Thread: Backfire Protector Valves (and a couple of other questions)

The first attempt to get sparks accross from the coil HT lead to the exposed rotor was inconclusive then I remembered what an old auto elect told me: "If you are looking for sparks, do it in the dark!"

I repeated the test with the garage door down & the lights out & sure enough there was a thin stream of orange sparks from the end of the lead to the centre of the rotor. Ergo a leak to earth= a misfire. It wasn't a huge loss but probably enough to cause idling problems & misfiring under load.

It's Sunday arvo so I'll try a new rotor next week.

Hey Guys!

This Bosch GB 864 rotor is a VERY tight fit. In view of the Stuck Rotor Syndrome, I was worried so I gave it the hot air gun for a while & it was a bit better so I assumed it would be ok on a hot engine & wear itself in.

There was no HT bleeding thru the new rotor so I was hopeful.

But, while it now runs OK with the FAM disconnected & starts very easily, it still won't idle under 2000rpm. & its much worse on LPG than petrol, wuth lots of little backfires.

Comments?

Originally Posted by geodon

Hey Guys!

This Bosch GB 864 rotor is a VERY tight fit. In view of the Stuck Rotor Syndrome, I was worried so I gave it the hot air gun for a while & it was a bit better so I assumed it would be ok on a hot engine & wear itself in.

There was no HT bleeding thru the new rotor so I was hopeful.

But, while it now runs OK with the FAM disconnected & starts very easily, it still won't idle under 2000rpm. & its much worse on LPG than petrol, wuth lots of little backfires.

Comments?

That's funny, I've not had a problem fitting the GB864. There must be a minor variation somewhere.

A hose fallen off or split open? Look around the back of the inlet manifold at the idle air bypass hose.

Well done mate! T'was blown clean off! Idles great now. Too late for a test run. Will report tomorrow.

Geez! I haven't had so much fun since my 1st major job: tracking down a misfire 40 years ago on my 1st car: a '56 Beetle. Not a good ending: it was a cracked head!

My Synopsis:
The rotor partially fails.
Random HT current bounces around under the dist cap. It randomly fires spark plugs sometimes when inlet valves are open. No biggie on petrol, there's no fuel in the intake!
Being a frugal chap I switch to LPG. KERBOOM! an almighty backfire blows off the inlet hose between The MAF & the LPG mixer & the air idler hose.

Thanks again!

Test run went fine.

I took of the cap & the rotor went off & on no problems confirming that it was "newness" that made it tight. A burr that I did not see?

It still has one feature that puzzles me.

It starts 1st hit on LPG dead cold but refuses to do so when hot. I have to switch back to petrol then to LPG when on the move again. Surely this is not some wierd safety thng?