Educate me about SU HS2 / HS4 Carbs - Marina needs spares

[Nomad]

For background, I'm a lot more familiar with carbs on classic Fords so Strombergs & SUs are a new thing for me.

My Marina cut out yesterday, the small bore flexible fuel line from the float chamber to to main jet is kinked and not allowing fuel to flow. This is a bad thing and hopefully the only fault.


The car came from a "make do and mend" chap so the carb may be from something totally different but its been running ok since I got the car (engine never felt crisp but was always smooth and reliable despite low power - it's a B series in an estate car so isn't a surprise).

My thoughts are to order a new pipe (comes with main jet), also a new standard needle in case what's now fitted isn't correct.

Everything else seems ok (float needle, no wear on the throttle spindle etc)so I'm happy to keep using the carb as it is.

Any advice or words of wisdom? I'm looking for reliability not race car performance.

Example of what I think I need

Shop our HS Jet Assembly .100in | AUD 9148 | SU Carburetters

HS Jet Assembly .100in

sucarb.co.uk

Guide to dismantling them

HS2, HS4 & HS6 Carburetter Dismantling – Step-by-Step Guide | SU Carburetters

Comprehensive dismantling guide for HS2, HS4, and HS6 carburetters, covering suction chamber removal, jet assembly disassembly, float chamber access, and throttle spindle removal.

sucarb.co.uk

Carb setup guide (wish I'd seen this years ago)

HS Carburetter Tuning – Single Carb Adjustment Guide | SU Carburetters

Step-by-step guide to tuning HS single carburetters, including idle speed, mixture adjustment, emission control checks, and fast-idle settings for optimal performance.

sucarb.co.uk

Education crash course needed. Tell me what I don't know

 

[minimutly]

They are the simplest of simple, operate on the velocity through the throat generating vacuum, with the spring above the piston providing the balance, and oil in the dashpot providing damping, which gives you acceleration enrichment. You item will have a biased needle, so a new jet is a good idea, they wear oval and cause rich idle mixtures. The only thing I would say is don't be tempted to put 3 in 1 oil in the dashpot - the piston will lift too quickly, giving you a stumble. 5W 30 engine oil is about ideal. Set idle mixture by adjusting the jet up and down!
Oh, whatever you do, don't drop the piston or dashpot, you may well wright it off.

 

[The_Yellow_Ardvark]

The flanges warp, easy to sort with plate glass and grinding paste.
The damper needs oil, enough, do not flood.
That pipe is a know issue. The new style is suitable for unleaded. Used to be a common AA/RAC spare.
The jets do wear, spares used to be available, do not know if they are now.
The floats are ok, but do like to be run at different revs. They seam to "acquire" a memory were they are happy.
If fitted with a brake servo, the one way valve is tosh, as are the hoses. The BL ones break down internally.
Get a decent fitting screwdriver to adjust the needs etc. The BL brass ones were like cheese.
I do recall about lifting the jet up to increase the revs as part of a test, but in my ill state it hides in the long distance memory.
Check the piston for score marks.
If you can get an original Haynes book for it. They in their day were great.

Oh yes, the plastic brushes in pedal box can fail, giving false idle speed.
Engine earth lead needs to be good, or the engine earths out through the throttle cable. this can cause the throttle not to return to rest.

hope that helps. Bck in the 80'ss I had one, blasted it many miles from Plymouth to Wiltshire. broke down a lot, but hay oh. Car only cost me £45

 

[tigdlo]

What is your ignition setup? If it's less than optimal, a higher power ignition system with the spark plug gap and advance curve to suit would help performance and economy, there is really no downside other than spending money.

The damper, spring and oil are all tunable parts for acceleration, there is no way of knowing what any of those should be without testing.

It could need the oil to be 3in1, 20/50 or something in between, everything is made to a tolerance, the piston bore for the damper could be on the upper limit and the damper piston on the lower or the other way round, these would both need different oil to give the piston the same rise and fall rate. Push the piston to the top and fill the dashpot with oil, any excess will just lubricate the carb.

The damper will alter immediate throttle response in the same way as an accelerator pump on something like a weber, different parts are available to tune this if needed, I think it's the free play that does it, but I'm not 100% sure if it's just that.

Springs do sag, might be worth changing anyway if they are still as cheap as they used to be or obviously wrong.

The problem with adjusting the idle mixture by adjusting the jet up and down is that is often used to correct other issues, ruining the fueling at all other engine conditions.

 

[Robotstar5]

Needle and spring are normally specced for the car make/model.

 

[tigdlo]

Needle and spring are normally specced for the car make/model.

Which was probably only optimal for a small percentage of the cars produced, good enough for most and just plain wrong for some. Production tolerences of the engine, carb and ignition system, the combustion champers, ports and the inside of the manifolds were all rough castings too, this is all before there is any wear.

Even with improved tolerences of modern cars, they need closed loop engine management with learned parameters for open loop conditions.

Carbs can be very good but every one and the engine it is fitted to, even if the specs are identical, is different so needs to be setup to achieve best efficiency and performance.

