Background:
Reconditioned A+ 998 converted to unleaded
RA40 exhaust system with extractors ( bought as a stage one kit)
Electric fuel pump with the capacity of 4 to 6 psi
Second hand twin 1 ¼” Carby’s that were taken from a running mini (engine size unknown)
Pancake filters
The engine will idle easily.
The engine will respond and hold revs when the accelerator is pressed when stationary
The carby’s, including the fuel bowls and linkages, are clean and function correctly.
The vacuum is connected and working
Using the colour tune I can get all cylinders showing a blue colour.
Fuel bowl setting correct and bowls correctly filling with fuel

The issue:

As soon as I drive off and the revs begin to increase the engine starts to die. I am not talking race car increased revs I mean that the car simply starts to die off under normal operation.

I can get it to second or third gear however very slowly being careful to keep the revs as low as possible, changing gears miles too early.

What I don’t understand, and can’t figure out, is that the car shows no sign of dying off while stationary and the revs increase, however while under load (driving on a flat road. I haven’t even contemplated trying a hill) the car seems to struggle as soon as the revs increase.

Not enough fuel? Air? Too much perhaps? Could it be the needle?

I have the Carby’s as tuned as best I possibly can and to listen to the car idle and look at the colourtune blue colour (and equal air intake) I would have thought that the Carby’s were set correctly.

I am going crazy searching the net for suggestions.

Also note that the car has been a entire rebuild so it has never run before.

I have checked and rechecked the tuning over and over and while setting them up I can get what appears to a good tune but it just doesn’t like to rev while moving.

Any ideas?

It could be advance (vacuum or mechanical), the also carbs need to have the correct needle, dashpot spring and oil (what do you have now?). At the moment it sounds like it is tuned well at idle, but not necessarily under load. Similar story with the fuel bowls, they might be fine at idle but are emptying quicker than they are filling? Could be a manifold/gasket leak somewhere too. What type of pancake filters do you have? The choke is adjusted properly too?

Are all the brakes adjusted correctly? Possibly your brakes are binding?

There are some SU guides here:
http://sucarb.co.uk/technical-hs-type-c ... ng-general
http://sucarb.co.uk/technical-hs-type-c ... ning-multi

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Coil... BTDT

Cheers, Ian

Thanks Timmy,

Thanks for the link to the guides. I have seen simular ones in my search for answers and pretty much have followed them step for step. I think it may very well be the needle. If the carby’s came off a bigger engine the needle could be just wrong. I am not sure what the needle type is and the springs have lost all their colour so can’t tell what type they are. I am using SU damper oil now and have switched between this and various heavier oils thinking it was the damper. With the fuel bowls having an electric pump rated with a psi higher than normally required I would have thought the fuel bowls would be filled considerably quick, well enough to keep up with a 998.
I am doubting, but ruling out, a manifold or gasket leak as all this have been rebuilt and tested considerably while being installed.
The brakes are all new, working and not binding. Good thought though.
As for the pancake filters, I would have to measure them. They are just flat round looking filters that seem the same as all other pancake filters around.
The choke has been adjusted as per the tuning guides out there.
I may look at the fast idle adjustment again, it may be throwing things out and can’t remember playing with that since the first time to adjusted the carbys’s.
Thanks Again

Coil you say....hmmmm a very interesting concept.
I have a feeling that I bought the coil prior to realising that that the car has an electronic distributor.
I am going to assume that this would create some issues

You may indeed have other problems (what are those needles, and are they the right match for your engine), but a weak spark will cause missing under load, or a complete failure to fire.

To answer one of your questions, revving the car without load is not the same as driving up a long hill under high load.

The coil only rises to the minimum amount of volts it needs to jump the spark plug gap. It rises and drops in a sharktooth pattern. It will only rise to what it needs before it breaks over, and then it will drop away dramatically. If there's a fault in the ignition system (sparkplug condition/gap, leads, cap, rotorbutton damage), then the voltage may never rise high enough.

When you have a car under no load, or very light load, the cylinder pressure is quite low as the butterflies are shut and cylinder pressure is low. At low pressures, a spark finds it quite easy to break over the spark plug gap as break over voltage is proportional to the density of the air it is trying to traverse. The lower the air density, the lower the voltage required to break over the gap.

Once you open the butterfly, then large amounts of air flood in, and the cylinder pressure (air density) rises dramatically under compression. The break over voltage for the spark cab vary by thousands of volts, which in a poorly performing ignition system it may not be able to attain due to faults.

