62 Tempest major dieseling issue
 

3.2L 4 banger and 2-speed auto. Single-barrel Rochester carburetor was rebuilt & in good shape. Size 58 jet. Electric fuel pump with a regulator pushing it down to 3psi. Stock timing.

Purrs like a kitten once @ operating temps and idling, but bogs like crazy when it's put in gear & diesels on shut down, even if it's in gear.

I'm at a loss. Any help figuring this out would be greatly appreciated.

Back the timing off a few degrees and see if it helps the dieseling. Try a higher grade of gas. Check to see if the mechanical advance is actually working.

Usually dieseling is caused by the curb idle speed being too high. If possible slow your curb idle down more.

One other thing that causes dieseling is red hot carbon deposits in the combustion chamber. Take a water bottle, put your finger over the end of it, and dribble a bit of water into the throat of the carb at a bout 2000 RPM. This will loosen the carbon on the top of the piston and combustion chamber, removing the hot spot that may cause run on. You'll have a ton of carbon come out the tail pipe while doing this, don't try it inside, or when people will be around you while performing the operation. Run at least one bottle through the engine, be careful not to pour so much that it stalls the engine.

As a mechanic I've done this many many times over the years, and it will many times remove the carbon that is keeping the engine running in absence of ignition to the plugs.

As has already been mentioned check the distributor for mechanical and vacuum advance functioning for your acceleration hesitation. Possible deterioration of the vacuum advance diaphragm is likely after nearly 60 years. Also check point dwell, or gap.

I just purchased a 63 with the same problem. Vacuum advance as hooked to the manifold, carter has a port for it on the right bottom. I moved the vacuum line and the engine set down, idled great and correct rpm. No more diesel from the excess idle speed. Simplest fix for car the runs "rough" I ever had. Post a photo of you vacuum lines, it does matter, Rich

Same as others have said. My '63 195 dieseled badly as well. Found the vacuum advance line was attached to a ported vacuum source on the carb which had no vacuum at idle. Moved the hose to a constant vacuum port on the intake manifold and the added advance at idle increased the idle speed substantially enough that I was able to lower the idle at the carb throttle position which totally eliminated the dieseling. Much smoother idle as well. I ALWAYS prefer vacuum advance at idle, and personally have never had a vehicle that I didn't feel like it ran better that way.

Pictures are attached. Thank you for the replies.

Very interesting and much different from mine which is a manual choke, 3-speed car (and a '61 engine btw).

I would be looking for vacuum leaks. I am curious about that vacuum line running from the manifold distribution block to the upper portion of the carb. Is that part of the choke system that helps pull the heated air through the choke thermostat coil? Would be curious if that is leaky and bleeding off a lot of vacuum.

Is your vacuum advance mechanism functioning correctly? You should be able to pull (and plug) the line from the distributor while the engine is running and experience a noticeable drop in RPM.

Maximizing the timing and vacuum levels so that the car will idle at the lowest throttle blade opening will keep the carb fully on the idle circuit and minimize the chance of dieseling.

On cars with lower vacuum levels like some of the Ram Air engines, Pontiac used an idle stop solenoid that basically closed the throttle blades when the ignition switched off to prevent dieseling.

Just found out the junction block for all the vacuum lines in those pictures is one of the leaky parts.

Gonna pull it off and see if I need a replacement.

Also need to find out if the hard line going to the transaxle is still in good condition or leaking as well.

Update: Got the junction block for the vacuum cleaned and reinstalled.

It stopped sucking ether through the block so that leak is fixed.

Still bogs down pretty bad when put in gear, but pops and I got it to move out of the yard and by the garage. Also still dieseled pretty badly.

Going to check the vacuum line going back to the transaxle and check the vacuum on the transaxle itself for leaks tomorrow.

Never had a 4 but recall some cars had an electric idle step up solenoid that opened the idle setting a bit when the ignition was on and dropped back when turned off.

Update #2:

Small rubber line connecting the vacuum hard line from the motor to the transaxle was shot. Replaced it with new rubber.

Also checked the vacuum port/diaphragm directly connected to the transaxle, it is not holding pressure at all. Likely the cause of the bogging when I throw it into gear.

Anyone know why the 61-63 lemans catalog is unavailable online from Ames Performance?

Anyone know if I can order a new Vacuum Modulator for the 62 Tempest w/ a 2-speed auto transaxle?

Not sure of availability new but there are a fair number of used ones still out there. For testing purposes, you can just plug the vacuum line at the modulator. That device will have no effect on the engine bogging or dieseling once the vacuum leak is plugged off. The modulator valve effects shift timing and feel only. So without it functioning, you will get a very late, hard shift. So something else is still not right with ignition or the carburetor.

I put a call into FATSCO about one back in December and they do not carry them anymore. I bought one on eBay and it came damaged. So I got one from Clarks Corvair. Part number C876 page 135 of their online catalog.

Thank you for that reference. New modulator and gasket purchased.

I plugged the line going back too and started it up today.
Adjusted the carburetor a bit and it ran really well.
Operating temperature only saw it diesel a single time after shutdown compared to a good 15-20 seconds.

I don't know the actual specification, but is your idle speed adjusted to spec? Is your initial timing set to spec with the vacuum advance plugged and no other vacuum leaks? If initial timing was set with the vacuum advance connected, it would be very retarded and require more throttle blade opening to idle which causes dieseling. Also, be sure and adjust your idle mixture for maximum RPM and smoothness and then reset the idle speed if necessary.

Not sure on the idle speed.

But yes, timing was set to 6 degrees BTDC with the vacuum advance plugged.

Also found out there were two different distributors, a small cap (just spots for 4 wires), and a large cap (with blank spots in between the 4 wires)

I have the large cap, so I need to set the dwell angle on my points.

Remember the dwell will effect the timing. Set the dwell first, then recheck the timing. I bet if you just drop the idle speed 100 more RPM, it will quit dieseling. Sounds like you are getting close.

Didn't even get to set the dwell. Set point gap to .016" and the car wont start at all now. It's trying to throw spark to the plugs even with the distributor cap off? I have no idea...

Don't mean to be insulting, but hopefully the gap was set with the points at the top of one of the lobes? If not, they are staying open all the time.