Help. Serious misfiring and need to drive to UK on 22/05

[RobinLegin]

Hi all you brilliant mechanically minded guys
We have been rallying around the Loire when a serious misfire developed. So far have changed the coil and fuel pump. The fuel filters are running clear and the car starts on the button. Have checked the distributor and contacts and all good. Other than a failing plug it looks like dirt is hindering fuel delivery in the carbs. Most of the classic car owners are telling us to check the main jet on the Strombergs. Problem is no one has ever touched a Stromberg.
With limited tools please can someone tell us how to strip the carb so as to access the main jet and check for dirt. All bits will need to reassembled.
Any photographs, link on the web as to how to will be much appreciated.
Cheers
Nigel

[Ian Durrant]

I doubt its dirt blocking the jet. The jet in CD carbs like the stromberg has a needle that gets thinner the more the piston lifts, so a bit of dirt that blocked it when the piston is down would shift as it rose. dirt more easily blocks the float valve, but that normally causes a smell of fuel as the excess is dumped out of the overflow and tends to affect idle far more than driving under load. it sounds more like an ignition fault to me, maybe an ignition lead has broken down, the rotor arm is leaking energy to earth or the dissy cap is tracking.

some float valves have a bronze gauze that get get clogged so that is a possibility.

it would really help a long distance diagnosis if you can tell us how this misfire presents itself. Is it all the time, dependant on load (ie how far your foot is down) is it only at speed or higher revs etc

[Arbman Al]

What about failing plug leads? Have look in the dark to see if there is any arcing going on when the engine is running/revved.

[Hettiherald]

Split diaphram on one of the carbs??

[Ian Durrant]

Split diaphram on one of the carbs??

yup, good call that would do it!

[RobinLegin]

The problem started coming off the ferry in slow traffic. It lasted until we cleared Le Havre and were able to open up the throttle and cleared it itself completely. All has been well till yesterday morning driving in slowly around Saumur. Took the car onto some dual carriageway and opened up. Got up to 70 but the misfire / splutter remained. Last driving into town at 30 mph was no different.
The car starts on the button and idles normally.
If a split diaphragm how does one do a temporary repair to get home? Will be checking plugs and leads shortly in hope it is an HT lead failure as that can be sourced locally.
We will loose wifi access till tonight so unless in the next hour or so, please PM some further thoughts advice etc. Sadly can't remember my codes for SOC forum and access from my phone. Age getting to me.
Cheers
Nigel

[RobinLegin]

I should perhaps add it was dry when we left Le Havre but then the heavens opened up and we drove in torrential rain all the way down. It has been dry and warm since down here in the Loire valley.
And there have been occasions when there has been a smell of petrol after switching off.

[davidf]

One thought from the smell of petrol - is one of the carb float chambers overflowing (needle valve sticking)?
This might also fit with the problem clearing on the open road - if it was only slightly passing the needle valve, it would be running very rich at idle, but on the run, you are using the fuel fast enough to stop it over-fueling.
Sometimes, this can be recovered by running the engine, and stopping the fuel pump (assuming wiring is original, lift the plunger top on the inertia switch).
It takes an amazingly long time for the engine at tick-over to consume all the fuel in the float chambers.
When the engine stops, re-connect the fuel pump. If you are lucky, this can flush out any muck from the float valve because the initial flow is 'full bore'.
It doesn't always work, but a few of us worked on a Stag with this problem at the half-way break on the New Forest Run last month, and it cured it.

[RobinLegin]

Hi all. Made it to Ducy les Cheris just near Mont St Michel. ''Twas an HT connection issue I think. More later.
Bw
Nigel

[Rod1883]

Hope you get back OK Nigel. In my (limited compared to many others on here) experience, issues that are thought to be fuel usually end up being electrical.

It's a shame we missed the APPF rallye this year as we have thoroughly enjoyed it for the last three years, but it clashed with a TR event about which I've posted a few words on the "What did you do with your Stag today" thread.

[RobinLegin]

Before set off for the return journey home I set about making sure all the plug leads were properly connected. A couple had a slight wobble at the dizzy. Loaded the car and fired up. Not any misfire. The car performed perfectly from Saumur to Ducy les Cheris. Despite the heat, the car performed without a hitch.
Having said that apart from replacing the dizzy cap and plug leads, I will follow up on the fuel issue. There are occasions when the garage has a distinct perfume of motor spirit.
We are due back on the overnight from Cherbourg to Poole tomorrow night. I'll let you know if we get home ok. Btw, I could get spare HT leads here in France. Now all ready cut and prepared for the individual make of modern car.
Bw
Nigel

[HersnotHis]

Hi Nigel
I have had similar experiences and thought I had found the (fuel starvation on evidence)) culprit several times and driven faultlessly for 200+ miles after apparent fix. However it re- occurred again last year less than a mile before local petrol station at which I intended to fill up. Whatever I thought I will continue to the filling station and then limp home to investigate.

After filling up (OK £40 worth) I re-started and the Stag went like a dream! I now suspect that there may be a problem with the fuel pick up as since then have covered some 400 miles without problem but have not let fuel guage fall below 1/4.

Just by chance were your rough running experiences associated with low fuel levels?

Hope to become near neighbour soon as hope to move to Blandford area as soon as somebody buys present house for acceptable price.

Hope you made it back OK

Please advise any further findings

HTH
H

[Seaking]

H sounds like you have rust in your tank when fuel gets low a flake of rust is pulled to the fuel pickup pipe and obstructs the slot. Once you filled up the rust was dislodged and away you go.
The pick up pipe in the tank has a slot in the side to try and avoid this problem but it dose not always work

Cheers Glenn

[RobinLegin]

Hi Glenn. Because the fuel gauge shows half full aafter 100 miles or so I tend to fill up at this point. The tank is ever more than half empty. But that is definitely another avenue to be explored.
Nigel

[MandM]

Hi Glenn. Because the fuel gauge shows half full aafter 100 miles or so I tend to fill up at this point. The tank is ever more than half empty. But that is definitely another avenue to be explored.
Nigel

add another filter before the pump,but best to clean the tank out first