Are Su's poo?
Turbo Mini Forums

Been having loads of issues with the car running lately. Got myself a wide band kit, one min the cars running great then its running crap.

It looks like there is something wrong with the fuel delivery its getting too much. I rebuilt it using a Burlen kit thinking the choke mech was letting fuel in when it was closed. but no despite all of the love and attention its not wanting to play ball...

I'm running a suck through setup its had a NOS dashpot, piston, damper, float, jet, jet holder, bimetallic strip, float needle, filter, some love and a wipe over with a clean rag. yet it still doesn't love me... There must be either something I have over looked or some sort of fault with the carb body?

so are they crap.. thinking of switching to a bike carb and give that a go..

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

SU's are simple, reliable and (I believe) one of the eaiest carbs' in the world to set up.

This also means one of the easiest to get wrong.

Too rich is a wrong needle or spring. Simple. Start by telling us what you're trying to do HP wise and the spec of your carb and needle...

Edited by turbodave16v on 9th Mar, 2009.

do the bike carb. was thinking about something like that for my SC12 setup...

would need to be a big carb(s) though...

Dave, I must have something strange going on.
The carb is a HIF44. I have a custom needle polished by my local rolling road. I have measured the stations the maker of my SC12 kit in AUS has measured his needle and the profiles match his is slightly richer but then he is running a 1275.
I'm running a 998 Sc12 suck through, HIF44, ram pipe and sock, 12g295 running 8.7:1 and 1.5's

I have a techedge wide band kit so I can get more independent. I have been having issues I take it back to the rolling road they have it running bang on; on the rollers and I take it home next time I drive it is rough. You then leave the car and it runs ok.

I spent all day yesterday with the wideband kit trying to understand what was going wrong and it was behaving stangely. e.g

I got the car warm then checked the idle AFR and it was in the low 12's so I changed the jet height, then again and agian best I got was high 12's this was with the jet about .5mm from the bridge..

So I pulled the spring and put a red one it still the same, I took the piston and dashpot off got the wife to turn the pump to check is fuel was pumping out but all ok.
Then got a fresh needle and spent some time polishing it down a bit as it was like a fat cut chip. I got it close to my profile at WOT but left it thicker at idle.

I went for a run in with this new needle and the AFR's were in the 6's!! I would hardly go. So I take out the new needle put the old one back in have some lunch and try again. The Afr's are now close to 30 on idle as they should be with the jet that high, I reset the jet and get an idle of low 14's take it for a run and its great, at WOT (10psi at high revs) I have an AFR of about 12.2 and an idle in the low 14's. great but this is how it started in the morning... There must be something else at play here...

I did some youtube searching on SU's and there was some info on correctly matching components etc.... I can only assume that the body has some fault that when it feels like lets too much fuel in...

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Float chamber needle valve worn/sticking? Fuel pressure too high overcoming said needle jet? Float height set wrong?

Have you got another carb to try?

Is it pulling air in somewhere? there are a fair few gaskets between the carb and the engine...

Show us a pic of the install. This might reveal something obvious,,,

hmm think about the float height. was going to whip it off and have a look. the fuel pressure is about 3psi and I can turn it down on the regulator.

Its an arse of a job to remove the carb wasn't sure when to cut my losses and try a bike carb. No more dash pot oil etc and plastic inners so might be better dealing with the cold.

I have the float needle is new and I have checked the fuel pressure with the dashpot and piston out and it didn't piss out of the jet so I think the pressure is ok.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

an old pic whilst it was getting megajolt

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

cant see much in the pics but:

Float breather is vented to atmosphere and routed via some copper tube under the car.

Carb breather is blocked off with the old pipe and bolt trick.

Vac is used and plumbed to the SC breathers as it should be.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Do youhave the two holes on either side of the itake (on the filter) that go up to the dashpot?

yes but I was thinking that these might be blocked but the sock as its a short ram pipe. Are these holes are to aid the piston lift? if so will it be rich if blocked? I was thinking of trying a Rover V8 intake and then a universal K&N?

A quick questions what are the symptoms of a low or high float height?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Do you have a heatshield at the bottom of the carb. It is maybe struggling with the heat once the car is up to temp.?

may also be worth replacing the bimetallic strip with something that doesnt change with temp (theres a few threads on it) also.. is it possible the temperature of the charger is affecting the fueling, allowing more or les port wall wetting/atomisation.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

well your firing fuel suspended in air through the charger, some of it wil lend up onteh walls and floor of the plenum, some of it will end up in the engine. depending how hot (or some other variable) the charger and its surroundings are will change how the fuel is distributed in the air.

just thinking out aloud as you said the RR operators can replicate there own results time after time (RR room is a fixed environment) but you cant on the open road. so somehting is different between these two.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

I remember hearing about charger temperature problem's on these. I think some of the people in Aus use water injection to cool things down...

There's a few people on ausmini recomneding water/methanol injection when running fairly high boost.

Start by opening up the holes or slitting the gasket to allow air into the dashpot like a factory setup is.

That'll at leat eliminate that potential.

IMO its not a heat thing.. I think its a carb thing as I couldn't get the car in decent AFR's at idle even with the jet all of the way to the bridge. So its got to be an SU thing.

will chech the gasket and float height.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Are SU carbs in most instalations on standard inlet inclined?

Who is your local RR. If its a particular one I am thinking that closes the roller shutter when its on the dyno so you cant see, I have heard mixed responses

nope they dont have a roller shutter.... are you thinking of the one that races Citroen's?

These guys are grass track racers. Its not them I have the profile of the guy that builds the kit in AUS and my profile matches it except mine is a little leaner but then he is running a 1275 and I have a 998. So you would expect it to be correct. But then the car seems to get richer by witch craft.
The float looks like a starter it must be getting more fuel from somewhere, and I cant remember setting the float height.. rushing too much at my end

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Could it be the WBO2 playing up?