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Discussion Starter #1 (Edited)
Good afternoon,

A new post because I need help. I am about to complete full restore of my motorbike. 2 monthes ago, I start the engine and stop it quickly. And I never succeed to restart again.

I checked spark plugs, wires, ignition coils, CDI, pulse generator, valves and carburators.

Everything seems to be OK...
 

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It takes three elements to get an explosion.

Air
Fuel
Spark

Which one are you missing? What test did you do to acertain that "everything was okay"

To test the system, start by the simplest. Spark. Pull the cap and put an old spark plug in it. Ground the tip of the sparkplug on the block and crank the engine. You should see a spark. If no spark is seen, then you found your problem. Why no spark? Maybe no voktage at the coils. Chech that. Perhaps no voiltage at th CDI. Check that. Perhaps faulty CDIs. Perhaps no spark because of the clutch lever switch or the side stand switch. Check them.

If you have spark on all four sparkplugs, maybe you have no fuel reaching the combustion chamber, or at least reaching the carbs. Either carbs are faulty (stock closed float needles) or bad fuel pump. Or no voltage to the fuel pump at all.

Verify that you have your 12v at the pump. If you do, then verify that the pump works by disconnecting the outlet and see if fuel spills when cranking the engine. If no fuel, then the pump is bad. If there's fuel, problem might be with carbs. if the pumop is bad, you still can bypass the pump. First make sure the fuel level in the gaz tank is higher than the carbs and feed the carbs straight from your fuel tank

If you have no voltage at the pump, then investigate why.

As you can see, you have many tests to do. ;-)
 

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Discussion Starter #3
Hi,

Then, first, I checked the sparks. I removed the 4 spark plugs and test them one by one between spark plug and a wire connected to the frame: all 4 are firing.

I cleaned allthough the carbs using utrasound.

For trials, I am using a workshop tank and I by-pass the fuel-pump.

Concerning air, I removed air pipes...
 

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Well. You did a good job already. You're almost there.

You have spark
You have fuel reaching the carbs.

Now you have to check if fuel goes out the carbs. ;-) Crank the engine for a few seconds. Theorically your spark plugs should now be wet. Remove one of the spark plugs and verify if indeed it is wet. If it's dry, then the problem is within the carburator. Is it possible the inlet needles The ones controlled by the plastic floats are stuck closed, not allowing fuel in the bowls ?

Lee
 

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Discussion Starter #5
This morning, I checked the inlet needle controlled by the plastic floats: with the bowl bottom opened an the workshop tank connected, i saw the fuel entering the carburator. It seems that the fuel doesnt go out the carbs....

I will check again the spark plugs after trials but I already checked them before and they all were dry.

Then I dont unterstand what's happen...
 

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Discussion Starter #7
Hi, one more question concerning production of sparks. The whole cycle need 2 revolution of crank shaft. Then, there are 2 sparks per cycle for each cylinder ? One usefull, and the other unused ? Is that right ?
 

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Both spark plugs ignite at the same time in the same cylinder. The reason is to have a better flame propagation. Many bikes, including BMW flat twins, have two spark plugs per cylinder.
 

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Discussion Starter #9
I think we misunderstood. I think one spark is produced at the end of compression and a second one at the end of exhaust time. Am I right ?
 

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Yea Cpt, I havnt looked at the the Africa twin setup, but a lot of four strokes I have worked on have a second spark (wasted spark) at the top of exhaust stroke.
 

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Discussion Starter #11
Then, it should be normal to be able to see sparks trough intake valves during the overlap between intake and exhaust valves at the end of exhaust stroke... No ?
 
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