72' Cutlass-S 350 2Barrel 80,000miles

Symptom:
Rough Idle
Nothing usable over 3000 RPM (Breaks-Up/Complete loss of power)
Never able to get the idle below 700 with throttle plates at full closed

What has been done:
New Vac Advance driven from manifold Vacuum.
Vacuum Solenoid nearest Thermostat Bypassed Completely.
All new ignition bits (point/condenser/coil/wires/cap/rotor/plugs)
-Spark Quality is good at stock gap on a test plug
-Spark Quality is thin at large gaps(>.5") desteriorating to nothing as RPM increases. Maybe this thin spark is normal for stock points style ignitions???
Ignition Dwell and Timing Set to Stock Sticker per Sticker procedure
Carb Kit completed. Float to Chiltons Book spec. Nothing telling found. Clean
Spray for intake leaks. Found tight.
Vacuum at 1000rpm idle: 17 with variation of 1 up/down per the rough idle
Cold/Hot makes no difference
Choke Open or restricted makes no difference
Compression:
85,75,68,86,68,83,68,82 (Engine Cold / No Added Oil)
95,82,72,95,72,82,82,85 (Engine Cold / Added Oil)
No backfires ever
No black/blue smoke
No large pops out the exhaust



Really nice car. Exhaust is seperated and on straight pipes. Performance has degraded slowly over several years.


Thoughts? Thank You guys!! Really bummed this really pretty care runs sooo badly.

 

Did you set your dwell/timing? Is it advancing with RPM?

 

Spark shouldn't drop off. You have cheap set of points or a bad condenser, coil or bad dwell angel. Hows the point cam look? Nice sharp edges or rounded off? Did you clean the point set with contact cleaner after setting? A dirty feeler gauge will take out new points in a hurry. Check for a chafe in the wire to the point set where it goes through the dist base and where its close to the breaker plate. IMO Those compression numbers look low. How many revs are you allowing before reading the gauge?
Have you investigated fuel starvation. Are your plugs white?
Consider a Corvette point set. The spring is stronger and usually of OEM quality. Ecklers or Mid America sells the good blue streaks(still?).
Also check the dist housings top bushing for slop. Up n down movement ok, side to side not.

 

Dwell and Timing:
Per initial post, Dwell and Timing set per stock sticker. Advancing when v.Advance is plugged in, and further when the mechanical advance is doing it's thing.

Spark Quality:
Using the large gap as my read of spare quality, drop off to less than a .5" progressively fades to nothing at over 3000rpm. Spark never fails at the plug gap .040"

Assuming this seems normal with the dropping charge time of the ignition coil. Points ignition penalty.

Points:
The points are new. Paralleled/Trued, set to .020" initial gap for Dwell fine-set prep, cleaned outside of distributor prior to installation. The points cam looks good and the foot is new and well lubed with provided grease.

Fuel pump:
Pump is new. Hoping it is doing it's job. When the float was not set, it quickly overflowed the bowl before the float was reset to stock spec.

Plugs:
Plugs are new. After driving on them for approx 20miles, they still look new with absolutely no valuable indicators of combustion quality. grrrr

Distributor Shaft Play:
the car has 80k on the clock. I did not specifically check the play, but will.

Points to Coil Wire:
Looks great upon inspection


Thanks for chiming in guys! Look forward to hearing this thing purrrr

 

What is your dwell and timing set too? What is it advancing to at 3000 rpm with vacuum and wihout? Your idle rpm should be 650 in drive with the brake on.

 

Dwell: 30Deg at 1100rpm
Timing: 8Deg at 900rpm

Idle at 650 is hardly achievable with the rough idle. Static idle is currently at 800 in Park. At this setting, stays running with AC on in Park. (Yup, AC still works!!!!)

Note on power at 3000:
All power disappears at 3000. must back off on the throttle at that point. Will check the absolute advance later though I can hardly get an absolute advance without a device that can monitor #1spark-event and a true crankshaft position. Well off the stock timing indicator plate and not easily identifiable at that point.

 

Have you changed your fuel filter? Are your plug wires in the right order and secure? Have you adjusted your air/fuel on the carb for the best idle quality? They have nothing to do with cruise. When you raise the rpms look down into the carb and see if the fuel flow is consistent and not surging.

On a side note, has the timing set ever been replaced?

 

Fuel Filter was swapped with the carb kits.

Plug order is correct. Car runs OK below 3000RPM. Just not silky V8 smooth.

I get smoothest idle at 4 turn from seat on the low speed screws. Base is 2 turns per the limited documentation with the carb kit. Nothing in the Chiltons. Always seemed ALOT more spins than it should be. Cannot find info on what is typical for this car anywhere. If I have an intake air leak, I may need this elevated fuel to compensate? never found said leak though.

Timing Set: Stock and never removed

Looking down carb at up to 3000RPM:
Circuits appear to function. Mains start showing delivery at 1500. At breakup, there is a real mess of fuel moving about in the carb. Hard to tell with all the misfiring going on though.

