So here's the story... I bought the car, an '84 Trans AM with a 5.0L HO L69 about a month ago, the engine was (apparently) rebuilt about 10,000 miles ago. It has a California Emissions CRANE Cam in it, and a Holley 4 Barrel with mechanical secondaries and no choke on an Edelbrock manifold. Yesterday the distributor coil blew up on it, so I bought an MSD Street Fire Distributor and installed it, along with new wires and plugs. Set the #1 piston ATDC per the timing mark on the balancer and the embossed mark on the timing cover, marked with white nail polish some positions on the old distributor and on the engine of where the rotor was pointing ATDC and where it was pointing after I pulled the distributor out. New distributor went in easy as pie and everything lined up perfectly. Got the car running after some minor adjustments, and it seemed to run MUCH better than before. But there's still a problem...

Ever since I got the car, it's had a problem with dieseling (running on after the ignition is turned to the "off" position) and I suspect it may either be timing, or carbon build-up in the combustion chambers (the old plugs were pitch black coated in carbon deposits, and were gaped way too much) and after I put my new distributor in, I'd hoped it would help solve the problem, but it didn't. The real problem is I don't have anything of any kind on the timing cover that tells me how much timing I have, so there's no way for me to use a timing light to see where it is exactly so I can adjust it properly. I can get Piston #1 ATDC with what I have (The mark on the balancer and the raised pointer on the timing cover) but other than that... I have no way of knowing. Another thing I'm afraid of is that they may have set the camshaft advanced, which I would probably have no way of knowing unless I took the timing cover off.

For the time being, I disconnected the vacuum advance, and whipped out an old Sears Engine analyzer, rotated the distributor slowly until I achieved my highest stable RPM, and then synched down the distributor and reconnected the vacuum advance. My vacuum advance is adjustable, and I know how to adjust it, but I have no idea how many turns out I should give it, so for now it's just as it's factory setting.

Any tips, tricks, or advice? I'll be glad to try and provide any more information needed.

 

You make a lot of references to ATDC. If your timing is set to ATDC, it is set incorrectly.

Sounds like you need to remove all the variables (variable vacuum advance, etc.) that affect timing and re-establish a baseline. Disconnect the ESC wire near the heater box, find a timing light and set yor timing per the emissions sticker on the radiator support (typically 6* BTDC). Setting timing with a tachometer is NOT the way to do it.

 

Did you read the part where I don't have a timing pointer to know where 6* BTDC is? My only point of reference at all is ATDC for Piston #1, which is the notch on the harmonic balancer, and the raised part on the timing cover.

 

Are you sure there's no pointer on the timing cover? GM has put the timing pointer on the timing cover at 12 o'clock on some engines. You can see it if you look behind the water pump from above.

If you don't have a timing pointer on your timing cover, you can buy a bolt on one.

 

Donut - I have a feeling you are using the term ATDC to mean 'at top dead centre'? ATDC actually means 'after top dead centre', which is causing some confusion here.

So are you saying that you have timing marks that line up when AT top dead centre, but don't have any graduations after that?

How do you know where TDC is? Have you found it exactly using a piston stop, to verify it coincides with your timing marks lining up?

Sounds like you are probably close with the timing by ignoring the lack of timing marks, and rotating the dizzy till it's happy. Since that's close, the dieseling is probably the throttle blades open too far at idle.

 

Heh, that's actually what I did after I got out of work. I was looking up on Summit for timing pointers and I saw they made bolt-on tabs. I picked up a Mr. Gasket timing tab from the local parts store, just have to install it now. I'll look for that mark you mentioned too.

Yes, sorry that is what I meant. At Top Dead Center.

That's correct, it has no tab with graduations on it to show where the timing is at exactly.

No piston stop unfortunately... what would one use as a piston stop? Just a long bolt that goes into the spark plug hole, or is it something specific? We just used a wooden dowel and a breaker bar and a healthy dose of patience to determine where TDC was, and the marks on the timing cover and the balancer lined up right where we thought it was.

That's definitely another possibility. The carburetor on there is a Big Holley 4bbl. I do have a book on Holley carburetors, I have to read up on it and try to find out what model it is and then try to adjust it properly. If I can't get it to adjust properly, I'll have to take it off and inspect it to see what's going on with it and try to fix it or replace it.

*EDIT*
Though I'm really leaning toward replacing it outright... it has no choke pull off and mechanical secondaries. I'm tempted to just buy a used Rochester Q-Jet off Ebay or Craigslist with vacuum secondaries, and rebuild it rather than mess around with this Holley.

