Thread: Misfires badly when engine is cold, slight when hot

There IS a Bosch rotor button that works... but it needs a little modification. A Falcon XE rotor part no. GB786 is made in Australia. It has the same bore as the Rover. You need to cut about 7mm off the botton and it fits straight in. The contact strip is screwed on with a single philips screw, you can remove it, slot the holes about 2mm and adjust it for minimal tip clearance. Never had one fail yet.

I would probably cut a bit off the ends of the contact to match the Lucas rotor. I do not know for sure but the dwell and rise time of the coil may be affected. Did you check whether the ignition timing was affected ?

BUT what a great mod. How on earth did you work that one out?
Regards Philip A

Originally Posted by PhilipA

I would probably cut a bit off the ends of the contact to match the Lucas rotor. I do not know for sure but the dwell and rise time of the coil may be affected. Did you check whether the ignition timing was affected ?

BUT what a great mod. How on earth did you work that one out?
Regards Philip A

I suspect the coil rise time is mainly determined by the ignition leads' construction. My (seat-of-the-pants) engineering says using inductive core leads slows the rise time most, the evidence is in the amount of RFI when you are listening to a marginal AM station.

As far as timing is concerned, my timing light always stays on until I've finished, can't say I've noticed any change. You would recall that the vacuum advance moves the magnetic sensor, so the rotor alignment isn't always square on to the cap terminal. Near enough seems to work fine. I always look where the burn mark is on the end of a rotor, that tells me if there is a potential timing problem.

The Bosch rotor is actually shorter than the Lucas one. If you measure the inside of a Bosch cap I think its about 2mm smaller across the terminals than the Lucas. Best spin the GB786 rotor in your dissy to get a witness mark for the centre, then measure. The locating tang lines up in the same direction. Filing a different profile on the ends is fixable, you can always lengthen it again.

When faced with a worn genuine cap and rotor, I rarely replace them when the plastic isn't damaged (Why risk cheap junk?). It's quite easy to peen the end of the brass strip with a small hammer to reduce the tip clearance. One of my cheapest individual ways of reducing back firing on LPG!


I have been gas converting since 1980 and have done factory style electronic ignition conversions on many different vehicles. 20 years ago the XD-XF Falcons were my bread and butter, there were always bits lying about. Then when your mate rings up with a dead RR on a Saturday night you get to rummage in the rotors box and make do. He told me it can't be the rotor, he had just fitted a new one.

Hi, I was just at Performance Ignitions in Nunawading getting new leads, Vaccum Advance and rotor button. I asked for a Lucus and explained the problems people have with Bosch ones. He said there are a lot of cheaply made ones that break down but recommended a Bosch one the is used for a Ford. It is a GB864. He assured me it will work fine and has not had any problems with them. It looks a lot more solid the the one pictured above. Has anyone tryed this one without any problems or has he fed me B.S. Will have to see how it goes.
Cheers, David.

Dave, I doubt that the people at Performance Ignitions will feed you bird seed. What they don't know (or haven't seen) would be tiny !!!

Cheers

Pete

That's what I figured Pete. They seem like a good bunch of guys and gave good info and advice, I recomend anyone to go and have a chat. It's just I have read so many post about bosch rotors it got me a bit worried. May be it's only one type of bosch rotor causing problems.
Cheers, David.

GB864. My Bosch catalogue identifies this as XF Falcon. It has the same removable tang as the GB786 and is made in Australia. Dang! Why didn't I spot that? I will buy one Monday and check it out.

Did some checks, some sparking off the leads where they come in contact with other leads and along the runs. Vac advance appears to be broken, but will be checking the hose too.
Will be checking the rotor make tomorrow when I fix and tidy other bits.
Chris