79 302 Vacuum Advance
02-02-17, 08:01 PM
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79 302 Vacuum Advance
So this isn't a V8 in an rx7, but I don't have accounts on other forums and don't want to bother with it. Seems like some people here might know about the 5.0.
Did some work on a 79 302 in a big van today.
He told me :
He bought the van with a new carb, plugs, wires, cap, and rotor all installed. The vehicle was running perfectly. He drove it home, and ran out of gas. (2 tanks and he filled the wrong, broken, tank)
He put some gas in it, tried to start it up, and the battery was dead.
He decided to just put a new alternator on it.
After installing the new alternator, the van would not start. It would just backfire when he tried to start it.
He sent me a picture and I could see the #3 and #7 plug wires were swapped on the distributor. He corrected that before I arrived. The vehicle would start but ran very rough.
He had a new Accel coil in the box, and since it was right there I just threw it on to see if maybe it got a hard knock (PO had it just laying in the engine bay unsecured)
No change at all with the replacement coil, so I put the original back on. Still no change. Would start but not stay running without throttle manipulation and got some backfire through the carb.
I disconnected the vacuum advance and hooked up a timing light and tach.
Started and ran perfectly, and timing was set to ~10BTDC.
I reconnected the vacuum advance and it died out immediately.
With the vacuum advance connected and the distributor loosened, I had him start it. It ran very rough and he had to keep his foot on the gas to keep it going, but if I gave the distributor a very slight bump counter clock-wise (Retard) the engine would smooth out, reading about 35* total advance at this point, approx 1000-1200 rpm (Digital tach was cutting in and out?)
If he punched it or other wise loaded the engine (trying to drive) the motor would sputter and pop.
I tried moving from manifold to ported vacuum and the idle was terrific, but as soon as he gassed it the it would shudder or stall.
We ended up just disconnecting the vacuum advance, plugging the port and took it for a drive. Did great, no issues.
I checked the vacuum canister on the dist and it holds vacuum well, and obviously it is advancing the timing like it should.
One last note in this disorganized post, the vacuum line on the carb and the vacuum advance canister had to be "cracked loose" with a twist before they could be slid off. Also the distributor was a bear to move at first, so it would seem neither of those had been changed recently.
The engine just doesn't want to run well with the advance connected, and the only events were running out of gas and changing the alternator.
Anybody else run into this?
Did some work on a 79 302 in a big van today.
He told me :
He bought the van with a new carb, plugs, wires, cap, and rotor all installed. The vehicle was running perfectly. He drove it home, and ran out of gas. (2 tanks and he filled the wrong, broken, tank)
He put some gas in it, tried to start it up, and the battery was dead.
He decided to just put a new alternator on it.
After installing the new alternator, the van would not start. It would just backfire when he tried to start it.
He sent me a picture and I could see the #3 and #7 plug wires were swapped on the distributor. He corrected that before I arrived. The vehicle would start but ran very rough.
He had a new Accel coil in the box, and since it was right there I just threw it on to see if maybe it got a hard knock (PO had it just laying in the engine bay unsecured)
No change at all with the replacement coil, so I put the original back on. Still no change. Would start but not stay running without throttle manipulation and got some backfire through the carb.
I disconnected the vacuum advance and hooked up a timing light and tach.
Started and ran perfectly, and timing was set to ~10BTDC.
I reconnected the vacuum advance and it died out immediately.
With the vacuum advance connected and the distributor loosened, I had him start it. It ran very rough and he had to keep his foot on the gas to keep it going, but if I gave the distributor a very slight bump counter clock-wise (Retard) the engine would smooth out, reading about 35* total advance at this point, approx 1000-1200 rpm (Digital tach was cutting in and out?)
If he punched it or other wise loaded the engine (trying to drive) the motor would sputter and pop.
I tried moving from manifold to ported vacuum and the idle was terrific, but as soon as he gassed it the it would shudder or stall.
We ended up just disconnecting the vacuum advance, plugging the port and took it for a drive. Did great, no issues.
I checked the vacuum canister on the dist and it holds vacuum well, and obviously it is advancing the timing like it should.
One last note in this disorganized post, the vacuum line on the carb and the vacuum advance canister had to be "cracked loose" with a twist before they could be slid off. Also the distributor was a bear to move at first, so it would seem neither of those had been changed recently.
The engine just doesn't want to run well with the advance connected, and the only events were running out of gas and changing the alternator.
Anybody else run into this?
02-02-17, 11:54 PM
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some things to think about
Does the vacuum advance thingie actually move the guts inside the distributor when you put vacuum to it?..or whatever it is supposed to do?(mine was seized solid.)
Also older carbed 302 and new roller cam EFI 302 had a slight variation of firing order.
Does the vacuum advance thingie actually move the guts inside the distributor when you put vacuum to it?..or whatever it is supposed to do?(mine was seized solid.)
Also older carbed 302 and new roller cam EFI 302 had a slight variation of firing order.