tr3a Carburettor pistons

[Richardtr3a]

I have a problem with the pistons on my H6 carbs. I am trying very carefully to tune the front carb after changing the needle because the old one was bent. The front piston falls smoothly and there is a metallic click. The rear piston fall much faster and there is a loud metallic click. I have polished the front one and tried it without the damper or the jet in place and it is slow.

 

Which one is correct ? I would like both to be the same. The leaks have gone away and the carbs were overhauled last year.

 

Any advice would be very welcome. Thanks Richard

Edited April 2, 2018 by Richardtr3a

[Fireman049]

Hi Richard ~

 

Try swapping the pistons around. This is what I did with my 3A. Forget the old wives tale that pistons shouldn't be swapped!

I attach video's showing the process. I hope it works?

(The second Video is more informative).

 

Tom.

https://youtu.be/UES5tpjuY2g

Edited April 2, 2018 by Fireman049

[RobTR3]

I've had similar issues with my carbs. The front carb. piston falls nicely with a clear sharp metallic click. The back carb. piston hits the bridge with more of a soft dull clunk!. Even testing it free of the carb. body, the piston slides at a slower rate within the chamber than the front carb. I tried swapping them around but it made no difference. I was satisfied the needle was centred accurately and the car runs fine so I am not concerned.

 

I believe the piston and chamber are matched during manufacture/assembly and certainly if you buy new they are sold together. It maybe that at sometime in the past they have been renewed interchanged - piston/chamber - and they aren't quite right as a pair. Maybe that's your issue as well.

 

Rob

[BlueTR3A-5EKT]

I have had precisely that issue of one piston dropping faster than the other - simple swap rectified it.

Peter W

[Tonyloz]

Are your springs matched?

[Lebro]

The drop test should be done with springs removed, & jet fully raised.

 

Bob.

[Richardtr3a]

Thanks to all answers. I have swapped the two covers and now they both fall with a fast movement and a clear click. It has not worked like that for two years. They must have been swapped over when the carbs were rebuilt.

 

So now I am on to tuning, which should be much easier. Watch this space for any new problems.

 

Thanks again

 

Richard

[Fireman049]

Told you so!

All this bullshit about not swapping pistons/chambers!!

 

Tom.

[Lebro]

Surely the point is that someone had swapped them which was why one was slower than the other ?

 

Bob.

[stuart]

Surely the point is that someone had swapped them which was why one was slower than the other ?

 

Bob.

Exactly, never assume.

Stuart.

[Richardtr3a]

Both pistons working well and after priming with new petrol the engine fired up, with the choke only on the front carb. I am hoping that this will save the jet seals at the back.

 

Soon it will be a road test and I should be able to make the local car show on 21 April and Le Mans and the IWE which are a bit close together.

 

Next stop is to fit the overhauled rev counter and the sat nav socket with a positive earth.

 

Thanks Richard

[Lebro]

Why positive earth ?

[Richardtr3a]

My car still has a dynamo and positive earth. I could not find a sat nav to suit so I have wired it to work and have mounted it on the underside of the glove box away from any metal parts. It seems to work OK. It also has a fuse.

 

Lucas oil sounds good. has anyone else tried it? Leave a review here.

 

Thanks Richard

[Ian Vincent]

Because it was a nice sunny day in the SW I had a play with my carbs (HS6) and found that although they were close in terms of the 'drop time' of the pistons they were better when I swapped them the other way round. Put them back on the car and took it for a decent run and it is definitely idling and running a but smoother.

 

Thanks for the suggestion.

 

Rgds Ian