Also, if there is a problem with the components due to dirt or moisture causing tracking, then the voltage will rise until it can find another path to ground. it may choose to pass through the dizzy cap, or the rotor button, the leads or the plugs to the engine block. Spark don't care. Spark goes down the easiest path. As it does so, it creates carbon, carbon is a great conductor, so the situation only gets worse in the case of dizzy caps and rotor buttons.

With respect to your SU, you can tune just about any engine with just about any needle at idle. Its just that once you open the butterfly under load, and the damper piston begins to rise, then any result is possible and all of them are wrong without the right needle. The air/fuel mixture is going to be anything but correct. And much the same thing goes with the needle. Under load is not the same as not under load. For a given rev as a comparison, you will need different amounts of butterfly opening. This changes the volume of air consumed by the engine, which alters the height the SU piston will rise to. Hence the needle is very important.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Here are a few needles to compare to http://www.7ent.com/pages/articles-tech ... eedle.html

997 Cooper GZ / AH2 / EB
998 Cooper GY / M / GG
998 Clubman GX / M / GG

If you think it is the mixture, when you try to take off and the engine starts to struggle, pull out the choke. This will add more fuel so if the engine feels better, you need more fuel, if the engine feels worse, you need less fuel. Only do this at operating temp so you know what the engine actually needs. It will give you something to aim for if the problem is indeed carby related.

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina

Throwing another spanner in the works - I think your pump pressure might be on the high side.

45DCOE are meant to run a maximum of 3.5psi, and from memory SUs seats tend to be on the softer side.

We need to know what needles it has.
Also, check the hoses on the main jets. If they are black with no spring cover, they are Fuel Miser jets. These rubbers can swell shut if used with some fuels; it happened to me once, I barely got it home from the Caltex servo after filling with `Vortex 98?'. Supposedly.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks for the ideas. I will check out the needles and find out what they are. I am going to buy a new coil as Ian suggested and Mick explained (I appreciate that) adn I will do some investigating into some of the other ideas such as the jet hoses and the choke.
Any receonmendations for a better coil?

I like 12V Bosch coils, GT40 is good. Or a Bosch blue one. Don't use a GT40R (marked `use with resistor') unless you fit a 1.5 ohm ballast resistor as well.
Check the plug leads' resistance, cheap leads with a carbonized string core increase their resistance as they age. I bin them if over 5K ohms. Ditto the coil lead.
I use Bosch inductive core leads, this type don't have the problem.
Graham Russell sells a tailored set of inductive core leads for A series that fit neatly.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Some good and interesting ideas put forward, but the first thing I'd check (and it's free) is fuel flow.

Grab a screwdriver, go for a drive and when in a quiet and safe place load it up with a fairly wide throttle so it dies until it just about stalls or stops then turn the ignition off and press the clutch in before you lift off the accelerator.... then coast to the side of the road.

Lift the bonnet and take the top off a float bowl. If the fuel is not up at the height it should be, you have found the problem... then just need to find the cause.

It is not the fuel pressure that is as important as the flow. The pressure just helps achieve the flow you need by overcoming the restrictions such as the needle and seat.

If the fuel bowls are not full on the road-side test, once you get it home you can check the fuel flow to the engine bay into a bucket or similar, and if it is not fantastic then start looking further.

If it does look like a fuel flow problem, my money would be on a restriction/blockage in the pick-up pipe laying in the bottom of the fuel tank. Especially if the car has been laid-up for a while.

Tim.

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Don't listen to what I am saying... just understand what I mean.

I will get onto all this over the weekend and report back. Thanks everyone.

I am getting really confused and the more I Google the more my head hurts.

Although I am going to look into advice that has been given regarding the carbys/fuel supply, all this needs to wait until the weekend. In the meantime I am seeking to replace the coil as Ian and Mick suggested.

The current coil is the GT40T which can be either bad or not correct for my car. I have read in some places that based on my engine/ignition system that I should be using a different coil however in other places it reconmends coils like the GT40T. I have read that electronic needs 1.5 ohms and other that claim sports coils at 3 ohms would be fine. Is the GT40T classed as sports coil?

Can anyone give me a heads up on what they are using? My engine is a a reconditioned 998cc A+ built somehwere between 1980 and 1986 (yeah I know specifics would be handy) and I can't even tell you what car it came from. I am using the 59d electronic distributor.

I just want to buy a new one and be done with it but dont want to cause more problems for myslef.

Once I have this power under load problem sorted I will be ready for the roadworthy.