Troubled problem

L.A.B. said:

Danno said:

Sounds like an ignition issue. Possible problem at the pickup. Try switching those two wires and see if the problem switches sides.

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I seriously suggest he does NOT try to swap the Tri-Spark module wires.

Even swapping the wires on a conventional Boyer, Pazon, etc., where the pickup is a separate component would not transfer the problem to the other cylinder, only alter the timing considerably and 'fix' the advance.

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Not familiar with the Tri-Spark's differences, but with both cylinders firing every 180 degrees (wasted spark on exhaust stroke) wouldn't switching the wires (effectively changing the timing 180 degrees) give you the same timing? And if not, how does a single twin-lead coil function?

Craig said:

seanthomasking said:

The fuel taps/filters are brand new as are the stainless braided fuel lines, both sides flowing fine. Sorry to troubleshoot so late.. I can't smell petrol, the spark plugs never dampen.

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Seems like it must be fuel related if your plug is dry and you can't smell gas
Craig

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I would agree, I think you should strip and inspect the new carbs and check everything out . I once bought a new set of factory assembled amals for a T140 that had a 280 main jet in one and a 160 in the other, so not even close !
There maybe swarf or other obstructions in there, only takes a short time to have them apart.
sam

Danno said:

L.A.B. said:

Danno said:

Sounds like an ignition issue. Possible problem at the pickup. Try switching those two wires and see if the problem switches sides.

Click to expand...

I seriously suggest he does NOT try to swap the Tri-Spark module wires.

Even swapping the wires on a conventional Boyer, Pazon, etc., where the pickup is a separate component would not transfer the problem to the other cylinder, only alter the timing considerably and 'fix' the advance.

Click to expand...

Not familiar with the Tri-Spark's differences, but with both cylinders firing every 180 degrees (wasted spark on exhaust stroke) wouldn't switching the wires (effectively changing the timing 180 degrees) give you the same timing?

Click to expand...

No. Reversing the pickup wires shifts the timing by more than 50 degrees.

http://www.boyerbransden.com/faultfinding.html

Check the pickup wires do not change colour in the wiring loom, as swapping these will make the ignition fire over 50 degrees retarded.

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http://www.pazon.com/news/9/SUREFIRE-FAULT-FINDING.html

SPARKS ON CRANKING BUT ENGINE WILL NOT RUN

Check the polarity of the wires from the ignition module to the trigger.
The Yellow-Black wire connects to the left-hand terminal on the connector block (marked Y-B on the printed circuit board).
The White-Black wire connects to the right-hand terminal on the connector block (marked W-B on the printed circuit board).

If these wires are swapped the ignition will still produce sparks, but the ignition timing will be very retarded.
It will also retard even further with increasing engine speed.

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advance-t14015.html#p166594

reverse pickup wire retards the timing by 30+ degrees. Recorrecting them advances the timing by the same. The normal wiring makes a single sine wave negative going first the positive is ignored....reverse wireing makes a single sine wave, positive going first which is still ignored by the box and the negative is now always starting as the magnet goes by the post/pickup....and you get fixed /no advance

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The Tri-Spark Classic Twin module fits inside the points housing with no separate pickup plate, therefore, there are no pickup to box wires to swap, only a positive, a negative and a coil output wire.

http://www.trispark.com.au/images/Class ... 20Inst.pdf

Have you checked that you have not got one tight tappet. If one valve is being held slightly off it's seat .... ?

If you are certain of your ignition system. - Setting carburation means checking the float heights then leaning off all adjustments separately until you induce a miss then backing off slightly. If both carbs are near identical, then a mechanical problem is the remaining alternative - most likely valves.

seanthomasking said:

Brand new premier carbs, working perfectly. changing them over would be obsolete.

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Did you have this problem BEFORE fitting these new premiers ?

Rohan said:

seanthomasking said:

Brand new premier carbs, working perfectly. changing them over would be obsolete.

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Did you have this problem BEFORE fitting these new premiers ?

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I believe he said it was worse before them.

Bckfiring and spitting back would be an improvement over a cylinder not running at all !?

Could still be a cracked cylinder head or blown head gasket, if all the other possibilities have been explored.

Try tipping a teaspoon of petrol down the duff cylinders plughole, replace the sparkplug, and see if it comes to life.
Watch for spillage = a fire hazard.

seanthomasking said:

I should have included that rebuilding the bottom-end is something that will be tiring for me, considering I've spent a lot of time on this bike already.

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Fitting a new top end to a tired or unknown bottom end is not a good formula for future trouble free motoring,
regardless of how much you have already spent on it.

when you installed the new premiers...did you make certain that they were the proper type...Norton only...that were shaved on the inboard side so they would clear each other? Same with the gaskets?

#2...sometimes when installing the slide the needle gets wound up in the spring and REALLY throws off the carburetion. I have been caught a number of times with that problem and learned to check for it quickly.

#3 A long shot...I worked on a commando that had been in mothballs for 30 years...and discovered that it had blown out a section of the head gasket due to an inferior type of gasket. You can easily hear the problem. Try fitting only one spark plug and kick it over. Then try it on the other side. Poor man's compression test.

Have you checked for any air leaks from the carburetor(s) to the head?