Why is my sump filling up with fuel ???

[Tony Griffiths]

As we don't know which model of 7 you have - and if it might have been modified in some way - can you post some pictures of the near-side of the engine and the engine bay?

[bob46320]

My 7 "makes" oil, rarely top it up but change the oil every year. I don't have a fuel pump (Gravity feed). Its got to be fuel which passes via the bores however fuel consumption is good and no sign of condensation present in the engine / oil.

[flywheel1935]

OK guys, here's the full story. Having used my 1935 ARQ Ruby, very enthusiastically since 1991, and having received a small inheritance, I decided to treat "Ermintrude" to a birthday present of a newly rebuilt engine. I enjoyed sending her up places like Kop Hill, Brooklands test hill, the odd Production car trial, and general everyday use for close to 27 years. An engine builder was recommended to me !!!! and in discussion with regards to the cars future use we discussed several areas to consider. Anyway the mods included, Riccardo Head,Fully balanced f/wheel/clutch assembly, Mini oil filter housing mod, and increased oil pump volume + other stuff on G/box and Back axle. On stripping the original engine the crank was deemed suitable, the rods were re-whitemetaled, new pistons were fitted to a 'replacement block' as my was deemed to be unusable. On the face of it all sounded good and I collected the engine , fitted with my original dizzy & possibly my old carb, or a rebuilt donor carb ??? Anyway due to events at the time ( hence the inheritance) the engine was not fitted immediately, but a few months later. Anyway, despite numerous attempts over several days the engine simply would not start, and when it finally fired up would only run for a few seconds. the builder agreed to take a look at the engine again, and I returned it. It was during the first investigation to the non starting that the sump was found to be full of fuel, the f/pump being to blame ??? More to follow after tea !

[Bob Culver]

Has it been proven by draining? There is no connection apart from the diaphragm between the top and bottom of pump. Is there water in the sump raising the level and a lot of petrol from starting attempts?

[flywheel1935]

After the 'second rebuild' that I believe may have included a new set of rings and fuel pump rebuild with new diaphragm, new gaskets, fresh oil and spin on filter. I was told the engine was test run, and come and collect ( close to a 400+mile round trip) ( my 4th ). this was around the time of the first lockdown. The engine was refitted to the car for a second time, but then left alone while wife on furlough etc, anyway about 6 months ago I decided it was time to finish the total recommission of the whole car. Could I get the engine to start and run, it simply failed to do more than cough and never run for more than 2-3 mins, then stop and refuse to start, this sorry saga has now gone on for the past 6 months. My own observation is that the carb as a standard Zenith is not compatible with the comp ratio the Riccardo head gives (about 110 psi ) and the excess fuel (unburnt due to lack of starting/ possibly because of over rich mixture) is washing the bores dry and filling the sump by close to 1/2" plus above the high oil level mark. Several long term Austin 7 owners have looked at the engine in question, and they simply have run out of ideas as to its inability to run as expected, NGK A6 plugs were fitted by the builder, but has now suggested Champion 16D ??? Over to you guys again.

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Hi Bob from NZ, there is no water in the sump, purely oil diluted to the point it is as thin a milk, when I drained it. Plan is to replace oil filter, fill with fresh 20-50 mineral oil and fit Champion plugs, + strobe the flywheel at 20 degrees BTC ( As suggested by the builder) as I run a Electronic Dizzy from Powerspark. My fear being the re metaled rods have been damaged !!!!

[John Cornforth]

Hi again

I know that bore wash can have alarming effects. It seems to me that you have got to get this engine running, hot and preferably under a realistic load driving the car rather than on the bench. Once the oil is hot there is no way that the lower cylinder walls should be short of oil ! I guess you could add a little two stroke oil to the fuel for an initial period (or genuine Redex if you can find any) to keep the upper cylinders lubricated. Then the essential running in process can begin. There are as many opinions on running in as there are A7 owners, but an oil that allows controlled ring/bore wear is better than one that is too "good". Some just say use the cheapest to start with, and change it very frequently.

The carb doesn't "know" about CR, it only sees airflow and is calibrated to give the right amount of fuel for any given airflow assuming a standard engine. The new head might change this requirement slightly, but I would start off with standard jetting. I don't think Austin bothered re-jetting when the Ruby HC head and 3 bearing setup was introduced. Take a look at your jets and make sure they are stamped with the right number, haven't been got at by poking wire up them and the two in the bottom of the bowl have a fibre washer underneath. Also worth checking that the needle valve is fully cutting off and has the right thickness washer under it, the petrol level should not be so high that fuel exits into the venturi unless air is actually flowing past.

