Kr1 wont rev + backfire

[scooby_hugh]

First off hello i am new to the forum and have just bought an 89' kr1 and this looks like a great source of information.


Iv bought a project kr1 which idles well and starts first kick but will just die if i try and rev it, if i blip the throttle abit it will backfire/spit from one exhaust, the backfire switches sides if you swap the ht leads which leads me to believe its an electrical problem. Both carbs are squeaky clean inside and brand new plugs. Ht caps look new aswell. The previous owner had it running well after he rebuilt the top end and it developed the problem when he came to ride it one morning.

Any help appreciated,

Cheers

[Luders]

Welcome to the forum.

Your problem does sound electrical related and electrics not being my strong point, I'll let someone better qualified offer you advice.

For what it's worth, I would start with the coil as being the source of your problem.

Good luck, I'm sure JanBros will be on soon

[scooby_hugh]

Thanks mate, i have a friend with 2 kr1-s so i can borrow bits to troubleshoot, il see about borrowing some coils/ a coil

Cheers

[ScottaKR]

the backfire switches sides if you swap the ht leads

That definately means that theres a problem with the coil/ht leads, just as Luders suspected. Swapping it out with a known good coil from your mate will confirm this.
Welcome to the forum mate.

[JanBros]

Good luck, I'm sure JanBros will be on soon

I am

but there"s nothing more to say

[scooby_hugh]

Cheers guys!

Will test asap and let you know results

[scooby_hugh]

Fitted a new coil and theres no change, the backfire is staying on the rh side though even if the leads are swapped (origionally it was on the lh side and did swap sides when i switched leads)

Any ideas? Cheers guys

[Luders]

Again, not really my area, but check your pickups.

[scooble]

if its sticking to one cylinder, then check the condition of the reeds (cracked, split or lifting). Also worth doing a compression check. WOT, no plugs and push along for a few yards. Can't remember what the readings should be, but both cylinders should be pretty consistent.
I also had backfires with broken rings so also worth checking up the exhaust port too for damage.
Have you also swapped the carbs over to see if the fault stays on the same cylinder

[scooby_hugh]

It has a new top end, checked the reeds they are perfect, carbs are very clean, the backfire was on the left before and has now switched to the right, it wasnt always on the same side, i can compression test but im still sure its electrical.

Going to pick up a stator and cdi tomorrow

[JanBros]

have you tried other plugs ?

I know you said they are new, but that doesn't mean anything
or swap them to see if the problem switches to.

[ScottaKR]

have you tried other plugs ?

I know you said they are new, but that doesn't mean anything
or swap them to see if the problem switches to.

+1

[scooby_hugh]

I did try different plugs, pulled the exhausts off and span the engine slowly with the flywheel and my bores look a little dodgy, so im not sure how well the claimed top end rebuild was carried out, i should be picking up a set of barrels from a mate and il rebuild myself so i know its good. How long will a standard bottom end last on one? Is it worth doing that too while im there?

[Luders]

Crank rebuilds are £200+ and well worth doing if you are unsure of the condition. The problem with cranks is they are getting harder to find, so my philosophy is keep what you've got in good serviceable order.

[scooby_hugh]

I spose i better get on and do the lot, is there anything else worth doing while the cases are split? Il do all seals, mains and big ends