better!

T.C.

[petejw]

Hi Bill,
If the bikes bogging down on acceleration
then the floats are more than likely set to rich,
not sure off hand what the float levels are for the 80 model,
what measurements did you have them set at?

the slides will rise when the engine is under load,
find yourself a road with a hill and crack the throttle wide open.

did you do the compression check with the engine cold or warm?
even tho they might be a little low as long as they are fairly even
across the board then you should be sweet.

[XS1100_OEM4ME]

Good advice

Good advice from all on here, 1st, I doubt your carb sliders are the prob, unless one is leak in die. on one, and you would have seen that on the rebuild. Next, what do you mean when you say "acts and sounds like it might be the carb's"?

[dbeardslee]

Does anybody know if low compression would produce the symptom of the slides not moving up at lower RPM's?

On TC's video, he's showing what the slides do with a load. If you're looking at them in the driveway with no load, they're not going to move very much.

[wmengers]

XS11 bogs down on acceleration - reply

Nathan, Larrym, T.C., pete anddbeardslee,

thank you all for your responses. I learned a few things. I did sync the carbs. The floats are set to .906" and I did all the work myself and took everything apart and thoroughly cleaned. I made sure carb cleaner did not touch the diaphrams. I did not soak them. The engine was warmed up before I did the compression test, but I did not have the throttle open. I missed that. I went back and read my manual and that is one of the first things they tell you. (dumb! I have a habit sometimes of missing things) Hopefully that is the reason the readings were low. I will check it again.

Even on the highway at 50 or 60 mph in 5th gear it will bog down. The reason I said it sounds like the slides aren't going up is because of the sound. It isn't a miss, it more like it is across all cylinders. I might be wrong about the slides, just a relatively inexperienced guess. I will definitely try the spray to look for vacuum leaks.

Funny thing happened last night when I was messing with it. It started to run worse. I decided to take the coils off my 78 to try. It didn't really make any difference. I also swapped the ignition unit which didn't make any difference either. I measured the coils. The secondary windings are supposed to be about 15K ohms. They were both reading open so I took the ends off the wires and probed the wire itself and they measured just what they were supposed to. Then I ohmed the ends and I couldn't get a reading. Not sure what is going on there. They don't look particularly corroded. I am going to look at it some more tonight.

Thanks for everybody's help.

Bill

[dbeardslee]

Sounds like your plug caps are shot. Normal reading for stock plug caps is 5k ohms plus or minus 10%. Might try the old 'clip 1/4" off the end of the wires and change your caps' trick.

[TopCatGr58]

Hey again,

Okay, the plug caps have an internal resistor, you can actually get to it by unscrewing it from the spark plug insert end. Then you can inspect it, and and check for corrosion, a bad resistor, etc.! Sounds like you may have found your real problem...poor spark often can mimic carb problems!! At lower rpms, the ALT is pumping out less power, and could also be source of less voltage/power to the coils vs. higher rpms.

Also, remember that these OEM coils are only pumping out 15Kvolts at best, and less since they are running on ~9 volts instead of 12 due to the supply from the ballast resistor....intended factory design to not burn out the coils. Hopefully you can either fix or replace the caps, and all will be right in your world again. Also, FYI, hi power/output ~35+KV coils at decent prices are available from MikesXS.net and other places...from ~$70.00 to $140 a pair depending on whether you get the black or green ones. Several folks here have gotten either types.....cheaper than Accel or Dyna and just as HOT!

T.C.

[wmengers]

XS11 bogs down on acceleration

T.C.,

Thanks for the response. I will look into new coils, but first I think I'm going to try one other thing. I am going to try my 1978 carbs on it to see if it makes any difference.

I did all of the electrical checks called out in the manual except for the spark test. I ordered a spark tester. Everything else checked out. I had it out today and I think it is running worse than it was before I rebuilt the carburators. I meticulously set the float levels at .906". I know I adjusted them, but I can't say how much, I didn't really pay attention. I can't help thinking it might be the float levels, but I am not that familiar with high or low float level symptoms.

I had it out today and I am starting to get angry at it. It is very annoying. It more or less boggs down all the time now, unless you are in a gear going a speed with it turning between about 2 and 3 K and you very slowly open the throttle and feel it responding with normal power, then roll the throttle open fairly quickly and it will respond with full power. I was on the highway doing about 60 in 5th gear and all it would do is bog down. It has a very little bit of power because it will accelerate, but very slowly, so it isn'[t dead. And it isn't a miss, it seems to be even, but just very lame. Once you get it accelerating under full power it will keep going without bogging until you let off and then open up again. I can't figure it out.

thanks again for getting back,
Bill

[3Phase]

It has a very little bit of power because it will accelerate, but very slowly, so it isn't dead.

Bill, it sound like the floats are wrong. When you reset the float height how far did you have to raise or lower the floats to get to 0.906"?

When you set the height did you measure from the carburetor body without the float bowl gasket to the top of the float?

[petejw]

Hi Bill,
Sounds like it could be your float levels,
if the acceleration is flat then your floats
could be slightly on the lean side.
try richening your floats by .2mm, doesnt sound like
much but can make a big difference.

[Toolmaker Tim]

Float level

Hi Bill, What do your plugs look like? I noted that you were careful not to get carb cleaner on the diaphrams, but how about the throttle shaft seals? When you set your float heights, did you measure up from the gasket seat to the bottom of the floats, or did you use a clear hose and check the fuel level in the bowls in relation to the gasket seat. Are you running stock airbox or pods? Are you getting any popping from your exhaust? Is the exhaust stock or aftermarket. If these questions have already been asked, my apologies, I didn't read carefully enough. There is a thread in the tech section I believe on coils and how to check them. It sounds like you have some ability as a mechanic, just be patient. It took me about 10 tries to get the carbs kind of close. I now know I have leaky throttle shaft seals, that can wait until riding weather is over. Your idea of swapping carbs has merit, but try to fix one problem at at time. That way you won't have the problems that I had figuring out what the heck is wrong.

[wmengers]

XS11 bogs down on acceleration

Toolmaker Tim,

My plugs look like it it lean. I think I could have a throttle shaft seal problem, but maybe not too bad. I sprayed with ether and noticed some change, but not a lot. Can the seals be replaced? When I set the floats I measured from the gasket seat. I didn't know about using a hose. That sounds like it might be a better way and I would like to try, but a little fuzzy on the exact procedure. I have stock air cleaner and stock exhaust. I do get some popping from the exhaust.

Thanks for your help.

Bill