Everything old is new again.
Ported vacuum for vac advance
- Thread starter landcruiserrich
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I am glad it got brought back up. My 76 has a PO installed HEI w/vacuum advance and was hooked up to the vacuum box on drivers fender. But it was pulling manifold vacuum not ported. Checked Haynes and reconnected to factory but this was for stock 76 dizzy. Checked that it was not pulling vacuum at idle anymore but never to see if pulled vacuum off idle. Just checked port on engine side of carb and it is ported vacuum so hooked dizzy and will check out tomorrow. I have never been sure the vacuum advance has been working so I will see if this makes a difference.
John
John
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The 76 vacuum system is set up to apply vacuum to a vacuum retard dissy under certain conditions to reduce power and NOx emissions.
Do not connect the 76 emission vacuum system to a vacuum advance dissy, because it will do exactly the wrong thing at the wrong time.
Do not connect the 76 emission vacuum system to a vacuum advance dissy, because it will do exactly the wrong thing at the wrong time.
JimC,
Just got back from work, drove the 40 and it definitely seems to be running better.
It has a HEI with vacuum advance and I had incorrectly hooked it up per the Haynes diagram for a stock 76 dizzy. Just checked vacuum at that port and 0 vacuum even when revved up. Any easy way to tell if this dizzy was curved for a 40 versus the advance curve for a GM motor? It is my understanding that GM distributors have way to much advance for the 2f. Now that the advance is working I do not want hurt the motor.
John
Just got back from work, drove the 40 and it definitely seems to be running better.
It has a HEI with vacuum advance and I had incorrectly hooked it up per the Haynes diagram for a stock 76 dizzy. Just checked vacuum at that port and 0 vacuum even when revved up. Any easy way to tell if this dizzy was curved for a 40 versus the advance curve for a GM motor? It is my understanding that GM distributors have way to much advance for the 2f. Now that the advance is working I do not want hurt the motor.
John
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The advance curve should be close enough for a 76 2F. It is the hi-compression closed chamber engines (81-later) that are more sensitive to excessive advance.
I bumped this thread because I acquired a non-usa vacuum advance dissy, to replace the vac retard unit, and I was researching how to do ported vacuum, as I thought my 8/75 Cal spec carb did not have it; but after looking at some pix, here, I looked at mine and look what I found!
I had forgotten that Mark Algazy had rebuilt this carb for the PO, so he must have installed the ported vac, then.
Mark is da man!
I had forgotten that Mark Algazy had rebuilt this carb for the PO, so he must have installed the ported vac, then.
Mark is da man!
That's good to hear
John
John
I don't have Jim C or Mark A's knowledge but this happened to me....
Long before there many commercially made Landcruiser HEI units available I installed one that I picked up from a small cruiser shop. It was pretty simply done and I believe it still had the GM gear on it. I knew better but it was going to be temporary as I had been putting a bug in Davis' ear about these and was pretty certain I had convinced them to manufacture a "good" one. ( My apologies to Mudrak and Up n' Over who were apparently doing excellent versions already. I just didn't know it.) The shop's instructions were "Drop it in, set timing to 10ºBTDC, and go".
About five minutes into the first test drive the engine stuck a piston (or something) and shut down. That's the only way I can describe it. I was doing about 40mph. After pulling over and regaining composure I restarted it. The engine fired right up and I drove off. About five minutes later it did it again. I was ten miles from home on a empty road and no phone so, after a brief pause, I restarted it and limped home. I only drove the vehicle for a few miles at any one time for the next couple of years as I was working on it at two different locations depending what tools I needed. The symptoms never recurred. I never heard any pinging and the engine always seemed to run a little hot but better when really warmed up.
When I put a better unit in (not a DUI) I tested the advance curve on the old distributor and was a bit surprised. It had something like 17º of vacuum advance, maybe 24º mechanical at around 2500rpm (iirc), plus the 10º initial. I'm pretty sure it had never been rebuilt and had probably been pulled off an old Nova or something.
The engine eventually needed rebuiding much earlier than I anticipated and I'm pretty convinced that the few, short miles I put on it with the over-advanced GM spec distributor really helped wear it out prematurely. The machinist said the cylinders/pistons/rings were especially bad. This whole time I had the same Jim C. carb I still run and yes, vacuum advance comes in at 6" and ends at 12".
Tale over.