THROBBING/PULSING

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CHRISYD
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THROBBING/PULSING

Post by CHRISYD »

While I was tinkering with the excel today I noticed the hose between the servo and engine was throbbing or pulsing when you held it with engine running. It felt like you were hitting it with a hammer. Is this normal? cant say ive noticed it before.
I REALISED YOU CANT LIVE WITHOUT A LOTUS!!!

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AndyD
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Re: THROBBING/PULSING

Post by AndyD »

Hi,

Yes it certainly is normal. It's the suction of the 4 stroke cycle amplified through a small hose.

The reason I know is that if the non-return spring on the servo vacuum connection (white connector from this hose at the servo) goes weak the sealing ball rattles with each pulse and sounds like a serious top end issue. I thought I had bought a pup...

Fortunately a new non-return is only a tenner on eBay and sorted it.

Andy

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Re: THROBBING/PULSING

Post by RED BARON »

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Last edited by RED BARON on Mon Apr 20, 2020 19:00, edited 1 time in total.

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Re: THROBBING/PULSING

Post by AndyD »

Hi Ian

Mine is Girling (86 SE), but oddly enough and just to confuse matters the original nrv was white as you correctly identify it is on the Bendix.

The new one is black, eBay item no 392068577346 but I note it's now £15, not the 10 I paid.

The hose lengths are really useful thanks - I suspect mine has been shortened as it was so sensitive that tightening the clips made a difference too. I will check it now I have the dimensions ☺️

Much appreciated,

Andy

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Re: THROBBING/PULSING

Post by RED BARON »

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Last edited by RED BARON on Mon Apr 20, 2020 19:01, edited 1 time in total.

richardw
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Re: THROBBING/PULSING

Post by richardw »

As the engine is fed through four separate intake runners, the servo vacuum take off only takes its vacuum from the one it is attached to, thus creating the 'throbbing' sound you have noticed. I believe it can also be heard as a speed related 'ticking' sound behind the dash.

Good info about the non return valve and hose length - thanks AndyD and Red Baron.

Cheers, Richard
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CHRISYD
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Re: THROBBING/PULSING

Post by CHRISYD »

Thanks for the info. I thought it might have been sucktion from the engine (honest!) but wasent 100% sure. going out to check the length of my hose now!!
I REALISED YOU CANT LIVE WITHOUT A LOTUS!!!

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Re: THROBBING/PULSING

Post by Pete Boole »

Why does the length of the hose make any difference?

Pete

CHRISYD
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Re: THROBBING/PULSING

Post by CHRISYD »

Dont know but mines only 630mm long.
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Lotus-e-Clan
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Re: THROBBING/PULSING

Post by Lotus-e-Clan »

Mines only 150 mm :(
Peter K

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Re: THROBBING/PULSING

Post by RED BARON »

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Last edited by RED BARON on Mon Apr 20, 2020 19:02, edited 1 time in total.

CHRISYD
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Re: THROBBING/PULSING

Post by CHRISYD »

Lotus-e-Clan wrote:
Sun Apr 19, 2020 20:08
Mines only 150 mm :(
:wink:

Is it cold in Gods own county today?
I REALISED YOU CANT LIVE WITHOUT A LOTUS!!!

Pete Boole
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Re: THROBBING/PULSING

Post by Pete Boole »

CHRISYD wrote:
Mon Apr 20, 2020 11:48
Lotus-e-Clan wrote:
Sun Apr 19, 2020 20:08
Mines only 150 mm :(
:wink:

Is it cold in Gods own county today?
:lol: :lol:

Pete

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MetBlue
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Re: THROBBING/PULSING

Post by MetBlue »

Hi RB. I saw your earlier post. It was far from clear to me where the frustration had arisen from.
I've come and gone from the forum over the last couple of years, and find the contributions from many regular and senior posters invaluable in my persuit to return another of our cars to the road.
A bit of light hearted banter, especially in these challenging times can't be a bad think as long as it doesn't turn personal and I'm sure nothing in this thread has been posted with such intent.
Hopefully you'll soon be back
What goes together.... Must come apart.

RED BARON
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Re: THROBBING/PULSING

Post by RED BARON »

MetBlue
Just look at the two comments above yours.
It was said on another site that so many have left this site.
The type of some posters left on here now, means I do not want to lower to that level.
I left before because of the "P" taking I just think if you can't say something good then keep your gob shut.
Since Angus left the reason is probably the same.
I don't need this site as I get all my technical info direct elsewhere, and just thought I could help others.
I am gone for the last time now, as I don't need it so hope you people are now satisfied.

RED BARON.

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