Yamaha SR 125 91-92

Draco87 · Renault 5 Driver Joined: 04 Oct 2013 Karma :

Ok so I have this issue which is driving me bonkers, hope someone can come up with a different idea that ive not already tried. My bike when riding would backfire and pop turned out that was due to a hole in the exhaust, so replaced it and it still did it. So after several hours and days figuring it out I replaced the ignition coil and it stop and cured an anoying vibration too. But after these its still not solves the issue the bike will go any faster than 45 mph while travelling at this speed the bike rums like a bag of nails its very jurky and bogs down alot and im having to keep downshifting to keep speed. This to me sounded like a fuelling issue, so off the carb came and cleaned it checked the float height and everything was set right I even replaced the rubber seals. Not sure if mixture is set right the spark plug electrode is white but with a very! Light brown tan (can upload picture). I replaced the fuel line and checked flow this is interesting because I cleaned the fuel filter but it seems fuel isn't getting to the carb as the flow doesn't fill the tube. The bike will sometimes cut out on me when stopped and takes ages to fire again, it also does this when first started. When started the throttle is very hesitant and if opened too quick will also kill her. Also when riding when I let the throttle drop and twist again there is a frequent pop of air sound coming from the idle screw. I can't for the life of figure out what is exactly wrong, does anyone have any other ideas?

smegballs · World Chat Champion Joined: 28 Oct 2007 Karma :

Sounds running lean for poor fuel flow and white plug. Empty out tank and strip and clean fuel tap, quite possible full of rust/shite. Also make sure tank vacuum breather is clear.

Draco87 · Renault 5 Driver Joined: 04 Oct 2013 Karma :

Thanks for the advice man I will strip the tap down over the weekend I'll also take a look at the filler cap because I think it's not closing properly. I'll post any findings I get over the next few days

Draco87 · Renault 5 Driver Joined: 04 Oct 2013 Karma :

So the update, ive stripped our the fuel tap gave it a good clean the fuel now flows as it should. Breather pipe is ok double checked the carb and adjusted the mixture screw. So far the bike will run very well and keep speed, sometimes will jerk slightly and pick speed up, the bike still will cut out and is very hard starting, will check the valves again, but what happens is once I hit the start the lights on the instrument panel will flicker fast sometimes I need to bump it. Once its hot and I shit it off it can take 5 mins for it to start again I think it may need a new battery too does that sound right? Lastly when I rev the bike it holds its revs for a sec then drops to normal idle is that a symptom of still running lean?

nathan k · Spanner Monkey Joined: 28 Mar 2012 Karma :

RodYork · Scooby Slapper Joined: 11 Apr 2014 Karma :

I would confirm the air filter is clean & check the coil/HT lead & put in a new plug. If it makes no difference- then that's not it- but you have them as spares now & will need to change them at some point.
Cleaning the carbs & the main jet is also a great idea- as the previous poster suggested.