xr125 will not run

[pedwhisperer]

HELP!!!!
I have a honda xr125 03 plate i have tried every thing i can think of but when the bike gets warm it starts to miss fire and struggles to keep running things i have done and changed are CDI changed,coil plug lead and plug renewed,regulator/rec changed,stator changed,carb changed,valves ajusted and still it misses somtimes it runs for 30 seconds and stops and somtimes it runs for 3/4 minutes and stops but theres always a miss with this dose anyone have any ideas.
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if your not living life on the edge your taking up to much room

[el_oso]

the choke is off isn't. even if you have pulled the lever. make sure that it had turned it off and not sticking
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Duke 390
Previous: '05 XR125L | '96 XJ600S Diversion |'05 Suzuki GSXR1000 | '05 Honda CBR125-R | '97 YZF 600R Thundercat | '11 Honda CBR250
Car: Jeep Wrangler 4.0L

[pedwhisperer]

All checked the choke is working fine thanks for the thought
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if your not living life on the edge your taking up to much room

[N cee thirty]

the bikes got the same engine as the cg,so probs the same carb

the choke lever goesdown for off and up for on,confuses many people.

checked the air filter?
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[Teflon-Mike]

XR 125 has and has always had, an Single Over-Head-Cam, single cylinder engine. It is NOT repeat NOT the CG push-rod engine as many believe. Its a completely different engine, with a very different design layout, and very little shared design heritage, and even fewer common components.

If you have eliminated ignition faults by replacement with KNOWN good items, then that takes those faults off the diagnostic tree, but I would reccomend revisiting it.

Were the subbed parts you fitted known good? Were they genuine Honda spares or reputable after-market replacements from some-where like wemoto or Dave Silver spares?

If the bits were second hand items or cheap chinese copies, they may not be much cop, and depending on the fault and the order you replaced bits, there is still the pottential in there that the 'fault' was in one component, say the regulator, or generator windings, but that casued an over-load that fried the CDi, so if you replaced the CDi, before the regulator or stator, the 'new' CDi could have been popped like the first by the regulator, and the fault replicated, even though you've fixed the causal problem, the regulator or whatever.

Presuming the electrics are fine though, next candidate is the carb. You say you have changed the carb? again, whats the source? If second hand, could be crudded up inside. If cheap chinese copy, likely to be jetted wrong for your bike, and or made badly. Cheap Chinese copy carbs have a reputation for innacurate castings, and that often effects the operation of the float valve. When the engine gets warm, the alloy expands, but the innacurate casting means that the float bowl twists as it expands, making the float 'stick' and the engine flood or starve.

Personally, I'd be inclined to return to the original carb, stripped and cleaned and properly fettled, if the new carb hasn't fixed teh fault, and look for air-leaks in the inlet tract.

First thing would be to order a new inlet rubber from Dave Silvers, the bit that attached carburettor to the inlet manifold on the cylinder head, to eliminate the possibility that the old one is perished and gone pourus or actually spit. New clips would be worthwhile too.

Also, I believe that the XL has a similar arrangement to the CB125 on the inlet manifold, in that rather than a paper gasket between the head and manifold, the manifould has a milled groove and a rubber O-Ring seal. Order a new O-ring at teh same time as inlet rubber if so, likely thats old hard, been on and off more than a tarts nickers and not sealing.

Next thing to look at is the exhaust, and the exhaust manifold gasket would probably benefit from replacement, but wip the pipe off and inspect for perforation and or leaks.

You never know, some dim-wit previouse owner might have tried drilling holes in it to 'de-restrict it' from net descriptions of how to de-restrict a DT! But more likely, as pretty sure its a black-painted mild steel item as stock, its simply rusted, and an intermittant miss like that could be due to a leaky zorst.

THAT though is about as far as you can go without opening the motor.... and where I suspect you are likely to find the root of this problem.

Will mean lifting the head. If you've tackled everything you say you have, even though its an OHC motor, this shouldn't be beyond you. Just follow the manual, apply patience and attension to detail, and a bit of method. And you'll need a torque qrench for re-fitting.

Possible that the head-gasket has gone, or is at least on its way out. Mis-fire will be the engine 'blowing' when its hot and the joint has opened up.

Slightly more dire, but easily fixed if you have lifted the lid, possible that you have worn valve seats or minorly burned valve. OR you have severe carbon build up and pre-ignition from the hot-spots the deposits create.

That would most likely be a symptom of a worn bore and or worn valve guides letting oil into teh cyclinder. Does it run a bit smokey, or does it need its oil topped up fairly frequently?

Anyway. Up to you whether you pull the barel off. Easy enough once you have lifted the head, and get it rebored. If its running, probably wont need much machining & you can refit with the old piston & over-size rings.

Head, if the gaskets gone, may also benefit from a little reconditioning machining, possibly a head skim, but a valve & seat grind would be worth while.

If I remember right, may be worth having a good look at the cam and rockers. Think that these engines can suffer if starved of oil and the cams can eat into the head. DOUBT that would cause the symptoms you describe, BUT, if the cams wobbling a bit and then 'picking up' it may. Can be solved I believe by having the bearings bored and fitting needle rollers.

Sounds involved, difficult and expensive.... actually, depending on your point of view it probably is! BUT, actually, if you have a decent engine reconditioners near by, it needn't be too onerouse.

Your probably looking at perhaps £15 for a skim, maybe £25 for seat & valve grind, perhaps £70 all in with new valve guides, £150 in total if they needle roller your cam bearings. (all at a guess!)

But then it can be put back together, and should run like a gem, but if THAT lot hasn't fixed it....... well, got me stumped!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Billing]

Are you sure the XR125 wasn't an OHV engine Mike, both the cylinder heads for XR's on evilbay seem to have holes for the pushrods
https://cgi.ebay.co.uk/HONDA-XR125-05-CYLINDER-HEAD-COMPLETE-/390233887942?pt=UK_Motorcycle_Parts&hash=item5adbc094c6
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'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
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[Teflon-Mike]

[Billing]

good bit of digging on the recall thing there Mike Was the call replaced for a used one or a second hand one? and would it be possible for a bad contact to the coil (like a loose wire, we used to take the wire off my mates bike with the same engine as a form of immobilising) to cause this? if the wire was loose it could be making a contact for a few minutes then moving with the engine vibration
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'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
BCF Eastern members map here ---> g.co/maps/2tm8b PM me to be added to it!

[kingsknight]

sounds to me that you need to change the rings my friend. what is the mileage?
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TS50 (sold) NS125F (sold) NSR125R-K (write off after 2 crashes) CG125 (nicked) XR125L-3 (Sold )-: ) DR125SM '11 (sold yay) XL125V '12 (In love with this bike) XT600E '04 (fun on the dirt)