SU Carburettor Refurbishment.

[Black Cat]

After nearly two months I have finally got my carbs back from Glen at SU Carburettor Restoration and Exchange and what a great job he has done, they look like new.

Glen had not only cleaned all the parts he had also replaced many components as well. Apparently there was wear in the bodies, throttle spindles and the mounting faces weren’t flat. The earlier plastic type jets were fitted along with solid butterfly discs, previous one had been soldered up and this was disrupting the fuel/airflow and new ethanol resistant floats and short flue lines fitted. He also replaced my dash pots as mine were in a sorry state. Because the car has had a few modification to improve performance he fitted AAQ needles along with stronger 8oz piston springs, the previous needles were AAR and as they were not in a bad condition they have been returned in case they might suit better.

 

Hopping to continue working on the cards today but as it’s undercover outside and it’s been raining all morning no chance of that just yet, maybe this afternoon.

The few jobs still to do are first fill the dash pots with some 20-50 oil, fit a return spring to the throttle cable, connect up the chock cable and then set the carbs up and hopefully the car will start a lot better than it did before the carbs were refurbished.

The car is booked in at Hanger 111 for a rolling road and carb set up later this month and I’m hoping to drive it the short distance there.

[Black Cat]

Right, fitted the cards and all the associated parts, clean and checked the plugs, they were quite black with a wet deposit on them from before the carbs were refurbished.

Topped up with fuel and after a few turns the car bust into life made some slight adjustments to the mixture to get them in balance and waited till the car came up to temperature, after a while the fan cut in and the engine started to slow and stalled, then it wouldn't start again.

I know the carbs are probably still not set up but why did the engine slow and stall when the fan cut in and it seemed to be running quite well up till then?

[NonMember]

27 minutes ago, Black Cat said:

why did the engine slow and stall when the fan cut in

Because you'd coincidentally run out of fuel then? 😛

More seriously... if the carbs are set very rich, the extra load of the fan drops the speed to the point where it's not so tolerant, and the plugs then foul. It won't re-start because it's too rich for a hot start (effectively flooded).

[johny]

Yes dont panic, balance the carbs with a flow meter and then set the mixtures on each and give it another try....

[Black Cat]

Firstly plenty of fuel, secondly checked the plugs and having earlier cleaned them and checked the gaps they are now oiled up so mixture may well be the problem. 

[daverclasper]

2 hours ago, NonMember said:

More seriously... if the carbs are set very rich, the extra load of the fan drops the speed

Interested in this. It's basic stuff, though not something I've ever read about before as such in detail (usually as such, just a problem regarding failing ? failed parts within ignition system).

So extra load, or a problem with ignition not getting enough power (from what ever cause), makes the car idle/run slower, or I assume probably misfire? 

[Pete Lewis]

if the mixture or anything else is making the idle less powerful that at its best any ancillary adds load that can be anything from pressing the clutch to 

alternator/dynamo demanding charge ..like running an electric fan it will put the brakes on a poor idle

and slow it down    ive just done a fairly modified 2500s road rocket that was doing just that all down to mixture settings

the start basic adjustment for SU is with the jet level with the bridge its 2 full turns down to get a basic running point  fine tune in small increments from that once hot 

I would hope with all the bling and shine that the basics were set up by the reconditioner but it would seem not

how many time does this old nutshell pop up     shiny doesnt make them work 

Pete

 

[NonMember]

It's the extra load (I'm assuming from the "cut in" wording that this is an electric fan). There is no idle speed control on our cars - you adjust the air flow so that the power produced balances the power lost in friction and other loads (including the water pump and alternator). If you then suddenly increase the electrical load, by turning a big fan on, the balance is no longer right - the power generated is less than the power consumed, so the difference is made up by removing energy from the flywheel - i.e. reducing the engine speed. That's universal. On carbs, this loss of speed also causes a mixture disturbance, which is normally a momentary enrichment. If it's already running too rich for comfort then this reduces the power generated even further.

[Bfg]

5 hours ago, Black Cat said:

they are now oiled up

Oiled up or sooted up ?    As this was an issue previously, might I ask - have you tried the next hotter sparkplugs ?

12 hours ago, Black Cat said:

fill the dash pots with some 20-50 oil,

By coincidence this was being discussed at our last TSSC meeting, and a number suggested that 25w/50 was too viscous.  I didn't have an opinion, but was interested to learn.  One of the chaps said that it was one of the first things their rolling-road did - to flush the oil out and replace it with very light oil. 

Perhaps with a lighter oil in the dash-pots, and lighter springs, the carbs might have responded more quickly to the drop in revs (and venturi flow) at tick over, rather than stalling.  I don't know - I am asking.  I'm wondering if Glen has set the carbs up for faster road use ..and those springs necessitate a faster tickover ?  again I'm only asking.

4 hours ago, Pete Lewis said:

I would hope with all the bling and shine that the basics were set up by the reconditioner but it would seem not

how many time does this old nutshell pop up     shiny doesnt make them work

...You are a heckling toad at times Pete

     your implication regarding Glen's work sounds rather unfair to me.  ..be careful you don't topple off that high horse of yours.

Personally, I don't read BC's posts as being in any way dissatisfied. On the contrary he was simply asking a very sensible question ..which I thought was answered well by NM.   It certainly enlightened me.

Furthermore,  BC did state that . . .

12 hours ago, Black Cat said:

the car has had a few modifications to improve performance he fitted AAQ needles along with stronger 8oz piston springs, the previous needles were AAR and as they were not in a bad condition they have been returned in case they might suit better.

