My 67 4.2L engine seems to be lacking a lot of power. I have
the carbs tuned correctly, and there is enough air flow, but
aside from taking the engine apart to see if there are any
issues with compression, pistons etc., I was hoping to see
if any one here has any ideas as to what may be going on.
I think that this is way too little information for anyone
here to help, but I wanted to check to see if there are any
suggestions. If not, anyone know a cheap place to take the
car to be checked out in the Seattle area?
Thanks!
Joe
1967 420–
JCarver
Seattle, United States
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In reply to a message from JCarver sent Mon 23 Mar 2009:
Hello; My 67 420 had some lack of power/poor running issues. I
added a paper filter to the glass fuel bowl (Napa 3034) and cleaned
out the filters inside the SU HD8 carbs. I had a bad contact
between the LT (low tension) lead from the - minus side of the coil
and the points because of a break in the wire inside the harness
AND a bad connection from the water shield to the points. BUT the
main problem was that the ground strap from the left front motor
mount to the engine block had not been reconnected after the engine
was rebuilt. I only found this as you have to get under the car to
static time the engine after you remove the distributor. Timing
marks under the engine. What were they thinking? Pete Sellers–
Pete55Tbird
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In reply to a message from JCarver sent Mon 23 Mar 2009:
Hello Joe,
Yes, more info would help. Have you had the car long and is this a
sudden change ? Does it have the original air filter set up ?
I would check the high speed ignition timing. It is not enough to
check the timing with a light at idle, you need to see if it is
advancing with rpm up to around 30 BTDC @ 3000 rpm. If the timing
is OK, I would look at the spark plugs for a clue about the
mixture. You could also have poor fuel delivery under load, you
should check the fuel filter and see if the symptom is the same
after switching tanks. It is unlikely that both pumps fail at the
same time. Check the archives, some listers have had a problem
after altering the air filter, which may require a carb needle
change. Other possibilities could be a temperature related
problem, blocked exhaust, a stuck starting carb, or dragging
brakes. An IR thermometer helps to identify dragging brakes. Good
Luck.
Paul–
The original message included these comments:
My 67 4.2L engine seems to be lacking a lot of power. I have
the carbs tuned correctly, and there is enough air flow, but
aside from taking the engine apart to see if there are any
issues with compression, pistons etc., I was hoping to see
if any one here has any ideas as to what may be going on.
I think that this is way too little information for anyone
here to help, but I wanted to check to see if there are any
suggestions. If not, anyone know a cheap place to take the
car to be checked out in the Seattle area?
Joe
In reply to a message from PS sent Mon 23 Mar 2009:
Hi Pete & Paul,
The car has been in my family since the late 1970’s. I
recently inherited it from my father who could not take care
of it any longer. The car was sitting for a number of years,
but I was able to get her running with a little TLC. The
power seems to be very limited throughout the RPM range. I
have checked the plugs, and they are not receiving a rich
mixture. The air intake was recently replaced, and I noticed
an improvement from the original:
I have replaced the fuel pumps, and changed all the fuel
filters throughout the system.
I have not yet checked the timing, so this will be next on
my list. Good call on the brakes, I know that they have been
grabbing, but this seemed to go away after a thorough cleaning.
I will check the archives, and follow the advice you both
have given. Thanks for the help, I will let you know what I
find out!
In reply to a message from JCarver sent Mon 23 Mar 2009:
Do or get a compression test, that will give you an idea of the
basic condition of the motor.
Listen for misfires. While it is idling, do you hear it misfire
once in awhile? If so, check the valve clearances.
A faulty coil will decrease power, especially in the upper rpm
range. I don’t know how to really test a coil other than replacing
it. Maybe you can borrow a known good one. Ballasted coil, unless
others here say otherwise for your car.
P.–
Peter J. Smith, 1966 3.8S MOD
Carson City Nevada, United States
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In reply to a message from JCarver sent Mon 23 Mar 2009:
Hello Joe,
If you take a look through the archives, you will find several
people who experienced problems with power under load after
changing the air filter system. The SU carbs are calibrated to the
original paper filter restriction and the swap to a freer flowing
system may require a change in carb needle to restore the mixture.
Your new system is picking up air in the hottest part of the engine
compartment. While this may be good for warm up and mileage, it is
not good for performance. The SAE correction factor for hp is 1%
for 10F degrees intake air and the underhood temperatures can be
+180F. There is also an increase in octane requirement as you
increase in intake air temperature. If you are interested in
performance, you need to pickup ambient air outside the engine
compartment.
Paul–
The original message included these comments:
Hi Pete & Paul,
The car has been in my family since the late 1970’s. I
recently inherited it from my father who could not take care
of it any longer. The car was sitting for a number of years,
but I was able to get her running with a little TLC. The
power seems to be very limited throughout the RPM range. I
have checked the plugs, and they are not receiving a rich
mixture. The air intake was recently replaced, and I noticed
an improvement from the original: Redirecting...
I have replaced the fuel pumps, and changed all the fuel
In reply to a message from JCarver sent Mon 23 Mar 2009:
Joe;
Some of the things that I learned while trouble-shooting my 67
420 might be of use to you. The 420 ignition system is identical to
an E-Type as is the brake system. For info go to the E-Type forum.
The ignition is 12 volt NEGATIVE GROUND. Distributor is a Lucas
22D6, and they have had a lot of trouble with a distributor rotor
from an aftermarket source. The coil is a 3.5 Ohm resistance and
does NOT USE A BALLAST RESISTOR. I got a volt /ohm meter from
harbor freight to check mine. It also has a dwell meter to check
the points (35 degrees) desired. The compression on my 9.0 to 1
compression head is 145/155 PSI cold. I notice from your cam covers
that they are from an earlier year engine. I got some insight from
going to YOUTUBE Moss Motors on how to check a coil and high and
low tension ignition. Go to University motors to see how to set
static timing. Do the compression test first. Give the Forum a lot
more facts, details of what you experience and your chances of
getting the RIGHT ANSWER will improve. Pete Sellers–
Pete55Tbird
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In reply to a message from Pete55Tbird sent Mon 23 Mar 2009:
Thanks for the good info. I had a feeling that the air
intake configuration was not the way it should be, I will be
working on routing the intake to pull cold air instead of HOT!
The info you all have supplied is very helpful, and
appreciated!