Rough idle with choke off. Series I

Hi,

I am having problems getting my 1966 E-type to idle unless the choke is engaged. In the interest of full disclosure, let me start at the beginning. The car has an aftermarket fuel pump with an in-line fuel filter between the tank and pump. I was considering replacing the pump and started poking around with the fuel system. Shining a flashlight down the fuel filler neck, the bottom of the tank looked really flaky. I started scraping at the crud on the bottom of the tank with a rod to see if it was really loose. No, it did not seem like a great idea at the time, but I was curious. The idle problem may have developed right after the fuel tank exfoliation, or that may be a red herring.

The car starts right away with the choke engaged. I used to be able to turn the choke off by the time the water temp reached 70, and the car would idle smoothly. Now, even with the car fully warmed-up, if I turn off the choke, the car sputters and coughs at about 500 RPM for a minute and eventually dies. If I leave the choke on it idles pretty well, although I think I hear a misfire now and then. If I turn the choke off while driving (2000-2500 RPM) the car keeps running and accelerates ok, but I can hear pops and spits.

Here is what I have tried in hopes of fixing the problem:

I removed the fuel pick-up from top of the tank. The screen on the end of the pick-up seems clean enough.

I replaced the in-line fuel filter.

I removed and cleaned out the glass fuel filter near the firewall.

While the glass bowl was off, I switched on the ignition. I did not measure the output, but I filled a small jar with gasoline in no time.

I removed and checked the filters at the banjo fittings of all three carbs. They were all clean.

When I put the glass bowl back on the fuel filter and switched on the ignition the gas flowed in quickly at first, then slowed a bit. Maybe it slowed because it was building pressure?

I cleaned the points and checked the distributor gap (0.015). Any feeedback on the various electronic ignition systems available would be appreciated.

Is it possible that there is sediment at the bottom of the tank where the fuel pick-up lives? Without suction from the fuel pump, the screen would appear clean when I remove it, but clog as soon as the fuel pump starts pulling. Should I drain the tank?

Thank you for any suggestions or insight.
Sincerely,

Jamil Haque

Submitted by jerry@moutons.org on Thu, 11/03/2005 - 00:03

Jamil,

YOur changes should have eliminated further gunk from being introduced into the carbs. Consider the possibility that it's just a coincidence that you stirred the fuel tank just when this started.

I'd check the float bowls for junk, and clean them out. While you are at it, replace the needles and seats and adjust float bowl level according to the service manual.

Then put in new plugs (NGK BP5ES or equivalent), new points, new distributor cap and rotor, new spark plug wires if they are old or look questionable. Adjust points dwell and timing to spec, very carefully.

All this is mandatory before adjusting the carbs -- it's a waste of time without it (ever hear how fickle British car carburetters are? This is the reason for that myth. Carburetter is French for "leave me alone!")

Then check carb synchronization. A simple way is to use your very close vision and feeling to check that all 3 carbs open at exactly the same time -- I mean tenths of a millimeter, as small as you can possibly detect. It's really not hard, and gets as good results as the other methods, and requires less in the way of tools. Adjust them as in the manual until they open *exactly* simultaqneously.

Check choke linkage to insure that it does *not* affect the throttle opening until it's open somewhat. i.e., a small feeler gauge can be placed between the fast idle screw and its rest when the choke is off. Make sure they are all equally far from their seats...

I assume your idle screws are close, but you could set them carefully until they are the same number of turns out (whatever the book says).

Set an electronic tach on the car, and get it started and warmed up. Open the idle screws if it still tends to die, until it idles.

Turn one carb's mixture screw slowly back and forth until the car idles fastest. Do the next one, then the next, getting a rough setting. The car should be running faster -- screw in the idle screws evenly until the car idles as slowly as it will run, or 500 RPM whichever is higher.

At this point you can listen to the air flowing into each carb with a rubber hose -- adjust the idle screws until they sound the same. It's not hard to hear this.

Go back and repeat the mixture adjustment, setting each one until the RPM is highest. Idle should be getting smoother and smoother. One or two repetitions (re-lowering the idle to 500 RPM) should get you a very good idle.

Recheck idle balance with the hose (*don't* change the throttle balance, only the idle screws).

Double check that the fast idle screws are a small feeler gauge away from their seats, and all the same size gauge. Check that the choke lifts fast idle until it gets past HOT, then starts lowering all the jets at the same time. Adjust until thius is true.

Then keepa you hands off those carbs.

Jerry

Jerry Mouton '64 E Type FHC

Submitted by jerry@moutons.org on Thu, 11/03/2005 - 00:00

Re.: Rough idle with choke off. Series I

Edited on 2005-11-03 0:02:04

Jamil,

Your changes should have eliminated further gunk from being introduced into the carbs. Consider the possibility that it's just a coincidence that you stirred the fuel tank just when this started.

I'd check the float bowls for junk, and clean them out. While you are at it, replace the needles and seats and adjust float bowl level according to the service manual. How about the rest of the carb? Replace jets and center them if there's any doubt.