Timing/Timing curve on 350 ... need inputs

[cray1801]

As far as I know my `72 350-4Bbl motors ignition is completely stock (points and all). I have always had a problem with spark knock with anything more than 6 deg. initial timing. The motor was re-built ~20K miles ago by someone else and it has a different (“energy”) cam. The vacuum advance is connected to the lower driver side of the Q-Jet.

I see no difference in timing whether the vacuum is plugged or connected. I've installed a John Osborne 800 cfm a few weeks ago (will go on the 455 when done). Here is the timing information I gathered today.

Initial timing - reads 10* for about 10 seconds after throttle blip... but reads 8* after that, the idle is 800 --> 750 rpm in neutral.

At 1000 rpm - 12*
At 1500 rpm - 16* estimated
At 2000 rpm - 20* estimated
At 2500 rpm - 21* estimated
At 3000 rpm - 24* estimated
No change after 3000 rpm, the vacuum was connected for all readings.

Additional note:
My paint close to the headers is burned indicating lean or retarded timing. I thought with the new carb. I'd try to bump the timing a bit; maybe it was lean before? The new Q-jet (with no change in timing, 6* initial) was .3 sec. quicker in the 1/4 mile.

Today’s drive proved that 12* initial causes spark knock when motor is 190* or more, so I reduced it some for the readings above this afternoon.


:confused:

[CyberBuick]

Hey Cray,

I have a '71 350-2 auto trans. The manuals state 10deg initial timing on it. It ran from the factory that way, it should run fine now at 10deg. I'd say there's a problem somwhere. Have you tried replacing the points, condenser, rotor, cap? What about spark plugs?

As for timing curve, from when I've read and asked, it's about the same as the 455's. 34-36deg in by 2600rpm. I run on 12* initial, then with the curve kit I put in, it runs around 14* idle (N) and 12* (D). Have it all in by 2600 and runs perfect. Initial timing on the 350's can make all the difference in 'spunk'.

If you don't mind spending a lil but getting a bit in return, maybe think about getting a Pertronix kit and an open air cleaner w/ K&N filter (if you don't already run a 360* cleaner).

The reason you don't see a diff when the vac advance is plugged or not when setting timming is because it's a ported vacuum, that doesn't start to open up until your on it a lil.

In a nutshell, check everything in the distrib, and the spark plugs. You may have worn out parts, or the wrong heat range plug in there. I noticed when I upgraded my ignition I went from R45's to R43's.

Hope some of this helps

Scott

p.s. One last thing, did you reset the idle mix screws after you swaped carbs back and forth? err on the rich side...

[cray1801]

I did not re-adjust the idle mixture with the new Q-jet, since it ran stronger, I will check it though.

About a year ago I replaced the points and condencer they should be fine. No sure I got the dwell exactly right though? I'm not sure which plugs I used probably what ever the book called for. How would the heat range effect spark knock?

The car runs fine, but it has always had a tendency to spark knock easily, specially when hot. If the AC is on on a hot day it will spark knock with 6* initial.

[Darryl Roederer]

Are you having this problem on both premium and regular gas?
A low compression 72 should be able to handle about 10*-12* or more initial timing with no problems.......

What do you know about the rebuild???? Compression?

I'm kind of thinking it may have a multi-keyway timing set, and it's set wrong

Also, could be high compression pistons [10:1] and not enough overlap on the cam to bleed off the excess cylinder pressure......

Also, it could have a carbon build-up problem

If it were my engine, I'd start with points/plugs... Use the accell brand. [yes, the yellow plugs,,, there a little "cooler"]
Then a tank full of premium gasoline. If the problem persists, I'd then pull the front cover and spec the cam out with a timing wheel to make sure it's not set too far advanced. Also might try a cooler thermostat.

[Darryl Roederer]

Waaaaait a minute:puzzled:

What do you mean "energy" cam????????

Are you running a "Cam Dynamics" brand energizer or high energy cam???????

If so, that may be your problem.....
Cam Dynamics builds cams with very little overlap and tight lobe centers designed to increase cylinder pressure in low compression engines.
Also, if I remember correctly, they have about 6* advance built into the cam.....

