Series 3 Weber 32/34 DTML on 2.25 petrol vapour lock woes

Don’t know if this is the same issue for sure, but downdraft Weber carbs on Ford v6’s used to suffer from similar problems. The main reason for this, is the carb base where it bolts through the spacer to the inlet manifold can deform when it gets hot. This causes the fuel mixture to lean out and it only resolves enough for it to start when the carb cools down. The way you check, is to take the carb off and put a straight edge across the metal base diagonally and parallel to the sides to see if it is distorted at all. If it is, sometimes you can fix it by gluing fine sandpaper to a pane of glass or heavy metal sheet and rubbing the base of the carb across it to make it flat again. if this doesn’t resolve the issue then unfortunately it’s a new carb that will be required.
Another issue to check for is that the plastic baseplates can crack almost imperceptively, which when the plastic heats, up admits air below the carb causing rough running when hot and this is due to the air leak causing the manifold pressure to change, this leans out the mixture and that’s why it runs rough. One more thing to look for is the brass fuel pipe inserts where they meet the cast alloy body of the carb being loose and can cause fuel leaks. And lastly, check the butterfly spindles for excessive play on the spindle bushes….
If you have access to a fuel mixture (CO) checker, you could put it into the exhaust when it starts to run rough to see if it is running excessively lean?
To be honest, they are not great carbs in my opinion, and a decently set up original Zenith works really well, although I do believe that the SU conversion works well but I don’t have any experience with it personally. Hope some of this info might be of use. Best of luck!

The SU is a great carb and that's not just my opinion, there's a reason they were very successful on sports/performance cars.
On the series, you get a more instant throttle response and application of power which is useful when you're off road and generally a better driving experience

Agreed. They're the ultimate easy to source and tune carb. Weber DTML is only good if you've got a good one, else as bad as the others. Needle choice for me was a custom based on a BAO, Green Spring. Upped oil to 20W/50 damper as AC Dodd's dictum.

HNJ Recommend:

BDL - Green Spring (Richer)
BDL - Yellow Spring (Nominal)
BDL - Red Spring (Leaner)

BDM - Red Spring (Leanest)

Tried and failed with those.... got mine dialled-in via a Wideband gauge, umpteen AC Dodd vids on Youtube and:


Made a custom needle. You'll never get it spot-on with any other carb as easily as you can with an SU. Wideband gauge essential.

I have come back to this thread as recent fuel/carb issues (I think).
If anyone can help 'strap in' for background.
Set up is 17H 2.5 petrol in 1972 88" Station wagon.
OEM Facet pump and filter on the rubber mounts under drivers floor that came with the engine, added filter on bulkhead, no swirl pot.separator.
I had issues many years ago with misfire, surging and, after replacing points, distributor, coil, stripped and cleaned carb, replaced both solenoids. Eventually I swapped to electronic ignition and replaced the carb with identical one from Fast Road Cars.
Bliss thereafter for some years, easy starting, smooth running, decent economy and would run up to 80 in overdrive top (including one memorable mercy dash 120miles almost flat out, door tops flapping, etc). Regretfully old it to a friend for couple of years and later bought it back. For reasons I now forget I stripped and refurbed then refitted the original carb with genuine Weber kit. It has run very well for couple of years only it seemed to have fuel starvation issues if running under load for more than a few minutes (would run up to 70plus but then cough and splutter and once you backed off and waited for a minute it would then tootle at 45-50 all day). As it has been my daily driver 10miles each way through the lanes if persevered.
I wondered about blocked filters/rust in tank (which then started leaking from rust holes when full). So whilst I fitted a new tank and replaced filters, I could not remover the filter in the fuel pump so I replaced it with a Facet identical to the original.
Now I've got the original spluttering, surging at 30mph or under load, just as it did all those years ago. Weird. I wondered if I had introduced air into the system whilst replacing the tank and pump and I did purge the fuel line into a bowl with good flow - that evening it ran beautifully for a 5 mile test run. However it has returned to spluttering again, despite a proper warm up.
I have ordered a swirl pot, but struggle to understand why it ran so well for so long with carb no 2 without a swirl pot, but now needs one?
I am minded that I will need to add a return line into the tank from the pot and have seen reference to adding a restrictor to the 8mm pipe in the return line, although no suggestions as to why?
If you have got this far I would be interested in thoughts and suggestions.....................