 

I'm thinking your timing set is maybe due for a replacement.

 

Suggesting that the sheet metal stationary mounted timing gauge, for setting base timing, is ready for replacement?

 

I think he means the gears and chains that attach the crank to the cam inside the front cover.

 

I agree those compression numbers would dictate that.

 

Yes, your timing chain set.

 

I once had an issue with upper RPM breakup back in the 80s that I traced to the resistance wire to the coil. The wire had been spliced and had corrosion at the junction. Apparently the corrosion caused increased resistance and decreased voltage/current to the coil.

 

Timing Chain Set:
So, the theory is that I am tooth off on the timing chain/gears/cam? Can I easily double check this externally without removing that cover? TDC mark at the flywheel on the exhaust stroke. Look at the #of degrees on the intake valve opening?

How likely is this on a 350 that has never been opened with 80,000 miles?


Ignition Coil Positive Side Resistor Wire:
Never found the actual resistor on this car. Does measure 6V with key on the RUN position. When running, this should climb to 12V? How is that resistance inserted/removed from that circuit?


Thanks again guys!

 

I am concerned by the compression numbers, which are too low, and by the fact that you say the spark "drops off" at a 0.050" gap (presumably with a spark plug not installed).

Did you check compression with the throttle completely open?

Visually, that spark should jump a 3/4" gap with no problem.

Consider your coil, and reconsider your other ignition components.
Condensers that are bad out of the box are not only "not unusual," they're common. Still have the old one?

Welcome to ClassicOlds.

- Eric

 

Compression:
Throttle/Choke was held plate wide open
Cranked several revs till the reading peaked

What is considered an average normal for a 350 with 80K?


Spark Quality:
.5" not .050". Gap is created using a test lead clipped to a nylon tie .5" from the bolt it is tied to. Other end is clipped to the spark plug wire conductor clip

I have the old condenser. Can swap that in quick enough. My coil is new. Old coil did the same. New coil is shiney.

 

Personally, I'd say about 115 to 130 psi.

As for the spark, it shouldn't drop off. This strongly points to something in the ignition system, and the condenser is a very likely culprit.

- Eric

 

The plate Eric was asking about was the throttle plate, the one on the bottom of the carb.

 

That was my 1st thought

LOW compression - retarded cam, jumped a tooth maybe?

 

Hate the idea that an engine with 80K is jumping a tooth on the timing chain, ughhh. Does this sort of thing really happen on these motors? Nobody has ever been inside this motor less the 'UAW'. Anything IS possible.

Am I correct in thinking the valves are in good shape, and rings are probably OK since the compression numbers did not increase much with the addition of oil to the cylinders? The low intake vacuum also indicate a timing chain skip?

Anyone know a quick check to confirm the timing is off without removal of the big messy front cover? I can only come up with a method via comparing intake valve on the TDC Exhaust/Intake stroke. Would have to know when the valve starts to open. As messy as just taking the front cover off, perhaps??

Will swap the condenser this afternoon. Nobody wants to pick on the carburetor. These old 2barrel carbs pretty reliable?

 

When did this problem rear its ugly head, after you worked on something?
What typo of fuel filter is in the carb inlet...pleated paper or bronze sintered?

Hopefully you have the pleated paper? Try pulling out the rubber end on the pleated type filter then install it in the right direction with the bypass spring on the right end, then road test. If you have the bronze filter Ill bet thats part of the problem.

Safely Tee in a fuel PSI gauge and take it for a kill run. You should see 4.5 - 6 psi at the carb. That will indicate the pumps doing its thing.

Said fuel pressure gauge usually comes as a combo gauge, PSI & Vac. Give us a vacuum reading number at idle. Try to achieve the highest vac reading by adjusting the base timing with the vac advance can working and adjusting A/F mix screws, then road test. Problem still there?

If the ignition sys checks OK, my next move would be to eliminate the fuel delivery system as the problem. Sounds like either the pumps not keeping up, theres a restriction or the floats fill level and drop are not set right. What type of needle and seat came with the carb kit? There are at least 3 designs. The integral windowed type sux, if its even still being made? You want the separate needle and seat per OEM. Not all carb kits are equal...read no chineasium junk.

On a point ignition system, yes the running voltage is less than 12vdc. 8-9vdc is normal running VCD. The "resistor" is a wire designed with built in resistance, not the commonly seen ceramic ballast type component. Upon start up there is a full 12+ VDC supplied to the ignition system off the start solenoid to get it going. Once you release the ignition key to run position the voltage drops to the 8-9 range via the resistance wire. This was by design to give the system full VDC upon start up and to increase point contact longevity by dropping the VDC down once running.

Jumping a tooth only happens when the nylon teeth wear off the gears or the gears are so badly worn the chain has nothing to bite on.

