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Jaguar Repair/starting car


QUESTION: when I go to start my car , when it is  cold start , it starts right up. But if the car has been running for  a while and I turn it off it will not start. I did some thing I should not have done I turned the screws on the carburetors , I have triple su. I believe it is running very rich, and was told that when it is cold it will start with no trouble if it is running rich , but after it warms up it will not start till the car has cooled down. If I wait 20 minutes or so it starts right up. I changed the plug, the old ones were either black a little wet , or some were white, I believe the put on the plug is called the core , that is the part that was white. I just want to no that if the carbs are running to rich , if it is true that it will not start when it is hot , and has to cool down
thank u

ANSWER: Hi Mike,

First I need to know what kind of Jag you have. A 150-S has a different choke system then some E-Types and if it is an "E" Type does it have manual chokes (enriching device)for starting?

Spark plugs "Black", "Wet" and "White" are all different indications of different problems so which number cylinders had which plugs? But all of that may be of no importance, because if you had brought the car to me in with those symptoms (which do point to fuel as the problem) I can not count on that because there are a dozen other possible causes for your symptoms. I found from working in Jag dealerships from the first "E" Type to the last that symptoms only lead to a solution sometimes and as a line mechanic I needed to have a 100% fix rate and the ONLY way to do that is a test procedure. Don't skip a single thing in this test procedure thinking "I don't think that is the cause so I will skip that".

First wipe all thoughts of the item that may be causing the problem out of you mind. Don't even look for an item but look for the system first that is causing the problem. There are only 3 systems so it makes it easier.
Compression, Fire and Fuel and they MUST be looked at in that order.

Compression can affect fuel mixture. So test compression first. (Be sure to hold the throttle open when running the tests on each cylinder and be sure to spin the engine so as to hit compression at least 6 or 7 times to get a reading and write it down. If you don't have a compression gauge they are not expensive and can be used on every type of gasoline engine.
You should see form 130 PSI to 170 PSI on every cylinder and only a small difference between cylinders. If any cylinder is down close to 100 or below you are wasting your time trying to tune it. Be sure to Remove the small wires off of the (+) side of the coil before the test.

If the compression it ok test "Fire" (Ignition). You don't need any high tech equipment to test ignition. You already have all 6 plugs out so plug the small wires back onto the coil and put the plugs onto their plug wires and lay each plug so the case of the plug contacts metal ans so you can see a few plug ends to watch for spark. Now have someone spin the starter so you can watch the plugs fire (not in bright sunlight) You should see a blue colored spark and it should be as thick as a pensil lead. If you see a hair thin spark that is colored Orange or Yellow the spark is bad and will cause hard or no starting. Now move the #1 plug and wire (called #6 by Jaguar) over so you can see it but are able to put your thumb in #1 hole and have someone spin the engine and note that each time you get compression on #1 it will blow your thumb off of the plug hole with a "Pop" and at the same time you will see #1 plug spark with a "Click". It will seen as though the "Pop" is causing the "click" or vice vera. This is a rough test of ignition timing. It does not mean that the tming is correct but does mean it is close enough to start and run.

If all up to now is correct and ONLY if it is ALL correct should you proceed to testing Fuel.
Now run the enigne until you get it up to the temp that makes it not start and confirm that it will not start. Then spray a few shots of "Starting fluid" into the intake of the carburetors.
If it starts and runs, run it for a minute or two at about 1500 to 2000 RPM without moving the throttle and shut it off and remove all 6 plugs and look at the center electrode. White is either correct or too lean and Wet is fouled and Flat Black it rich. Clean the plugs or replace them and test fuel pressure. You don't need an expensive Jaguar gauge, any low preasure gauge will do and you can get a "T" fitting to fit the line and get a short piece of hose and don't forget clamps at each joint you make. You should see form 1.5 PSI to 3 PSI.

If all is correct up to this point you will probably need to try to adjust the SUs and that is a process and you first need to tell me which SUs you have or at least what Jaguar you have as some SUs are different. You don't need any expensive equipment to do the adjustments, just hand tools. I can walk you through the process.

Let me know,


---------- FOLLOW-UP ----------

QUESTION: thank u first of all . I all do every thing u have said exactly the way u said. I will be running the test tomorrow.  
 Car is 1969 serie2 the carb. are su8
Starting fluid into the intakes of  the carb. how
 T fitting to fix to line , is line the one    that comes out of the fuel filter,to the carbs?
Fire ignition test do u just test the # 1plug and is the #1 the one in the front of the engine or the one by the bulk head
I ask these ? just to  make sure I do every right.
Thank U and will get back to u with the results.

Starting fluid into the intakes of  the carb. how
It comes in a spray can so just spray it into the air filter intake horn or if you have the big top piece off just spray a shot in each carb just before trying to start.

Yes the fuel line that comes out of the fuel filter to the "T" and from the "T" connect the carbs and the fuel gauge and turn on the IGN to "ON" (not start) and the electric pump should start running and give you fuel pressure on the gauge. (but be sure to put clamps on all joints so you don't blow a hose off.

It does not matter which hole and plug you test. Either the one closest to the fire wall that Jaguar calls #1 or the one at the front of the car like all Americans call #1. As long as you have the correct plug wire on the plug.

Let me know,


Jaguar Repair

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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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