Swirl pot…

Mine used it on the 2.5. as fuel starvation. & No return from carb caused vapour locks.
Even with the electronic facet pump(instead of in tank pump) set to correct pressure nothing overcame the problem.

Spotted no swirl pot fitted so found the standard LR one & fitted. Ran/raced as a dream.
What confused me is as there is no pump between swirl pot & carb,the carb must suck its own fuel into the fuel bowl.

i used to get vapor lock all the time and others i spoke to had never heard of it, its like a odd one that only very few will get it and others never, fuel is shi-te today it aint like it used to be, even with no lead it still is sh-it as early unleaded fuel in australia was good i only really started having issues around maybe 2008 or so and i had tried many things,
the best solution was i used a electric fuel pump a solid state facet brand im running but i was still getting it so i did what others had suggested and run a return line back to the tank on mine i have a t piece that sits up and its restricted a bit so only some of the flow will return and then cause i have a britpart tank it is universal i ran the return back to the tank and so far it works well in combating fuel issues as it circulates the fuel when it not being consumed and it seems to keep the line cool. and my vapor lock would happen summer and winter no matter what temp day or night.

i heard a few fellas in america with carb older cars do have vapor lock issues and most of them run a filter thast incorporated a return line.
ethanol blends dont help either and high octane fuel makes no difference i run 91 and i seem to go ok i run higher and it will still have issues before i did the fuel return and pump upgrade.
a tip, dont always buy a generic chinese fuel pump i had and i got 18months total and then the second one a few weeks, but with the Facet brand 8 years roughly with the first one i still think its ok but i replaced with a second one a few years back.

same can be said with ignition parts try to opt for oem spec and not the lucas (chinese-taiwan) or the generic chinese junk it wont last as long as oem spec. i would run Bosch parts and i would get many years from them i have recently went with a generic set of parts but i am not at all confident it will last many years.

Have you tried super unleaded? Ethanol has a lot boiling point than petrol so will cause vapour lock issues more readily. In my opinion

kermit_rr said:

Have you tried super unleaded? Ethanol has a lot boiling point than petrol so will cause vapour lock issues more readily. In my opinion

Click to expand...

do they sell that in the uk, i recall years ago they had it but it was a leaded stuff and w2hen unleaded came in its all marketed as unleaded but at different octane ratings we have 91 which is the low end 95 and 98, all of those are unleaded as is fuels now, but i noticed that the higher octanes had no difference on anything some swear 95 is better then 91 but i have run 95 and 98 its a waste of money to be honest and 91 has had little effect on running at all, we could pay up to 20 to 30cents more for 98.
but i know people can have different outcomes and most i have spoken to that has land rovers have never had vapor lock issues and they are lucky. but then again it could be something i have on the engine fitted that causes the issues as do others.

but anyway i was looking at ignition parts and over here we would have bosch parts that were oem spec and it was made in the uk but just yesterday and no one sells it anymore its like we are stuck with the inferior chinese and or taiwan made junk, i really have no trust in the cheap trash componets as i have many parts that was chinese rebrand lucas fail at least 2 condensers that was lucas made in china fail, its getting harder to get good quality parts even paddock spares and other land rover parts places dont seem to wanna stock good stuff. its getting to the stage where people will have to stock what they can of good parts.

At the risk of tempting fate it would appear that my 'shed'is now fixed.
It now has a swirl pot on the bulkhead, freshly rebuilt Weber, new Facet electric pump with filter under the drivers floor.
I have filters in pump, filter housing, extra filter on the bulkhead and in the carb inlet. K&N conical filter on the stock plastic air intake. Electronic ignition etc. New fuel tank (the one that fits!).
Importantly I also replaced the wires to the solenoids as the feed wire had wicking of corrosion below the crimp.
Starts very briskly now with flick of ignition switch but does need choke for a few mins (it is chilly here this week).
No kangaroo petrol and I can floor the pedal for as long as I wish. Going to try flat out on A14 in o/d top when time permits.
I hope the OP has had similar success.