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Desprate Help needed. Yam SR125

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Nagasaki24 This post is not being displayed because the poster is banned. Unhide this post / all posts.

stinkwheel
Bovine Proctologist



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PostPosted: 16:09 - 27 Dec 2018    Post subject: Reply with quote

How does the plug look after you've been trying to start it? Should be wet with fuel.

Have you tried a new plug in it? If not, do so.

Have you tried bump starting it? Smetimes they can be reluctant to fire up after a rebuild and bumping it down a long-ish hill in second does the trick. Sometimes putting a few drops of fuel directly down the plughole gets them running for the first time.

Could you have the engine timing 360 degrees out? This is quite easy to do. Not sure how an SR is setup, it may or may not make a difference.#

You have a spark but do you have a GOOD spark? Fat, blue and jumping bewteen the electrode and the tang?
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Nobby the Bastard
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PostPosted: 16:34 - 27 Dec 2018    Post subject: Reply with quote

Is the plug wet/smelling of fuel after you try to start it?
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jaffa90
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PostPosted: 17:12 - 27 Dec 2018    Post subject: Reply with quote

""""Spark yet, Its yellow but fairly bright."""
I like a blue spark with a crack with good hearing. (pardon)
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stinkwheel
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PostPosted: 17:15 - 27 Dec 2018    Post subject: Reply with quote

If you have been repeatedly kicking it over and the plug is dry afterwards, fuel is not getting through for one reason or another. Most (but not all) of these problems would be to do with the carb.

How do you know the carb is working?
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Nobby the Bastard
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PostPosted: 18:08 - 27 Dec 2018    Post subject: Reply with quote

I bet it has one of those stupid vacuum fuel taps. Not quite sure how they add anything.
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Nobby the Bastard
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PostPosted: 20:51 - 27 Dec 2018    Post subject: Reply with quote

Nagasaki24 wrote:
The carb is from the bike that died the other day and is defo working.


I'll say this slowly so that I can be sure you understand.

Is. The. Plug. Wet. After. You. Try. And start. It?
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Teflon-Mike
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PostPosted: 21:35 - 27 Dec 2018    Post subject: Reply with quote

Sorry but me and my tool-box are about 150 miles east of you, and my spidey senses to be able to diagnose by telepathy and voodo sont seem to be working at the moment....

Meanwhile you are insistant that the thing SHOULD work, whilst NOT aactually answering pretty basic questions asked....

like... is the plug wet..... with "Well its had abother carb off another bike, so it MUST be getting fuel!!!!"

Eh? Sorry, but how does that bit of illogic work? It sure as heck doesn't answer the question asked,. meanwhile, it suggests actually a very good reason WHY the motor might not be getting charge..... your misguided fiddle-fingers.... just out of curiousity.... did you use NEW gaskets when you fitted alternative second hand carb? Why are you so sure that cant be 'the' problem, coming off, I poresume another bike, that also conked out?!?!? It makes no bludy sense, and tells ME that you are pigging in the wind, HOPING that the thing will just start working all of its own accord, or that enough of us can fix it by Khamatic good will, that you probably dont deserve right now!

ANSWER THE EFFIN QUESTIONS YOU HAVE BEEN ASKED NOT the ones you would LIKE to have been asked!!!!

IS THE PLUG WET!!!!

NOW go look at the fuel tap. Re-look at the carb! You MAY like to make some new gaskets from a cornflake packet! BUT either which way.... it wont fix itself, and we cant do it by voodoo for you, or telepathy.... so go look, and answer, simply and directly the questions simply and directly asked of you... and STOP bludy guessing and hoping.

More daft questions out of more interest....

You say you timed in the cam..... Oh Kay.... why? I wouldn't need to do that on an engine unless I had stripped it down.... possibly to replace the cam-chain, and I would, like a carb swap have used a nice new head gasket.... did you?

Compression? How did you test this? Its a little engine, and most car type compression testers are pretty hopless and inacurate on engines this size, especially iof they aren't spun up fast enough to get much compression, and or are spun up with the throttle closed so there's nothing sucked in the pot to squash...... So how are you measuring if there's enough compression, and why are you so convinced there must be? Especially if you have taken top off the motor and likely not used a new gasket and probably not torqued it down critically.....

TAPPETS.... otmh these are old fashioned screw and lock nut affairs. Oft neglected by DIY maintainers cos it means looking at oily bits; and book says they shgould be done pretty often, as in every other oil change, which on small engine like tyhis could be as little as every 1000 miles or so..... have they ever been critically adjusted?

Should have been dont when the cylinder head was lifted and or cam timed in... so.... done? Done wrong? Can we eliminate THIS variable please.

What state is the exhaust in? Has it been butchered for the sound or bodtched to get through an MOT? Is it rotten, or has the maghix restriction washer, AKA the exhaust gasket been omitted.... if head lifted a new one should have been used, like the Head-gasket... was it> Is old one still in the port, blocking gas flow? Have a look....

