Another timing curve question
I measured the slots on the stock piece and they are .445 which corresponds well to the table that's floating around here and elsewhere (attached): 13 distributor degrees, or 26 crank degrees.
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But the 18 degree holes on the FBO plate measure out to more like 20-21 degrees by that chart, so I decided to leave it in place. I got the superlight Mr. Gasket 925B springs from O'Reilly (the package looks like it's been on the shelf for 30 years). One superlight, one OEM heavy spring with long loop. Put it back together and then I realized I'd forgotten to put the dist on #1 TDC when I pulled it. :BangHead: My favorite quick way to find the compression stroke TDC without pulling a valve cover is a compression tester and a timing light - point at the gauge and make sure it flashes at the same time the needle kicks. Turns out my 50/50 guess was correct (for once in my life) :)
Now it starts easily cold or hot, idles at 28, and very slowly advances to about 33 deg by 4000 rpm. Up to the mid-to-high 40's with the ported vacuum connected (didn't adjust the can). It could probably use a couple more degrees of initial but I'm being conservative given the crappy pump gas. Not sure where it stopped advancing since I get nervous lying on an engine revving that fast ;) May need to open the FBO slots a bit more, get a weaker heavy spring, or just have more confidence in my short block and rev it to 5000 or so while holding the timing light! Doubt I can find a spec for the Jacobs ignition retard (slew rate) anyway.
I took it for a short run and it's definitely better off-idle and low-speed cruise. So far so good ;)
I measured the slots on the stock piece and they are .445 which corresponds well to the table that's floating around here and elsewhere (attached): 13 distributor degrees, or 26 crank degrees.
But the 18 degree holes on the FBO plate measure out to more like 20-21 degrees by that chart, so I decided to leave it in place. I got the superlight Mr. Gasket 925B springs from O'Reilly (the package looks like it's been on the shelf for 30 years). One superlight, one OEM heavy spring with long loop. Put it back together and then I realized I'd forgotten to put the dist on #1 TDC when I pulled it. :BangHead: My favorite quick way to find the compression stroke TDC without pulling a valve cover is a compression tester and a timing light - point at the gauge and make sure it flashes at the same time the needle kicks. Turns out my 50/50 guess was correct (for once in my life) :)
Now it starts easily cold or hot, idles at 28, and very slowly advances to about 33 deg by 4000 rpm. Up to the mid-to-high 40's with the ported vacuum connected (didn't adjust the can). It could probably use a couple more degrees of initial but I'm being conservative given the crappy pump gas. Not sure where it stopped advancing since I get nervous lying on an engine revving that fast ;) May need to open the FBO slots a bit more, get a weaker heavy spring, or just have more confidence in my short block and rev it to 5000 or so while holding the timing light! Doubt I can find a spec for the Jacobs ignition retard (slew rate) anyway.
I took it for a short run and it's definitely better off-idle and low-speed cruise. So far so good ;)