Find out exactly what cam your using, also what compression pistons went into the rebuild, and let me know.

[cray1801]

Darryl & Scott,

I don't know any more about the cam than I already stated, thats the problem when the car changes hands a couple of times after the work is done. I do know the cranking compression is on the low side for all cylinders, ~110 psi.! Leak down testing shows only 1% leakdown. I guess the valve timing of the cam is such that pressure is bled off more than with the stock cam with the same low compression it came with from the factory.

I always run 93 octane to minimize any pinging. I think the engine still has the stock pistons and the block was honed and ringed.

I don't think there's carbon buildup, I've poured water down the carb. while revving it, and I exercise the engine often.

I am running headers and a 360* 4" K&N filter.

[CyberBuick]

Cray,

A year is abit for point/condenser set IMO, replace them with Delco parts. They're cheap, can put all new distrib parts on for less then 40$ Heck, if you can do w/o a cap you save about 15-20$.. :rolleyes: Also ajust your dwell! Stock is 30 +/- 2*, so 28-32.

Plugs can effect knock, just like after upgrading to Pertronix here, when I ran high load passes it would knock and in high temps too. Go down a heat range or two.. Plugs that get too hot cause nasty probs just like to cold a plug. You saying that the problem is worse when it's hot out or with the AC on, the engine just gets hotter and the plugs load up..

I'm with Daryl also on the cam, might wanna pull it to nab the numbers off it and go hunting.. It's one way to findout what the thing is doing inside there. :-)

Pressure and leakdown are both good, 110 i think is a lil low but still if they're all runnin the same it shouldn't matter much.

Unless you have a hot cam in there or somebody went crazy with the engine, it should run fine set to factory specs on 87octane.

Make sure to reset the carb mixture screws.. Best do it with a vacuum gauge routed to the manifold. Run it a tad rich and it'll be yer best friend. Lean mixes cause high heat, and all kinds of probs as well. Hence why it's better to run a lil rich then lean. Just set it for highest vac on both sides.

Excercising the engine is the fun part. :Brow:

Scott

[Darryl Roederer]

OK, that helps some....
110 psi does seem low... really low. I just did a 71, re-ring job with an iski 262 cam installed straight up [4* advance built into the cam] and I got 122 psi avg on all cyl's.

I set the initial timing at 10*, and a distributor re-curve kit that gave 32* total [without the vacuum advance hooked up]... With the vac, it's close to 40*....[HEI distributor]

Not a bit of ping.....

Something is up with your engine.....
How much "cam" is in there???? Is it really lopey, window rattler, slightly hotter than stock???? Try to give me an idea of just how raticle it is...

I'm still thinking the cam is installed out of time.... Perhapse a poorly manufactured timing set.... It happens that way sometimes.

Fatten up the carb for sure, that will help to cool it down. Also, look around for a cheap used HEI for a buick 350... Junk-yard maybe. Just drop it in bone stock and see what happens. The HEI is a far superior unit to the points distributor. If you see an improvement with the HEI, consider keeping it, and beefing it up.

Ultimately, you may be looking at a cam swap. No, not cheap, but it's worth it to get it right.

Let's hope it dont go that far... It would be nice if you could solve the problem without opening up the engine, but I think you may have to.

[cray1801]

I'm planning to swap this engine soon, with the 455 on the engine stand within 3 months (projects going too slow). I have a HEI and I could install it and I could swap the 455 dist. gear with the current one in the 350. I've been tempted to do this.

The engine has a nice little lope, but not rough. You know, it sounds really good when you first fire it up then smoothes out some ... after it gets warmed up.

[Darryl Roederer]

cray1801 said: I have a HEI and I could install it and I could swap the 455 dist. gear with the current one in the 350. I've been tempted to do this.



HEI..... Go for it...
If you have a bigger radiator for the 455, this would be a good time to swap that as well

OK, so we have a mild thumper cam in an 8.5:1 motor, that pings at anything over 6* of initial timing, and you run it on premium gas at all times.

