View Full Version : TR6 Ignition timing on TR6

06-10-2008, 04:01 PM
this is a little bit different than the previous post. I have a distributer that I have had on a couple of different TR6s and have run on this engine with out trouble. I modified it to take a vaccuum ADVANCE. I had engine problems and I fixed a bad piston and when I started running again it started to surge and almost pop at high vaccuum conditions. I'm sure I had timed it to 12BTC before but maybe I should time it at 4ATC. I have the vaccuum line disconnected and it's sitting at about 18-20 BTC and seems to run fine and does not ping. My cars have always seemed to like more advance than stated. I'm almost wondering if because the engine is running so much better it's pulling more vaccuum at cruise speed and advancing the timing much more than it did before.

06-10-2008, 04:29 PM
With that kind of initial advance, IMO either your damper has slipped (meaning that's not the true timing); or you are getting knock and just can't hear it. That leads to things like "bad pistons" ... BTDT. Another possibility is that the centrifugal advance is not working properly; or the camshaft timing is wrong.

Do your carbs have the bypass valve ? That might explain the surging, as it basically opens the throttle under high vaccum conditions

IMO, 4ATDC is never the right setting unless you have vacuum retard, or one of the dizzys with huge amounts of centrifugal advance (used on some Spits but not TR6 AFAIK)..

The basic idea all along is that initial + centrifugal should give the optimum advance for full throttle operation. Then the vacuum advance tweaks that for cruise conditions where the engine can tolerate more advance due to lower combustion chamber pressure/temperature. Thus choice of vacuum advance should not influence initial advance.

06-11-2008, 09:39 AM
"bad pistons" was a PO installed option.

06-18-2008, 02:51 PM
Seems I shot myself in the foot again! After looking at the distributer I realized I had moved the opitcal sensor for the Allison Ignition to align the rotor up. Anyway, I moved things around abit to make a better angle for the tach drive cable and forgot I changed the sensor. Even though I varried the timming everywhere from to BTC to ATC The problem came I think was when it got fully advanced the rotor began to cross fire to another plug. It's sitting at about 20 BTC now and runs great with vaccuum advance attatched and all.