Several people have had spark plug troubles of late, and I'm inclined to think that modern production techniques and materials may assume clean running modern engines and the plugs are thus more inclined to foul and then misfire when excess oil or fuel is encountered. Could be worth having a spare set to swap to at the first sign of any trouble.

A timing setting checked by strobe at 20 crank degrees maximum advance sounds like a good starting point. 20 degrees at the flywheel is about 1.8 inches /45.4 mm, and 20 degrees at the camshaft pulley rim is about 0.37 inches / 9.4 mm. In theory the later DK4 has an advance range of 16 crank degrees, so the static advance will be 4 crank degrees. I don't know the Powerspark specs.

Stopping after a few minutes could be due to all sorts of things, but that sort of timescale suggests heat related. This would include ignition components like condenser, coil and plugs. I take it that it's not simply something getting tight after warmup, and that cranking over on the handle isn't more difficult ? No doubt you have seen the recent thread about valve stems seizing in the guides when warm.

Anyway, enough rambling - keep the faith !

[flywheel1935]

Hi John, firstly, thanks for a viable answer to this strange situation, what numbers should I be looking for on the jets & yes the fibre washers are in place. you say about the float chamber ? when I pre fill the float chamber before attempting to start,on full choke, a little fuel will 'spill' from the top of the carb. the CR of the Riccardo head is 40% greater than a standard LC head. could this 'kill' the plug spark, using the NGK's ??? For 27 year my standard starting technique was pre fill carb, full choke, 5-6 swings with the handle, then on with ignition, 95% of the time it fired first time, ( by hand) and became a bit of a party piece at car events, since the "rebuild" it simply refused to start, until desperate measures such as a 12 volt hit to the the s/motor are employed, then it sounds like a box of spanners in a tumble drier.

[John Cornforth]

Hi

Here's some data I have noted down for the standard Zenith 26VA for the Austin 7.  The body should be stamped CS548 (Contract Sheet 548), and there should be an identity mark 7 (Not a 10) cast into the flange.

Choke tube diameter 17 mm
Main Jet 57 (Smaller Brass Jet in bottom of float chamber)
Compensating Jet 50  (Larger Brass Jet in bottom of float chamber)
Slow Running Jet 60 (Tiny brass jet near top surface of bowl)
Progression Jet 100 (Hidden under a screwed inspection plug on underside of main body, near throttle plate)

The idling circuit is as follows:  Fuel passes through the idling jet, and has air mixed with it through a small hole.  Additional air is mixed in via the tapered air bleed screw (Idle mixture adjustment).  The mixture then passes down internal drillings and out of the idling hole just downstream of the throttle plate.  There is a parallel circuit through the Progression jet which exits just next to the throttle plate, and is supposed to prevent a flat spot as the throttle just opens.

I presume you are priming the carb using the lever on the fuel pump ?  If so, the needle valve ought to stop flow well before the point where fuel seeps from the bowl to body seam.  I don't know the spec for the fuel height, but would guess at 5 or 6 mm below the seam. Once cut off, the priming lever will offer less resistance and sounds of fuel flow should stop. The fuel level should settle at something like 1 or 2 mm below the point where it can pass out of the nozzle into the venturi, so that fuel is only siphoned out and introduced once airflow into the engine starts.

[Robert Leigh]

I suggest running the engine from a test tank hung from the central bonnet stay, gravity taking petrol to the carb. Obviously you would need to disconnect the fuel inlet to the mechanical pump. If the engine runs satisfactorily without petrol getting into the sump you will have proved where the problem is (the original pump?). I suggest that an old lawnmower tank may prove suitable for your needs.

[flywheel1935]

Hi John and Robert, thanks for the posts. both very useful.
Another thought; is the addition of ethanol into petrol also an issue, think current levels are 5%, but going to 10% in the near future.
and is it also possible that this is causing issues with the rubber coated fabric used in the f/pump???
John, I'll check out my carb jets, but if found not to be as you state, where can new jets be bought from ??
Robert, I'll call tomorrow for a chat.