KR-1S.co.uk Forum

Help before i loose the will to live. This Kr1s of mine is not starting just backfiring loudly out of the r/h exhaust. I have rebuilt the engine replaced stator,pickup and ht coil stripped carbs bypassed sidestand and clutch switch and still no joy. I have got sparks at the plugs and fuel to the carbs but still backfires on r/h side. I have checked the flywheel hasnt sheared the woodruff key knocking the timing out. Has anybody had similar problems? Any help or advice would be appreciated as i am all out of ideas. Cheers.

Have you checked the float heights in the carbs? Is the float leaking and flooding the cylinder?

The bike won't start but just back fires on one cylinder, you seem to have covered most of the obvious things. Where abouts are you, cause I'm sure if your stuck and someone on here lives nearby they'll be willing to drop round and give you some help.

Cheers Elf, yeah ive stripped the carbs twice just in case i missed something and checked the floats and heights. I even managed to try my cdi on another forum members kr1s who lived here in gloucester and guess what, yep it worked. I was sure that was the only thing left it could be but no.

Well if the fueling is right then its got to be electrical. Pickup coil springs to mind cause if they come loose and hit the flywheel it kills them and you get a simular problem but you said you've replaced the pickup coil and stator. Loose or dying HT leads in the coil? do you get a really good spark on both cylinders?

Yeah pretty healthy spark and reed valves arent damaged. Hell if its got fuel and good spark then the loathsome swine should go but it just wont play ball.

couple of ideas,
It may sound a bit stupid, but check that you have the plug leads going to the correct cylenders (have made this mistake on my KR250).

After youve kicked it over, check the plugs to see if theyre wet with feul. Perhaps it's flooding

That's about all I can think of right now.

Good luck, Scott.

OOH THOSE MISGIVINGS... CHECK IT LOGICALLY I NOW ITS HARD I HAVE PULLED MY WHATS LEFT OF HAIR OUT WITH A SIMILIAR PROBLEM..
RIGHT YOU HAVE REBUILT THE ENGINE..YOU SAY.. ALL OK NEW SEALS ETC..NO LEAKS ANYWHERE..REED VALVES OK SEATING OK.. KIPS VALVES SET PROPERLY.. NEW BATTERY FULLY CHARGED..COIL WIRES AND EARTH WIRED PROPERLY..CHECKED FOR SPARKS BY TDC BY SPINING THE MAGNETO FLYWHEEL AND CHECKING THE PICKUP COIL TO SPARK PLUG SPARKING AT TDC.. CHECKED CARBS FUEL GOING IN NO LEAKS SET TO PRIME THE TAP..

NOW ARE THE CARBS SLIDES THE RIGHT AROUND ROUND NOT BACK TO FRONT..SLIDE AT THE BACK.BOTH ADJUSTED CORRECTLY..CLEAN FUEL

COMPRESION OK NEW PLUGS...IT MAY SEEM ODD BUT TRY SOME NEW PLUGS BELEIVE ME..TRY..PLUG CAPS OK ..AIRFILTER CLEAR
SHOULD GO REALLY IF THATS FINE..

ONLY ONE THING WILL STOP IT GOING IS COMPRESSION AND WRONG TIMING IE THE PORTS HAVE BEEN DRASTICALLY ALTERED..BUT THAT CAUSES MISSING UP THE REV RANGE...

GO ON THOSE.. FIRST..

THEN WHEN YOU HAVE DONE AND NO JOY PM ME AND I WILL SPEAK TO YOU..

GARY

ScottaKR wrote: It may sound a bit stupid, but check that you have the plug leads going to the correct cylenders (have made this mistake on my KR250).

it does sound stupid

a KR1 has a parallen twin, only one HT coil, that fires both the plugs at the same time, meaning that when one cylinder fires and burns the fuel, the spark ignites also in the other one when the piston is at TDC. so you can't misplce the plugs

thats the way a wasted spark system works, or should do!!! it may be the plugs, dodgy,coil,stator etc etc but start at the cheapest/easiest option first. this may sound equally dumb but easily done, make sure the pilot jets have been fitted since you mentioned you had the carbs apart. this sounds like a possible symtom, ive done it before!!! yes i know and as a result had to wear a h***a tshirt for a month!!

i agree..if its on one side could b a dodgy plug or cap,float hight on that side bit i think the pulse to the coil would knock both out(cos its a wasted spark)...
pull the cap off and check if the lead will spark onto the head bolt,if it does its not electrical...
think the reason the kr needs the plugs the right way round is that it has a seperate cdi for the front and rear(think one has an extra wire but work on either cylinder?)...also check for air leaks on that side...spray some wd40 or carb/brake cleaner around the carb to see if the revs rise..if they do youve got an air leak...that can make it pop n backfire.....let us know how u got on....n didnt think you could get the carb slides back to front??they wont go in..

and wakasaki..please dont shout.....cos your making my ears bleed....

unless you were to use a 10t press and exremely ignorant of how a motorcycle carburretor operates then the slides been placed in wrong way round is very unlikely!! unless you mean wrong carb ie mixed the slides up?

...wakasaki, speak up plz im hard of hearing many thanks!!

JanBros wrote:

ScottaKR wrote: It may sound a bit stupid, but check that you have the plug leads going to the correct cylenders (have made this mistake on my KR250).

it does sound stupid

a KR1 has a parallen twin, only one HT coil, that fires both the plugs at the same time, meaning that when one cylinder fires and burns the fuel, the spark ignites also in the other one when the piston is at TDC. so you can't misplce the plugs

ok then, it's official, I'm a git!
I didn't realise the KR1 had a wasted spark ignition.

Thanks for all your info guys. I'm 100% sure there is nothing wrong with the carbs, i've been over them with a fine tooth comb. Yeah your right it is a wasted spark system but i still swopped the leads around hoping the backfiring would switch to the lefthand side resulting in a eureka moment. Needless to say no eureka moment just a trip down the local spar for a stella moment instead. Does the cdi as well as the pick up coil control the point at which current is triggered to the ht coil and spark plugs? Maybe i should get another cdi just to eliminate that. Oh decisions decisions, the stella option is looking rather tempting at the moment.

are you running premix? just wondering if you could have an air leak ie where the oil pipe goes in
have you tried the flammble spray trick? to see if you sre sucking extra air in...

Check the stator and pickup coil as per the manual.