We know it's jetted a little lean,,, fatten it up... see if that helps.
Is it actually running hot? Has the radiator been serviced? Is the thermostat good? .....Where are you taking the temp reading from? The intake manifold coolant passage I presume...

I feel were quickly narrowing it down.... One of 3 things...

#1, carb too lean

#2, problem with the cooling system... Blocked radiator, bad water pump, stuck thermostat, etc.

#3, The cam is installed too far advanced...

How does it run [ping] and perform if you back the timing down to, say, 2* or 4* ??? Big drop in power? Still ping?

Go ahead and install the HEI, and some cooler plugs... Like I said, I like the accell plugs [personal expirence] as it could be a spark related problem... Sure cant hurt:Do No:

[72skylark]

do you have a temp gauge on it? I had some pinging problems... put a temp gauge on it and found out it was running at 240deg!!! After I fixed the colling prob it never gets past 210... usually nowhere even close.
just a thought.

[cray1801]

O.K. I going out for some testing today. I've got a temperature guage (mounted under the dash) and will record the temperature at the front of the intake, I also have a pyrometer to measure the temperature at the head (just before the header). I'm running 93 octane and will test what I have before changing any hard parts. I'll play with the timing (plugged and unpluged vac. adv.) and how it relates to pinging and record perfmance (AP22 performance meter). It's ~60 degrees out today, I'll post the update later today.:laugh: :puzzled: :jd:

[JohnK]

One thing you want to do for sure is replace the thermostat. The stock 72 smog motor thermostat is 195* for both 350 and 455. You want a 180*, or even possibly a 160* thermostat, that they used in the older 60's cars before smog equipment.

Another possibility - outer ring on balancer has slipped on the dry, cracked, 30 yr old rubber?

[cray1801]

Lots of testing today:Brow:

First temperature readings at various timing settings, the engine was allowed to idle at each setting to stablize temperatures:
initial timing/temp. at head/water temp. taken at intake. Note, the temperature of the head (at the exhaust) was taken from the #1 location, readings from this cylinder were consistantly 40* more than cylinder #2.

2/419/191
6/403/187
8/403/183
10/398/180

These readings were taken at idle in park. I did not experience any pinging today the engine never got over 195*, the high today was maybe 68*. I figure I'm running lean with these high temperatures at the head.

I did (6) test runs today, each test consisted of a 2-way timing average. These (first four) results were done with the dist. vac. plugged. The time between speeds was chosen to eliminate tire spin, each run was timed between 15 and 70 mph, 0 - 60 times listed second. All times were done electronically to eliminate human error.

timing / 15-70 mph / 0-60 mph
2.5*- 7.90 sec. / 7.15 sec.
5* - 7.50 sec. / 6.98 sec.
7.5* - 8.10 sec. / 7.33 sec.
8* - 7.45 sec. / 6.98 sec.

It turns out the car ran just as well if not better with the dist. vac. plugged?? Here are the runs with the dist. hooked up, the timing was set to 8* (the best result from above).

8* - 7.60 sec. / 7.00 sec

I then checked the vac. with the gauge and adjusted the idle mixture. It turns out the initial adjustment was 2.9 turns out. This resulted in 14.2 to 15.8 psi. range of vac. Trial and error showed that 3.5 turns out gave more vac., new range between was between 15.5 to 16.8 psi. One more test run:

8* - 7.85 sec. / 7.05 sec.

QUESTIONS:

I always forget?? On a Q-Jet if idle mixture screws are turned in (clockwise) will this make the engine more rich or lean??

How is do you make the mixture more rich?? I don't know yet what jets or rods are in the carb. it was prepped by John Osborne. If the jet size goes from .073 to a larger number will that provide a richer condition? How do you change the jets on a Q-Jet and will the rods need to be changed if the jets are?? Do you have to take the carb. off the engine or take the top 1/2 off the carb?

Thanks!

[CyberBuick]

Impressive! I never do testing like that.. lol

So when you got the carb it was running lean, 2.9 turns out. You adjusted it to 3.5 turns out. That richens up the idle mixture and gives better vacuum. It should also make the engine run cooler, as well as increase the idle rpm a bit.