And if you want our help, help US help you, answering the questions asked NOT the ones you simply wish to, as randomly as you are describing the symptoms.....
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Riejufixing
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PostPosted: 23:30 - 27 Dec 2018    Post subject: Reply with quote

Test it using the top part of a cleaned & dried squeezy bottle as a fuel supply to the carb, these Fairies are good 'cos the nozzle usually fiths the pipe. You should have what they used to call a "fat" blue spark at the plug which is nicely descriptive (I assume you've tried a new one). You should check your timing again if there is any question at all.
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Suntan Sid
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PostPosted: 01:39 - 28 Dec 2018    Post subject: Reply with quote

As Stinkwheel said, check the cam timing again, it is so easy to get this 180 or 360 degrees out.
If there's fuel in your carb, but none in the cylinder then something is stopping it getting to cylinder, the inlet valve being closed when it should be open could be the cause.
When refitting the cam and cam chain, both the inlet and exhaust cam lobes should be pointing upwards at about 45 degrees, in other words, not in a position where they are causing either of the valves to open.
If you refitted the cam chain and the cam was not in the position I've described, when you started, then your timing will be out.
I don't know your bike so this may not apply but, I assume you refitted the pulse generator back plate in exactly the same position it was in originally, if you didn't your ignition timing will be way off, even a millimetre or two either way will cause you problems.
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mentalboy
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PostPosted: 01:40 - 28 Dec 2018    Post subject: Reply with quote

^^^ Classic! You must be the first person to respond to each one of Tef's points.

Robbing bits from the dead bike has the drawback that you don't know how good those parts are, the carb should be ok (but it may have varnished up a bit if it was left standing unused for a while) whereas I wouldn't even bother with the old spark plug.

First, get yourself a new plug.
Second, check 'new' carb for clear jets and passages.

Edit: not you Sid, the OP! WTF are you doing up at this ungodly hour?
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jaffa90
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PostPosted: 03:08 - 28 Dec 2018    Post subject: Reply with quote

"""Edit: not you Sid, the OP! WTF are you doing up at this ungodly hour?""
Says you with a name like that. Laughing
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bikenut
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PostPosted: 10:59 - 28 Dec 2018    Post subject: sr125 Reply with quote

You do not say what year the bike is, the one that died when you got to work??

Flywheel key?????
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mentalboy
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PostPosted: 12:45 - 28 Dec 2018    Post subject: Reply with quote

jaffa90 wrote:
"""Edit: not you Sid, the OP! WTF are you doing up at this ungodly hour?""
Says you with a name like that. Laughing


Except that with a five hour time lag on most of you lot it was still too early in the evening for my nightly Horlicks!
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Nobby the Bastard
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PostPosted: 14:42 - 28 Dec 2018    Post subject: Reply with quote

Nagasaki24 wrote:
Been fiddling a little again today.

Valve clearances where a little off so re-done them.

I took the airbox connection off the carb and turned it over and I cant really feel anything "sucking" air in... hmmm.

But that said, It did sound like it tried to start, more than I got before at any rate.

For now the battery is on charge.


Are you a bit hard of understanding? I'm adding you to the list....
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Teflon-Mike
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PostPosted: 14:56 - 28 Dec 2018    Post subject: Reply with quote

Nobby the Bastard wrote:
Are you a bit hard of understanding? I'm adding you to the list....

Despitye radio-active user-name suggestion, profile claims he's in North Wales, probably some-where around Chester, and likely talks with a Liverpudlian accent....... SOME, allowance might be made for the language barrier here.... but else-wise you are right....

Try typing "I-S----T-H-E----P-L-U-G-----W-E-T?!!!!" in big bold capitols one more time.... if he still doesn't get the message well.... we could try and translate it in to welsh... I think, that it's "Iz Ya, Effin, Ploog, We-at, you taffi-twit?" with a lot of spittle thrown about (He says with more than a little Cymru ancestry!!!) But if that don't work... yeah... lost causes, prey to St Jude.... it's probably as much use as perpetuating the random here.
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Robby
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PostPosted: 15:23 - 28 Dec 2018    Post subject: Reply with quote

Is there any fuel in the tank, and how old is the fuel? If its the tank from the bike that died ages ago, the fuel could be as flammable as dilute water.
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Teflon-Mike
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PostPosted: 17:30 - 28 Dec 2018    Post subject: Reply with quote

Another bike? That will give you three to frigg around with, pigging in the dark, NOT actually finding the fault!!!!........ Not really too sure that this is even close to a solution to the problem here, and one does have to wonder how long it would be until you popped back up with a post, "Scrapped the SR's... now YBR wont start.... Help!"

Howeblier.....
You need 3 things for signs of life.... Spark, compression, charge.

You SAY you have spark.... by the sounds not a great one.

Wet plug, indicated charge getting to the pot..... so leave the chuffing carb alone, for now!!!

Compression.... has been considered, and you 'reckon' you got some, from the rule of thumb over the plug hole.... which on little bike, 'can' be about as useful as anything.... but.... you are guessing some here, its not known to be enough.

Back to the plug.... its wet... this is a bit 'good' but also bad.

If plug gets wet, spark will track through the wet and not arc between the electrodes and set fire to anything.