 

[Mick Annick]

For spares and advice: https://sucarb.co.uk/shop

 

[Migmac]

For spares and advice: https://sucarb.co.uk/shop

I phoned them when I was putting an SU on my vitara, very helpful people

 

[Melvyn Best]

Burlen Ltd is also a good place to get spares, the small triangular tag on the float chamber will give the part number for the car enabling identification. Don’t forget to centralise the jet otherwise it can affect the piston movement. Also worth replacing the needle valve , always good practice

 

[Nomad]

Thanks for the education, from the comments so far :
"Simplest of the simple.." @minimutly
"good enough for most and just plain wrong for some" (from new) @Tighobby
"the pipe that has failed is a known weak point - rac used to carry that as spares" @The_Yellow_Ardvark

Summary: SU carbs are super simple but unreliable and often wrong when they left the production line"

The plan is to ring Burlens and SU-carbs on Monday and take whatever pipe / jet / needle / spring mix they recommend (I'm still doubtful that what is on the car is / was ever Marina spec so prefer to start from scratch..)

It's all appreciated, expect updates before next weekend

 

[Laurie Tedcastle]

Thanks for the education, from the comments so far :
"Simplest of the simple.." @minimutly
"good enough for most and just plain wrong for some" (from new) @Tighobby
"the pipe that has failed is a known weak point - rac used to carry that as spares" @The_Yellow_Ardvark

Summary: SU carbs are super simple but unreliable and often wrong when they left the production line"

The plan is to ring Burlens and SU-carbs on Monday and take whatever pipe / jet / needle / spring mix they recommend (I'm still doubtful that what is on the car is / was ever Marina spec so prefer to start from scratch..)

It's all appreciated, expect updates before next weekend

Nomad,

Burlen bought all the rights from SU. They make spares for all models as well as new carbs. They have changed some materials to suit the newer ethanol fuels. They told me, some years ago, that their products should be good up to 15% ethanol.

Laurie

 

[jo1010]

One simple test - lift the piston with the lifting pin underneath. When you let go the piston should fall freely down with a satisfying clunky - if it doesn't inspect the piston and bore......
One carb is quite restrictive on 1800cc. Mgb type twin carbs mean airflow is much improved - probably like rocking horse poo now though to find some

 

[mr haynes]

I will look out the SU book with the official specs if you can't find online

 

[Nomad]

The genuine Haynes Marina manual I have only gives 1 spec for the 1.8 engines:
SU HS6 carb, yellow spring, 0.10in jet, BAQ needle

The supplement has a couple of others :
late MK1 - BAS needle
MK2 - BCW needle

If it's dry tomorrow I'm planning to check if this is a HS6 before ordering parts on Monday.

 

[Dapph2]

The flanges warp, easy to sort with plate glass and grinding paste.
The damper needs oil, enough, do not flood.
That pipe is a know issue. The new style is suitable for unleaded. Used to be a common AA/RAC spare.
The jets do wear, spares used to be available, do not know if they are now.
The floats are ok, but do like to be run at different revs. They seam to "acquire" a memory were they are happy.
If fitted with a brake servo, the one way valve is tosh, as are the hoses. The BL ones break down internally.
Get a decent fitting screwdriver to adjust the needs etc. The BL brass ones were like cheese.
I do recall about lifting the jet up to increase the revs as part of a test, but in my ill state it hides in the long distance memory.
Check the piston for score marks.
If you can get an original Haynes book for it. They in their day were great.

Oh yes, the plastic brushes in pedal box can fail, giving false idle speed.
Engine earth lead needs to be good, or the engine earths out through the throttle cable. this can cause the throttle not to return to rest.

hope that helps. Bck in the 80'ss I had one, blasted it many miles from Plymouth to Wiltshire. broke down a lot, but hay oh. Car only cost me £45

RE the BL pistons and needles .. Several times I had to araldite the needle in then before it set tighten the set screw . Not much fun being on the M11 and suddenly the dam thing dying just before knock off time because of that fault .

 

[bricol]

Summary: SU carbs are super simple but unreliable and often wrong when they left the production line"

Well, I've been running one on a 1600 Ford crossflow in my trials car for 20 years. The damper piston retaining ring has come off twice in that time, but other than occasionally topping it up with 3:1 oil, it simply works perfectly. Car starts within a turn or two however long it's been left - if it doesn't, it means I've done something silly like not put the coil lead back on, or put a battery in it. Trials cars need to run at tickover, or a revs above when "trickling" and snap into full revs as fast as you can shove the pedal down when wheel speed is needed - and it does.

 

[tigdlo]

I'm not quite old enough to have driven brand new cars with carburetors but old enough to remember plenty of stories how people got a "good one", "bad one", "Friday afternoon car", etc despite them being built with the same set of parts on the same production line, some just went better.

I don't personally think they are unreliable, my old Triumph was just fine on a single HS4 but setup is everything and not predictable based on the supposedly correct parts or what was correct for another car/carb, they need setting up properly to bet the best out of them, good enough is easily achievable though.

There was a thread recently with a forum member setting up an engine/car specific weber replacement. Although I'm sure the carb was setup correctly by weber when it was tested, unsurprisingly it asn't correct for the forum member's engine as it was not the same engine.

 

[james butler]

handy link i used when seting up my datsun SU carbs

http://www.mintylamb.co.uk/

 

[mr haynes]

Looks like an HS6 which would make sense.
If it were me, i would find someone willing to donate a HIF44 to the cause.
An update and improvement on the HS

 

[mr haynes]

The mystical world of SU tuning is truly something to behold.
Think i settled on sticking with the SU oil for standard factory setups and 10w40 for most modified. That was just the damper oil, never mind the gazillion needles and needle file to start your playing at getting the fueling just so on that modified engine