 

*UPDATE*
I put a Mr. Gasket timing tab on, and set the timing for 6* BTDC as per the emission sticker (and as Paulo noted) and the engine was running choppy, I readjusted the carburetor idle air mixture screws to get optimum idle speed, and then adjusted the idle speed screw up to 600RPM.

The car runs a lot better now, has a TON more power than it did before. The timing was WAY off before... it was running smoothly at idle, but compared to now, it was an absolute dog on the road... the timing mark was coming up at the 12 O'Clock position... I couldn't even see it at first it was so far off, and I made sure to make it highly visible by putting white nail polish into the groove so it showed up clear as day, and then putting some white nail polish on the 6* mark on the timing tab, and then wiping it off so that only the little groove was white. You can't miss the marks now.

But even with the timing set, and the carburetor readjusted, it still diesels on after the key is turned to the off position. I'm convinced that the carburetor is the cause of the problem now. I was looking over the carburetor more closely, and I found some startling things: The secondary actuator is blocked off about half way by a screw going through the guide rail for the linkage. At WOT, the secondaries are held at about half-open position by this screw. The throttle plates are black as night, yet the throttle plate screws are bright and shiny. One thing I noticed before, which is worth noting is that the carburetor is on top of a 1/2" spacer which shows that the previous owner was looking to get more top-end power out of the car. No choke as I mentioned before, the idle mixture screws are wet with gasoline leaking from them; no matter how I adjust the carburetor it reeks of gasoline... and who knows what other problems there are that I haven't noticed, or can't see.

On the bright side, I checked over the intake manifold, and it's an Edelbrock Performer model 2101, which has a spread-bore pattern. On Craigslist I found a 7043202 model Rochester Quadrajet out of a '73 350 SBC with an Automatic Transmission for 40 bucks. I'm just going to buy that, rebuild it, and put it on in place of the Holley. Then, I'll rebuild the Holley, (the RIGHT way) and sell it to make back some money. With the power differences between '73 and '84 as well as the cam kit in my car, the carburetor should be just about perfect for the engine. Minimal emissions and no computer controls on it are another huge plus.

 

Ok well its not your carb, the cylinders are too hot and are reigniting the fuel. Once u turn the key off the ignition gets shut off. Your engine is gonna burn up if you dont fix the real problem. Try running 91 octane fuel.

 

That's another possibility I had considered in the back of my head... after all the engine was rebuilt. I'll put in 93 octane since most if not all the pumps in my area jump from 89 right to 93. Right now I'm running 89. If that doesn't do it, then either the compression ratio is through the roof, or something else is going on.

Either way though, I'm definitely going to swap to the Quadrajet... I just love them. I love the sound and the feeling when the vacuum secondaries kick in. Plus, after inspecting the Holley more closely, I really want to spend some quality time rebuilding it and righting all the things that was done wrong to it.

 

Once you get tuning issues - like timing and leaky carbs - out of the way, stuff like dieseling often get resolved in the process. Ie fix what you know is wrong first. If the Holley leaks and reeks of gas, it probably has bad gaskets, stripped screws etc. A rebuild kit would do wonders. So might the carb swap

Now that you can measure the base timing, are you in the 12-16 degree range? And can you add some timing tape to the balancer, or get a dial-back light, to verify that you at getting 33-36 degrees advance @ 3000 rpm total timing? Once those two ends of the timing range are in the ballpark, you can then fine-tune it by finding the sweet spot both ends for best idle vac and best WOT power.

I've got a 1/2" phenolic spacer on mine to help combat fuel boiling, not in a quest for top end.

 

I certainly hope so, but for safety sake I'm going to run 93 Octane until I get everything squared away.

For timing, all I do know is my base timing without vacuum advance is 6*BTDC. We put the timing gun away once we started using the engine analyzer to tune in the carburetor at idle. Part of the reason I didn't go back to the vac. advance or measure timing with it on is because honestly I'm not sure how many turns "out" I should do for the adjustment. It came with this chart and instructions in the package, and this was the look on my face:

(Note: I just read on another forum from an MSD Tech that you're just supposed to turn it all the way in, and then test drive it... if it feels like it can take more, give it two turns out... keep doing this in 2 turn increments until it starts to "flutter" under a light load, then turn it back two turns. I wish the instructions would have just said that... )

Heh, I didn't think of that. You learn something new every day

 

6 degree sounds a little low, then again it's probably higher than that now that you've given it what it wants. Of course all this is done with the vac advance plugged up.