Surely, Glen might only make an estimation of the settings required for any particular engine and environmental conditions ?  ..according to the information he is given & whether he has direct experience or feedback of those particular 'modifications'.   By the sound of it - setting things up on the rolling road was on the cards anyway.  Otherwise he's done right in returning the previous needles "in case they might suit better".  That may be read as a disclaimer ..as he hadn't set the carbs up on the car himself. . .

Glen rebuilt a set of carbs for me, but then I did send him the complete setup with rods and linkages still on the inlet manifold. He refurbished the lot beautifully. Perhaps he then has a better chance of adjusting n' balancing things to work straight-out-of-the-box, so to speak. 

Personally speaking, I will use Glen again for Katie's  SU carbs.

Pete

 

[Iain T]

I believe most needles start around the same base diameter for a given jet. It may be the spring is slightly too heavy hence reducing the bridge gap and increasing air speed and fuel. You could try using your old lighter springs. An easy fix to try. 

Iain 

[Clive]

Indeed, lots going on in terms of (what appear) minor mods. K+Ns will affect things and whatever has been done to the engine. 

AAR and AAQ are both "go to " needles for such mods. But as Iain says, the idle area of the needles are all very similar. 

I would do as Pete suggested, check the jets are 2 turns down. Get the car started and set the idle to 1000rpm. That gives leeway when you are balancing and adjusting. Get that about right, then maybe back the idle to 800rpm, but if going to a rolling road session that probably isn't worth fiddling with.

And as above, what plugs are you using. I believe NGKs don't like getting wet and can be a problem after. I also know some people, whom I have a great deal of trust, swear by the bosch multi-electrode plugs.

[Iain T]

Adjusting carbs is too a degree a black art. Unless you have lots of experience you really need some gizmos to help, I certainly do! A basic carb synchrometer to get the airflow the same on both carbs makes life soooo much easier. Then it's only needle choice, dash oil, air piston spring rates, needle centering and fuel mixture to play with🤔

Iain 

PS, forgot potential air leaks! 

[Iain T]

I also measure the depth of the jet to bridge with a micrometer. Every little helps to synchronise the carbs. 

Iain 

[Black Cat]

I'm happy with what Glen has done on my carbs, I told him all the modifications that have been carried out to the car and using his best judgment he has set the carbs up from the information I gave him, it may not be quite right and I could try and adjust some of the settings myself but I doubt I would get it quite right and this would cost me time and possible money and I'm keen to get the car back on the road and knowing that its booked in for the rolling road  at Hanger 111 and they have a carbs specialist on hand to set the carbs up I think I'll let them sort it out.

I let you know what the outcome is.

Many thanks for your comments

[Pete Lewis]

there is no black art if you use the very basic settings 

what do you think Triumph did , out of a stillage came a carb  set to pre determined settings , like 1.5 turns on the idle screw and jet 2 turns down 

bolt it to the engine and off down the line it went and started no balancing no rolling emmision road ,    it runs as expected 

the base settings all set to the same mechanical positions will give you a runner , 

yes if things are modified you need to move needles and maybe springs away from the working triumph spec but 

much is simple mechanical settings anyone can perform with simple tools and listen to the results you get 

the ears can tell you a lot 

Im not knocking Glen at all  i just have found on here and in life  shiny is one thing  making it a runner it doesnt i wont say where these nightmares come from 

many have paid 100s of £££sand gained very little  

Pete

 

 

 

[Iain T]

I've taken cars to rolling roads and tuned by 'mature experienced' mechanics who have made a right cock up. Getting the basics right is relatively easy, to get the best out of your modified engine is where the black art of trade off comes into play or alternatively spend hours and many pounds trying different permutations. But then we all love a challenge! 

I do agree your ears and spark plugs will tell you if all is about right. 

Iain 

[Ian Foster]

Recent Wheeler Dealers with a Volvo B18, describes a basic SU refurb and set up.

Electric fan will put load on the alternator and decrease idle revs slightly. Known by tuners as 'the curse of the electric fan'.

Ian

[Pete Lewis]

1 hour ago, Iain T said:

I do agree your ears and spark plugs will tell you if all is about right

so  that gets an ear ear   from me  ha !

 

anyone noticed with modern cars running of fresh air that the engine ecu ups the idle speed if fans or air con cuts in 

dont forget any power used for whatever  all comes from ................the fuel tank 

Pete

 

[NonMember]

26 minutes ago, Pete Lewis said:

anyone noticed with modern cars running of fresh air that the engine ecu ups the idle speed if fans or air con cuts in

If it's a good, well tuned ECU then you shouldn't notice. The intention is always to exactly compensate for the extra load, so the idle speed remains constant. But knowing how much load the aircon will require and exactly when... can be tricky, so the tendency is to play safe and over-estimate, resulting in a brief increase in idle speed.

[johny]

10 minutes ago, Mathew said:

If your modern idle keeps fluctuating, check when the cam belt is due! 

Hmmm 2019 but the idles nice n steady🙂

[Pete Lewis]

mines a 3 cylinder 1200 makes no noise  so the ears become redundant 

just spec savers for the warning lamps  

Pete

 

[PeteH]

On swmbo`s Qashqai, the A/c cut-in is not noticable, unless you happen to be watching the rev counter at the same time. To be fair, it (A-C) only gets used on cold/wet start mornings to help clear the screen more quickly. "My" little Pug, don`t have a/c😭

Pete

[johny]

Also I think aircon is variable operation now so comes in much smoother than the old electro clutch system of old....

[Iain T]

I never turn my climate control off. I've had climate control on cars for over 25 years and can't see the point of not using it. My wife's dad doesn't turn his a/c on and still has to wipe the moisture off his windscreen! Barmy! In my view the best invention to make modern driving less onerous. I would choose it over power steering! 

Iain 

[Peter Truman]

Climate control and AC seldom off here but I do have to choose recirc air or outside or cabin/windscreen so there is some input reqd