Please help me diagnose this 273

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SeattleQQ1Fish

SeattleQQ1Fish

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The engine in question here is the 67 273 in my Barracuda. It has 80,000 original miles and I don’t think it’s ever been apart.

Symptoms:
-The car won’t idle smoothly under 1000 rpm. Anything under 950 and it starts to shake violently.
-The idle slowly goes up and down on its own, making it tricky to set the timing. Currently it reads 13 degrees btdc @ 1000 rpm. I can look at the balancer with the timing light and watch the timing move by itself.
-When I put the car in gear, it sputters and dies.
-A couple of the plugs I pulled out of it (I can’t remember which ones off the top of my head) were very fouled with wet oil.

Previous owner bought the car from the original owner 6 months ago. He pulled the original 2bbl and manifold to install a weiand action plus and a new 600 Holley 4160 w/electric choke. He also installed a crappy eBay distributor. He swears the car was running/driving and the timing just needed dialed in. I think he’s full of **** and decided to sell when he couldn’t get the car to run.

The car is a little hard to start, but fires up easily once it’s warm.

What I’ve done so far:
-Verified TDC on #1 with a piston stop on two different occasions.
-Timing set at approx. 13 degrees btdc at 1000rpm.
-replaced the burned up skip white distributor with a newly rebuilt 273 Commando piece from halifaxhops.
-installed a Mopar electronic ignition harness, ignition box, and a solid state VR and coil from Standard. Plugs and wires were replaced.
-backed out both screws on the carb, squirted in carb cleaner and blew it out with compressed air.

Nothing so far has helped at all, and it keeps getting worse. Just did a compression & vacuum test:

Compression Test:
Cylinder
1 - 65/75
3- 130/125
5- 105/105
7- 80/80
2- 105/115
4- 115/115
6- 120/130
8- 105/105

Vacuum:
It pulls 15 at 1100 rpm, 14 @ 1000, 12 @900 as the engine shakes and dies.

I’m not sure how to interpret vacuum readings, but I assume the compression test means the heads need rebuilt. Can anyone offer some insight?
 
Where do we start? The carb needs to be proper and working correctly before it can be adjusted properly. The distributor probably needs points, condenser, rotor, cap, wires. The valves probably need adjusting. A new set of plugs is in order. The oil burning could be something as simple as valve seals or as complicated as worn rings and the engine needing a complete overhaul. Start there then report back with your findings. Don't overlook the obvious!
 
Maybe a burned valve in #1 and 7. Your vacuum readings seem a little low for idle in neutral.
 
I agree, vacuum seems low for a stock motor, even if it's worn. I'd look for a vacuum leak... a cracked hose or missing vacuum plug could cause the erratic idle and sputtering. Does the engine smoke when first started? Worn valve guides might be contributing to the variance in compression.
 
Ever check the slack in the timing change? Something is making the timing vary. Has to be one of a few things. Bad distrib, doubt it I remember that one, loose worn chain, could remotely be slack in the oil pump drive gear, really not often do you see that. You do need to find out why two cylinders are low on compression. If any one you know has a scope see if you can put the car on it. Also a leak down test will let you know if the valves are bad in those cylinders.
 
No1 cylinder compression is pretty low. I'm with "above" Adjust the valves. Frankly, sounds like the engine may need serious work. Get/ make a leakdown tester and do a "leakdown." That will tell you about valve/ other cylinder leakage
 
Also check that you're getting a good blue spark from ignition setup. When running pull 1 plug wire at a time to see where the bad cylinders are. This is a time consuming process but if you want to fix it it has to be done. Devote the time and with the above recommendations you should be able to sort it out.
 
No 1. Take the cap off and see how far you can turn the crank back and forth before the rotor moves. That is how much play that factory nylon sprocket type chain has That will efect compression.

No 2. Adjust the valves they should be solids in a 67 273. start there.

You may need a distributor also you'll find that after you get the compression correct.

One thing I thought I would bring up due to the intake installed.

I always see guys check the compression with the carb closed at idle position. Check it at wide open throttle also. Compression can vary from cylinder to cylinder at idle position if you have a bad intake leak on those ports. Check it both ways. You did say the guy installed an intake.

This may not be your problem but here is some info for every one.

Port alignment will effect the car a lot if you have a 340 intake on 273 heads or the opposite Like a LD4B wher you should have been using a LD340 due to the fact that the ports are narrower and wider and can be misaligned easier.

The pins front and rear in the center of the block can change port alignment also if he used a intake that was drilled for a different motor .

When installing a new intake put a mark at the top of the center of each web on the intake where you can see the center of each web between the ports while installed. Those lines you put on should align with the exact center of the valve cover threaded holes.

