PI to carb

[alandrover]

I want to convert the straight six in my Stag from PI to carb. Can anyone point me in the right direction on how to do it and what parts i would need.  :)

[James]

I'd imagine that it's to get rid of the "complexities" of PI.

In which case any set of HS6s straight off a 2500S etc would work great.

[alandrover]

I dont really know much about what is available. Probably a twin set up as the engine is in a standard set up. I am not after a quick motor just a reliable one. One problem that i am getting at the moment is poor starting from cold. I think this is down to the PI system. Carbs are a bit easier for the diy mech to work on.
Also is there a specialist in the West Midlands who might have what i need second hand.

[Tim Bancroft]

I'd be tempted to spend a hour or so with the car and a chap who understands the Pi system. Admittadly the car will be more economical and easier to tune on a set of HS6s, but think about the power and of course the noise.

[thescrapman]

I suggest to ring Dave Pearson at Canley Classics, and make an Appt to pay him for an hour or 2 of his workshop time.

It may be a simple as poor adjustment of the cold-start lever.

Or maybe just technique ona cold morning.

Cheers

Colin

[Glenn]

Seems a shame to ditch the PI.  Having said that I'm sure a 2000/ 2500 owner will give you a decent sum for all the PI kit, particularly if you keep it complete.

It's easy enough to do if you are completely sure that's the way forward.  SU HS6s are a good way to go to minimise the loss of power and torque you will experience - you might want to measure first as on the saloon there is very little clearance between airbox and o/s suspension turret.  The late saloons with these carbs use a different engine mount crossmember which has the mount holes offset to the n/s.  You can emulate this by drilling new holes if you need to.  Use a standard 2500s plenum and air filter box.

Your PI pump will deliver the fuel at too high a pressure.  You could go for a Facet or similar mounted in the same place using the same wiring.  I used a standard 2000 AC cam driven pump, glass bowl type.  This bolts to the engine block beside the distributor.  As standard there is a metal pipe that runs from this pump behind the coil and round the front of the engine clipping onto the water pump.  Ditch the PI petrol return line and plug this at the tank.

Get a new inlet/ exhaust manifold gasket, don't muck about trying to reuse the old one as it will probably leak.  You could run the car very successfully without connecting the inlet manifold plumbing to the cooling system.  Unlikely to be a problem unless you do a lot of driving in very low temperatures.  If you are fussy however you will need to remove the blanking plug from the thermosat housing and fit a suitable outlet to connect a hose to the inlet manifold.  You will also require a different metal pipe (running behind the exhaust manifold from water pump to heater hose) which has 2 outlets instead of the PI's one.  Chris Witor can sell you these in stainless steel and while you're at it he will supply a pair of carb needles to ensure you have the correct mixture throughout the rev range.

I think it is best to keep the PI distributor to make sure you get the optimum certrifugal advance through the rev range (providing your one has the vacuum advance capsule).  You will need a drive dog from a 2500 carb engine.  You can take the PI drive dog to bits and cut it to make it a suitable length if you need to.

A picture of a saloon setup will help you plumb it all in.  You'll get plenty of help here if you get stuck.  Good luck.

[Richard B]

alandrover wrote:

One problem that i am getting at the moment is poor starting from cold. I think this is down to the PI system. Carbs are a bit easier for the diy mech to work on.

Shame to convert it, I would suspect worn injectors, these will leak petrol from the injector leads whilst the car is standing. When you try to start it you are having to re-prime the system before it will start (guess who's had this problem) :)  

With the engine running take the injector captive plates off and pull each injector off in turn to see if there is a nice spray of petrol or whether the injector dribbles. Watch where you point the injectors whilst doing this!

Exchange injectors can be got for £20 each, you probably don't need  6 new ones.

[shenderson]

I ran a PI for 15 years and have set up a few in my time; I'm in Birmingham and willing to take a look.  Now running a Stag...

Send me a PM if you want any help.

Steve H

[piman]

Hello Alan,

There is a thread on the Triumph 2000 register forum from a member who wants to convert from carburettors to P.I.
Maybe you should get together.

As a P.I. driver, normally cold starting is a plus point of the set up. virtually instantaneous no matter how cold.

Alec

[alandrover]

Oh wow what lot of replies so quickly.
Well it seems the general concensus is to keep the PI system.  So i think i will have to look further into this option. Shenderson i think i may need to take you up on your offer, i will pm you.
As far as the cold starting is concerned, it will start under its own battery if i turn the ignition on and off several times allowing the pump to prime the fuel lines. The other thing which may not be connected is that the car dont drive smooth. It will accelerate fine but just cruising along at 40/50 it feels lumpy and not at all how a six pot should feel.
I put this down to the PI system perhaps through ignorance. I have fitted an Aldon ignitor electronic ignition to rule out any trouble with points etc. New plugs and leads have also been fitted.
Regards.
Simon.

[piman]

Hello Simon,

although electronic ignition requires less maintenance than points it does not eliminate ignition problems. The distributor should be in good condition and be the correct unit for your engine. Over the years distributors or internal components may have been replaced by whatever comes to hand. It is worth checking that yours is in good condition and is suitable for your engine.
The P.I. system earned an early reputation for unreliability because garages were not familiar with the system so it often got the blame. For a P.I. to run correctly, everything in the engine must set correctly first.

Alec

[Richard B]

Quote:

it feels lumpy and not at all how a six pot should feel

Definitely sounds like the injectors are dribbling. PM your phone number if you want to chat about testing them. The lumpyness is because there are large drops of petrol getting into the cylinder, not the fine atomised spray that is required for smooth running.  


ps could be the metering unit need overhauling (faulty non-return valves), but I would suspect/check the injectors first.

[alandrover]

Thanks for the help all. I have ordered a set of injectors to cure the starting and lumpy running. So when the postman turns up with them and it stops raining i will fit them. Then i will report on the repair.
As you can see i am not changing to carbs as so many people think PI is far superior.
Thanks again.  :)

[Richard B]

Alan, did you check them before ordering a replacement set?

If so how bad were/are they.

[alandrover]

Hello there.
The postie turned up today with a nice set of injectors from Malcolm @ prestige developments. Before i fitted them i changed the fuel filter so it is all clean. The injectors were a doddle to fit ensuring they were bled first before fitting. The engine now runs lovely and smooth. The only thing to test now is the cold starting after been left for a few days.
Richard, no i didnt check them first before replacing them. I suppose i should have done but too many people suggested the injectors were at fault as all of the evidence pointed towards them.
The injectors i took out were rather odd. Two came out with little spikes on the end the rest were blunt. I dont know if they were supposed to be like this or they had burnt or rotted off. All the new ones are of the spikey variety.
Thanks again for all the help. Speak soon.
Simon.