1978 351M Advice
Hotshot
Joined: Mar 2001
Posts: 13,548
Likes: 77
From: Manhattan, KS
Sounds like you should fix the distributer/vac advance issues before changing a lot of other stuff. I have 400 that I changed the heads on because of a miss and I checked the firing order a number of times. I still screwed up and had two plug wires crossed and even after the heads were changed I still had a miss. Fixed the plug wires and it ran like a champ. The heads/valves I pulled were in bad shape, but that wasn't my main problem.
You might also post up on the 335 engine forum for the "experts" over there to help out on the issues you have.
Good luck.
You might also post up on the 335 engine forum for the "experts" over there to help out on the issues you have.
Good luck.
New User
Joined: Jan 2008
Posts: 0
Likes: 24
The timing on this engine can be anywhere from 6*-14 *
It depends on the EXACT engine ID.
You can see the specs on this page of mine.
http://mil1ion.clubfte.com/78Calibra...e-upSpecs.html
I come up with a calibration code of 7-72-R11 which has a timing setting of 14*BTDC
Have you checked the vacuum advance for being seized or having a broken diaphram ?
You definitely have a vacuum problem
It depends on the EXACT engine ID.
You can see the specs on this page of mine.
http://mil1ion.clubfte.com/78Calibra...e-upSpecs.html
I come up with a calibration code of 7-72-R11 which has a timing setting of 14*BTDC
Have you checked the vacuum advance for being seized or having a broken diaphram ?
You definitely have a vacuum problem
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
I think you would be wise to invest in a good dynomometer tune-up. That way you will isolate problems and get the best out of what you have.
You could easily have a problem with cam timing or something simple.
They can recurve your distributor and determine the dynamic timing that is optimum for your truck.
You could easily have a problem with cam timing or something simple.
They can recurve your distributor and determine the dynamic timing that is optimum for your truck.
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
Something is wrong in the distributor if it starts missing with the advance hooked up.
Also, it should have ported vacuum to the dizzy, not manifold vacuum. It should not advance until you open the throttle.
Also, it should have ported vacuum to the dizzy, not manifold vacuum. It should not advance until you open the throttle.
Thread Starter
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Freshman User
Joined: Mar 2008
Posts: 39
Likes: 0
Ok. Spent the better part of the day checking:
1) Spark plug wiring - checked out good, no crossed wires.
2) Distributer vac. advance - very stiff from no use. Used some PB blaster and got moving freely again. Verified diaphram was good with no leakage using a hand pump.
3) Reassembled dist. and went to check the timing.
4) Loosened dist. holdown.....dist. was frozen solid....couple of hours later I got it completly freed up.
5) Set the timing to 10 degrees and the rpm at 700. Set the idle air mixture screws equally on the carb.
6) Idle is fairly smooth, response is decent now and the vac. secondaries will open under WOT. Vacuum at idle is 16 inches.
7) At this point, everything seems decent enough to try connecting the vac. advance on the distributer again.........No luck....engine immediatly starts to miss and run rough. Timing goes to something like 32-34 degrees best I can tell when the timing light actually fires.
1) Spark plug wiring - checked out good, no crossed wires.
2) Distributer vac. advance - very stiff from no use. Used some PB blaster and got moving freely again. Verified diaphram was good with no leakage using a hand pump.
3) Reassembled dist. and went to check the timing.
4) Loosened dist. holdown.....dist. was frozen solid....couple of hours later I got it completly freed up.
5) Set the timing to 10 degrees and the rpm at 700. Set the idle air mixture screws equally on the carb.
6) Idle is fairly smooth, response is decent now and the vac. secondaries will open under WOT. Vacuum at idle is 16 inches.
7) At this point, everything seems decent enough to try connecting the vac. advance on the distributer again.........No luck....engine immediatly starts to miss and run rough. Timing goes to something like 32-34 degrees best I can tell when the timing light actually fires.
Thread Starter
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Freshman User
Joined: Mar 2008
Posts: 39
Likes: 0
The vacuum advance on my distributer is ported to a vacuum line off of the Edelbrock carb. Is this the correct location? Keep in mind that it also has a Edelbrock Performer manifold as well.
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Thread Starter
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Freshman User
Joined: Mar 2008
Posts: 39
Likes: 0
Originally Posted by luckyranger79
Is the hose going to the spark advance pulling vacuum at idle? If so, then it might be hooked to the wrong port on the carb. Worth a shot.
Super Moderator
Joined: Apr 2004
Posts: 34,481
Likes: 2,801
Originally Posted by 1967bird
To 85e150six4mtod The timing is set to 8 degrees. The one thing I discovered this morning is the vac. advance going to the distributer is blocked off. When I reconnect it, the truck seems to run on about 5 cylinders, warm or cold. It so bad that my timing light triggers about a 1/4 of the time. The engine pulls a steady 14 in of vac. at idle. What gives?
As for your vacuum advance, it sounds like the diaphram in the distributor is bad and connecting the vac adv gives you an instant vac leak.