Setting initial advance values...

Spitty · Post by **Spitty** » Fri Mar 29, 2013 3:38 pm

Hi,
I've installed the MJLJ and so i can replicate my 'standard' ignition setup as a good start point i've measured the advance at static then for every 500 rpm increment thereon by increasing the engine speed whilst in the garage ie presumably no load(?).
I've then put these values into an ignition map and saved it ready to flash to the MJ.
Now, do these values represent hi or low vacuum ie do they go in the load bins '20' or '230' for example?
I'm guessing the '230' as it's off load and therefore hi vacuum?

cng1 · Post by **cng1** » Fri Mar 29, 2013 5:31 pm

I am afraid that your efforts to date may well have been in vain. To extract useful figures you need to do it against known load. The easiest way to do this on a distributor setup is to disconnect the vacuum hose and run the engine through the range of speeds. This will give you the values for wide open throttle (100KPA). For partial vacuum one way to do it is to have a vacuum gauge and a syringe connected to the vacuum advance feed on the dizzy. Use the syringe to pull and hold the appropriate vacuum level and run through the RPM range again. Do this at say 30, 50, 60, 70 and 80 KPA and you should have a reasonably complete set of numbers to put in the map.

Spitty · Post by **Spitty** » Fri Mar 29, 2013 8:34 pm

Cheers bud,
I had disconnected the vacuum line when i took the readings; does that help at all or, are my readings still against an unknown load?
I'm running a lairy cam (on cam at circa 2700 rpm) with twin solex C40 ADDHE's so it's not a 'normal' setup!

Cheers,

cng1 · Post by **cng1** » Fri Mar 29, 2013 8:54 pm

If the vacuum line was disconnected then you've got the 100kpa results.

Spitty · Post by **Spitty** » Sat Mar 30, 2013 7:25 am

Cheers bud,
Forgive me if i sound a bit naive, but do the 100kpa readings i have represent no-load and therefore lo pressure/hi vacuum and are therefore the initial readings that go in the bottom of the ign map?

cng1 · Post by **cng1** » Sat Mar 30, 2013 9:26 am

100kpa is full-load (wide open throttle) on a nat-asp engine. You put the 100kpa values in the 100kpa row in your map.

Spitty · Post by **Spitty** » Sat Mar 30, 2013 6:23 pm

Thanks, i'll put it in exactly as you advise.
I know you're right, but i'm trying to get my head around this being the 'wide open' settings as when i took them, i was revving the engine in the garage and the throttle was only slightly open as there was no load on the motor; am i right in thinking then that full load is therefore the same as the readings i took and that the lowest kpa (vacuum) would be achieved with high engine speed and throttles closed?
Cheers

cng1 · Post by **cng1** » Sat Mar 30, 2013 8:19 pm

The dizzy senses load from engine vacuum. With the vacuum feed disconnected it sees full atmospheric pressure which is exactly the same as it sees when the throttle isn't errm throttling the intake.

Spitty · Post by **Spitty** » Sun Mar 31, 2013 7:05 am

Thanks bud,
I was obv concentrating on the 'wrong' bit there! Focused on the carb where it was pretty obvious now that you've pointed it out, that i should have been thinking more of tge dizzy - schoolboy error there i reckon

Thanks again, now all i need to do is to get the tacho working; have tried everything but still no joy...

Done the tacho driver, pullup, pulldown ...... Only one left to try is the two IN4004 diodes without the zener...

Spitty · Post by **Spitty** » Sun Mar 31, 2013 7:06 am

Thanks bud,
I was obv concentrating on the 'wrong' bit there! Focused on the carb where it was pretty obvious now that you've pointed it out, that i should have been thinking more of tge dizzy - schoolboy error there i reckon

Thanks again, now all i need to do is to get the tacho working; have tried everything but still no joy...

Done the tacho driver, pullup, pulldown ...... Only one left to try is the two IN4004 diodes without the zener...

Spitty · Post by **Spitty** » Sun Mar 31, 2013 7:06 am

Thanks bud,
I was obv concentrating on the 'wrong' bit there! Focused on the carb where it was pretty obvious now that you've pointed it out, that i should have been thinking more of tge dizzy - schoolboy error there i reckon

Thanks again, now all i need to do is to get the tacho working; have tried everything but still no joy...

Done the tacho driver, pullup, pulldown ...... Only one left to try is the two IN4004 diodes without the zener...

Spitty · Post by **Spitty** » Sun Mar 31, 2013 7:06 am

Thanks bud,
I was obv concentrating on the 'wrong' bit there! Focused on the carb where it was pretty obvious now that you've pointed it out, that i should have been thinking more of tge dizzy - schoolboy error there i reckon

Thanks again, now all i need to do is to get the tacho working; have tried everything but still no joy...

Done the tacho driver, pullup, pulldown ...... Only one left to try is the two IN4004 diodes without the zener...