If they don't move the intake around to get them as close to equal as possible. When they are where you have the intake positioned where it aligns the best to all ports , Tap the intake using a leather mallet. This will put marks where to drill the pin size holes in the intake to keep the intake in the desired position using the pins in the block while torquing. Even if you use Gasket maker instead of a gasket you should still use the pins. Put an intake on loose without pins and see how much you can move it front to back . It do't take much to have misaligned ports

I use those pins on every small block. I have seen many removed when they buy a new intake because the intaked are not drilled. Why do you think new intakes come without being drilled but the protruding bosses in front and rear are always there for pin support.

The valve cover bolts are always in the center of the web.

even if you use factory iron heads and a Iron intake off of a different engine this can be off. Its worth checking. Its easy and no special tools required when installing your intake.
A balanced charge of air/fuel is just as important as mechanical balancing. This was the easiest way to explain this .

This is what I have done for years. Some may not agree There are always the critics on this site .
 
First thought was vacuum leak, then I read the results of the compression test. IIRC there should be no more than 20% variation from lowest to highest, you have 50%. Valve adjustment may help or even resolve it, assuming the possibility of carbon buildup, but I would expect at the very least the heads need to be rebuilt, burned seats or valves is my bet. Agree with Oldmanmopar on the timing chain, seen it many times on small block Fords.
Good luck and keep us informed.
 
After the valve adjustment go around to the back of the car and put your hand over the exhaust pipe. The outgoing gasses should push your hand off continuously. If it feels like every once in a while your hand is getting sucked onto the pipe, that would indicate a faulty exhaust valve, and she needs either a valve job or a new spring.

Then after proving the firing order is correct, pull one wire off atta time. The one that either makes no difference, or runs smoother with out it, is the pesky cylinder. There may be more than one.
You also need to test for an intake leak, it may be that the replacement intake is leaking at the ports, or in the valley, or under the carb.

The rest is already covered except;
With electronic ignition, your pick-up needs to have one ORANGE wire on it.
If it has one gray wire, it is probably for a reverse-rotation engine. The proof is this. you can adjust the timing to a number (below the rpm at which the D starts advancing). And it will idle just fine. But as soon as you try to increase the rpm, that backwards polarity pick-up, will start randomly dropping sparks, and spark anywhere it feels like; either retarded or advanced; it's just a mess. If you see that, you need a different pick-up.
 
how long has it been running on unleaded fuel ,exhaust valve seats gone, timing gear jumped?
 
HEMI-ITIS said:
Were the vacume readings steady or was the needle bouncin? Have you verified what size power valve is in the carb? Do you know how to check for vacume leak??
Click to expand...

The needle was bouncing around during the vacuum test. Not severely, but it wasn’t perfectly steady. I’m not sure what power valve is in the carb. It’s only a few months old, so whatever Holley is putting in new 4160s off the shelf. The way I checked for a leak was to spray carb cleaner all around the intake and base of the carb looking for a change in rpm.
 
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brian6pac said:
First thing I would do is adjust the valves.
Click to expand...

THIS^^^^ should be the FIRST thing done. Adjust the valves correctly and then recheck the compression. If the compression on those two is still low after the valve adjustment, might as well take the head off.

If it has a burned exhaust valve, there's your vacuum leak right there.
 
Auto Shop #101- electrical must be correct before you can diagnose fuel. If after you check ignition and valve adjustment, you concider the carb being bad.
 
If it was my car I'd push it in the garage and change the timing chain. The nylon cam sprocket gears will crack over time. And when they do, pieces of the nylon break off the teeth. If enough pieces break off, the chain will skip teeth and then push rods will bend, all the intake valves will bend, and maybe some exhaust valves will bend. [personal experience].

After the chain is installed [double roller is preferred], adjust the valves. Because you have solid lifters, any exhaust valve seat recession will tighten or eliminate the valve lash. If this happens, it is likely that an exhaust valve will burn. -------- good luck -------
 
SeattleQQ1Fish said:
The needle was bouncing around during the vacuum test. Not severely, but it wasn’t perfectly steady. I’m not sure what power valve is in the carb, it’s whatever Holley put in it new from the factory. The way I checked for a leak was to spray carb cleaner all around the intake and base of the carb looking for a change in rpm.
Click to expand...


I would always refrain from using carb cleaner or any flammable liquid. I have seen many lose their cars doing this. A bad spark pug wire , Or spark from anywhere will ignite The liquid. Use a small hand held propane torch with a hose on the end to reach all areas. If a spark ignites it you can pull it away . A gas is way better than liquid. Its not soaking the motor that once ignited on an oily motor or wire is not always easy yo put out.

