Bike from hell

[loughy]

so, hello! First post and looking for help

AJS JSM 125 Trial (has a lexmoto 125 engine in though)

Background - bike was bought for £500 as a stop gap before getting my "big" bike license, however Ive had nothing but issues with it, from every angle.

I've managed to have the majority fixed but 3 things still concern me!

Electrics - the damm fuse keeps blowing, I've checked for bad connections etc but can't see anything - I think this is a case of keep looking to be honest!

Chain - God knows how many times Ive had to retort (is that even a word???) 'tighten' the chain but each time the little tw*t keeps slipping off, its had a brand new sprocket so its not the teeth!

Engine (I think anyway) - this is the most concerning part and im not sure I can describe it accurately but I'll try. When I'm accelerating/deccelerating its generally fine, but when im coasing at a steady speed/revs the bike is AWFULLY jumpy/jittery, it literally shakes/rocks back and forths. ive done a lot of googling and its definitely not the "kangaroo hopping" as the revs/speed are not affected, its just rocky.

I already know how unreliable Chinese bikes can be but I only need this for another 3-6 months then I can get rid.

Any ideas on the above please (im fairly new to bikes so dont use too much jargon )

THANKS!!!

[loughy]

Should have tagged on what I've done to the bike as I think i know what the replies will be.

In relation to the rockyness, the bikes had a brand new exhaust, brand new air filter and has just had the carb cleaned.

[tom_e]

Electrics like you say you've just got to keep looking. There'll be a bad earth or a fur'd up connecter somewhere.

Chain sounds like the actual chain is fucked rather than the sprockets, check for stiff links. This may also explain the rough ride as the chain bounces all over the sprockets.

[Rogerborg]

How slack is the chain? Pictures would be good.

Is the rear sprocket aligned with the front? Wouldn't be the first some someone has put spacers in wrong.

The rear sprocket is bolted onto a plate called the sprocket assembly. In between that and the actual wheel will be some rubber blocks.

With the bike parked up and in neutral, grab the rear sprocket and try and rotate it in both directions. A little bit of play is OK. If the sprocket and sprocket assembly rotate significantly independently of the wheel, the cush drive rubbers are likely wrecked. That could explain both the chain jumping off and the lurching.

Although the latter is more likely to be fuelling - you'll want to let it lurch for as long as possible, immediately kill the engine and whip the plug out to see what colour it is.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[loughy]

[Rogerborg]

[tom_e]

Sounds like I wasn't far off then. Stiff links will eventually snap.

[bikenut]

you have a wiring diagram and multimeter? if not get one of each.

jerkiness solved via bad chain/snapped.

chains need little and often maintenance, more when its raining.

lexmoto cg125 copy, push rod engine post a picture.

a cheap multimeter will have an ammeter section, read instructions to test for load, but since its blowing fuses, be logical.

when doers it blow a fuse, when the horn works, brake lights work, side lamps work, indicators work, neutral light works??

do any lights misbehaeve when steering turned from lock to lock??

how is the wiring in the headlight and under the saddle, any snagged wires under there??

rule out each circuit one by one, or, disconnect every circuit that is battery dependant, like horn, inds, lights etc. but not charging system.

does it blow a fuse then??
if niot, add a circuit at a time, like horn, brake lights, inds, side lights until it blows a fuse, the last thing connected that blows a fuse will be at fault somewhere.

get a multimeter and wiring diagram.
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nuts about bikes

[loughy]

[tom_e]

[loughy]

Its a temp fix until Ive got time to go through every wire again (this weekend)

[bikenut]

As tom says, you have effectively removed the electrical safety feature, namely the fuse, and replaced it will a 30 amp fuse, may as well be a 6 inch nail!!

The fuse protects the wiring, blowing at 15 amp, now has a 30 amp fuse, can the wires handle a 30 amp load without melting and causing further problems or a fire!!

Get a wiring diagram ( or draw your own form the bike ) and a multimeter which has an ammeter function, which will show you the load experienced, and take it from there.

You have been around the bike, any crushed/caught wires anywhere ( anywhere ) on this bike, like by the head stock or under the saddle/battery box area/engine or anywhere else ?

Is the charging system fused on this bike, probably not, but may be.

Get a wiring diagram etc before this bike and you burn/cause bad accident ( accident ha !! bit more like negligence judge rinder would say ).

Do you live in north wales ? no, thank god for that.
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nuts about bikes

[bikenut]

I've done a lot of diagnosing, checking the fuse after each thing has been used and came to the conclusion it had to be the horn, as the fuse blew twice after using it instantly, job done, So i thought. Turns out it blew again a day later and 100% hadnt used the horn!!



still could be horn circuit related, is the horn live and earthed via the horn button, see other horn fault thread.
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nuts about bikes

[Islander]

Look for chafing on the wiring loom especially around the headstock. I'll bet something's shorting to the frame.

[loughy]

Bikes been in the garage and apparently the whole back wheel needs replaced, even with a new chain/sprocket it wont work

so the guy reckons, (prepare for amazing terminology) that the bolts which hold the sprocket in place are fine, however the rubber holder bits on the wheel itself which hold the bolts in place, are completely knackered. He reckons a whole new back wheel!

apparently the bearings are on their way out too! ffs

[bikenut]

See "Transmission Backlash" thread exploded view of rear wheel, similar??

The silent block bushes are replaceable but difficult to remove. They are an outer steel tube, with a rubber bonded steel inner tube.

The rubber bonding can break up due to certain chain lubes, pins drive via outer steel tube and wear the alloy hub holes, making them egg shaped.

Then new wheel or some "engineering" to make good.

Post some pictures.

Any progress with the fuse blowing ? :karma:
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nuts about bikes

[tom_e]

[bikenut]

I would love to watch you replace the bushes ( if the silent block pressed into alloy hub type, hopefully picture to come for this ) and wheel bearing in that time, should be entertaining. :karma:
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nuts about bikes

[tom_e]

You're right half reading it while I'm supposed to be working made it sound like he was talking about cush drive rubbers rather than anything more fixed

[loughy]

I'll chuck some pictures up this afternoon, he did mention cush drive rubbers and the block being knackered.

[Kickstart]

[Rogerborg]

[talkToTheHat]

Try asking at a different garage if it's uncertain that the rear wheel needs replacing. Perhaps the place you are going just lacks a decently sized press.
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Bandit. does. everything.

[loughy]

I managed to get rid of the bike to a young lad (did tell him what was wrong etc) took a hit of about £500 in total.

So glad to be rid tbf

[Polarbear]