XL125 Weak acceleration / power loss after visit to the mechanic
 

Hi guys,

After a recent trip to the mechanic, my XL125 is no longer accelerating as it should.

For a quick recap: the mechanic cleaned out the carburator (there had been a strange problem of the engine sputtering when it rained), checked a sound coming from the timing chain (turned out to be nothing) and adjusted it, and replaced the chain kit.

Since that visit, for whatever reason, the bike lacks power at low revs and takes quite a while to gain speed. This is especially noticable in 1st and 2nd gear, where there is a significant acceleration gap until above ~4000-5000 rpm. It's even worse when the engine is strained by going up a steep hill or with the extra weight of a second person, as the power is almost insufficient whereas before it could handle it easily. Also, if I throttle hard at low revs (even on neutral), the engine sounds bogged down and almost drops out before stabilizing.

Other than that, the bike starts instantly and idles fine. Outside of the power loss, there is no obvious issue. The carburator has been checked and double-checked by both the original mechanic and another with no obvious issue. The original mechanic also rechecked the timing chain and currently has no idea as to how they could have messed up the bike.

I'm certain that something the mechanic did is the cause of the problem, as I had done some fairly consistent riding in the weeks before without issue. Unforunately though, I'm running out of respectable mechanics to troubleshoot with as I'm located in Madagascar. Anyone have ideas on what could be the cause?

Appreciate any suggestions.

Kellen

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Not fun!

Sounds like somewhere in the re-assembly process the mechanic got something wrong.

If it is idling OK, and running fine at wide open throttle it seems like the idle circuits and main jets are fine. This points the finger at the needle that passes through the main jet and meters fuel at mid throttle settings. Its possible when re-assembling the carb this has not seated properly in the slide and now is sitting too high. This would cause the symptons you describe by making the engine run too rich (ie get too much fuel). To check all you have to do is unscrew the top of the carburettor and pullout the slide when you can then have a look to see if the needle is fully seated. If this is gibberish to you even someone with basic knowledge should be able to do this check.

If its not that I'd still be suspecting an error in reassembly somewhere as the cause, so get a good parts diagram / manual and just check everything over on the carburettor against the standard assembly process and settings.

Good luck

Are you sure the mecanic replaced the chainkit with a similar one?
If you now have a different gear ratio (bigger front sprocket or smaller rear) you could have the symptoms as described.

when you say chain kit, do you mean the timing chain or drive chain?
if he has got the timing out by a tooth or two (easy to do), that would give you the symptoms you describe. This is easy to fix.
Quick way to check, using a straw and a torch (nothing solid) take the plug out and get it to top dead centre, (or use the proper timing marks ideally). Then look at the cam timing marks.
My guess is that the cam is a tooth retarded, will give poor lower revs running, but free it up a bit at high rpm.

Thanks for all the replies guys.

Oil is not something I had thought of but I re-checked and although it is close to topped off it is not out of the ordinary.

The carburator has been the primary suspect all along. While I personally haven't taken it apart and verified, I've watched as one of the two different mechanics opened it, cleaned it, and adjusted it several times with no change. My eye is somewhat untrained here as I've only just started doing my own maintenance, but I feel like if there was a problem with the needle it should have been obvious to at least one of these guys.

The drive chain was the piece replaced and the sprockets are almost exactly the same size. Again, the bogging down is obvious even when I throttle hard in neutral so I don't think this should have an effect.

The timing chain issue sound likely, although the initial mechanic shop (who created this problem) did go back and re-adjust it again when I brought the bike back in. I'll give what you've mentioned a try and post the results.

Thanks again for all suggestions, really hoping I can bring this frustrating issue to a close!

Hi all,

I'm back for more advice after a disappointing week.

After doing my best to try out the various suggestions posted here with no success, I decided to take the last resort option of bringing in my bike to the local Honda dealership. I originally bought the bike here (albeit used) and they are the sole Honda importer in the country and the majority of the bikes they sell are the XL125.

After fully explaining the issue and having the mechanics do a test ride to make sure they understood, they agreed to check the carburator, timing chain, and the motor itself. I called in two days later to check in and they told me that they had verified all of these but were unable to find any problem and would keep investigating.

