New engine

[Jeff G 78]

Sure is purdy Guy!

I fired mine up today. After many stupid problems that appeared out of the blue, it fired up within about 2 seconds and purred immediately. So far, the new MSA exhaust sounds great. I went with four hangers and it really helped the alignment. Other than the muffler hanging lower than I'd like, the rest fits really well.

I have an ignition timing question. I *thought* I remembered checking the idle timing with the vacuum hose removed, but the '78 FSM didn't say anything about the vacuum advance when setting timing. When the distributor is at mid-slot, it idled at about 1300 RPM (pulled the carbs from my race L26 and didn't touch them) sounds great, but the timing light shows a ton of advance. It was something like 20° or more. I adjusted the idle screws to get the idle down to ~800 and then turned the distributor and got the initial timing down to about 14°, but it started running rougher and had a delay in throttle response. When I clamped the vac hose, it wanted to stall. With the vacuum advance in place, I checked the total advance at 2800 RPM and it was 46°. I am running the stock '82 NA distributor which, according to the distributor advance curve excel file, that dizzy should be at around 55° total advance. I'm really shooting for a lower number like high 30's with the higher compression.

So, my question is, how do I set the initial timing with that distributor? What am I doing wrong?

[Diseazd]

Jeff....I plug the vacuum advance and run 17 degrees advance at idle. It seems with the higher duration camshaft, you almost must run more advance at idle. I have no idea what my total advance is, but I run the stock European distributors or the stock Datsun distributors on all mine.

[madkaw]

Jeff,

Not sure if I've ever seen timing checked WITH VA attached. The 55 you are seeing is probably with 17 degrees vacuum advance. I think that dizzy adds 17 degrees mechanical. Is this a race motor? If so , I would forget that VA and run around 17 initial. How much mechanical advance does the spreadsheet show?

[Jeff G 78]

Steve, I thought exactly the same thing about pulling the vacuum hose, but the FSM never mentioned it. I reread the instructions several times and it wasn't to be found.

It makes me feel better that 17° initial is normal. I can probably get it to run there. The chart shows 8° static, 17° mechanical and 30° vacuum for my '82 distributor.

So, I should run the 17° initial, and plug the vacuum advance? I have never studied timing, so I'm at a bit of a loss as to what the vacuum does. I understand the mechanical better, but not the vacuum part of it.

[madkaw]

Hope Guy doesn't mind this thread diversion. VA is to help with emissions and MPG . It should only be involved during low load high vacuum situations. That's why I asked if this is a racing motor. Running a street dizzy on a race motor is a compromise anyhow, but having the VA working will probably limit total timing under full load( using OEM figures)- which you don't want .

[madkaw]

Vacuum Advance- how is it supposed to work? - ChevyTalk --The Social Network for Chevy Fans

[Lazeum]

If that could help, with my Rebello cam & Megajolt system, I have to run 20° to 22° at idle to be good. With overlap on aggressive cam, you need a lot of timing advance compared to stock unit at low rpm.

I run 49° at cruise under low load.

[240260280z]

I am with Mathieu. I ran 40 advance at idle on a triple weber 240z and could get momentum from stop with no ping if gently accellerating..too much pedal made it ping. It was a quick experiment when setting the timing. I ended up with 20 at idle and 38 at max.

[Jeff G 78]

Wow, thanks guys. I never realized that I needed that much initial with the cam.

[Diseazd]

Just remember......much better to run a little less advance if in question. Detonation destroys engines!

[Diseazd]

Installed the L24 crank in the L28 block......spins like a top!

[Diseazd]

Installed the .040 over ITM pistons. Torqued the main and connecting rod caps. Looking good. BTW Madkaw...the pistons are flush with deck.