Weak spark wont start race in 3 days Please Help

[jic44]

Hi guys really running out of ideas here and stuck for help so ill try and give as much detail as possible and hopefully somebody can help me out. Ive a race in 3 days and 2 days ago I decided to change the engine in my bike for a freshly rebuilt one i had sitting on the bench due to a slight oil leak from the engine in the bike. 3 hrs had the engine swap done happy enough but it wouldnt start. I did all the usual things plugs out petrol in plug holes, heated plugs 3 different sets of carbs etc etc... its really trying to start but the best it managed was about 5 seconds before dying again. tried jumping it off a car, pushing it down a hill even went wheel to wheel with a moped. did a compression test all fine and its definatly getting fuel. since it started for a few seconds and ive timed a fair few zxr engines at this stage im confident the timing is right which leaves me with the spark. there is a spark on all cylinders but its very weak. Can barely be seen in the shed with the lights on and i know from experience it is weak. I took the plugs out of the running engine i removed from the bike and tried them and they were the same. I also tried another random brand new plug i had lying around and it was the same.
When i removed the running engine the only wires i disconnected were the 4 plug leads the temp guage sender wire the lead to the starter and the main earth cable from the battery the the engine crankcase and the wire from the pick up
The bike runs total loss.
I didnt move the coils in any way.
There are no fuses on the bike except the main 30amp due to a modified loom being a race bike.
I have tried 2 known good batteries and jump leads form the car.
if you watch the spark it gives a very odd strong spark and you can actually hear it trying to start on the other 3 cylinders when it does this.
I also tried a spare pick up cable i had lying around as that is the only electrical component that is changed on the bike from when it was running 2 days ago with the other engine and no difference although i dont know this to be a good one but i can take it from the running engine if its worth trying.

Really stuck here lads as i wont have much time between now and friday to work on the bike with work on. im hoping i wont have to swap the engine back over but im fairly sure its not a problem with the engine anyway.

Thanks for any help.

[Deswilkie]

What CDI are you running? If it was an SP one removed and a standard one fitted (then tried)it'll not work. I'd swap with a space CDI in any case just to eradicate the doubt. Other than that all I can think is a bad earth, I've had this before and it was a pain in the butt to find but easy to sort once found.

Good luck, hate electrical problems.

[jic44]

im running a std cdi and tried my known good spare onew and no difference. I don't really know electrics and the only earth I know is the main one from the battery to theengine and its good so where else do i lookfo
a bad earth?

[Davw]

If the bike was running (starting) fine before the engine change over then the only thing that has changed is the obvious things. You didnt say where the new engine had come from or it history prior to rebuild so:-

1) Engine (are you really sure about the valve timing) I once spent a week trying to start a new engine until I realised that the inlet camshaft had shifted on the cog (engine had been rebuilt following a blow up). the timing marks were fine but the timing was still well out. I now have that brazed!!

2) Electical connections to the engine (earths) and the coil HT leads. Are they all secure? Is the pickup on the new engine OK - try changing for the pickup on the old engine. Make sure that the new engine pickup rotor is a standard (not SP) rotor

3) have you got the electrical connections to the coil right (sorry if this is obvious but I have done it myself)

If yes to all above then try a blast of easy start and a car battery jumper. Hope this helps