Backfire at carb

odie · Post by **odie** » Fri Sep 16, 2022 6:38 pm

Hi all
Have a strange one, with the throttle closed i have a ring of blue and a chuff around the throttle flap in #1 carb intermittently and randomly 1 2 3 4 ,sec intervals with no real pattern. I would have thought that if it was a valve it would do it all the time. The bike. just started running rough on the way home a couple of weeks ago when i was pootling through town. any ideas would be gratefully received as I am clueless. Took ages to find it had to start the bike in the dark garage (was looking for an ignition fault somewhere).

Goshreally2 · Post by **Goshreally2** » Fri Sep 16, 2022 8:14 pm

If it was me I would be looking for a fault in lead, cap or spark plug at no.1 or a blockage in carb no.1 idle jet.

odie · Post by **odie** » Sat Sep 17, 2022 2:08 pm

Turns out it was the replacement coil that a garage fitted a couple of years ago, I had a spare genuine coil swapped it and problem gone ran fine. The coil was corroded around the screw terminals where the lead connects in the coil. Don't know why it would fire at odd intervals but it did (probably just pants). Thanks for all the pointers chaps helped me go in a new direction.

odie · Post by **odie** » Sat Sep 17, 2022 6:02 pm

I was hoping it wasn't a valve but feared the worst. Lucky boy

bunk · Post by **bunk** » Sun Sep 18, 2022 3:13 pm

Is it just me, or do older yamahas have the most unorthodox ignition issues?!

Nicoxj · Post by **Nicoxj** » Mon Sep 26, 2022 2:31 pm

bunk wrote:Is it just me, or do older yamahas have the most unorthodox ignition issues?!

I'd say yes, and it is due to the way the coils and leads are placed. They are not so much protected, and get corroded with time.

I've had the experience with 3 different Yamahas (900XJ 1984, XTZ660 1994 and FZR 1000 1989), but never with the VFR750 (1988) or the Ducati (1998).

Each time I changed teh leads and protected the coils better, and never again had the issue.