2.3/2.5 Carb Upgrade Weber 34CIH to 32/34DMTL

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thspeller

Active Member
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Location
London
This is a long story so bear with me...

I have a series 3 with an 11H 2.25 petrol (branded 2.3) engine from an early 90. It came with a Weber 34 ICH carb and I recently replaced it with a new Weber 34 ICH exactly the same as part of the restoration.

I have struggled for power (especially on long hills) even though my truck is very light (no roof, single occupant, etc.). I assumed this was just a series.

I recently had the chassis changed and new springs fitted which has given it a bit of a lift. I was always running small tyres (215/70r16) which now look silly on vehicle that sits higher. I want to replace tyres to 235/85 or 7.50 size. I am concerned what that new tyre increase will do to the car's performance with only just enough to power to survive my hilly home town.

So, my initial reaction was to get the head gas flowed to compensate for some of the performance but Turner have identified that my big issue by far is the undersized carb for the 2.3 engine which actually came with a 32/34 DMTL which (as the name suggests) has twice the breathing diameter.

So I am now considering converting back to what must have been the original 32/34 DMTL setup. My intake manifold has two ports so I assume that suggests my engine will take the upgrade. I know that I have to play around with the throttle (lever to cable operation), install a fuel return and wire solenoids.

My questions are as follows (if you could try and answer whichever ones you can):

(1) Does anyone know whether the 34ICH to 32/34 DTML have a significant power advantage / enough to offset changes in tyre sizes?

(2) Can anyone confirm that my intake manifold (photo attached) was indeed designed for twin choked carbs originally?

(3) Is there any issue with me having a series stainless exhaust (i.e. would a wider exhaust from a ninety be more efficient)?

(4) My fuel tank doesn't have a return - how important is this? I have hard some people just block off this fuel return or let it drain under the car as it is rarely used?

(5) Any suggestions for the throttle rigging?

Thank everyone.
 

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I'm in the process of building a 2.5 engine for my Ser 3 so have gone some way down this road already...

(1) Does anyone know whether the 34ICH to 32/34 DTML have a significant power advantage / enough to offset changes in tyre sizes?
I'd be surprised if just changing the carb makes a huge difference with the 2.25 motor. The 32/34 DMTL does breathe more freely than the 34ICH and that makes a difference with the 2.5 engine (which also has the bigger bore exhaust), but the 34ICH should be fine for the 2.25 as long as it's in good condition and has the right jets installed. Worth checking that the ignition timing is correct at full throttle (not retarded) and that the throttle is actually opening fully.

(2) Can anyone confirm that my intake manifold (photo attached) was indeed designed for twin choked carbs originally?
Yes, that is indeed the manifold for the DMTL carb.
(4) My fuel tank doesn't have a return - how important is this? I have hard some people just block off this fuel return or let it drain under the car as it is rarely used?
There are two 32/34 DMTL variants used - one with a single solenoid that doesn't use a fuel return and one with two solenoids that uses a fuel return. The return is intended to allow fuel to circulate and keep the fuel cool - apparently this carb suffers from heat soak with the LR engine. I think you can blank it off, but I wouldn't let it drain anywhere near the engine - sounds like a recipe for a fuel fire to me...
Note that the twin solenoid Weber used an electric fuel pump and a swirl pot. Facet pump is easy to find, but swirl pots are no longer available - I'm still thinking about how to solve this issue - maybe someone has been this route and has a suggestion?

(5) Any suggestions for the throttle rigging?
I'm planning to use the throttle cable from the 2.5 engine and keep the Series throttle linkage, but some fabrication will be needed. A simpler way that I've heard about is to drill a hole in the accelerator pedal and run the 2.5 cable to that.
(3) Is there any issue with me having a series stainless exhaust (i.e. would a wider exhaust from a ninety be more efficient)?
I'm not convinced that a wider exhaust will make a big difference with the 2.25 but if you are using full throttle a lot of the time then I guess it can't hurt.
 
What about the SU ACR carb?
Not tried it myself, but there are threads on here where others report good things about this conversion.

Looking for extra power with the LR engines is always a challenge. Making the engine breathe better (big-bore exhaust, gas-flowed manifold/head) should add power but probably only towards the upper rev ranges, so you have to rev the engine more to get the benefit. And there may be some loss in low-end torque, which could be an issue if you drive offroad.
There's a good discussion of the various carb options here (doesn't mention the SU though):
http://www.expeditionlandrover.info/landRoverFAQ/FAQ_carbs.htm
Until recently, the standard answer on how to get more power was "drop a 300 Tdi engine in", but this seems to be less fashionable these days ;)
 
What is a "swirl pot" ?
Land Rover call it a "separator, vapour" NRC9772
20371-nrc9772-vapour-separator-4-cylinder-90110.jpg

It appears to sit between the fuel filter and the carb, with the third pipe as a return to the tank. It is supposed to keep the fuel circulating to avoid vapour lock. I think it was fitted as standard with the 2.5 engine, but was missing from the pile of bits that I got, so I'm not sure if it's essential or not.
It's no longer available, but I guess it can't be too difficult to make something similar :(
 
Land Rover call it a "separator, vapour" NRC9772
View attachment 229494
It appears to sit between the fuel filter and the carb, with the third pipe as a return to the tank. It is supposed to keep the fuel circulating to avoid vapour lock. I think it was fitted as standard with the 2.5 engine, but was missing from the pile of bits that I got, so I'm not sure if it's essential or not.
It's no longer available, but I guess it can't be too difficult to make something similar :(
Screenshot_20210129-173649_eBay.jpg


Still available but not cheap :eek:
 
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