hi   I have a 1980 yamaha sr250 us custom had her moted on the 5/11/2010 when I left the mot station she was popping slightly but put her on res and she was fine went out to start her today and she took awhile to start on choke she runs fine but when warm and no choke on she starts to pop and cuts out have changed the sparkplug but still the same going to drain the fuel tank and see if there any thing there stopping the fuel coming through any help greatfully recived with many thanks                                                                                                                                                                              

Air filter could be clogged just try starting it without filter see if there is an improvment                                                                                                                                                                                                                       

just emptyed the fuel tank and there was a red sludge in the bottom of the tank going to clean it and refuel and try without the airfilter as well                                                                                                                                                                              

My 125 (Ziggy) pops and fa*ts all the time.. hes called Ziggy Ziggy Bang Bang !!   Just ask anyone that knows me and Ziggy on here...lol   I've been told its unburnt fuel.. but nowt to worry about.                                                                                                                                                                             

dont think it it unburnt fuel as she was fine before the mot think I might have let the fuel get a bit to low but not sre as I got nearly a full can of fuel when I empted the fuel tank                                                                                                                                                                              

Hey rob, also drain carbs and flush out. modern fuel is full o chemicals which can block up carbs if left for a period of months unused.                                                                                                                                                                              

hmmmm....well I hope you get it sorted                                                                                                                                                                              

carbs been flushed and stripped down today still the same wish I never got this bike now lol                                                                                                                                                                             

Not sure what carb is on that bike but check diaphram if it has one, & take it out for  a blast, that often works                                                                                                                                                                               

Popping & farting is USUALLY caused by a weak fuel mixture. If this happens more on pulling away from junctions / roundabouts etc, then prob that is the cause. If it happens more on the over run .. throttle closed after accelerating .. this is USUALLY caused by an air leak in the exhaust system.   The exhaust is one thats USUALLY easier to fix ie loose head/exhaust clamp or loose silencer to down pipe.   Weak mixture can be harder to find the cause, .. .. clogged fuel filter on the tap for instance,..  been standing sometime and the additives in fuel have partially blocked one or more jets,  ..  carbs with diaphrams could have a tiny hole not allowing the slide to fully raise etc etc etc....   Note USUALLY in bold, as each case can be different.   Robert, if you can, remove and clean the float bowl, check for crap etc in there. I feel yours is more a mixture problem as you say its fine whilst on choke.  HTH                                                                                                                                                                             

will have another look in the morning as it is getting dark and the bike has done my head in today the carb on the bike is a bs34 mikuni carb think it does have a diaphram will try again in the morning many thanks for all the help so far                                                                                                                                                                              

GT... regards my bike.. I think you're right on the exhaust problem as I've had a loose plate and lost a bolt, but got another one on and it still does it, but probs an ill-fitting plate or something, cheers                                                                                                                                                                              

going to take the exhuast of as well tomorrow and rebuild from the ground up see if it stops the popping and f*****g lol you never know but the carb maybe up the shot hope not lol                                                                                                                                                                             

GT... regards my bike.. I think you're right on the exhaust problem.   Karey .. I'm hurt .. You think I'm right  !!!!   Come on hon, I'm a bloke .. we're always right           Yeah, yeah, I know how to duck !!!                                                                                                                                                                             

Hahaha.... yeh yeh.. i forgot..you blokes like to think you're right!!   ..ok GT... yes I admit you are right   robertb....hows it going?                                                                                                                                                                             

many thanks for everyone help with my problem the bike is  fixed and it was a very simple fix cost me £2.50 for some gasket paper turned out to be some red sludge in the bottom of the carb which has now been cleaned out must say the bike runs better so once again my many thanks to evryone for their help

Glad you sorted it Rob.   Have you enough room to install an in-line fuel filter on your fuel pipe, between the tap and the carb ??   A small one from Halfords etc should only cost around a £ or so. Although there should be a filter built in to your tap, rubbish is still getting through by the sound of things.   Belt & braces   springs to mind  ..... !!                                                                                                                                                                             

will look into the inline filter looks like I should have enough room to fit one once agian many thanks for evryones help
                                                                                                                                                                             

If your tank is contaminate I have just done a rusted tank off a kz1000 I got off e-bay used a product from frost with postage it came to £38.00 did a great job will highly recomend it (motor cycle tank repair kit) was given the advice by (scorpio 54   Ken)    it works great                                                                                                                                                                               

will look into that as well got my fuel tank from ebay as well but not sure if it was rust in my tank but well worth having a look at many thanks for that