Timing mark- engine backfiring through carburetor

Kjell · Jul 7, 2023

I installed a tri spark electronic ignition and a dual 12v coil from cnw. Ran the test mode on the tri spark and excellent spark on both plugs.
Tried to start the bike and it is backfiring through the carburetor. I suspect the timing must be way off. Installation done as per instructions received with the tri spark. In other words, I aligned the only mark I could see in the window with the mark for 28 BTDC on the degree indicator by rotating the rear wheel forward.. Since these systems fire every 360 degree I did not bother to which cylinder was on its firing circle.
I believe the mark I was looking on was a mark on the rotor ? Is there any other mark I should look at ?

Then

L.A.B. · Jul 7, 2023

Kjell said:
In other words, I aligned the only mark I could see in the window with the mark for 28 BTDC on the degree indicator by rotating the rear wheel forward..

There are normally two timing marks on the alternator rotor 180 degrees apart so are you sure you've used the correct timing mark?

kommando · Jul 7, 2023

Some rotors have 2 marks 180 degrees apart, picking the wrong one will give you the result you are getting. You have to be sure you pick the mark where you are coming up onto TDC, ie on one cylinder the valves are both closed, so take one exhaust rocket cover plus the inlet cover and look at the valves as you slowly turn the engine over. Alternatively take the primary cover off, set the engine to TDC and mark the correct one with tippex.

Timing mark- engine backfiring through carburetor

Kjell · Jul 7, 2023

L.A.B. said:
There are normally two timing marks on the alternator rotor 180 degrees apart so are you sure you've used the correct timing mark?

Not sure as I was not aware of the fact that there were 2 marks.

This makes sense since I sure sounded like it was 180 degrees off

Kjell · Jul 7, 2023

kommando said:
Some rotors have 2 marks 180 degrees apart, picking the wrong one will give you the result you are getting. You have to be sure you pick the mark where you are coming up onto TDC, ie on one cylinder the valves are both closed, so take one exhaust rocket cover plus the inlet cover and look at the valves as you slowly turn the engine over. Alternatively take the primary cover off, set the engine to TDC and mark the correct one with tippex.

Thanks again. I was not aware of that. It makes sense listening to the bike. I will check as per your suggeestion. Thanks

L.A.B. · Jul 7, 2023

Kjell said:
Not sure as I was not aware of the fact that there were 2 marks.

This makes sense since I sure sounded like it was 180 degrees off

The correct mark should be the one to the left of "LUCAS" (opposite to the keyway) in kommando's picture if it's an original Lucas rotor.

Kjell · Jul 7, 2023

Kjell said:
Thanks again. I was not aware of that. It makes sense listening to the bike. I will check as per your suggeestion. Thanks

The bike started right up !

Thanks again

Kjell · Jul 7, 2023

Made sure the valves on one cylinder were on TDC and found the mark on the rotor. Re installed tri spark and the bike fired right up!
Thanks again

ashman · Jul 7, 2023

Yes so many have been caught out with using the wrong timing mark on the rotor, I always pull the spark plugs out and see if the pistons are up for the right timing mark.

seattle##gs · Jul 7, 2023

The easiest method is to remove the spark plugs and move the pistons to TDC...then select the correct timing mark.

Fast Eddie · Jul 7, 2023

seattle##gs said:
The easiest method is to remove the spark plugs and move the pistons to TDC...then select the correct timing mark.

And then paint the timing mark so it’s instantly recognisable next time.

ashman · Jul 7, 2023

Fast Eddie said:
And then paint the timing mark so it’s instantly recognisable next time.

Been that long since I done my timing over 12 years ago now, but when I set my timing the plugs are always out makes it easier to get onto the timing marks using the back wheel.

Timing mark- engine backfiring through carburetor

Kjell

L.A.B.

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kommando

Kjell

Kjell

L.A.B.

Moderator

Kjell

Kjell

ashman

seattle##gs

Fast Eddie

ashman

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