Author Topic: Timing Question  (Read 2253 times)

Offline bigben5054

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Timing Question
« on: July 21, 2020, 04:51:25 PM »
Hey all.  Working on getting a recently rebuilt 350 purring like a kitten.  Have a few Qs about timing.  Engine is a 350 bored .40 with flat tops and vortec heads. 

I let engine warm up, unplugged vacuum advance (and capped) and set timing at about 8 degrees BTDC.  Seems to run good and start back up fine there.  But once I plug back in vacuum advance, it wont start and does like a starter kick back thing.  I think that means way too much advance.  My carb is a Holley and most every Holley I have seen has a timed vacuum port on the primary metering block that goes to the vacuum advance.  This one does not, so it's plugged into a full vacuum port.  I suppose this is why I have way too much advance when trying to start with vacuum advance hooked up.  Short of buying a new metering block (with timed vac port), any other options?  I have read in more places that one to just not run vacuum advance.  Is that ok?  If I go that route, should I change the initial timing to compensate?  Also, where should I aim for total timing and at what RPM?  Thanks!

Offline bigben5054

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Re: Timing Question
« Reply #1 on: July 21, 2020, 06:20:57 PM »
oh, and where should I set idle? (it's a manual trans)

Offline Captain Swampy

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Re: Timing Question
« Reply #2 on: July 22, 2020, 11:12:28 AM »
You wouldn't think it would pull enough vacuum while cranking to change the timing much. Possible problem with vacuum advance can or the distributor?
1987  350TBI 700R4  4X4  4.56 gears  33" BFG All Terrain


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Offline bigben5054

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Re: Timing Question
« Reply #3 on: July 22, 2020, 11:31:24 AM »
Both are brand new.

Offline bigben5054

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Re: Timing Question
« Reply #4 on: July 22, 2020, 11:47:42 AM »
Actually, it was doing this before I rebuilt it.  But now pretty much everything is new except the starter, battery, and carb.  I'll have to see if I can take a video and post a youtube link.  Maybe I'm barking up the wrong tree thinking it is a timing issue.

Offline Curt80

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Re: Timing Question
« Reply #5 on: July 24, 2020, 03:46:27 PM »
Your starter kick back thing sounds like a backfire.  Assuming you're non-emissions, vacuum advance should always be plugged straight into manifold vacuum, not timed/ported Reason being at idle, you need more advance for the leaner / no load condition.  Omitting your vac advance on a street truck will just cause it to run hotter and less efficient at idle and highway driving.  It sounds to me like you set your initial timing right so I'd start looking at the carb next, especially the idle setup.  Just going on memory but for a holley, I used to take the carb off, set the throttle blade adjustment on the bench so it was just showing a bit of the transfer port (small square port at the bottom of the barrel).  Then bolt the carb back on and use the idle fuel screws to adjust the idle.  Not saying you did this wrong but I used to see alot of guys try to adjust the idle by adjusting the throttle blades and run into all kinds of sputtering and trouble idling.  As for total timing, a good starting point is 8* initial plus 26* mechanical for a total of 34*.  Most street engines do well with 34-36* total timing all in by 3000rpm.  Don't factor your vacuum advance into this.  Set up your timing with it unplugged.  If you want to check it after, plug the vac advance back in, and whatever your vac advance is (roughly 8*) should add to your initial advance of 8 and give you about 16* advance sitting at idle warm.  A good curb idle speed is 800-850, dropping to about 600 in gear. 
« Last Edit: July 24, 2020, 03:51:39 PM by Curt80 »

Offline bigben5054

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Re: Timing Question
« Reply #6 on: July 27, 2020, 04:18:33 PM »
Thanks Curt.  The more I messed with it and thought about it, I started to blame the starter.  Starts fine when cold, but then acts like it has a dying battery when hot, even when I put the 200 amp charger on it.  Maybe not so much a "kickback" problem as it just can't quite turn the motor completely over so it just gives up and sort of free spins for a second.  It's hard to describe.  Anyway, I figure with flat tops and Vortec heads, I've bumped the compression up significantly.  Maybe too much for the old stock starter.  So I ordered a high torque one and it will be here tomorrow.  I also pulled out the positive battery cable and it was burned very badly.  In one spot it was melted at least halfway through the copper and what was left was really hard and brittle.  Once I get the new starter and power cable installed (with some sort of heat protector this time), we will see what happens.  Appreciate the tip about the Holley.  I didn't do that.  Plan is to get it idling, warm it up, them use a vacuum gauge to set the idle mixture.  Then set the final idle speed.  Its a manual transmission, so I'll aim for around 600rpm.

Offline bigben5054

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Re: Timing Question
« Reply #7 on: July 29, 2020, 01:48:53 PM »
Wow.  That was the answer.  High torque starter and new battery cable.  Fires right up like a brand new truck.

Offline JohnnyPopper

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Re: Timing Question
« Reply #8 on: July 30, 2020, 09:15:40 PM »
Glad it worked out!

I bet it was the cable all along though.

I had the same thing happen on my '66 Toronado, bought a starter for the 502 CID Eldorado, high torque. Same prob.

Turned out to be my coil was failing.

Variables are not our friends...
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction