Need a Mopar guru: 273 part-throttle ping driving me crazy!

[fazeka]

Hi all,

Newbie here. I have a '68 Barracuda Fastback with a '68 (April) 273 (original 318 gave up the ghost a long time ago).

Engine was "refreshed" a couple of years back, from the previous owner:

"Took engine apart to short block, flushed cooling passages, cleaned carbon and 'lapped' valves, all new seals and gaskets. Engine was clean when taken apart. Only removed top end of engine and oil pan. I pulled engine out of a 4-door Belvedere. It had headers and 2-barrel carb. With a/c to weigh down, ran pretty strong in that car, I just chocked it down with single exhaust. Cleaned carbon from piston top and valves, opened up heat crossover in the intake."

(Note: the engine now has exhaust manifolds instead of headers and a Holley 2-bbl (2280, I think?)).

Ever since I got the car (6 months), it has pinged on part-throttle. Full throttle, fine, no ping.

Initially played with the timing. Everything from 5 ATDC to 20 BTDC (initial/mechanical, and with vacuum advance disconnected/plugged). Still pinged.

Tried the mixture screws on the carb thinking it was running lean, no noticeable improvement.

Went to a one-step "colder" plug NGK ZFR5N (from NGK GR4GP) recently (about 50 miles ago), no noticeable help.

Went to 100 octane racing gas (4 gallons) mixed with Super 91 or 92 octane (can't remember, 14 gallons). This was the biggest help. But impractical as racing gas is 4x more expensive!

I can move the heat riser/flapper by hand (with motor off), so I don't think that's stuck to cause a lean condition...

I don't detect any vacuum leaks (removed and plugged the line to the power booster and still pinged, also sprayed starter fluid around the base of the carb, manifold, etc. without effect).

I read about a plug in the manifold here (a little past midway down the page "Pinging on V-8s") that may be a cause of a lean condition. But then read here and am confused. Is there an EGR valve on the '68 273? Could this be the problem?

I'm pretty desperate at this point as I thought retarding the timing would have solved this.

Any advice GREATLY appreciated.

Thanks,
Paul

P.S. What does "opened up the heat crossover in the intake" mean? Could that be related to my problem?

 

[67Dart273]

Ever since I got the car (6 months), it has pinged on part-throttle. Full throttle, fine, no ping.


I read about a plug in the manifold here (a little past midway down the page "Pinging on V-8s") that may be a cause of a lean condition. But then read here and am confused. Is there an EGR valve on the '68 273? Could this be the problem?

I'm pretty desperate at this point as I thought retarding the timing would have solved this.

Any advice GREATLY appreciated.

Thanks,
Paul

P.S. What does "opened up the heat crossover in the intake" mean? Could that be related to my problem?

======================================================

From the page you mentioned: Is this what you are referring to?

"The manifold was made from cast metal. The molten metal was poured into a mold through a little hole and when the manifold was finished, the little hole was plugged up with a little rubber plug. Well, after a few years this little plug would dry up, shrink, and fall out, leaving a hole in the manifold."

======================================================

I've never heard of such a thing as a factory rubber plug. YOU MIGHT HAVE an early (72) intake which DID NOT use an EGR valve, BUT DID have EGR. The first year or two that Mopar used EGR, Ma just drilled into the bottom of the intake, into the heat crossover, which of course is exhaust, and "jetted" it for a continuous leak of exhaust into the intake. On those early manifolds, YOU MAY or may not be able to see them with a flashlight down through the carb throats. You may have to look down through the bores with the carb removed, see below

Once again, these early EGR manifolds HAVE NO external EGR valve. No external clues that I know of

http://i54.tinypic.com/29w4wtz.jpg


You mentioned very high octane fuel. ARE YOU CERTAIN that what you hear is spark knock and not some other noise?

 

[fazeka]

From the page you mentioned: Is this what you are referring to?

"The manifold was made from cast metal. The molten metal was poured into a mold through a little hole and when the manifold was finished, the little hole was plugged up with a little rubber plug. Well, after a few years this little plug would dry up, shrink, and fall out, leaving a hole in the manifold."

Yes.

I've never heard of such a thing as a factory rubber plug. YOU MIGHT HAVE an early (72) intake which DID NOT use an EGR valve, BUT DID have EGR. The first year or two that Mopar used EGR, Ma just drilled into the bottom of the intake, into the heat crossover, which of course is exhaust, and "jetted" it for a continuous leak of exhaust into the intake. On those early manifolds, YOU MAY or may not be able to see them with a flashlight down through the carb throats. You may have to look down through the bores with the carb removed, see below

Once again, these early EGR manifolds HAVE NO external EGR valve. No external clues that I know of

OK. I am a little confused as you are saying no EGR valve but did have EGR... Let me see if I understand your point: Are you saying my 273 has an intake manifold with a "hole" in it that is allowing/leaking exhaust into the intake? If so, how would I plug it (looks like a thread plug? in your pic above) and would it even be possible with the carb removed?

So the recirculated exhaust could be causing a lean condition?

You mentioned very high octane fuel. ARE YOU CERTAIN that what you hear is spark knock and not some other noise?

I am not ABSOLUTELY certain, but let me answer you another way (not trying to be a wise-guy here): what else would cause a knocking sound at part throttle to improve when I used a mix of 100 octane with 91/92 octane? Feel silly for asking in light of your question, but... could there be an issue with valve adjustment?

 

[fazeka]

By the way, not sure if it matters but I live in a WARM climate year-round (lowest temp at night is 60 F).

 

[d55dave]

What is your total (all in) timing. It should be no more than 36 degrees. At part throttle the manifold vacuum is quite high, pulling in the vacuum advance and causing the pre ignition (pinging). Are you checking timing with the vacuum advanced disconnected? There are different advance cans with smaller amounts of advance - we need more info here, total timing, amount of mechanical and vacuum advance.

Have you tried the distributor out of the old 318?

 

[66fs]

Can you take pictures of the intake and carb? What distributer did you use? can you see a number on the distributer? 273's were relatively high compression, typically almost 9:1 for a 2 barrel engine, since they were never a smog engine. Disconnect the vacuum advance, and time it to 35 degrees total advance, that should work, then check where the initial timing is. Drive to check if it pings. If not, reconnect the vacuum advance and check for pinging. If it pings you are getting too much vacuum advance at part throttle. Luckily Mopar vacuum advance cannisters are adjustable. Use a allen key and "Turning it clockwise ('tighten') will REDUCE spring tension so advance is very responsive to even low vacuum levels. CCW ('loosen') compresses the spring, meaning you need high vacuum conditions to get full advance." from DodgeCharger.com Forum.

 

[d55dave]

Can you take pictures of the intake and carb? What distributer did you use? can you see a number on the distributer? 273's were relatively high compression since they were never a smog engine. Disconnect the vacuum advance, and time it to 35 degrees total advance, that should work, then check where the initial timing is. Drive to check if it pings. If not, reconnect the vacuum advance and check for pinging. If it pings you are getting too much vacuum advance at part throttle. Luckily Mopar vacuum advance cannisters are adjustable. Use a allen key and "Turning it clockwise ('tighten') will REDUCE spring tension so advance is very responsive to even low vacuum levels. CCW ('loosen') compresses the spring, meaning you need high vacuum conditions to get full advance." from DodgeCharger.com Forum.

Are all of them adjustable, or only the ones used on mopar performance distributors? I kind of suspect (but could be wrong!) that only the later and performance ones were adjustable. That old 273 distributor may be a cast iron unit as well.

 

[d55dave]

BTW - your issue could be as simple as having the vacuum advance hooked up to the wrong vacuum source.

Manifold vacuum (drawn from below the throttle plates, true manifold vacuum) is quite high at part throttle and will pull in the advance.

Ported vacuum (drawn from the carb, above the throttle plates) will be lower at part throttle as it is closer to atmospheric pressure. How about a picture of the carb and connections?

You can tell by pulling off the vacuum line at idle - at idle vacuum will be present at the manifold port, but much less or none at all at the ported port.

 

[67Dart273]

OK. I am a little confused as you are saying no EGR valve but did have EGR... Let me see if I understand your point: Are you saying my 273 has an intake manifold with a "hole" in it that is allowing/leaking exhaust into the intake? If so, how would I plug it (looks like a thread plug? in your pic above) and would it even be possible with the carb removed?

It would have to have a later manifold installed. The first couple of years (around 72) that Ma implemented EGR, they did not use a VISIBLE EGR valve on the external part of the manifold. They simply drilled the "floor jets" as outlined in the drawing.

I've never tried to plug these, don't know.

what else would cause a knocking sound at part throttle to improve when I used a mix of 100 octane with 91/92 octane? Feel silly for asking in light of your question, but... could there be an issue with valve adjustment?

Could be a number of things, depending. The engine torking over under throttle and "rattling' against something, IE header or broken engine mount, etc. Any chance it's a rod, piston pin, broken piston?

"What do you think" the compression ratio is? Did the pistons have valve reliefs? Does it seem to have good power, that is, the cam must be in time?

How big a role does engine temp play?

 

[66fs]

Are all of them adjustable, or only the ones used on mopar performance distributors? I kind of suspect (but could be wrong!) that only the later and performance ones were adjustable. That old 273 distributor may be a cast iron unit as well.

They are all adjustable. The "normal" ones use the hex key, while the cast iron Prestolite distributor used washers. I really hate to say all anymore, I guess almost all...

 

[66fs]

BTW - your issue could be as simple as having the vacuum advance hooked up to the wrong vacuum source.

Manifold vacuum (drawn from below the throttle plates, true manifold vacuum) is quite high at part throttle and will pull in the advance.

Ported vacuum (drawn from the carb, above the throttle plates) will be lower at part throttle as it is closer to atmospheric pressure. How about a picture of the carb and connections?

You can tell by pulling off the vacuum line at idle - at idle vacuum will be present at the manifold port, but much less or none at all at the ported port.

Good thought!

 

[fazeka]

Hi d55dave and 66fs,

I had vacuum advance disconnected + plugged. Right now initial timing is at 5 BTDC. Had it at 5 ATDC as well (retarded), and it still pinged, with vacuum advance disconnected + plugged. Started poorly at anything ATDC, so left it at 5 BTDC having run it at 10BTDC and still pinging. I can't remember, but I think mechanical is advancing to 25-ish BTDC at 2.5k - 3k RPM. With vac connected it was somewhere in the 40s (yes, above the 35 max), but I can't adjust the vacuum canister (see below).

Distrib is out of old orig 318 is n/a as it was sold for parts/traded by previous owner... =(

This distrib (Prestolite 3438225) won't allow me to adjust the vacuum advance canister with the 3/32 hex wrench, the vacuum hole is too small for it to fit... However, with vacuum disconnected/plugged, it still pings...

Attached are some photos from a few months back. Best I have for now as my phone broke last week...

What model Holley is this?

 

[66fs]

That is the original 273 intake, so no EGR. The Holley is a replacement for the carter 2 barrel. Looks like a "LIST" R7890 number? If it pings with the vacuum advance disconnected, adjusting the advance will not matter. The 35 is just for initial and total timing, you can go past that with vacuum advance. I would not go lower than 0 for initial timing. Does it ping if you set initial at 0? What octane? The vacuum adjustment is to add or subtract washers, can't remember which off the top of my head, inside of the removable vacuum nipple. Is the 273 solid lifter or hydraulic? Can you remember?

 

[d55dave]

Have you checked that the damper marks are correct, is it the right damper for the engine?

 

[toolmanmike]

The vacuum adjustment is to add or subtract washers, can't remember which off the top of my head, inside of the removable vacuum nipple.

Thanks for that info. I never knew that. This place is amazing. You can teach a old dog new tricks. LOL

 

[67Dart273]

Have you checked that the damper marks are correct, is it the right damper for the engine?

Good thought I completely scattered this. Get yourself, or make, a piston stop and check TDC

Here's my old one, I made in the mid 70's........

I actually misplaced this, for awhile, some time ago. I actually had withdrawal pains. Then one day there it was........when I'd pulled the teen outta the 67, I'd shoved it into the PCV grommet in the valve cover to plug it!!!!!!!!...............and forgot it......................

 

[fazeka]

Thanks for your reply.

That is the original 273 intake, so no EGR. The Holley is a replacement for the carter 2 barrel. Looks like a "LIST" R7890 number?

What does "LIST" mean?

I found this, but I am confused: is my carb a 7890 or a 2280?

If it pings with the vacuum advance disconnected, adjusting the advance will not matter.

Yes.

The 35 is just for initial and total timing, you can go past that with vacuum advance. I would not go lower than 0 for initial timing. Does it ping if you set initial at 0?

I had it at 5 ATDC and it pinged. 0 and it pinged.

What octane?

Unocal 92, then 100 (4 gallons) mixed with 92 (14 gallons).

