Packard Forum Index » V-8 (1955-56)

Some of you may have noted my changing the fuel pump on my 56 Caribbean enroute to the Henry Joy Tour. Even after the change, fuel starvation problems continued on long upgrades (and it was HOT) though I could still breeze along at 70 on the straight-aways; I thought some of you might be interested in what I've done since.

Checked the gas tank cover to be sure the vent was clear. Drained the gas tank thru a fine strainer, gas was clean. As best I could I viewed the inside of the tank with a borescope, tank not lined but looked bright, shiny and new. Put a filter over the gas line at the front, and blew it from the back - gas was clean as a whistle. Did an autopsy on the removed fuel pump and it was clean inside, as were both the carburetor float chambers. I didn't remove the fuel filter bowl on the road because I didn't have a spare gasket for it and they often break when you remove them, but the bowl was free of sediment. Subsequently removed the filter and did the "blow thru" test compared to a new one, only a very slight difference. Checked the new fuel pump, 4 psi outlet, 10 inches of Hg on the suction side, and just over 2 pints per minute. Did a vacuum test on the fuel line to the tank, held vacuum overnight.

The car always had somewhat low manifold vacuum and only gave good low speed performance with richer main jets so I decided to pull the manifold. It was also a hard hot-start engine. The gaskets were the original NOS-type steel shim style. Checked the choke stove pipe (OK) and replaced the manifold using Kanter's composite gaskets which I like better. Installed two Daytona rebuilt 4GCs. Cleaned the air filters (modest dirt, last done about 2000 miles ago).

Still have to synchronize the carbs, set the 2 fast idles and idle mixture, so I have no road test yet. I'd be curious what you think I may have missed and what the problem might be; one fellow suggested a case of borderline vapor lock. No, I don't have an electric fuel pump. Gasoline I was using was generally Premium Mobil (with EtOH of course), with 1 qt. of tetraethyl lead added every other fillup.

Checque the heat riser in the exh. manifold to make sure it is not stuck in the closed position. I would make sure it is fully open and tie it open with some baleing wire for test purposes.

Also checque the rubber fuel lines to be sure they are not cracked. Ther eis one at the front and one at the rear. I have had 3hree different incidences over the last 40 years that i can remeber where the neoprene fuel lines were sucking air on a sporatic basis and was not detectible until they were removed and flexed for inspection revealing conspicuous leaking cracks but never exhibited any fuel leak.

Be sure an exh system is not plugged up on one side due to mouse nest or something. That will cause hot weather vapour lock. Place your hand near the exh. outlet and feel for the pressure of the exhaust and compare from side to side.

Also, it is not always reliable to do the blow thru test on filters even if u let them dry out first. Try a new filter or just a few test runs with NO filter. An 88 F ranger 2.0 4cyl (carb) filter can be easily addapted to the single carter 4bbl without removing original filter unit. I don't know about the Carib dual quad set up tho.

The 4#'s on the output of fuel pump sounds a bit weak to me but i havn't looked in the manual yet for specs.

My very original 56 Exec with 352 has always had low manifold vacuum too. Did a valve job and no improvement. My guess is that it has something to do with valve timing. So Packard may have been sloppy with timing gears. Just a guess. I have not checked the valve timing yet.

As a side remark. I would seriously consider removeing the dual quad set up and build a glass display case arounf it. A 350 cid engine has a 100CFM draught per 1000 rpm. So unless u plan on turning the engine up over 4000 rpm AND HOLDING THERE SUSTAINED then any 400-500 CFM carb will be more beneficial than the dual quad set up. Mite cure your low manifold vacuum too altho the low vacuum is probably a non issue. Many of the road course racing machines (N'Burg, Lemans, sebring etc) engines will run low manifold vacuum due to valve timing. Check the vacuum at 3k to 4k sustained rpm in high gear on level ground for a mile or two to see if it picks up to the 20 to 22 inHg. I've never checked mine at that speed yet.

Also check for exh leaks that mite occur near fuel lines on BOTH SIDES OF pump.

Thanks for your thoughts. I did in fact change the fuel pump inlet hose when I changed the pump, and there is no hose at the rear other than the tank vent. Also there is no manifold heat riser valve, I removed it when I put on the new exhaust system some years back.

For all I know I've solved the problem without actually seeing it, but I'm not about to go back and try those hills again to see.

Regarding your comments on the cfm situation, the carbs are special units and have two modifications to give good performance over the full range of rpms. They have a ring staked into the venturi cluster on the 4 primaries to improve low speed performance, and both sets of secondaries have a second set of butterflies that limit air flow at low speeds. When these carbs are done right, the performance is great at all speed ranges.

Intersting that you also had low manifold vacuum, do you recall the reading at hot idle? Mine is about 15-16 inches of Hg but rock-steady.

Yes, about 16 inHg and steady is my Vacuum reading too. I think if u check the Packard manual u'll find that it is in the range of normal. Most engines will usualy pull in 20-22 range. General shop talk of 20+ is usualy just bragging rights for no real technical reason. Again, i believe the "lower than normal" readings are due to valve timing (gears or cam grind). Possibly checque the timing chain. Mine has a new one. It can be checked by removing fuel pump and if u have long fingers then stick one in or get a bent up rod or something to check the slack in it. Mine was real sloppy at about 45K original miles. Gears were good.

If i were to replace it and need gears then i'd probably seriously consider Kanters roller chain set up.

HOw many miles are on your car?????

The engine has about 91,000 miles on it, though I did install a new timing chain and gear set about 10,000 miles ago when I had the front vibration damper off for revulcanizing.

I see others have confirmed my comment to you that there is no rubber fuel line at the tank.

Yes. Apparently i was having a grey moment on the fuel line issue.

Yes, about 16 inHg and steady is my Vacuum reading too. I think if u check the Packard manual u'll find that it is in the range of normal. Most engines will usualy pull in 20-22 range. General shop talk of 20+ is usualy just bragging rights for no real technical reason.

PackardV8, thought you'd be interested in knowing that with the replacement of the OEM-style steel shim intake manifold gaskets with Kanter's composite type (and also newly rebuilt dual quads) my manifold vacuum at hot idle is now 20 inches, up from about 15-16 previously. An added plus is that the TreadleVac is giving better boost.

Have you resolved fuel starvation problem?