Packard Forum Index » V-8 (1955-56)

G'day Guys, just wondering how you set your idle jets. I know the service manual says back out 1.5 turns but is that the best way with todays fuels? I was reading an engine tuners advice recently and he reckons Rochester Quadrajets should be backed out 2.5 to 3 turns. Would a quadrajet setting be similar to a 4GC? I don't have an exhaust gas analyser and could pay someone to do it for me, but if there was a way I could do it myself that would be better. By the way, I have just reset my timing to 9.5 degrees and am running a Pertronix kit in the distributor, plus Pertronix flamethrower coil. Further to Brian's advice in my brake topic, I also reworked the vacuum connection to the distributor just in case there were any leaks. I think the ignition system is in good health and now want to make sure the fuel system is too. Regards, John

I use the method preferred by all the other old farmers like myself: You turn the screws to obtain the best, smoothest idle, and that by ear.

With the car fully warmed up, I do one side at a time: turn out 1/4 turn. Listen. Better? Turn out another 1/4 turn. Repeat til it starts to sound worse. Turn back in til the best idle is achieved. Reset the idle speed if it is now racing. Now do the other needle the same way. Reset the idle speed if necessary. To be sure, repeat the whole procedure for both needles and reset the speed one last time. The whole thing takes 3 minutes.

Thanks Ross, I reckon I can do that. It wasn't clear to me whether the number of turns was the critical factor, but based on what you've told me it's more to do with smooth running. From your explanation, I gather that the actual number of turns is also irrelevant between both jets - that is, they don't have to be the same. Also, this might be a silly question but once this is done, apart from smoother idling, do these jets have any other influence on the carb's operation when driving? Regards, John

Well, I gave it a shot but it wasn't as easy as I thought it would be. By that I mean there seemed a fair few turns between each end of the spectrum when rev's started to drop off and I wasn't confident in picking the right adjustment in between. I guess my ears aren't attuned well enough to pick up the subtle differences between good and not quite so good running. So, I came up with a brainwave, possibly. I connected up a digital tacho and did the same adjusting while keeping an eye on the rev's and set the jets where rev's were at max, then reset the idle speed, and then did it all again. Sounds OK but I haven't driven it anywhere yet. However, tomorrow we go on a Packard Club run for a few days and will cover approx 450 miles, hopefully trouble free. Regards, John

Many here use a vacuum gauge for the best idle speed and mixture settings.

(o[]o)

JP as you surmise the number of turns is just a number. The idle settings have a small effect just off-idle, but beyond that nothing as the main jets take over.

In general, healthy engines with good spark and compression will idle quite OK even if the mixture is far from the ideal. As they get more worn it is often harder to find the sweet spot.

Similarly, engines with good compression are not usually too fussy to start. They will crank up even if the battery is low or the choke is dodgy. In contrast, with worn rings you have to follow the recipe just right and hope all contributing factors are ideal. Many older cars had 12 volts put in when they really needed rings.

Thanks Guys. Time for a report on what happened over the weekend, and I've got to say it's good news. We did a total of 550 miles under various conditions, most of which was highway but speed varied depending upon what we were doing, and the outside temperature determined whether to run the A/C or not. After saying all that the best mileage I recorded was 20.4 aussie mpg, which equates to 17.0 US mpg. That was for about 75 miles of pretty much flat highway at around 50 - 55 mph, and no A/C. The only other recording I have at the moment is 18.1 mpg (15.1 US mpg) for 160 miles involving high and low speed running, some hills and about 50% with A/C.

This is as good as it's been for a long time and best of all, it was trouble free motoring for the entire weekend. I can only put this down to two things, and based on what Ross has said, I'm not exactly sure if this could be why. Firstly, I redid the vacuum advance pipe connection at the distributor to try and eliminate any leakage (I didn't think there was any), plus the carby idling jet adjustment mentioned in a previous post. I did also knock the timing back fractionally but I didn't think this would make much difference, apart from potential pinging (there wasn't any). What I can say is that the engine is now idling nicely, pulls strongly from take off and feels good while cruising. I was unable to read Ross's post until we returned today so I was going to report that the idling jet adjustment did wonders for running and fuel economy, but now I won't!

I might try using a vacuum gauge just to see whether further improvement is available, and I assume the objective is to maximise the amount of vacuum being shown, similar to what I was doing with rev's. I have noted Ross' advice and definitely won't thinking about number of turns any more. I've got to say that fellas such as me, who are mechanically minded but don't have the wealth of experience that is available on this website, really appreciate the advice we receive from you knowledgeable gents. Thanks once again. Regards, John

Hi JP, at the risk of being repetitious, the two idle adjustment screws are only used to further adjust the carb for a smoother idle, at idle. As the speed of the car increases from idle to intermediate speeds and on to high speeds, the idle circuit is no longer in use and you are into the intermediate and power circuits of the carb. Usually the carb idle circuit is out of use around 25 mph. I hope this helps.

Gasoline ain't what it used be - It's no longer distilled from light sweet crude, but cracked from heavy crude. If the gasoline in your fuel tank is several months old it has already begun to revert to form - i.e., the lighter portions are long gone. Trying to get any engine to run right with old fuel is a frustrating exercise. Adding a stabilizer helps, but isn't a cure-all.