Info needed: JXD versus JXLD

[Big D]

Hi Mike

Thanks for the reply. Yes, I have checked the spark plugs and they are blackened (but not fouled) as you’d expect with a rich mixture.

I’ve gone back to 91 octane as I received advice saying these low compression engines don’t benefit from the higher octane anyway.

I connected a vacuum gauge to the engine yesterday and played around with the timing. The gauge showed a reading of about 17 1/2 (in the green) when I first fired the engine up today. I played around with the idle mixture screw but got no change in the vacuum. I then manually adjusted the distributor and got the vacuum reading up to 21. See the video here:

https://youtu.be/dlkhzon6CX0?si=wQJrhsXb42FoXoJ_

I think it is quite advanced at that point and I can't see the white mark I put on the flywheel at all with the timing light at that setting. That gives it the fastest idle but it hasn't changed the popping in the exhaust or the stumble as I blip the throttle.

I still suspect something isn't right in the idle circuit of the carburettor so I'll have another look at that.

Thanks for the assistance.

[Mike K]

Hi Darryl

The popping in the exhaust, it might be that some unburnt fuel is being ignited in the exhaust manifold.

You could try fitting a smaller sized main jet in the carby. I don't think the rich running and black spark plugs will be caused by the idle circuit- it might be a high float level or a sticking float causing it to run rich.