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Float heights

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This is the method I used for setting the float heights on my 81 T.E.

Makes sense to me.

I have copied this and pasted it from another site with the owners permission and he is very helpful if you visit and have more questions.

Scroll down to carbs.

How to :

Setup and adjust correct and accurate DHLA40, DHLA45, DHLA48 C,D,E,F,G,H,L,M,P,R,S,T emission and non emission fuel levels and float levels.

First we need to understand there are 3 types of float.


They all look similar! They all need to be catered for in their own setting.

Below shows the EARLY 10gram float, used in some, early types of DHLA40, DHLA40E, DHLA40F (early), also some early DHLA45 and DHLA48


Below shows the 7 and 8.5gram floats which became the "norm" for all carbs after about 1972.

These 7 and 8.5gram are similar in setting, but the 10gram needs a different setting.


I prefer the heavy EARLY 10gram float for some reason, more constant fuel level and running in my opinion. I always fit these to my carbs set at 17.5mm initial setting or 18mm using SUPERIOR Viton Tipped needle valves.

For a given fluid level, a lighter float will naturally ride higher .....

Either the weight or the float part number should be engraved on the float. 3 types the 7g, 8.5g and 10.0g floats.

The basic part number for the floats is 7298-_ _ with two final digits for each specific weight:

01 = 10g 16.5 - 17.0 mm (float height start setting)

02 = 8.5g 15.5 - 16.0 mm

03 = 7.0g 14.5 - 15.0 mm


Above and below images show the needle valve has a spring inside. ALL static adjustments to float heights MUST be done with the lever tab on the float touching the rounded tip on the needle valve shaft, but NOT compressing the spring at all when the measurement is taken.


Below shows the distance A, which depending on the float used 7,8.5 or 10gram and will be initially set to the figures quoted above. Fit the new valves and assemble the float and cover (with gasket!).

Set your calipers to the figure quote and to work with your float weight, check they are accurate with a ruler or micrometer and proceed to tweak the float, if needed, this is to obtain the correct figure at the floats furthest extremity (A) from the needle valve.

As shown below in other images, to adjust the float level tweak the floats.


As seen below. It helps to hold the carb top vertically or just off vertical unless you are an octopus. This is so the float tab rests naturally against the needle valves rounded tip.

This MUST be done with the top plate gasket in place.


Most people just finish here and call that setup. This is just stupid, as it often does not translate into a good fuel level in the carb. Depending on if metal or viton tipped needle valved are used and also the valve body can be No1 or No2, floats may have been "butchered" by previous "engineers".

So this is where my technique starts. I use the above info ONLY for reference and initial setup to start off the correct adjustment.


After the above is done, if the carburettors are not bolted to the car, fit them now, but do not fit the top linkage or filters, as you will be removing the float covers and floats and will need to look down the barrels for leaking.

Before adding the fuel pipes to the carbs test the fuel pressure first.

Set at 3psi if using metal valves and up to 5psi if using viton.

Once this is set, fix the fuel pipes to the carbs but do not fill the bowls or operate the electric pump yet. (I hope you are using one!)

Its important to do this on the car, as different fitments/manifolds give a different "angle" or rake to the carb, the main-jet stack must be supplied with a proper fuel level.

Firstly remove two of the top plate cover screws, so each top plate (float cover) is being held down with only two screws.

Below image shows why is it important to leave two screws in place till you are "perfected" in your technique here...

The choke plunger will spring the top plate upwards with no screws in place, so giving a poor reading and leakage if you allow this to happen at any time during this calibration.

Its VERY important to keep the float cover sat firmly on the carb at all times when setting the "fuel bowl levels" ~ to the all important setting so often ignored through ignorance or naivity.


Below shows where the top needs to be while the pump is filling, down on the mating surface, also it needs to be here all the time, till you quickly WHIP it off to check the fuel level.


The gasket needs to be under compression too.


Get your caliper and set to 27mm!!!!!!!! check the pointy end you will be using is actually set to 27mm in length with a ruler or micrometer and that its accurate to 0.5mm.

