Get your thinking caps on, need help before I go mad

2 months ago my lovely, well looked after Yamaha YBR125 2011 bike went haywire!!!

After 8 months of flawless performance, one cool spring evening the bike began to cut out when idling at lights/junctions and jerking or 'bucking' like mad when applying throttle and struggling to 'catch' and supply power to move forward, when this happened the rev counter was dipping massively almost struggling to 'catch'.

So.......nearly £400 later the following repairs have been made:

1. New battery

2. New regulator

3. New fuel pump (filter was black)

4. New clutch

5. 3x new spark plugs (new each time as a precaution)

6. Crack in the exhaust repaired (with gun gum, a coke can and jerry clips)

7. Valve clearances adjusted

8. Chain lubricated and tightened

9. Idle screw adjusted to 2000rpm (when set to 1400 or 1700 by default the bike struggles and cuts out)

Now here's the mystery.....with each repair the bike worked fine for a couple of days, until the fault slowly crept back in and it began cutting out again and the bucking came back at specific gear/revs but not as bad as the initial fault, just a more tolerable version. Currently it bucks in 2nd gear at 20mph and 3rd gear at 25mph, it also sounds like its spluttering a little at take off from 1st gear. BUT.....at high revs on the open road there are no problems at all, jus the lower gears and revs when going through the streets.

Running out of ideas, I changed the spark plug myself this weekend and noticed something odd....if I wiggle the spark plug cable/cap when in idle, the bike sounds like it sputters and cuts out, I've cleaned the cap and the plug and runs a tad better (made sure its firmly on) but still a bit of wiggling still causes the bike to loose power and cut out, I've even trimmed the cable by 1cm and re-screwed in the cap with no difference.

I'm assuming in my noob mind this 'touchiness' with the cable isn't normal, so would a replacement cable/cap solve the whole thing, or from my account above (especially as this bucking only happens at certain speeds in certain gears) is there still more to this problem do you think?????

I'm a proper biker without a proper bike, but this experience is starting to kill it for me and some days I just want to go back to public transportation, but I don't want to give up, just want a bike that works again. Any ideas guys?

A new HT lead would be my next move. Have you checked the plug and made sure it's clean and pushed in properly?

If that doesn't solve it I'd give the fuel tank breather a good clean, if it's blocked it can cause a vacuum in the tank thus starving the bike of fuel however at high revs it'll be alright. I had a similar issue with my old bike and it was a blocked fuel tank breather.

You have not mentioned the air filter. Has that been changed?

No air filter hasn't been changed, but has been checked and is in good condition according to the repair men.

Since it goes away and keep coming back AFTER mods it sounds like the ECU?

are you using spark plugs with the top removed or still fitted in other words is there a thread showing at the top where the cap fits,is the cap a very loose fit on the top of the plug ?does it need a firm push to fit on properly?,only asking as some plug caps need the top thread exposed others need the top cap fitted onto the plug

Still a thread on the plug, the cap itself makes a short vibrating sound when pushed onto the plug, as the cap seems threaded too. This might sound daft when you think about it, but the engineers used to just pull the cap off the plug (while still in the engine) remove the plug, put a new one in and slide the cap back on. I'm wondering if the plug is meant to be SCREWED into the cap and THEN put on the engine, rather than already in the engine and the cap just pushed on????

no it does not screw into the cap there is a metal pin in the cap that makes it grip the top of the plug

HT coil......Low end misfire, but ok at revs.....classic symptoms. ........

Just going to throw this out there, i had a YBR125 2012 from new, after 18 months it one day randomly refused to start whilst outside my local Yamaha dealer. It was fine up until that day.

They did some digging and it turned out, that it needed a new wiring loom (luckily under warranty).

Maybe something to look into to, should a new HT lead not fix your issue.

HT coil......Low end misfire, but ok at revs.....classic symptoms. ........

Also my idle screw has been set to 2000 rpm, according to specs it should be nearer 1400, but when I set it to this in idle, the bike splutters and cuts out, is this sounding more inline with a HT lead issue? Just want to be sure, as I've spent so much on getting this bike repaired over the last couple of months that I'm trying to keep anything else it could be to a minimum, if it helps, its also been very dodgy when left out in the rain, has trouble starting and misfires like mad till engine and all that has warmed up.

as a new coil can be bought for less than £20 its worth trying to see if it cured the problem

Could it be contaminates in the fuel clogging the pilot jet? that would starve the engine in low revs.

Just an update, I replaced the HT lead and all juddering and cutting out has stopped.......I feel as though I've been scammed by the guys repairing my bike, as everything that got repaired/replaced still produced the same fault, but a £15 second hand HT lead and all is right in the world. Cheers for the advice guys.

This is why I never take my bikes in for repair work any more! Bunch of cowboys!

moral to the story..........................ask about on a good friendly forum like this before parting with hard earned money but at least its not sorted so happy biking and never be afraid to ask