Turning the screws in leans it, outward richens it.

You can change the secondary hanger and rods with the engine running if you wanted to and they're easy to identify by letters. Changing the primary side tho requires you pop the top off. Thinner rods, richer circut I believe.

The vac advance is ported so it only comes on after your on it a bit and does nothing at idle. It runs better with it disconnected I think because you don't get to much advance when your on it. What alot of people do (myself included) is set the initial timming and then recruve the dist weights and springs to get 34-36 total in by around 26-2800rpm. Initial + Dist = Total. Then nab a adjustable vac advance and plug it to the manifold port and get it set nicely. What you end up with is good takeoff and idle mileage combined with good hwy perf...

I think your pinging problem should be about fixed since you've richened up the carb. Tho only a warm day will tell that story.

I'd go for 10* initial timming and see what she does, if all is well, head to 12. Shouldn't have to go above 12 tho. I couldn't notice a diff when I played with it up to 16*..

Impressive that these old monster cars have nice 0-60 times ain't it.. hehe

Scott

[cray1801]

Thanks Scott. I should go ahead and install that HEI.

Here's what I think I have to do (corrections or specifics requested):

1--remove old dist. and remove gear
2--remove resistor wire and replace with 10 AWG.
3--install 350 gear on HEI dist. (was set-up for a 455).
4--install dist.

I know this has been covered before but can't recall the details.

Anyone else use the AP-22 Performance Meter? Excellent capability to cost ratio. For less than $300 you get many features to evaluate performance, calibrate the unit with actual drag strip times and download data to the PC for more fun.

[JohnK]

Here's a couple of thoughts on your testing:
1. Vacuum advance only works at part throttle. At WOT, vacuum drops to near zero and there is no vacuum advance as part of the total timing. Only initial and centrifugal advance contribute at WOT.
2. Idle mixture screws are just that, IDLE. They don't affect the mixture ratio once you're moving at part throttle or WOT. And they affect the mixture quantity not the air/fuel ratio .
3. If you really want to mess with the rods and jets, go buy the Doug Roe book. It's too much for a post, that's why it takes a book.

[cray1801]

Been thinking a lot about the timing thing this week. Why not first mark the damper where the total timing you want is then rev. the engine to say 2500 rpm and rotate the dist. so this new mark is aligned with the 0 on the pointer? This would eliminate the guesswork relating to the total advance.

I've decided to upgrade to the HEI (on the 350), what is the resistor wire connected too on a `72 Buick Skylark? :confused: I assume ... the positive side of the coil and the ignition switch, and I should replace it with a 10 awg. copper wire.

Also wondering about the tach. My tach was upgraded to be compatible with points or HEI about a year ago. Can I just route the wire from the neg. side of the old coil to the tachometer labeled connection on the HEI? :confused:

Thanks!

[LARRY70GS]

Craig,
The resistor wire runs from the + side of the coil to the firewall connector( drivers side, down low). Along the way there is a wire that tees off the resistor wire to the "R" terminal on the starter solenoid( eliminate this). The firewall connector comes apart( bolt in the middle) The wire has a special barb type clip that can be released from the rear with a pair of needle nose pliers. You can either unsolder the clip from the resistor wire and use it on your 10 gauge wire or you can buy a replacement clip from NAPA or you can order the entire wire with proper clip and HEI connector from Year One(L00510). Your Tach wire hooks to the Tach terminal on the HEI cap. Hope that helps.

[cray1801]

Larry, that makes it clear.

Eliminate the wire that runs to the starter that "T's" with the resistor wire.

Replace the resistor wire, that connects to the positive wire on the coil, with a 10 awg or so wire.

It is so clear now :eek2:

[CyberBuick]

For the resistor wire, if you don't want to hassle with "replacing" anything at the moment. Run a new parallel wire using tap-in connectors. Put one end as close to the firewall box as you can, and put the otherend right before the metal split clip thats there. The wire should be a braided cloth covered wire, carefull tho as after 30years the cloth is brittle and comes apart kinda easy. If you goof up, plaster it with electricians tape :-) Use the 16-20gauge (i think is the range) tap-in connectors. 10gauge is to much imo. I used 14 or 16gauge, I don't remember which. Works perfectly and took about 10min once I found the wire.

Just another opinion and option for ya.

Scott

[cray1801]

Larry (or anyone else), how do you remove the resister wire from the back of the fuse block? This is a little harder than expected, do you grip the connector as shown (see attached .jpg)?

Also if the resistor wire is replaced and a new wire is routed from the HEI to the back of the fuse box why remove the wire that runs to the starter solenoid? Can't I just cut and isolate the end for now and remove it in a couple of months when I have the engine out?

[LARRY70GS]

Craig,
Kind of hard to see in the picture. If you have unbolted the firewall connector the clip has to be compressed from behind and the wire and clip will pull out from the front. When you see the clip, you will understand how it connects into the firewall connector. I wish I had a picture of the clip to post. The clip has a sort of barb to it and it actually hooks into the connector.
You can leave the wire that attaches to the solenoid if you like, just tape it off, that wire will have 12 volts only while the starter is cranking the engine. The wire you are running from the firewall connector will have 12 volts whenever the ignition is on.(which is what the HEI needs)

[cray1801]

Larry, not sure which side is "behind side", the view in the picture above is the engine compartment side (vs. the interior side). I have to assume the connector and wire comes out the engine compartment side, correct? I ordered the Year One replacement wire that has the correct ends, this should help. Thanks again.

[LARRY70GS]

Craig,
The wire comes out from the engine side, but the clip must be compressed from the interior side. When you get the year one part it will be clearer. Good Luck.

[cray1801]

Thanks, thats what I suspected.

Well I slid the HEI into position tonight but before I removed the points dist. I marked where the vac. and rotor pointed (I did this with the #1 piston at TDC on the compression stroke). I slid the HEI into place (after modifying the fuel line that was in the way) and the rotor pointed a small amount off the mark. I removed the HEI and re-installed it (one tooth?) and the rotor pointed a small amount to the other side of the original mark. Should the HEI rotor point exactly to the same mark or can it be a little off. The mark was made on some masking tape applied to the shroud and the variation from the first and second install was ~3" with the original mark in the middle. Is this unusual? Maybe I went two teeth instead of one?

[cray1801]

Well, I pulled the Bosch plugs (HR9BPX) today. They look good I think, the attached picture shows them laid out in order starting with the top left as #1, 3, 5, & 7 then on the right top #2, 4, 6, 8. The number 2 plug got broken (under the AC bracket you know). The main difference between them is color. I replaced them with cheap (R44TS) AC Delco and gapped them to .045", they should hold me until the 455 swap, They are one step colder than what the book called for.

[gstewart]

from the 72 shop manual - initial timing at idle
is 4 degrees 72 350 , running 91 octane fuel.
gerry
72 gs 350

[cray1801]

Well I got everything back together late last night. No luck getting it started though. It tried to "run-on" at very low rpm but never really got going, this was the first try. I then pulled the dist. and rotated one tooth, no luck I tried back one and forward one tooth. It was late and I had to hit the sack.

Today I tried again, first I hooked up the timing light to see where I was with the timing and the timing light never came on. I've got 12.8 volts at the connector (at the dist.) but no spark at the plug. I am using a new MSD coil, could it be fried?

:Do No:

Any suggestions on a radiator hose that clears the new larger HEI. This thing is huge.

Oh! I don't have anything that shows where #1 is on the HEI distributor cap, I think I know but I'd like to confirm.

Here's the new (and old) wire that I got from Year One to replace the resistor wire. It's easy to see how the tab clicks into the back of the fuse box now.

[LARRY70GS]

Craig,
Try using an upper radiator hose from a 75 Regal 350, that should work. Make sure you are getting a spark at the plugs. If you have been trying to start it for a while, check that the plugs are not fuel fouled. Good luck.

[cray1801]

O.K. I got it fired up :beer

I made a silly mistake just prior to posting earlier, I forgot to plug the dist. connector into the coil :Dou: You will not get a spark at the plug if it is not connected (no matter if everything else is connected) Duh..

Engine never sounded so sweet!

Thanks for the radiator hose recommendation, I'll pick one up tomorrow, thanks!

[cray1801]

Here is a picture of the HEI dist. with the cap and rotor off, anything look wrong?

This dist. was set-up for a 455 with good street performance cam but for now I'm using it on my 350. It seems all my vac. advance is all in even at idle. I know I have more vac. now with the 350 than I will with the performance 455 but I expected some vac. advance after say 750 rpm's???

Notice how the weight on the bottom is hanging down, are these springs too week. Anything else look wrong? The center plate does not look right to me, but I have nothing to reference it to. Will it hurt to run it this way, I'm hoping for a test and tune tomorrow night.

It runs noticably smoother with the HEI even with all the advance in at 600 rpm idle.

THANKS.

[TuBBeD]

Did you change the distributor gear going from a 455 to a 350? Just curious whether or not you did before switching the distributor over.

Rob

[cray1801]

Yes

[JohnK]

Craig,
How much end-play is there in that distributor? Is it a new rebuild or a junkyard treasure? Grab the advance weight plate and pull the shaft in and out. If there is enough play to give you a good thunk at the ends, and it seems to be measureable, like 1/32 inch or more, you've got too much. They make shim washers to take up the end-play, they go on the shaft just above the gear. I've never seen weights do what yours are doing. I'll look at my HEI conversion when I get home tonight and post again.

Let's see, what else, oh yeah. Set your initial timing with vacuum advance hose disconnected and plugged on the carb end. Because you have a lot of vacuum at idle, when you reconnect the hose, yes, the timing marks will show more timing advance and the idle speed will increase. You then back off the idle speed adjustment to get spec idle speed in Drive with wheels blocked and brake set.

[GSXMEN]

Craig - Have you had the weights off to check the condition of the pins and bushings? It's possible that there is excessive play in the weight's hole or the pin/bushing.

Could also just be gravity - you'll notice the top weight touches the center shaft and the bottom weight hangs down a bit. Our distributors are on a slight angle! Even with a new one, there will be a certain amount of 'play'.

To add to what John K. said, also move the shaft side-to-side. Too much clearance that way will have the pick-up and reluctor contacting each other. If you have alot of side-to-side play, the housing bushing is most likely shot. They can be replaced or just find another housing.

Scott

[cray1801]

I had this HEI completely rebuilt.

The center plate is angled and it seems one of the weights rides up onto the center plate as the weights swing out and the inside section swings in. Is this the way it should be (on the right side in the picture)? See small green arrow in picture above. One side goes over the center plate and eventually drags (arrow) and the other weight goes under the center plate, this just does not look right to me. Not sure what to call the center plate?

The timing stays the same whether the vac. advance is connected or dis-connected and plugged, revved or idling.

[Ron Lobb]

Craig, your right the weight shouldn't be riding on top of the center plate. I don't have an HEI to look at but the small end of the weight sould be against the little cam under the center plate like the weight on the left. I would say the way it is it would bind up and you wouldn't get any advance. Hope this helps.

[cray1801]

That helps a lot! I also noticed that the tip of one of the weights (small end) is broken off. You can just barely see it in the picture above, it's the weight on the left/bottom. Are new weights easy to come by? What information do I need to get the right parts, are all the HEI weights the same? I assume the replacement weights need to be the same and I should not use the weights from the points dist? The springs in this HEI are much lighter weight than ones in the points dist. and are red in color.

[Ron Lobb]

Craig, the HEI weights are different than the points weights. You can get the weight and spring kits from Summit or Jeg's. About the only difference in manufactures is the ones from MSD and Moroso are finished better. The weights are alot smoother, just makes them work easier.

[cray1801]

Thanks to all, the HEI is complete. I replaced the weights and re-installed medium springs (picture below shows light springs) and it runs perfect. I have noticed three things since the switch. Much quicker starts, smoother idle and better milage.

I did notice a change in my tach reading, but I'll post that on a new thread. Here is a picture of the corrected HEI (uncovered).

:TU:

[cray1801]

Oops, here's the picture...