Today, they called me to say they had fixed the problem, blaming a leak in a valve (unfortunately, I can't say which one as my mechanical French is still lacking some vocab) that was releasing pressure. Either way, it didn't matter much because as soon as I started it up I realized the bike still had the same problem. As I revved and the bike bogged down, they tried to explain that all these bikes do that when you throttle down hard and I couldn't convince them otherwise until we brought out another bike of the exact same model to test. The dealership manager (who was very skeptical of my claim) also rode my bike around the parking lot and begrudgingly agreed that it has an "acceleration gap" (i.e., lack of power until the revs build) and that they would take another shot at the carburation.

At this point, I've about lost faith. If Honda can't repair it, I'm not sure who else can, and it seems like a subtle enough problem that people try to pretend it doesn't exist when they run out of ways to try and fix it. I'm ready to tell them to just start switching out parts, but its incredible to me that no mechanic has had any idea so far. Is there something small we could be missing?

Again, thanks for all the help so far, really appreciate any further suggestions!

Kellen

I've had the same experience a time or two with my own bike (different make and model). Mechanics fix what occurs to them, then get all defensive and deny that the problem even exists when it turns out their work made no difference. I've also had the manager test-ride the bike in question when the mechanics claimed the problem was normal or had been fixed. He came back and told his service department to quit messing around and start getting results.

On one occasion my problem was eventually solved. On my fourth or fifth visit to various mechanics, following lots of carb cleanings and replacements of tiny parts plus valve and linkage adjustments, timing chain checks etc. etc. etc., I asked about the muffled clunk I'd heard. Turned out a baffle in my silencer had broken loose and was causing issues which we all thought were fuel/carburetion, ignition, valve or timing-related.

Another time the problem went away, apparently on its own, although the super-carb-and-combustion-chamber cleaner I used might conceivably have had something to do with it. Sometimes you never find the answer, but usually there's a light at the end of the tunnel. Unfortunately, getting there might require vast sums of money and/or time.

Sorry that I don't have any words of mechanical wisdom for you. I'm just here to acknowledge your frustration and to say that such things do happen.

Mark

Thanks for the words of support Markharf, good to hear that you've had similar experiences and I'm not as crazy as the mechanics make me think.

A minor update on the situation:

After re-checking the bike, the Honda mechanics now believe it is a faulty piston. Again, I don't have specific details as to the cause (mechanical French again), but they claimed that switching out the pistons for ones from another bike of the exact same model fixed the problem.

I have no way of verifying if their definition of fixed is the same of mine, but I wanted to know if there were any opinions on the likelihood of this causing the problems I've described previously. The new piston has to be ordered and will take over a month to arrive, so I'd like to have an idea on the probability of success before I commit myself to what is likely to be a large sum of money. Considering that the mechanics were previously skeptical a problem existed and now think that this is the source of the issue, I remain somewhat skeptical myself.

Appreciate any thoughts!

Kellen

Carburettor problems are often frustrating.

Its possible the carburettor piston could be the problem. This would be especially likely if it is a CV carburettor. In these the movement of the piston is controlled by a rubber diaphragm, which if it tears or has a pin ***** leak could certainly cause the symptons described. Pin pricks are easy to cause when disassembling and often hard to see, so might explain why it has appeared after the first service.

The trouble is I thought all XL125 had slide carbs and for these it isn't such a likely explanation. However a quick goohgle search has suggested some of the Honda 125 motors on scooters used CV carbs so it is possible yours has one as well. If you post the exact year and model I can check.

Good luck

The bike is a 2010 XL 125, appreciate you checking. It only has 15k on it, so I'm surprised I'm experiencing this type of problem even though I have ridden it pretty hard.

Since getting it back from Honda, the power loss is definitely getting worse - it's not so much that it bogs down (unless you rev quickly) as that it sounds throaty and has almost 0 acceleration even at higher revs. I took it out for a 20 minute ride tonight to run some errands and the motor area smelled like burning when I brought it back in. Overall, not looking good.

Is this an XL 125 with the V-twin engine or the single cylinder?

Ndoro, sorry about the delayed reply. The XL125V (the Varedero with a vtwin motor ) does have CV carbs. So if this is the model you could well have a damaged / leaking diaphragm on one of the two carburettors. This would certainly cause the symptons described.

Good luck

If the bike is a 2010 XLV model it may be Fuel injected, I know the Euro models got FI in 2007.