Yeah, that chart doesn't tell you how to determine how much advance you need. To set the vac, pretty much what you said in the note in your last post. Get your mech timing completely sorted out first. Once happy, hook the can back up to manifold vac, crank it all the way in, and iterate turning it out a couple turns at a time till you get pinging under part throttle with load, like going up a hill say. Then back it off till it goes away.

 

Well, I went and got my Quadrajet, it's sitting right here next to me at my computer desk. We're both just chilling out and relaxing for the moment. Picked it up at a place in West Haven for 40 bucks... it's all there too. Choke pull-off, all the linkage, it even still has a steel fuel line going into it, and probably has an old filter in there too. Not bad looking either... some of the linkage is a little corroded and there's some surface rust on a couple of parts, but for the most part there isn't much in the way of carbon fouling or serious rust. Even the vacuum choke pull off still works.

Might have to get an "Anti-Dieseling" solenoid for it since it doesn't have one.

*EDIT* I may also need to get an EGR since there isn't one on there now. That should help a bit with the dieseling I hope.

But, one thing at a time... first, rebuild the Q-Jet with an anti-dieseling solenoid and put it on there, then take the car to the closest gas station and fill it up with 93 Octane, then drive it around a bit and see if that takes care of the problem.

 

For giggles can you do a compression test and post results?

 

Sure. Luckily I do actually have a compression gauge in one of my toolboxes. (One of the advantages of my late grandfather being a mechanic for 48 years is that I have just about any tool I need at my disposal)

Just so I have an idea here, what sort of results are you expecting to see? A compression test isn't going to tell us compression ratio, only give us an idea to the health of the cylinder being tested. Not a bad idea to do that anyway though, it couldn't hurt to go through the engine as thoroughly as possible.

Speaking of engine health, the poor thing has developed a rear main seal leak. So it looks like I'm going to be getting down and dirty in the very near future! It almost looks like it either blew out, or was installed incorrectly. Funny thing though is that the oil coming out is pitch black and nasty, while the oil I check on the dipstick is clean looking. Definitely warrants investigation!

I feel like the little dutch boy trying to plug up all the leaks in the dyke with his fingers haha. Never a dull moment when you buy a half-finished hacked up project car. It's a good thing I'm patient, have some clue about what I'm doing, and that I'm not willing to do a job half-assed.

Just about the only thing I do half-assed is going to look for a job in the field. I just graduated last month from Porter & Chester Institute for Automotive Technology at the top of my class lol... I really do need to get a job though before it starts looking bad to employers that I've waited so long.

 

Well i hope to see the cylinders test good. Oh by the way my curiousity wants to know if there is a ministarter on that engine?

 

Nah, looked like a regular stock type starter. I need to reroute the cable going to it though, it looks like the last guy just got a 4-5 foot long cable and made the most direct route from the battery to the starter as he could, going through all sorts of different wires, and leaving slack that could touch the exhaust manifold. Could have been done much more neatly.

The negative side of the battery has a sort of quick-release on it though, which is kind of nifty.

 

Finally got around to doing the compression test. I would have done some wet tests, but my oil can was empty, and the only oil I had in the garage was synthetic 10w30 which I would rather save for doing an oil change down the road to my Caprice. Plus, MSD specifically warns against using synthetic oil of any kind in the motor during the break-in period of the distributor gear so I decided to stray on the side of caution.

Anyway, here are my results:

1 - 140 | 2 - 145
3 - 140 | 4 - 140
5 - 140 | 6 - 145
7 - 140 | 8 - 140

Looks pretty good to me.

 

Yep looks good, i still highly recommend 91-93 octane fuel.

 

Without a question, I agree. Until I get the carburetor rebuild kit from Cliff's, rebuild the Quadrajet, and get it firmly planted on top of that engine, it's not going anywhere for now. As soon as the carburetor is on there, first thing I'm doing is going straight out to get some 93 Octane in it, and then running down the gas tank a bit to flush out the lower octane stuff, and try to burn up any carbon in the combustion chambers.

 

to get you by until you get the dieseling figured out usually keeping the car in gear when you shut it off will stop it until you get it figured out .

 

That won't be necessary. I've got a daily driver and a parts getter car that I can depend on for now *knock on wood*. I'm safer just waiting until I get things sorted out and fixed for good first.

 

@DonutGuard Did you ever figure out what was causing the dieseling? I am having the exact same issue that you are having and it's rather frustrating. I too bought someone else's half-asses project car that needs to be done ASAP and sold.