SP1000 no spark it idle/low rpm on 1 cylinder

[1down5up]

Gents,

Having issues with an SP1000, I can't get it to run nicely at idle.

Ive figured out (using timing light) that the left cylinder isn't firing at low rpm/idle up to about 2000rpm,after that it's firing.

The right cylinder is firing at idle (again verified by timing light), I've also changed/swapped the coils over across the cylinders and the issue doesn't move so I'm fairly sure the coils/points/condensers are ok.

Spark plug fires fine out of the cylinder on the left (held against the valve cover, nice strong spark)

I've checked timing, points gap etc

Not sure what could cause this?

Bike has Phf36 but appart from that it's a stock motor/igniting system.

[Old Jock]

Could be quite a few things I suppose

I'd also swap over plugs and HT leads, I've had more than one issue like that where you'd get a spark out of the cylinder but still have running problems and it turned out to be either the HT leads or the plug

[Scout63]

Maybe pull the left side idle jet and see if it is clear.  They usually need to be physically cleaned out with a #78 drill bit or .016” guitar string - too small an orifice for chemical cleaning (spec for the stock VHB carbs).

Or do what I do and crab the frame, pull the engine and rebuild the whole thing. Then clean the jet.

[fotoguzzi]

Dumb question, How does a timing light show a plug is not firing?

[Frenchfrog]

By not flashing

[fotoguzzi]

By not flashing

thanks, I have not used a TL for like 50 years.

[pressureangle]

In the archives there is more than one thread where the culprit for this specific problem is the power wire between the two coils. I had this problem myself on my '85 LeMans. The right coil was fine but there's a simple short jumper to the left coil. Mine had a failed connection on the wire at the terminal, took some sweat to isolate. Try running a simple bypass jumper to see if it comes to life, if so then you can attend making a quality replacement wire.

[1down5up]

Thanks for the thoughts -

I have swapped the coils and points across and the issue stays on the left cylinder.

It must be due to fuel/air, have checked the idle O-ring etc and choke rubbers are new.

I didn't think a to rich/lean air fuel would cause the plug not to spark, just the mixture not to ignite.

Will double check the power link between the coils.

[centauro]

Gents,

Having issues with an SP1000, I can't get it to run nicely at idle.

Ive figured out (using timing light) that the left cylinder isn't firing at low rpm/idle up to about 2000rpm,after that it's firing.

The right cylinder is firing at idle (again verified by timing light), I've also changed/swapped the coils over across the cylinders and the issue doesn't move so I'm fairly sure the coils/points/condensers are ok.

Spark plug fires fine out of the cylinder on the left (held against the valve cover, nice strong spark)





I've checked timing, points gap etc

Not sure what could cause this?

Bike has Phf36 but appart from that it's a stock motor/igniting system.

The only other suggestion I can offer after every one else's comments is:
Remove the suspect spark plug lead from both ends and use an ohmmeter to check for continuity; it should be no more than..2-.3 Ohms. . While itis in your hands, inspect it carefully inch by inch to check for damage. .

[TOMB]

You could also try starting the bike up in a totally dark area inside the garage with the doors open or outside of the garage with no lights and look for the flickering lights jumping from the power cables spark plug lead spark plug caps to ground you'll probably hear some snapping sounds too if you can find the bouncing Sparks so to speak, you'll find your problem

TOMB

[yackee]

Just going off my Vespa experience, any problem with ignition, try new plugs. Cheap and almost always solves the problem.