PC's PI set up

[Ashley]

I read Practical Classics September issue with great interest as they ran an article titled "how to service your Lucas fuel injection" based on a TR6.

 

However I disagree with they Tech Tip and the way they suggest that the butterflies should be set. I would be very interested in what the rest of you guys think.

My understanding is that if the butterflies are allowed to slam shut every time the throttle is closed they will make a groove in the in the inlet tube in which they sit. For this reason the link rods should be adjusted so that the butterflies nearly but don't quite close. In this position blocking the end of the air valve pipe should stall the engine or cause it to almost stall. The throttle stop screws can now be set so that they just touch their stops. This way, when over time the adjustments in the vertical link rods have altered the throttle stop screws can perform their function and stop the butterfly damaging it's respective inlet tube.

 

In the article PC's Tech Tip is to remove the throttle stop screws altogether and to their advise in adjusting the butterflies is to have them fully closed.

 

Am I doing it wrong or have PCs given advice on how to damage your PI system?

[Peter Cobbold]

Looks to me that's how to bend butterfly valves.

The butterflies do eventually dig into the manifolds, and leaving the carbon to help the seal is ideal. But... allowing the butterfly disc to take the full force of slamming shut every time -- no not a good idea...for me anyway.

[Tony Millward]

Hi Ashley,

 

A tip I learned (and still practice), from the forums a few years back, is to use a cigarette paper as a feeler guage when setting the butterflies. This will give a 2 thou clearance and avoid the butterflies slamming shut on the ports. The small gap still allows the carbon to seal them in time.

 

I think it was the honourable Mr Alec Pringle who fed us this titbit and it works well.

 

Cheers

 

Tony

[peejay4A]

As far as I recall there are no throttle stop screws on CP cars. I always did my CP car to the book, balanced them off idle then make sure all the butterflies close fully. If they don't then something's out of kilter. I'm not sure about slamming shut. I always eased off on the accelerator rather than allowing the pedal to spring back unchecked. YMMV of course.

[Tony Millward]

Hi Pete, my car is a CP car and it definitely has throttle stops on the injector bodies.

 

Cheers

 

Tony

[Andy Moltu]

The 5s and I think some of the 6s didn't have the air bleed valve for setting tick over.

These have to be set up with the inlets slightly open so would need throttle stops.

I don't think these were removed when the air bleed was adopted to set tick over (with the throttles fully closed at tick over).

Unless you've fitted a jumbo return spring I wouldn't have thought there would be too much risk of twisting the throttle shafts or too much wear in the inlet body.

[Guest ntc]

The butterflies should NEVER BE SHUT or the bodies will be knackerd

Edited August 18, 2014 by ntc

[peejay4A]

Well that's me wrong again. No change there.

[Guest ntc]

No worries Pete you will learn my time on here is running out for a while

[Andy Moltu]

The butterflies should NEVER BE SHUT or the bodies will be knackerd

 

..........eventually - 45 years and waiting on my 6!

Edited August 18, 2014 by andymoltu

[Ashley]

Thanks gents for your input.

I have emailed Practical Classics to advise them of the issue, but as yet have not had a reply.

I'll let you know what they say if I hear anything.

[Quentin]

I must have tried to balance my butterflies more than times in the first two years of ownership using a flow gauges, best guess etc. In the end I used the cigarette paper approach. Set them all up to just gently close onto the papers then locked them off. Bingo! The result was a vast improvement. That was 2 years ago and I haven't adjusted them since. A strong vote from me for this approach.

Quentin