With the engine at 0 degrees on the timing tab pull off the dist cap, rotate the engine back n forth by hand to see how many degrees of play the chain has before the distributor rotor moves. Report back.

 

Ugly Head:
Degraded over time. I am not the owner, just a handy mechanic in the neighborhood. Lotsa worn/bad parts under the hood when it showed up. Water Pump leak is why it showed up.

Filter Type:
Pleated paper from NAPA

Needle and Seat Style:
Carb Kit from 'Advance Auto' $15. Needle is the viton rubber tip style. Seat is windowed. Had to remove the rough burs from the window before install. kind crappy really. Seemed a nicer kit than the NAPA kit. Car has run the same after both kits attempted.

Fuel Pump:
Stock Pump was leaking around the can seams. Replaced with a NAPA replacement. Car ran the same pre and post the pump change out.

All Else:
With your direction, I will check those things identified and report back!

 

Since you have a stock cam, just use the technique in the CSM.

- Eric

 

Points Swap:
No Change

Measured the voltage at the primary side of the coil with the engine running and in the run position. 12v. Something isn't right there. Points looked Good yet.

 

Would a worn cam do this?

 

universally low compression across all cylinders indicates all have a problem; when cams to bad they generally do so one ot two cylinders at a time. Or, they start wearing leather jackets and hanging around pool halls and other houses of ill repute.

Yes, you can per the CSM procedure, measure pushrod travel at two different positions of the crank and that should indicate if the timing set is skipped.

What if you were to pull the fuel pump and peek in there and see if any teeth are left at all on the cam sprocket? Fairly painless. If the teeth are all steel, in good shape, look elsewhere. If teeth at pointy and aluminum [or plastic and pretty but 80k old] then you are pulling oil pan and front cover.

It is NOT that big a deal. Put on your MAW-resistant helmet and do just what neeeeeeds to be done.

 

Will pull the fuel pump for a look see. The timing cover doesn't look to be a huge deal, less the oil pan mess.

 

Wow a good mech not getting anywhere. Makes me feel better that it's not only my luck (or skills).

I see two unknowns ignition and carb. A trashed distributor or a failing carb both will create that symptom where it falls on its face. Too bad you don't have known good parts to swap. I've inspected and put kits in carbs where I've seen no issues yet they still fail. Holley makes a nice two-barrel for a reasonable price should the owner agree it may make it happy. It bugs me that it's not backfiring pointing to ignition/timing. Also closing down the throttle plate should drop the idle to nothing. It may be sucking air through the throttle shaft ends? Carbs can be evil.

 

Yeah, this sort of thing is plenty humbling.

Going to prove to all if this is cam to crank timing first. Compression sucking on a low compression engine is bothersome.

Felt carb to me, yet stock/rebuild1/rebuild2 all the same performance.

 

Yeah man it sounds like a a possible possession where an exorcist may be in order? It occurs often in my dark world of electro/mechanical mysteries. Fortunately it's my problem with no "what's taking so long?" issues. Hope you find the gremlin soon!

 

Did you pull the fuel pump to see how much slack is in the timing chain? Or you could bring the timing mark on the harmonic balancer to zero, pop the distributor cap, and see how far the crank turns each way before the rotor moves?

 

Appears to be a cast aluminum hub with a plastic/nylon gear ring. From my view, looking ok. These prone to failure at low miles? 80S

Distributor to crankshaft is 8 degrees. Takes 8 degrees of crank spin to see movement at the distributor shaft, in either direction.

 

That looks like an original gear.



8° is too much play.

I'd consider changing the timing set with that amount of play, though from that angle, the gear looks to be intact.

- Eric

 

Hmm, 8º is the same amount I determined my old cam was retarded (made the mistake of not degreeing it at installation), and my engine had no low RPM power. Kinda the opposite of your problem.

 

What range is normal for degrees of play? How bad is it?

 

A couple of other things to consider if it's not totally due to worn out timing chain/gears, is that the fuel pickup sock in the tank can collapse & become restricted with crud over time. Also, the rubber fuel line sections between the tank & pump rarely get attention and may have rotted/cracked over the years, allowing air to enter the fuel supply line, heck they may even be original hoses from '72. That's a real easy inspection/fix, not so much for the tank sock.

 

Needed to post an update on the resolve.

Timing Set replaced. Car now runs very well.

Was never able to get the idle down. Suspect having connected the vacuum advance to manifold instead of ported has something to do with this. Lowest I was ever able to get it to idle was 900, in park.

Thank You to everyone who offered up help. This helped me get to this resolve.

 

Disconnect your throttle linkage to see if its whats hindering the rpms from dropping. Glad its running well, the stock timing set usually had a lifespan of 60k miles when they started to peel.

 

Compression:
85,75,68,86,68,83,68,82
==========================
psi?
That sounds horribly low
carb propped open, right?
sorry if I missed something, did not read thru all the above