A friend of mine lost his truck years ago. And he was burned pretty bad trying to put it out. with a old used shop rag that just made it worse. Just advise you may want to use. If you feel you are to experienced at doing this. Go for it but you have been warned. Seen liquid spray ignite many motors.

Check how fast a fire can spread with starting fluid and how long it burns . Just think if this was under the hood of a car with oil soak wires or rubber parts.

 
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  • The advice to adjust valves is good.
  • Ignore the compression readings and oil for now; they are not all that bad. Just put in some fresh plugs in the oiling cylinders. Those lower compression readings are NOT what is causing the running and idling problems. A 100% dead cylinder will not cause the idle to hunt up and down.
  • With a stock cam the idle vacuum levels are indeed very low. this very much points directly at a vacuum leak. You can get 14 in vacuum easy with good tuning and a moderate cam at lower RPM's. You ought to be able to get 18 in +/- with a stock cam and carb, just a bit less with a 4 BBL.
  • It's very probably a vacuum leak with the PO's manifold carb swap. When idling, slowly move a rag over the carb top to start closing it off and see if the idle improves. If so, then that is a very good sign of a vacuum leak.
  • Could be at the manifold but start by pulling the carb and looking at the carb base gasket. If it is a stock manifold, it did not come with a Holley from the factor. So it could just be a wrong carb gasket not sealing.
  • If no the carb gasket, then use the suggested methods to look for a manifold gasket leak. These tests are not foolproof, as a manifold gasket leak can come from the underside, in the block valley. The low vacuum levels are not normal so their is a leak somewhere.
  • Pull the PVC valve from the valve cover and put you finger over the end. If it makes a small or no difference in idling, then that is not the issue.
  • Check all hoses from the carb base or manifold to to anywhere for cracks.
  • Make sure the secondary throttle blades are on the stop and those blades are almost completely closed. There should be a tinny gap between the throttle blades and the bores.
  • Measure the voltage at the battery at a high idle... it ought to be 13.5 volts to 15 volts. This is to check that your new VR is OK.
BTW, I don't believe that a '67 273 would come with a nylon-toothed cam sprocket. So I don't think that should be pursued at this point.
 
SeattleQQ1Fish said:
The needle was bouncing around during the vacuum test. Not severely, but it wasn’t perfectly steady. I’m not sure what power valve is in the carb, it’s whatever Holley put in it new from the factory. The way I checked for a leak was to spray carb cleaner all around the intake and base of the carb looking for a change in rpm.
Click to expand...
With a stock or even moderate cam, the vacuum should be steady, not bouncing.

BTW, sticking intake valves would make this occur. Any clue on if this ran OK before the PO made the manifold and carb swap? Or how long it might have set? Running old fuel through an engine can create very bad deposits on the intake valve stems that can cause them to stick and even jam open. (BTDT). Have you pulled the fuel tank and drained it, checked for rust and so forth? Bad old fuel will mess you up every time, and the new ethanol goes bad (oxidize) very quickly, plus pulls in water and forms a gum if the fuel sets and the ethanol separates out.
 
Oldmanmopar said:
No 1. Take the cap off and see how far you can turn the crank back and forth before the rotor moves.
Click to expand...

The balancer moves about six degrees before meeting resistance and engaging the rotor. Is there an acceptable amount of movement?
 
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Murray said:
I would always refrain from using carb cleaner or any flammable liquid. I have seen many lose their cars doing this. A bad spark pug wire , Or spark from anywhere will ignite The liquid. Use a small hand held propane torch with a hose on the end to reach all areas. If a spark ignites it you can pull it away . A gas is way better than liquid. Its not soaking the motor that once ignited on an oily motor or wire is not always easy yo put out.

A friend of mine lost his truck years ago. And he was burned pretty bad trying to put it out. with a old used shop rag that just made it worse. Just advise you may want to use. If you feel you are to experienced at doing this. Go for it but you have been warned. Seen liquid spray ignite many motors.

Check how fast a fire can spread with starting fluid and how long it burns . Just think if this was under the hood of a car with oil soak wires or rubber parts.

Click to expand...


I've preached it and preached it right here on this forum to use water in a spray bottle to find vacuum leaks and always get ignored or argued with. So, I'm just gonna let people burn their crap up. You caint fix stupid, so I'm gonna stop tryin.
 
SeattleQQ1Fish said:
The balancer moves about six degrees before meeting resistance and engaging the rotor. Is there an acceptable amount of movement?
Click to expand...
It is not great, but would not cause the issues you are seeing. That would be about 4 degrees of timing retard due to chain stretch and chain/sprocket wear. The engine will be more sluggish off-idle and not have as good a throttle response, but it will not have anything like the low vacuum levels that you have found.
 
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