HD8 carb issue

[cooper66]

Hello,

This weekend, first restart of the etype after 2 years of restoration. I fully rebuilt the HD8, but I have a "flooding" issue (see picture below). I initially thought to fuel pump pressure or float chamber level / needle and seat + float. I disconnet the fuel supply, rechecked once again float which are new and floating + the float level, everything is ok. So I worked just with the remaining fuel inside the float chamber, I opened the starter to mid position saw the jet going down inside the jet bearing tried to start the engine and finally got the same initial issue.

What was done on carbs :
-full kit from Burlen
-new floats and float level correctly done at 7/16"
-new needles (standard ones)
-jet correctly centered with the metalic sound once the piston fall down
-Adjustement of the slow running valve (full and then unscrewed by 2turn)
-jet adjustement at bridge level and then 2,5 turn on the screw

Do you have any idea ?







Thanks

[Mich7920]

Hi,
Normaly it's the 11mm float level that is not good.
Mich

[christopher storey]

To get flooding of that extent , then it is one of 4 things

1.Float fork incorrectly set ( which you say is correct at a 7/16 inch / 11mm bar passing through the fork)

2.Faulty needle valves

3. excess fuel pressure

4.sinking float

You do not mention having changed the needle valves which control the input of fuel to the float chamber ( not the needles on the pistons )

Nor do you tell us what type of pump you have , and what the fuel pressure is set at. These carburetters need no more than about 0.2 bar = 2.8 lbs/sq.in ; anything more will overpower the needle valve and cause flooding .

My opinion is that it is one of these which is the source of your problem

[ralphr1780]

Pierre,
With the fuel supply disconnected (and choke at mid-position) such flooding is excessive.
Looks like the needle in the piston is fitted too deep. Worth checking.

[malcolm]

I had exactly that on a recent trip, and it was the needle valve in the float chamber sticking, despite it being a brand new one from Burlen. I took the float chamber lid off, worked the valve a few times and all was fine. Like Christopher, I imagine it could well be to do with the needle valve/float set up.

[ralphr1780]

Gents, the OP is stating:
"I disconnect the fuel supply, rechecked once again float which are new and floating + the float level, everything is ok. So I worked just with the remaining fuel inside the float chamber, I opened the starter to mid position saw the jet going down inside the jet bearing tried to start the engine and finally got the same initial issue."

[christopher storey]

Ralph : if the needle valves were not closing properly, then when connected, an excessive fuel level would have resulted. Even after disconnecting the fuel supply, unless fuel was taken out of the chamber before attempting to run the engine, the very high level would still result in precisely what is shown. However, I agree that if the carburetter needles were not put into the piston with the shoulder level with the base of the piston, the same might happen

[JerryL770]

Have you checked that the float chamber overflow pipe is clear? If new pipes have been soldered into the banjo's, any blockage there will cause flooding of that carb.

[cooper66]

Good evening Gentlemen,

first of all thanks for the comments, so let me precise :

@Christopher : needles valves are new from Burlen. You are right for the 4 options, but I observed the same "flooding" with fuel supply disconnected

Tonight I re-adjusted the jet at the same level (picture below) than than the bridge and unscrewed 2 turns, I tried to start the engine without the starter => no flooding




I tried with the starter and had a small flooding again ...

So the starter/jet position with starter creates this issue. What is approximately the displacement of the jet with starter to mid or full position ?


@Jerry : yes pipe clean tested with air compressor.


I miss something definitely ...

[abowie]

It sounds like your float is sticking, or the valve is sticking, making the fuel height too high.

Just to be clear, this is only on one carb?

[MarkRado]

Might be a slightly damaged jet diaphragm, I experienced this some time ago.

[Robbiee]

Usually if the float is at fault and the needle (petrol inlet)valve is functioning the petrol is continuously pumped into the float chamber and pours out of the overflow pipe

My float only floated up partially and slowly and clearly had a pin hole allowing petrol to fill it.

If the needle is stuck open the same happens
If stuck shut the no petrol enters the chamber

Is this helpful at all?
Robbie

[paulsco]

I'm not sure I understand this.

The fuel level at the jet will be the same level as the fuel in the float chamber, so if it is too high in the jet area it is too high in the float chamber

Often on first start up, I have found the float chamber floods and a tap on the side with a screwdriver usually solves this as it is just a sticking needle valve.

You state that you have adjusted the float height correctly, so it would appear that there is something wrong with the needle valve as it is still allowing the fuel to get higher in the float chamber.

You also state that the fuel level is still too high and flooding even when the fuel is cut off.
This must be because the float chamber is still full; i.e the fuel level is higher than the jet??

The only explanation that I can see is that there is something wrong with the needle valves.

Paul

[Mich7920]

Or with the float level...

[MarkRado]

Does flooding occur on all carbs?
What I usually do: 1 check if and from which overflow pipe fuel is pouring. If not, floats and valves are ok. 2 check that carbs are level, remove dome and piston of carb in question 3 remove fuel completely with clean rag, switch on fuel pump (choke off), check fuel level in jet bore- it should be down the jet approx 5mm. Fuel should definitely not be pouring out of the jet bore- in this case I decrease float height (increase fork adjustment from 11 to say 14mm- switching off fuel pump before opening the float chamber), and return to step 3. If this makes no difference at all, the jet diaphragm has to come out for inspection - together with the carb.

[Sarthe72]

As a point, do you use plastic or brass floats these days? I have had for years a stock of brass floats and still have a few left, so I've never changed. But what is the concensus of the members?

[1954Etype]

I had a brass float let go a couple of months ago. Luckily it was in the garage. Have now swapped both cars with plastic as the thought of that happening on Eurostar doesn’t bear thinking about!

[rswaffie]

I had a similar flooding issue and I replaced all the brass floats with the nitrophyl versions.
Also replaced the needle valves and arms.
It turned out to be the submersed fuel pump from SNG pushing out fuel at 5.5 psi.
Had to put a regulator in place to bring it back to 2.75.

[cooper66]

Gentlemen,

short update, flooding is coming from wrong carburetor needles ... ordered new at SNG baratt in the section 4.2 they propose "SC" needles, as you can see on the picture below they are completely different from the "UM" ones :





SC needles are thinner than the UM, so issue with jet functioning. I should receive the right ones this weekend.

[christopher storey]

Oh dear... how could SNGB make such an error? According to my catalogue from Burlen, SC are for a .100" jet on e.g. H6 carbs for a Bentley Mark VI