I forewarn you all, this may be a little long winded, but any help would be hugely appreciated, thanks in advance!!!

I will give a preface, troubleshooting and repair steps taken, and then let you guys have at it - because I'm stumped.

First, I wont provide a resume but I have built several GM vehicles throughout my years, this is not my first rodeo.

So - here goes: Bought a '70 98 Ragtop, nice straight car, all the sheetmetal is there. It seems to be an unmolested car.

On delivery, drove it to the top shop, new top installed. Started and ran okay, I guess. It was only two miles. Picked it up and drove it around some, then home. Idles like crap, but it starts and runs. I think - okay let's tune it up, right?

Upon further inspection, the carb and distributor looked kinda crappy, and I have a local rebuilder thats a true artisan. (J&C's Parts, 716.693.4090) I have used his services many times in the past, he's amazing. So off they went.

Carb is rebuilt and fully blueprinted, and it's the correct number. Distributor also the correct numbers and was also blueprinted, and I added a Crane XR-i to eliminate the points. On an testing bench, I observed a fully functioning ignition system coil and all, to the point of watching the proper advance curve apply, and 8 plugs actually fire. (see pics)

That being said, I have high confidence that the ignition and fuel delivery systems are functioning as new or perhaps better.

The car is REALLY HARD to start. It cranks just fine - but takes some real effort and tinkering around just to get it running. Once running, it seems to run pretty well. Just get it started... that's the huge fight.

I have verified:
* ~170 psi on all cylinders, it doesn't knock or tick. The engine itself seems healthy.
* 12+ volts at the coil cranking, ~12 running. The ignition fired at 8 volts on the bench.
* Coil Ohms out good as new
* New plugs gapped at .030
* New cap and rotor
* Verified proper firing order (started over at TDC, went CCW from there)
* adequate fuel delivery
* Proper choke operation

Observations:
* The car ran pretty nice (when it was running, even torqued the tires loose while testing) with nearly 18 degrees of initial timing (wow..maybe the balancer has slipped and that's not really where it was?) This was checked with an advance capable timing light.
* Vacuum gauge was at ~18 but has a very rapid fluctuation over a ~2 inch range (this I was told is due to a non dampened gauge)
* I was able to get it to idle at ~ 600 in gear, and was just a touch rough but kept running just fine and was crisp and responsive.
* The wires appear to be in great shape, and since the car started and drove previous with them, I have NOT YET changed them. That's next. Is it possible they just suck?? What else is there??

Parting thoughts:
* Wires are cheap, they are next.
* Rapid vacuum fluctuation makes me worry about the valvetrain, but I was told its due to the "non-dampened" gauge I'm using.

I welcome any thoughts, ideas and criticisms; I am at a loss. Thank you all in advance!

 

Well, try dribbling some gas into the carb throat, or spraying starting fluid, and see if it fires immediately. That will tell you if it's a fuel delivery issue or an ignition issue.

Could be as simple as a choke adjustment, but need to verify fuel or ignition.

 

Fuel is there, starting fluid yields no difference.

 

I think your timing's way off.

A stock distributor in a standard 1970 98 motor should be set to 8° BTDC at 1,100 RPM, and run on about 95 octane gas, by current US standards.

Either you're way too advanced, or the balancer has slipped.

Confirm TDC and you'll know.

- Eric

 

I have had it all over the place - still is a bitch to start.

 

Have you tried to start it as if the engine were flooded - hold the pedal to the floor while cranking?

 

Not sure what they mean by a dampened vacuum gauge. What would be the point of limiting its sensitivity. I you have regular fluctuations like at half crank speed. Then you have possible valve seating issues. I'm not sure that would make it hard to start since you say you have 170 psi compression. At the dealership factory training schools we were always taught to rule out base engine concerns before looking at fuel or ignition. Since the car is new to you you should verify the base engine is sound first.

 

I have to agree with this if your 18* initial is where your timing is set currently with vacuum advance disconnected and the timing curve is stock.

A dampened gauge would be liquid filled.

Is it hard starting when cold and hot or just 1 or the other? Your video is not a video link.

 

Thanks guys! The last image was a screenshot of the video on my phone, it wouldn't upload. I also agree the timing at 18 degrees initial seems like a ton, but when it was running that's where it "liked" it. As for the vacuum gauge, the jury is still out for me. I don't like the flutter, but the explanation I was given makes some sense, and having good compression on all 8 I ruled out a valve issue. Also - I have tried starting as if its flooded, no difference. Starting fluid makes no difference.

I am planning to do wires today as they are pretty easy; I had ruled them out prior because once started the car ran okay, but I am thinking startup needs a stronger spark. I am going to set the initial at 8 degrees and try new wires today. Wish me luck!

 

Not true. It's the opposite.

Good luck!

- Eric

 

Oy. Then what the F*** is making this car so hard to start? lol

 

You may have missed Eric's comment.

Take (or buy) a positive piston stop, the type that screws into no. 1 spark plug hole.

Put your degree wheel on the balancer.

