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Aragorn

V8 Performance Oddness

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You'd think wouldnt you. But theres a whole section on SU's covering various different types, including the HIF fitted to the Disco ;)

It also covers some Zenith Stromberg carbs too.

Its a PDF of haynes 10240 in case your wondering.

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You got the rapidshare link then? Didnt know if you might have it already...

Used the very same manual to rebuild my carbs! trust me its all good :) The fuel filter tip is a good one- when i first changed from 2.25 to 3.5 i couldnt understand why it would not go above 65- then i checked the fuel filter. It was crudded up and restricting flow enough to bother the v8.

Strange how the 2.25 didnt notice... :ph34r::ph34r::ph34r::D

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You MUST replace cam and lifters together as they wear against each other. If you just do one or the other the old component will eat the new in very short order. Some nice pics here http://www.v8engines.com/engine-4.htm#worncams

Do the chain whilst you're in there, if the cam is worn the chain & sprockets are usuallly as bad.

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The single most important part of setting up SU’s is to pay attention to the jet centralisation and that it is flush with the casting at full piston drop (fully closed). Also ensure the needle shoulder is flush with the piston.

However, you will more than likely find that the housing is worn at the throttle spindle and this allows a large amount of unwanted air to pass. You can bush them if you have the machinery and knowhow but it is a fiddly job for what is essentially an outdated piece of clockwork.

Balancing is best done by listening to the air flow at each carb with a stethoscope.

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^^^^

And that, ladies and gentlemen

ends the Public Announcement from Dr Cowboy :D

Nige

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Can i just clarify, should i be removing the entire carb from the manifold or just stripping the top (piston?) out of it?

I've taken the top off the first carb, and stripped and cleaned out all the gubbins, There wasnt very much oil in the top damper bit at all, certainly didnt pour out.

I'll strip the bottom half down too if thats needed, but i'm just wondering if i do that am i then going to need a pile of gaskets and seals to put it back together?

Also if i remove the body i presumably need to remove the throttle linkage, which i guess means i'll need to resync the carbs afterwards. Is this an easy task without a flow meter?

Cheers

Kev

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Depends how far you want to go ……………….

If its just cleaning out the float bowl , resetting the float valve , and cleaning the piston housing then (IIRC) it can be done insitu …………..

Yes you will need to reset the linkage if you remove the carbs …….. quite a simple job.

The carbs will only need to be balanced if you alter the mixture on either of them ……. But to get them right you will need to do that anyway.

You will need new gaskets for the float bowl anyway…………

Balancing does not require a flow meter ……. It can be done by ear …… listen to the air flow on each carb and the engine response.

Personally I would strip the carbs off and throw them on the bench ……… then take the rocker covers off and measure the cam lift at the pushrods, or measure the valve lift and then calculate the cam lift. The rockers are 1.6:1 ratio.

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Took the plunge!

Had to cut down a spanner to get to one of the securing nuts, but i got the offside carb off the motor. Will start stripping it down in a bit.

Looks like the throttle linkage link bar just has some balljoints on it, so i just popped that off.

Noticed that one of the carbs had a little tag saying something like "Wk 24 94" and the other one says something like "5 Wk 47 9" I think thats pointing to one carb being built in 1994 and the other one in 1995?

Which if true that suggests theyre not the original carbs? The carb i've removed also seems to have had some soldering done to the poppet valve as mentioned earlier in the thread.

Once i get into the guts, is there a way to ensure they're "jetted" correctly for the engine?

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BBC: Wont the hydraulic lifters affect the cam/valve lift? Ie with the engine off they'll "squash" and wont open fully?

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BBC: Wont the hydraulic lifters affect the cam/valve lift? Ie with the engine off they'll "squash" and wont open fully?

No...... they are not a bleed down lifters. Once primed you actually need to strip the lifter apart to drain them........ you would do this if measuring the lifter preload on a used engine.

To be absolutely be sure you getting full lift (but not entirely necessary) .............. do the job an cold engine......... just before you pull it apart, disconnect the coil HT and crank the engine until the oil pressure light goes out ............

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Kev ...........

Use this resource to strip, rebuild and tune the carbs

http://www.sucarb.co.uk/Technical.aspx

I remember that soldering of the poppet valves was very common on Stromberg as they used to fall apart .... but I am damned if I can remember poppet’s on HIF's..........

FWIW I used to race Mini's in the late 60's / 70's ....... in those days most of it was done at the track and I could probably still strip and reassemble HS6's blindfold ........ on of the biggest issues we had was fuel starvation when cornering at high speeds......... the fuel would get pushed to the wrong side of the fuel bowl. We fixed that by re machining the casting to made the fuel bowl sit at a different angle.

