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Vacuum test

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chaza
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Joined: 02 May 2018
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PostPosted: 11:26 - 17 Jun 2018    Post subject: Vacuum test Reply with quote

Hi guys,
I have an ajs dd125e8, I've just done a vacuum test, the reading is fluctuatino around 10hg, does this sound ok to you.
One side tappets are very slightly noisier than the other, but she runs fine. I have noticed she back fires a little when I am changing down, should I be concerned about anything.

Thanks it's appreciated

Chaza
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Teflon-Mike
tl;dr



Joined: 01 Jun 2010
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PostPosted: 16:12 - 17 Jun 2018    Post subject: Reply with quote

AJS DD125.. benly twin derivative engine, single carb.
What vacuum test have you done?
Usual place a vacuum gauge might be found on a motorbike is to measure manifold vacuum when balancing multiple carbs your bike shouldn't have, AFAIK.
What are you trying to do?
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chaza
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PostPosted: 17:01 - 17 Jun 2018    Post subject: Reply with quote

I'm not trying to do anything in particular, I was checking the vacuum routinely, I wasn't sure if the 10hg was correct, it does have two carbs.
Because of the backfire I was unsure if they are set up ok

Thanks
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Evil Hans
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PostPosted: 19:06 - 17 Jun 2018    Post subject: Reply with quote

10 what Hg? mm, inches?

It's pretty meaninglessness anyway, as Tef says you'd only usually use it to compare relative values.
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WD Forte
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PostPosted: 19:43 - 17 Jun 2018    Post subject: Reply with quote

it do got a twin carb
https://www.ajs-shop.co.uk/acatalog/DD150E-4-0109100-E8.JPG

Some fluctuation is normal because of the valves opening and shutting so you wont get a steady reading.
Many gauge lines have wee screw valves before the gauge you trim to minimise this.
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Nobby the Bastard
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Joined: 16 Aug 2013
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PostPosted: 19:58 - 17 Jun 2018    Post subject: Reply with quote

Evil Hans wrote:
10 what Hg? mm, inches?

It's pretty meaninglessness anyway, as Tef says you'd only usually use it to compare relative values.


Agreed.

Also, what revs are you using? More revs means more vacuum.
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chaza
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PostPosted: 08:24 - 18 Jun 2018    Post subject: Reply with quote

Thanks guys, I was doing the test on idle, as I increase the vacuum responds as I would expect.
Anyway, I'll be doing a good road test soon, so I'll see.
As I said earlier it does backfire very slightly when I come down from 3 to 2, but overall she runs ok, my main concern was the carb setup, it's got two that is what led me to check the vacuum.

Cheers men
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Evil Hans
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PostPosted: 10:42 - 18 Jun 2018    Post subject: Reply with quote

Evil Hans wrote:
10 what Hg? mm, inches?


So which was it? If it's mm you probably have a leak somewhere, but I'm assuming it's inches.
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chaza
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PostPosted: 10:57 - 18 Jun 2018    Post subject: Reply with quote

Sorry,
Yes it's inches he
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