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ignition timing with vac gauge

Posted: Wed Apr 10, 2019 11:37 pm
by steve00136
Well i have read a lot about how you should ignore manufacturers settings which was based on a totally different 1970s leaded fuel and use a vacuum gauge to set timing and not a strobe. I connected my Gunsons vac gauge up after slackening the distributor clamp and as soon as started engine the gauge was showing retarded timing (even though it was set at the prescribed 10deg). I advanced the timing bit by bit. Vac went up and so did tickover speed until it levelled out at 20" so retarded it 1" on the scale which measures in inches. Disconnected and went for a run and a massive difference in acceleration and sounds smoother. On return out of interest i connected my timing strobe and found it was now 20 deg advanced. Seemed a lot to me but will run it and monitor for any pinking.

Re: ignition timing with vac gauge

Posted: Fri Apr 12, 2019 11:11 pm
by steve00136
I did a compression test today again with the Gunsons tester and got 180+-3psi which i think is quite high but guess due to a PO doing 40thou rebore and skimming the head 55thou. Also K&N filter with AAA needles so engine is not really standard for standard settings to apply.
Is more advance better for a higher compression? Is that why engine seems to run better?
PS it's a 1975 RB with HIFs and 41610 distributor.

Re: ignition timing with vac gauge

Posted: Mon Mar 02, 2020 9:56 pm
by PeteK
Steve, the American MG guru, John Twist, recommends 30degree advance at 3000 rpm. After a lot of problems, particularly with starting the car, I tried this and it works wonders. The 30 degree would be for a standard engine of course.

Re: ignition timing with vac gauge

Posted: Mon Mar 09, 2020 5:20 am
by steve00136
Thanks Pete I'll check that out next time I have my strobe connected.

Re: ignition timing with vac gauge

Posted: Sat May 02, 2020 8:09 am
by Borotosh
Steve, where on the inlet manifold are you connecting your vac gauge, right now the only option I have (unless I drill and tap) is close to the base of my rear SU carb.
I have posted a couple of questions but waiting for admin to process

Re: ignition timing with vac gauge

Posted: Fri May 08, 2020 7:20 pm
by steve00136
My vac gauge is on the inlet manifold being an RB to CB conversion. I don't think you will get the correct results taking the reading from the carbs. I've read on another forum where they didn't use a vac just twisted the dist until they got the best tickover - disconnect the dist vac first and plug it. This method seems a bit hit and miss to me.