TBH carbs are troublesome and a compromise....... yesterdays technology.

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Just to add

MAKE SURE you put the covers back on the carbs you take them off, do not mix them about !

Nige

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Its Defo an SU.

Part number FZX2005 (LH/RH)

Thanks for the tips, i've laid the piston and suction chambers down in their own little pile with the LH/RH tag so i know which side they came from.

And ye, i'm fully aware these things are antiquated heaps, Megasquirt is in the pipeline at some point, but i'd rather get my garage kitted out with a nice workbench and suchlike before spending money on the landy! Stripping the carbs costs effectively nothing, and if it makes it run properly for now then i'll be happy.

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Probably best to limit the rebuild to stripping the float bowl and getting rid of the sediment.

The float valve setting was most likely correct if they were not flooding.

A common problem with HIF's (depends on age) is the bi metallic valve causing the jet to stick .......... symptom were usually a non starting engine and a tap on the base of the carb with a no2 adjusting tool would get them going again.

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If the carb dashpots were empty, it sounds like they were, then the symptoms would be poor acceleration caused by very lean mixture at wider throttle openings.

Actually just topping up the dashpots may have cured the problem (looking back at the first post).

The poppet valves were definitely used on the rover sd1, designed to lean the mixture on overrun and knacker up the engine improve the emissions. Often soldered up as the spring gets weak.

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Okies, well the offside carbs now stripped into lots of tiny tiny tiny pieces.

I cant really see anything wrong with them TBH. Float bowl was squeaky clean inside, and the only components ive had to clean up are the ones on the exterior of the carb, such as the thorttle linkages etc.

BBC: it doesnt have a bimetallic valve afaik, its just a manual choke. From looking at the parts, the choke lever does two things, it opens up the throttle slightly by pushing a cam against the throttle lever, and seems to open a small drilling that runs up to the suction chamber. I can only imagine this somehow lifts the piston a little giving a richer mixture.

Just need to put all the fiddly bits back together now!

One question: These dashpots that should be filled with oil... What stops the oil running down past the piston? there doesnt seem to be any sort of seal bar the little bit of nylon on ball bearings that runs up and down?

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One question: These dashpots that should be filled with oil... What stops the oil running down past the piston? there doesnt seem to be any sort of seal bar the little bit of nylon on ball bearings that runs up and down?

The oil just lives in the metal tube attached to the piston so gravity keeps it in.

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Hi

It should have a bi metalic mixture control in the float chamber and poppet valves, it may have been fiddled with before; if you replace one bimatalic strip you will have to replace the other . You can get most if not all parts from Burlin in Sailsbury ( have the number on the carb tag at hand they are very helpful and do refurb kits www.sucarb.co.uk.

Jon

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Bimetallic Mixture correction?

Where about inside the carb is this strip, i havent seen anything?

Offside carb is all back together. The only problem now is i need a new carb to manifold gasket.

Can i knock one up out of some paper/card?

As for the damper oil, can i just put some engine oil in there? I've got 20w50, 5w40 and some thin flushing oil on the shelf...

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thats the oil i used in the twin 1 3/4" SUs i had on my mini,

for some reason with thin oil i used to get a butterfly effect and the thicker oil damped this out.

SU's are very good IMHO - next best thing to injection, but would certainly go EFI as soon as you can.

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Hi Aragon

the bi-metalic strip holds the bottom of the main jet by the plastic elbow dont use card for the gasket might suck air and that would bring all sorts of woes upon you.My link have a look at the first image. Burlin have everything you will ever need.

Jon

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Slightly more interesting day today...

Took the nearside carb off and stripped it down. I wasnt going to comepletely strip it, but i noticed a few oddities. First off the poppet valve on this carb hasnt been soldered up (well it has, badly, and the solders broken off), secondly the mixture adjustment screw on this carb was in a completely different position than the other one (much further out).

I've now set both carbs to the default jet height (two turns clockwise from the jet being level with the bearing according to the manual) so at least they're now at a common starting point.

Not sure what to do about this poppet valve though. Clearly i cant leave it with one working and the other soldered up, but i'm not sure i have the equipment to solder it up myself? The "soldering" on the "good" carb is really dark in color unlike the shiney silver solder on the failed valve, and i wonder if its perhaps brazing? Either that or some kind of epoxy resin.

I think i might have some araldite on the shelf, but i'm not sure if that would be "petrol safe" to go inside a carb?

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