• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Overheating carburettor Jagf

Share this page

J

JohndeJong

Freshman Member
Offline
Good evening
Just registered. Hope to find more enthousiast people Own a Jaguar Mark 2 type 340 Have problems with carburettor at "slight"" overheating. That is with a rise in temp of aprrox 5 degrees c above 70C the petrol is leaking from the startercarburettor. Have tried a lot (electric waterpump Davies Graig) bigger radiator, hole in inner wings, extra vent. Wanna go the route 64 but without this problem. Who can help ?
 
Hello John,
I don't believe that the car requires extra cooling as the temperatures you state are quite normal. Where exactly is the fuel leaking from?. Apart from the banjo connection to the main carburettor or to the body of the AED it should not be possible for fuel to leak from there and I can't understand what the rise in temperature has to do with it.

Alec
 
Hi Alec, The fuel is coming from the airintake-pipes of the startercarburettor; although the watertemp is not too high I think that the ""taken heat"" by the coolingsystem is staying in the moterbay as it's uprising and therewith overheating the carbs making the fuel to vaporate to early. (One can smell the fuel when the temp is rising al little a idle) The problem occurs on a warm day when slowing down in traffic so there is no wind fro driving. It can be "handled" in the Netherlands but certainly not in Nevada dessert. Thanks for thinking with me Regards John
 
Hello John,
I'm still convinced that temperature cannot cause the problem you describe. The fuel level in the AED is controlled by the float level of the carburettor that the AED is bolted to and should be well down the intake pipes.
I would check the float chamber vent pipes for blockage and correct assembly of the washers that secure the float chamber lid. There should be a special shaped fibre washer under the pipe, This washer is circular outside but the bore has three cut outs on the inner bore, difficult to describe but the correct washer does not have a plain circular bore.
Does the car run roughly when the circumstances you describe happen, as it sounds to me as though it is flooding.

Alec
 
Hi Alec
There is such a special shaped fibre under the pipe.
I will reinstall the mechanical waterpump ans let it work in combination with the Davies Graig electrical pump. However I agree that it is fighting symptoms and not the course. After that I will therefore dismantel the SU's completely. I have already taken off the startercarburettor ckecked it and I looked at the needle of the first carburettor. This one was installed to far in. (There is a marked line that has to be aligned with the bottum of the cylinder) I thought I found the problem there but after reinstalling it was still there. Also the level in the floatchamber is normal. There are two HD8 carburettors mounted on a straight port cylinderhead as I have one of the latest models where this was an option. Also interestingt is the by-pass. As the manifolds is straigt forward the thermostat is in line withe the manifold (unlike earlier models) It is therefore not possible to install a thermostatc that will close the by-pass when opening as in other models. This seems to have lead to a bypass that is always open but with a very small entryhole. To work more in your line of thoughts (up untill now) : I will now completely dismantel the SU's and let you know later.
Kind regards
John
 
Hello John,
see how you get on, but check your float setting, 7\16" under the float arm to the lid. It very much sounds like flooding, but as I said I would expect the engine to run roughly.
Do you have a manual to help you check the S.U.'s?

Alec
 
Hello Alec,
Its nice to have someone thinking with you. ĂŤ let you know later ; I have to do some serious lawyerswork first
Kind regards
John.
 
Hello John,

OK, if you need some technical illustrations or advice let me know as I have a good reference manual. Oh, and by the way, I also own a MK 2.

Alec
 
John,

I'm with Alec on this one - these symptoms are caused by the fuel level being too high in the front SU and not overheating, which can be caused by lots of things. Check to see if there are any leaks in the float - shake it and see if you can hear anything, and immerse the floats in water or fuel to see any air bubbles - make sure you rotate and move the float round a bit when you do this. There can also be problems with the needle end of things.
 
Hello friends
I have now removed the electric waterpump as it makes no difference. In midsummer the temp rised again very muh with as result that the brakes worked without any moving of the pedal. Either the cups in the headcylinder have expanded by heath or the brakebooster. I feel I am further away from a solution
Neil, the fuel level in the front carb is ok
 
Greetings John and welcome to the forum. If you have HD8 carbs with a straight manifold, it sounds like someone has put a manifold/water rail with HD8 carbs from a 420 onto your Mark. This should give you about 20 more horsepower.

The 70 degree temperature is normal. Actually, anything from 70 to 90 degrees is normal so you are doing very well at 70 degrees. There are no problems with your water pump or cooling system.

I had exactly the same problem. Regardless of what you think, the front carb is not shutting off and it is causing the Aux carb to flood. You HAVE to make sure the lift arm that is pushed up by the float is not loose at all. BOTH arms on the lift have to come up at the same rate. If the arm comes up at an angle, the jet valve will leak and not shut off properly.

Forget the 7/16" spacing. It is a guideline. Bring the car to temperature. Shut it off. Pull the domes and pistons off the carbs and set them aside. Do not mix them up. Make sure the front goes back on the front. Disconnect the postive wire from the coil and protect it. Turn the ignition key and start the pumps. The petrol should pump until the float chambers shut off. Look into the carbs and you will see a brass ring center. Inside the brass ring center will be another brass circle which is the top of the jet. Petrol should be sitting at the top of the inner circle on both carbs. If it is not, you need to adjust the floats to make sure they are.

Stick the pistons, without the domes back into the carbs. Re-connect the coil wire and start the car. It should idle smoothly. You can observe now what is happening with the petrol flow.

You need to also make sure the needle is seating properly in the AUX carb. Also check with a meter as to whether you have power to the AUX carb when the car is at temperature. If you do you ahave abad otter switch or someone put an XKE otter in which operstes the opposite of the saloon switch.

Webserve
 
Back
Top