You are now ready to fill the fuel bowls. So flick on the pump...Wait for 20seconds. Flick it off, look down inside the barrel into the venturi, if you can see fuel dripping from the venturi the bowl has a bit too much fuel in or you valve is worn if they were not new or you got ripped off with some crap kits from EBAY.

No biggy if the valves are new and good, you will be adjusting and checking it anyway.


Now you need to remove the top plate and use the depth gauge part of the caliper.


Fuel level setting is VERY IMPORTANT AND IS 27mm from the top face of the carb body down to the fuel.

Pump is off, if not turn it off!!! Wait for a minute for pressure to fall BEFORE removing the carburettor top.

Work on one carb at once.

If the fuel lines are not flexible it may help to remove them from the carb you are working on.

Put your one hand spanning the top of the carburettor top, float cover and put on some decent downward force with your fingers at each corner. Now undo the two screws...Remove them. Drop the screwdriver and quickly (under 1second) whip off the float cover/carburettor top and move it to oneside.

You need to do this quickly before the float drops and more fuel is dribbled into the bowl when you raise the top away from the body.

You now have the fuel exposed.


Get the depth caliper in position as shown below. About 3mm off the wall of the central tower, at the back of the jet stack...Not at the edge or running down the wall as the liquid will radius here, but slightly away from the jet stack. The tip of the depth measure should just make contact with the fuel.


If its too high and the tip is well into the liquid, maybe use the container the valve came in to bail out some fuel, a good amount. (wear gloves! Yuck!). If too low, read on.


Below shows an unadjusted float.


Fuel level too low, tweak up the end of the float, as shown below. (this is a dramatisation! Do not tweak as much as this!!!) a millimetre or 0.040" at time. If the bowl is 2mm low, go up 2mm on the float!


Fuel level too high and venturi leaks? Tweak it down as needed.


If you have brought VITON Valves I recommend ONLY using them. They can "plump" up a bit after being exposed to fuel for the first time, so leave them to soak in some fuel for alteast 1hr before fitting them and calibrating fuel levels.

I have some stock of OE spec Kits or can supply.

You can do the above adjustment with the carb top on by removing the main jets and jet cover from the carburettor and sticking the depth probe down main jet stack hole, but its hard to see etc chances are you will need to make some adjustment and remove the top anyway.

Ebay KITS ARE JUNK. Bar some RCA Ricambi Kits...Its RCA or OE Dellorto or NOTHING!

Hope this helps demystifty something so simple!


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I'm going to go have a bash at this now as its just this second stopped pissing down with rain.... for once! LOL

I'll let you know how I get on.

Preliminary results not good.

Removed boost pipe and plenum cover, switch on fuel pump and petrol floods out of the venturis of cylinders 3 & 4.

1 & 2 not experiencing this problem but it was those 2 which initially started off with the flooding.

Investigations continue, sun is coming out here in South Wales? eh?

I've had to use my 2 spare top hats.

Cylinders 1 & 2 although maintining a good fuel height was found to have the botched repair on the post disintegrated away.

Cylinders 3 & 4 occasionally would hold fuel height, the correct 27mm could not be attained and occasionally the floats would fail to shut off the needle valve altogeather.

With the new hats fitted 27mm is now being maintained on 1 & 2 and 3 & 4. Its now stumbling from initial pickup although I guess this could now be down to mixture which has been screwed about with a little.

I'll have a search for some info on that now.

Thanks for this article Trevor.

Edited by Simon350S

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It's a good guide and I was surprised at how the mixture changed as I adjusted the float heights. I still have a stalling issue if I accelerate hard and then brake to a stop and whist the engine doesnt stop it runs rough at idle for circa 5 secnds before recovering to a steady idle.

Well done with your carbs though Simon.


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I was living with it but now the car is off the road for another head gasket I will re-visit this problem and determined to sort it out. It is related to G-forces and yes mine is also affected by hard right handers. I have the feeling it is going rich which indicates fuel spill from the float chamber.


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There is a member in the Portsmouth area (sorry forgot your name) who had similar problems and he changed his ignition system to an ecu based system with a coil pack and this cured it for him. Now I'm not suggesting that the ignition change was the cure of it as I fail to see how but in doing so I would have thought he had the carbs off and something cured it at the same time. Either way I am saying it is cureable which gives hope.


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