Thread: Backfiring Through Inlet Manifold - Ignition Advanced or Retarded

Originally Posted by 101RRS

Simple question. Solely from an ignition perspective, a backfire out the inlet manifold is that ignition too advanced or retarded?

I was trying to fire up a RV8 4.6 that has EDIS for ignition on starter fluid. With EDIS in default mode and while the engine is trying to start it is backfiring big time through the inlet manifold. It does not have petrol on it as yet but does have an old style LPG system but before I try to get the engine to run on the LPG I want to make sure it is not going to backfire on me.

I feel that the engine is advanced more than the default 10 degrees and will need to adjust the timing but just seeking advice whether a backfire through the inlet manifold has timing too advanced or retarded. I only need to set the timing roughly at this stage and once engine is actually running I will get it timed to run at about 8 BTDC.

Thanks

Garry

Hi Garry,

There can be a number of reasons for backfire but I was taught a rule of thumb that backfire through inlet is ign too advanced and popping in exhaust is too retarded all other things being equal.
Sometimes when they're too advanced you get a funny "nyah, nyah nyah" cranking sound as the engine is firing back at the starter. Yeah I know trying to put noises into text is weird.
Maybe there's also starter fluid lying pooling in the inlet and detonating when she's firing. Valves all ok - not sticking or a burnt valve?

Thanks for the confirmation - engine is a new build so valves etc are all OK.

I need to retard the ignition which is a bit hard without a distributor and timing marks.

Cheers

Garry

Have you got the firing order correct. wrong firing order will do that.

Regards Philip A

Thanks Philip - I will double check - right now.