Starts then stops after few seconds

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Hi. 1973 750. Kick starts but only runs for a few seconds then dies. The premier carbs have been cleaned, new petcocks and plenty of fuel in tank. I have tried no choke, a little choke etc but same problem. I have a Pazon electronic ignition. I have just finished a long restoration so I am looking forward to getting out of the drive! Any suggestions will be highly appreciated. Many thanks

How does it die?

Like it got switched off, or cough splutter and stop? I take it your tank is breathing ok? Does it start again as soon as retry? You confident that float bowls are clean. Vibration causing electrical disconnect? What do the plugs look like after it's run? Wet / dry, black / clean?
I take it the mechanical auto advance is disabled?
Electrical equipment all in good shape after it's run? Try the horn/ lights.
Something fails after start up, fuel supply, ignition system or over advanced setting on the ign.
Get more detailed results to work on.

cheers
Jon

Thanks Jon. I will work…

Thanks Jon. I will work through that check list. It stops like the ignition is cut, no splutter. I did clean the float bowls. I will make some other checks. Thanks again

Reverse Logic

Many years ago I came across a similar problem with a 750 Commando.
The owner had just fitted a new electronic ignition kit but it turned out to be for an Atlas.
The result being that once it fired up (which it did easily) the electronic advance took the timing in the wrong direction causing the motor to die.

Thanks Philip. It was…

Thanks Philip. It was running ok before I started renovation so I know its the correct Pazon. I have checked its working with its self test and both plugs spark ok. I am pretty sure in the fuel so I have found a local carb wisperer to come and have a look. I will report back.

Have you ridden an old bike…

Have you ridden an old bike before?

You know to use the throttle to keep revs up until the engine is warm enough to idle?

Not quite right.

The owner had just fitted a new electronic ignition kit but it turned out to be for an Atlas. This is a SEMI nonsense statement. Electronic ignitions ie Boyer, Pazon, Trispark, Lucas RITA, for the parallel twin are ALL the SAME,for Commando Atlas 650SS Mercury even Dommie 99

But if you fit it without taking note on DIRECTION of rotation then you will get a lack of advance!!
Another point, this problem CANNOT be the advance curve wrong as the bike would have been started and the fully advanced point set with a strobe, then of course the tickover mixture would have been set and tick over speed set.
So we await further information on this one. But an instant switch off could be a dodgy connection/wire.

Thanks Alan. I have checked…

Thanks Alan. I have checked wiring and all looks fine, but could be a fractured wire I suppose. I will rule out fuel first and get back.

Fuel cannot

Fuel cannot just stop, the engine will splutter as it goes weak.
A sudden STOP will be electrics. You start the bike, and then gentle move the wires and connections you can get at, to see if it stops.

Will we ever find out what…

Will we ever find out what was wrong with this bike?

I certainly hope so! I am…

I certainly hope so! I am working my way through electrics and fuel and will report back when I find the solution! I do thank all for your inputs and suggestions but so far success eludes me!

Its running, finally! The…

Its running, finally! The electrics are fine and all wiring checked. Good spark. The issue was fuel flow. I thought I had cleaned the carbs well but it turns out there were still some residuals of old fuel deposits and rust particles left before the tank was cleaned and epoxied. As a point of interest I was told that carbs set up in UK do not function well here in Portugal. The climatic differences, especially low humidity here, needs a jet change to increase fuel flow. Thanks again for your inputs.

Every old bike carburettor…

Every old bike carburettor anywhere, needs individual tuning and adjustment.

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