The vacuum adjustment is to add or subtract washers, can't remember which off the top of my head, inside of the removable vacuum nipple.

This is good to know. Once I get rid of the ping, I will adjust vacuum advance if I need to. But I don't think timing is the cause of the ping?

Is the 273 solid lifter or hydraulic? Can you remember?

It's a '68 273. My understanding is that by '68 these had hydraulic lifters. Doesn't "sound" like solid lifters, either.

 

[fazeka]

Have you checked that the damper marks are correct, is it the right damper for the engine?

It's a 7.25" damper and the previous owner said everything on the engine was original, he just "refreshed" it (didn't swap parts, etc.). I checked the damper mark with a piston stop before I timed the motor. It lined up.

 

[66fs]

When you refreshed it did you notice the pistons? Dome or flat top, 4 valve notches or two? Since it has a Prestolite distributor, did someone put a 2 barrel carb and intake on a Commando motor? You cannot hear the solid lifters in a Commando motor, pull the oil filler and look for adjustable rocker arms. Way out on a limb here, nothing else makes sense.

 

[d55dave]

Has someone perhaps put some light "recurve" springs in the distributor and the mechanical advance is coming in too early? Perhaps there is someone near you who has a small block distributor you could run in it to try.

 

[RedFish]

Do this, Start it from stone cold and blast off. Either direction I leave out from my place I have to go down and more importantly up hills. Anyway...
Run the dog crap out of it and I'll betcha you cant make it ping even up hill.
The ping will begin only after it gets too hot.
I did have the very same issue and tried everything imaginable except replacing the 35 year old radiator. New radiator was the cure all along.
Take into account that the 35 year old pizz poor gauge wasn't indicating too hot either so I was clueless to the actual condition.
You might also note that my stated experience took place in late 80s when there was no internet to ask.

 

[moper]

I think there's a few potential issues with this.
1st - the "opened crossover" more than likely means the factory apssage under the intake or possibly in the heads was plugged by carbon deposits. The '68 318, and any 273 would not have had any provision for EGR.
2nd - the pinging. I'd look at two things:
The carb jetting which is probably 2-3 steps leaner than it needs to be for the pump unleaded we buy now. Pull the top off the carb, find the main jets, and using a drill bit enlarge them very slightly. A little goes a long way. If you have pin drills, and wire gage bits, those are the best way to sneak up on the right jet size. You also want to make sure the power enrichment circuit is working. It might not be.
The timing curve is suspect. You need to know how much timing there is, what advance is putting it in, and when. You can ajust the mechanical advance with tweaking springs, slots, and weights. And you can adjust the vacuum advance but only the amount of vacuum required to move it - not the actual advance amount using that 11/32 hex key. My impression is there are lightweight springs in it (should really only be one, the other should be the factory "light" which is 5 times stiffer than the HP light springs) and the mechcanical is advancing too much. Get a timing tape and use that and a tachometer to fully map out your timing curve. Then post that.

 

[dodge freak]

Pull the top off the carb, find the main jets, and using a drill bit enlarge them very slightly. A little goes a long way. If you have pin drills, and wire gage bits, those are the best way to sneak up on the right jet size. You also want to make sure the power enrichment circuit is working. It might not be.
.

Pin drills, and wire gage bits are the only way to open up jets. You only want to go up to the next wire size drill. A set of wire drills close the jet size is the way to go, find the drill that goes in tight and use the pin drill to get the next size drill in the jet.

Otherwise you just ruin the jets

 

[moparlover]

it's probably an exhaust leak at the manifold.

i seriously doubt that 4 gallons of 100 octane added to 10 gallons of 91 put on a car with stock compression ratio was really fixing anything. just sayin

i'm speakin from experience about exhaust leaks. i would bet that is your ping you are noticing. maybe some lifter noise along with.

all new seals and gaskets. Engine was clean when taken apart. Only removed top end of engine and oil pan.

probably wasnt high end gaskets i'm betting.

get a set of percy's exhaust gaskets.

http://www.taylorvertex.com/gaskets/seal-4-good/header-flange/index.cgi/productListing?id=300779

i'd also recommend setting the valve lash. if he put stamped rockers (non adjustable) then skip that step.

 

[d55dave]

A float set too low will also cause a lean condition. It is easier to play with, and correct than drilling jets. Easier to go back as well if it doesn't work. Perhaps try raising the float.