Turn engine by hand (observe valve action with valve cover removed) until you are close to TDC. Screw in the piston stop.

Carefully turn engine in same direction until it contacts the stop. Adjust degree wheel until it reads zero.

Turn engine in opposite direction until it contact the stop. Note the degree wheel reading. Adjust the degree wheel half way back to zero.

Remove the stop.

Turn the engine until the degree wheel shows zero.

Remove the degree wheel.

Mark your balancer opposite zero on the timing tab.

Time the car as usual using your new mark.

 

The only other thing is your a/f mixture at idle. Was the carb adjusted for the highest rpm/or vacuum? Is the choke operating correctly? Do you pump the gas pedal 1/2-1 full pump when starting cold? Outside of the timing being high, really have nothing else without being there?

 

Yes, but...

He said spraying starting fluid into the carb made no difference, so that pretty much rules out a lean idle mixture, and if it were too rich to run, his plugs would be soaked - they'll run pretty darned rich before they quit.

- Eric

 

If they are wet upon start, starting fluid will not instantly start the engine, only expedite the drying process until a strong spark is present. Also if the plugs had been really fouled previously sometimes no amount of cleaning will make them perform correctly.

What brand and part number plug are you using?

One additional thing you might consider trying for grins and giggles and I know you stated earlier you checked volts when starting. Run a jumper from the battery + post to the coil + terminal and try starting it.

 

I was planning to index true TDC using a piston stop if the shenanigans continue for sure, that is on the list to verify the balancer.

I have "hotwired" the coil, no difference.

The plugs are brand new autolites, as I am not at home right now I do not recall the number.

As for the carb and choke, I was getting about 18-19 inches of vacuum with the rapid 2 inch flutter mentioned in the original post. The choke has been verified to be functioning perfectly.

The more I think this through for the millionth time, I am thinking the wires must be crap and just not carrying a good spark - what else is there?

 

Well I exhausted all my thoughts.

 

I feel ya! Thanks for all of the advice.

 

There's nothing wrong with changing the wires, but I doubt that's your problem.

Insulation on spark plug wires breaks down against higher voltages first, so the first signs of bad wires are problems at higher RPMs and greater throttle openings. Bad wires, unless they're REALLY bad (especially when it's wet outside) will show up at idle last.

As for the rest of it, my bet is it's timing.

- Eric

 

I am in agreement Eric, but I can have the timing all over the place and the damn thing wont start. I'm perplexed.

 

I understand, and I'm confused as well, though that's not unusual, since diagnosing problems over the interwebs tends to be a challenge.

It's just that from everything that you've said, the only true anomaly is the timing at 18 degrees, so it's the thing I would look at.

- Eric

 

Again we totally agree. This has me stymied.. especially since it drove in (albeit running like poo) with worse fuel delivery and ignition

 

Is it possible that someone did a timing chain and didn't set it correctly?? After 47 years anything is possible.

 

That is a very compelling question- I had pondered it myself. After 47 years.. who knows.

 

Welcome to the world of old junk. Half the battle is figuring out what went on in the past.

 

I would line up the balancer at the 0- tdc and pull the distributor cap see where the rotor points too, Make sure it's on the compression stroke.

 

You got that right! I encounter it with old houses too, un-f***ing what the prior idiots did. I hope its not that, I mean it drove ok...

 

I did that, as I located TDC compression and started there with firing order. I had the rotor right at tower 1 on the cap, balancer at 0. It took about 18 degrees of advance for it to finally start, and ran okay.. until I shut it off.

 

Just for laughs I would put a points distributor back in and see what happens, Maybe the electronic ignition is defective. Just because it's new doesn't mean it's good.

 

It's the original distributor, fully tested on a bench. See pics. I personally watched it fire 8 plugs in sequence all the way down to 8 volts before it stopped firing.

 

I thought of that also... What would that do if the electronic points replacement unit is firing correctly, then its doing what its supposed to, triggering the coil. If the timing is consistent and steady then its working just like the points would be, I also thought maybe to replace the coil as it generates the actual spark.

 

Coil also validated as working as expected. I wish it was that easy! LOL

 

I thought it might be breaking down as it got hot sitting in the engine. Might not due it on the bench, Just a thought.

 

Also a possibility... we let it "run" for a bout ten minutes on the bench... I am going to pick up wires later today. There's nothing else possible besides major valvetrain issues.

 

If this is an original motor, there is a procedure in the CSM for determining whether the valve timing is correct, involving checking rocker deflection at a specific point in rotation.

It's easier than pulling the timing cover.

- Eric

 

I think Chilton's has a spec for valve opening specs in it

 

If the timing cover has to come off you can bet a mild cam and intake swap will be going on lol

 

Be very cautious with Chilton's - they are known for inaccuracy in numbers like this.

The CSM method is very straightforward and simple.

- Eric

 

I believe it! What is CSM?

 

The Chassis Service Manual.

Get an original (not reproduction, not disk) copy on eBay. It will tell you everything you need to know.

- Eric