Three things to check for cold start and/or low-RPM performance problems - 1967

[67_Eldo]

We've all heard the generic adivce that surfaces whenever somebody complains about how badly their Quadrajet (QJ) behaves when first waking up in the morning or when running at low RPMs. "Check vacuum lines" ... and so on.

Many folks (rightly) follow that advice and still end up with a car that doesn't not meet the "Cadillac standard" for starting and idling. I am one of those people. So I kept (slowly) digging. Here is my Top Three list of items that (in my experience) rarely get mentioned during those advice-giving sessions.

[Note: The specifics here are for a stock 1967 Eldorado. Some details will vary across the '67-'70 models, but I think all three (or four) points in my list apply to all stock Cadillacs.]

1. Check your fuel pressure at the carburetor input. A normal QJ looks for about 5 PSI of fuel pressure. If the pressure is too low or too high, the carb will begin to misbehave in subtle ways. I'm going to focus on high pressure issues because those are more odd than low pressure (IMHO). My car is a California car that had its A.I.R. system unceremoniously yanked beck in the Mists of Time. Perhaps as part of that surgery, a former owner also removed the vapor-return line from the fuel-filter bowl (up front) to the gas tank.

In a stock air-conditioned Cadillac of that vintage, the fuel-filter-bowl housing has a built-in restrictor that leads to a vapor-return line. This restrictor acts as a fuel-pressure regulator for the QJ, keeping the carb happy with the properly pressured and cooled gas feed. If you yank the vapor-return line and block off (or remove) the vapor-escape path, the pressure and temperature of the gas at the QJ's inlet jumps.

In my case, my carb was seeing an input PSI of 8+! Only the poor condition of the QJ allowed it to keep running. When I swapped in a rebuilt carb, it flooded out within 30 seconds because of the overwhelming fuel pressure. Although I knew my old carb was out of whack, I dared not open it up because -- for some unknown reason -- it was the only carb that could survive 8 PSI input!

Ultimately I did install a new (rebuilt) carb and, along with it, a Mr Gasket fuel-pressure regulator and a fuel-pressure gauge. Life suddenly became significantly better when I could dial in 5 PSI of pressure and see it on the gauge. You don't have go as far as I did, but you should find some way to check your fuel pressure at least once. My idle became much less "bumpy."

2. Readjust your QJ's fast-idle circuitry. I've seen many articles that say that the QJ's fast-idle settings rarely need attention and they're probably right. But it behooves one to check.

Service manual (1967) in hand, I went through all the steps -- from 76 (Pump Rod Adjustment) to 90 (Secondary Throttle Closing Adjustment) -- on my new (rebuilt) QJ. Although I think the rebuikders did a fine job, I still readjusted just about everything. [I made the adjustments with the carb off the car, but the job can be done with the carb on the car too.]

Then at some point you'll have the carb on the car, ready to have its fast-idle jets adjusted. You'll (probably) need the special 1/4"-socket-on-a-goosenect QJ adjustment tool to reach the jet-adjustment screws. [I realized during this exercise that, out of all the GM makes, Cadillac is the only one that puts the A/C compressor on *top* of the engine, in front of the carb. The other divisions hang the compressor off of the left or right side. This makes Cadillac fast-idle adjustments uniquely challenging.] If your fast-idle tweaking has worked, messing with the fast-idle screws will produce gratifying changes in engine response.

3. Replace your divorced-choke spring thermostat with either a new spring or, better yet, an electric choke. This one really took me by surprise. What can go wrong with a simple spring? It turns out that, as springs (like people) age, they lose some spryness. My car was starting and idling immediately, but the choke was taking ten minutes to open. Until the choke opened (10 minutes, in this warm weather), the car was virtually undrivable.

Of course -- as with old Eldorados in particular -- parts references are sketchy and frequently incorrect. I could find electric choke kits for '68s and newer, but not '67s. Likewise for choke thremostat springs. There are some suspiciously similar springs and electric-choke kits listed for some Chevys, you can ask around.

Ultimately I found a place -- Mike's Carburetors -- that listed an electric choke kit for a '67. When it arrived, the base of the "67 - 69" kit didn't even remotely fit the '67 intake manifold. I began working on a simple adapter plate to make the kit work on my car while I also emailed Mike's to explain the problem. The '67 and '68 use exactly the same QJ (according to the Cadillac Master Parts list), but the locations for the divorced-choke spring are handled on the intake manifold completely differently. Mike's located both a spring and a kit that *should* fit a '67. But until I actually try to bolt it to an engine, I'd remain skeptical.

My little adapter plate worked. I wired the electric choke to its own power source with an inline 10-amp fuse. [The instructions don't call for a fuse and suggest wiriing the choke to sketchy sources. Although on average the choke wouldn't pull anywhere near 10 amps, it might pull a surge of almost that much at coldest startup time. Better safe than sorry.]

My car now runs beautifully from cold start to full warmth. Very Cadillac-ish!

One small problem remains: On the '67 (at least), the new electric choke housing interferes with the air-cleaner housing. I'm going to have to modity the curve of the bottom of the air-cleaner housing to get full, happy clearance between the electric choke assembly and the air-cleaner housing. But that should be very easy.

I hope this checklist helps those who are at their wit's end with regard to cold and low-RPM engine performance. Remember: There's always something else! :-)