And ALL you know is that you have a weak to possibly OK spark, in free air, plug out the pot.

In the cyclinder, plug keepiung charge in, under compression, you will have something like 10x the amount of 'stuff' between the two electrodes as you do when the plug is out, in free atmospherioc presure air..

Electrik takes the path of least resistance.... and compressed charge often isn't.... if the plug is sooty, and or err.. wet! the electric will go through the soot, which is carbon, same stuff as the HT leads are made of.... it will like going through that an awful lot more than trying to jump the electrode gap..... if dissolved by petrol, even more chance thats where the sparks go.

BUT... as of this moment, we have 'some' idea that the three ingredients for life are at least there....

So start by cleaning the plug... soaking it in petrol in a jab jar for a while, can help get rid of heavy oil and or soot deposits... but I find that a freyed old clutrch cavble used as a mini-brush to get down into the insulator recess between the central electrode porcelain and the metal 'bolt' bit of the plug, to dislodge as much crud as possible is helpful... NOT repeat NOT just running a bit of samd-paper twixt the electrode and tang... though that's last clean before setting the propper plug gap, as stated ion the manual....

IF plug gap too big, electric wont jump... if too small, electric will jump, but there wont be enough spark to set anything on fire... so set the gap.

Other old trick, is to pop the plug in the oven or give it a few minutes under a blow torch, to dry it off and warm, it up before re-fitting.... I advide holding it in a pair of mole grips so you dont burn your fingers to do this!!!

With a hot plug, AND a charged battery, and a damn good kicking, it aught to start, or at lest offer rumblings of willingness...

If NOT then time to revisit that compression test, and your valve clearances, and whether you have actually timed the cam in correctly.... remember it turns half crank speed; the crank has to do two full revolutions to achieve four 'strokes', so the crank turns 720 degrees for 360 degrees of the cam...

BUT.... for not, clean the plug, charge the battery, try again.

Fact you have spark, allbe-it by the sounds not so wonderful ones, pushes the likliuhood of it being a problem with the coil or CDi box evcen further down the list than they wer to start, and they shouldn't have been high, these are pretty 'inert' electrical devices, that tend to be pretty reliable, and not where you should start looking for problems to be, but the last after so many other much more likely candidates have been eliminated.

Out of interest, are we talking an early Kikc-only SR or later kick and e-start example, and are you trying to start on the button?

Another point about sparks; I'm pretty sure that the sparks on the SR are 'self exited', that is the ignition is separate from the charging system, the generator making electric on the end of the crank when engine turns over, to power CDi and make sparks.

This means that when you try start the engine, by kick or by e-boot, its NOT getting electric to make sparks from the battery; its getting them from the generator, which makes more the faster the engine turned over.

IF the engine is turned over lazily on a kick or tired e-boot, then sparks can be 'weak'......

If you are trying to start on the e-boot, it might not, with pressure in the pot have the oomph to turn it over fast enough to make a decent spark.... and a flattery wont help..... which can add chaff to the comundrum.....

However, for fault finding, I tend to eliminate this variable a bit, and use a spare car battery, and jump-leads, instead, not INSTEAD of the bike battery.....

Little bike batteries tend to be very small, and are 'killed' in quick time by the effective repetatiove deep-discharge of being suicked of amps so fast by the bikes e-boot..... and yours probably already has been.... but that's a problem for later.

Big car battery, have the oomph to give the bike starter the amps it needs to spin up quickly enough and make sparks, whilst the capacity also tends to give it a bit more resiliance to deep-discharge decay, a-n-d you get more turn time before having to wack it on a bench charger.

PLEASE NOTE... the car battery is NOT connected to the car when I do this! Bikes tend to have seperate regulators to the generator, and they tend to regulate volts to the battery at a pretty constant 12.5v. A car alternator has itrs own regulator in it, and oft wacks out maybe 15-16v to the battery.... if you have conventional 'jump-start' from car to bike, with the car engine delivering electric to car battery, jump-leads from there to nbike battery, you can end up with the poor little bikes seperate regulator trying to regulate the amps made by the enormouse car anlternator and getting fried in the trying.... so best to not do it!

JUST use car battery in place of bike battery JUST for fault finding starts.

Those tests performed.... bike will either work, or not or not work so well, but either which way, we MAY have better idea which way to steer you to find out why!!

For NOW the wet plug question ACTUALLY answered Rolling Eyes After protracted extraction like drawing a chuiffin tooth.... and probably more painfully..... we get round..... you got spark.,.... a poor one... you 'think' you have good compression... and there's charge wetting the plug, SO the ingredients 'sort' of should all be there, to get signs of life......

Help us help you here..... tell us the answers to what we asked! DONT forget the anawers, ans stop answering wht you'd like to answer not what you were asked ';cos its too wet, too dark or too cold to go get the answer to question actually asked!!!!! And 'we' might help you get some-where!!!!
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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?'
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cb1rocket
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PostPosted: 14:27 - 29 Dec 2018    Post subject: Reply with quote

whats the compression like? I bet it pants....
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