SICK SR250

[TOAD]

HI,I'M NEW TO THE SITE. I RIDE A 1994 YAM SR250 WHICH I BOUGHT ABOUT A YEAR AGO TO GET ME BACK ON THE ROAD AFTER A 15yr BREAK. WELL IT'S DONE IT'S JOB AND NOW I'M READY FOR SOMETHING BIGGER. BUT JUST LATELY IT HAS STARTED PLAYING UP.
IT HAS BECOME HARDER TO START,CUTS OUT WHEN I STOP AT JUNCTIONS AND GENERALLY RUNS VERY LUMPY AND BACKFIRES  A LOT. HAD THE CARB TO BITS AND IS SET UP CORRECTLY AND JETS CLEANED.  REMOVED AND CLEANED AIR FILTER COZ I THOUGHT IT MIGHT BE A FUEL PROBLEM. COULD IT BE THE PLUG BUT THAT LOOKS OK. I JUST DON'T KNOW.  ANY IDEAS PLEASE ?

[peterj]

First thing I do when starting gets hard suddenly is change the plug (make sure the gap on the new one is correct first). This rarely helps, but it's so cheap to do that it's worth eliminating it first. It has occasionally worked for me.

Other thoughts now you've cleaned the carb.

Valve clearances
Air leaks causing weak mixture - spray some WD40 around the inlet manifold whilst engine is running - if there is an air leak you will probably see an alteration in running.
Re-check the settings of the pilot air screw
Disconnect the kill switch/sidestand cutout if fitted/clutch cutout if fitted - see if that makes a difference

Best luck

[guest27]

Agree on the plug - they have to work under extreme conditions and can look good out of the head - nice fat spark etc and then fail in the head under pressure etc - and you also then have a spare one.

Is it backfiring on the over run or under load?

You say the carb has been cleaned - I have a great ability to take a carb apart, clean it all and then trap a bit of dirt in a jet as I put them together - difficult starting could be some dirt in the pilot jet or air jet, and as these tend to be real small they block easily.

Is there any leaks around the exhaust header as well as any leaks on the inlet side.

Compression - is there plenty, if it is a bit old and starting to loose compression this will make it harder to start etc.  Had a Superdream that would not run below 3000 rpm, when I eventually pulled the head off both exhaust valves had started to split through age and use - making the pot leak.  This had started as difficult starting / running and progressed.

Keep coming back with the info and we can scrabble around for other ideas.

R

[TOAD]

OK THANKS GUYS, I'LL DO THE CHECKS YOU SUGGEST.  THESE BIKES DON'T HAVE A MANUAL SO I'M STRUGGLING A BIT . WILL GET BACK TO YOU SOON.

[mini-thumper]

There are a few manuals for the SR250 on this site:

http://www.repairmanualclub.com/yamaha_manuals

Mostly in Spanish but its a start.........................

BB

[themoudie]

Copy and paste the text into 'Google' languages if it will let you and then translate. Might be of assistance!

Regards, Bill

[TOAD]

CAN'T SEEM TO DOWNLOAD THE MANUAL.THANKS ANYWAY.
I'M GOING TO BUY A NEW PLUG THIS MORNING AND CHECK THE AIR INTAKE AND WHATEVER ELSE I CAN THINK OF WHILE I'M THERE. IF THAT DOESN'T WORK I'LL JUST TAKE A HAMMER TO IT.

[Steve H]

IF THAT DOESN'T WORK I'LL JUST TAKE A HAMMER TO IT.

I see youve attended one of GC's bike maintenance courses.

[TOAD]

WHO'S GC?

[Steve H]

WHO'S GC?

Graham the Club chairman, forum name is 'onepot'

[guest27]

If the GC method does not work - I will be running a course based on my experience of using larger sized hammers for percussive maintenance just as soon as I get a new shaft for the 14lb sledge.  (Which broke whilst I was chopping wood.... sending the head flying of upwards - did not know whether to duck, look, run or just cry.)

R

[pigafetta]

How do you chop wood with a hammer?

Anyway Toad,

These chaps...
http://blackbears.ru/index_en.php?get=manual
...have SR250 manuals in English. I don't know if they're any good for your model. I don't know if they're any good, generally. Ought to be better than nowt though.

Dave B

[TOAD]

Thanks.downloaded manual,thats a start.
 Bought & fitted new plug.Made no difference. Sprayed wd40 around air intake to check for split hose. Engine sound didn't change but it produced a lot of grey smoke from the exhaust which says to me that maybe there is a leak somewhere but I can't find one.
Must get to the bottom of this it's beginning to wind me up.

[cloggy]

If you just sprayed in the general area of the intake then wd could have been sucked in through the correct orifice and even a faultless engine could then smoke. One old trick is to light a match whilst the engine is ticking over and see if the flame is drawn towards the inlet manifold between the carb and the head, just make sure there are no petrol leaks before you start though.... you can do the same thing with wd at the inlet manifold edges and watch if it dries faster in one place than others but not with a hot engine as it will all dry really fast. It sounds like tight and or knackered valves or an air leak on the inlet manifold but dirt in the slow running circuits of the carb will also cause this, mind you that normally badly affects starting as well.

[TOAD]

Now sorted!  Air was getting in through a gap where the rubber hose joins the air box.Sealed it up and its ok now.
THANKS FOR YOUR HELP!