660 build won't start, just backfiring

[660steelie]

Help! I'm at my wits end! Lol, I've built a 660 engine for my 1989 3he and like the title says it won't start. I've checked the cam timing and its spot on, the flywheel is sat correctly on the woodruff key, all four plugs have a good spark, I have shimmed the valves. I know the carbs are good as they are the same ones and are like new inside. I've tried fresh fuel and new plugs, but still when I try to start it it just backfires usually out the carbs sometimes out the exhaust? Please help!

[reelrazor]

I think you are 180° out of phase with your spark.

Swap the primary wires at teh coils. I think they are grey and orange. One at each coil, move one to the other coil and vice-versa..Try it and let us know.

[660steelie]

Thanks for the reply and sorry for the late response, been really busy at work. Yeah that's what I thought so swapped the plugs on the coils over but then it doesn't seem to fire at all then? It smells really rich but it's the same carbs I was using so should be running lean if anything shouldn't they?

[660steelie]

Right, I've tried tipping a bit of petrol down the carbs and it tries to start but then nothing, could it just be that I havnt rejected the carbs?

[660steelie]

For some reason I can't pm? So I'll post it up here:
Subject: 660 build won't start, just backfiring

reelrazor wrote:
I think you are 180° out of phase with your spark.

Swap the primary wires at teh coils. I think they are grey and orange. One at each coil, move one to the other coil and vice-versa..Try it and let us know.


Hi, sorry for the intrusion. I read one of your old posts and realised you used the same setup for your 660, Fzr head and carbs. I havnt rejetted my carbs yet as I thought it would start as they are? Did you find this? Or did you change the jets before trying to fire her up? Any help would be greatly appreciated! Thanks, John