SuzukiSavage.com - Vacumn Gage or Tach ?

Routy

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Re: Vacumn Gage or Tach ?
Reply #15 - 03/18/10 at 06:19:18

If its a tune up gauge like I have, it doesn't have restriction in it.
I'll find out about the "SunPro" in a few hrs. I'm sure w/ restriction it will stabilize at higher Rs.
jabman wrote on 03/18/10 at 05:14:13:

i just fitted one to my vac hose it flicks from nothing to full so fast the needle is a blur more work is needed here it looks

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

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Routy Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 2280 Winston Oregon Gender:	Re: Vacumn Gage or Tach ? Reply #16 - 03/18/10 at 20:12:59 Got it done. Sure looks nice, but I don't think it will make a good shift indicator. I didn't get a chance to really try it out at speed. More later.
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Routy

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Re: Vacumn Gage or Tach ?
Reply #17 - 03/19/10 at 05:23:00

Shown....10" Vacuum at dead idle.
At 1500 R's it dropped to 7-8"
That seems low, but I've never put a vac gauge on a single cyl either.
The reading was quite irratic at idle,.....0-15 and stabilized some at 1500 R's, ...like 8-12. The restrictor in the gauge was .030, so I added a .020 in the hose, and now it is perfectly normal w/ reaction time still ok. I'll try it at speed when the weather warms a little. But if it fails to serve the purpose, I have another place for the gauge, and my custom made ss mount will hold a tach just fine.

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

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jabman Senior Member Offline Posts: 411 England Gender:	Re: Vacumn Gage or Tach ? Reply #18 - 03/19/10 at 05:35:39 hey my vac gauge goes from 0-30 like that one what did yer do to make it work? does it need blocking of with a 0.5mm hole in the middle?
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Charon

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Re: Vacumn Gage or Tach ?
Reply #19 - 03/19/10 at 06:01:31

I am going to make a guess, here. I am guessing your vacuum gauge is "averaging" or "integrating" the vacuum in the manifold. During the intake stroke, about 180 degrees, there is a pressure reduction or vacuum in the manifold. During the other strokes, about 540 degrees, the pressure is near atmospheric. So vacuum is present only about 25% of the time. The restrictor in the vacuum hose (or in the gauge) "damps" the gauge response so the needle responds more slowly, and you see the average vacuum instead of the instantaneous vacuum. I expect this phenomenon would exist in the manifold of almost any multi-cylinder engine with individual carburetors and manifolds, and no balance plumbing.

I have to wonder whether this very pulsatile flow and vacuum makes setting carburetors more difficult. I wonder whether the throttle slide on CV carburetors is constantly jittering in response to it.

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Eschew obfuscation.

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Routy

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Re: Vacumn Gage or Tach ?
Reply #20 - 03/19/10 at 16:01:51

Your guess about average may be correct. Like said I have never done this on a single cyl. But I'm convinced there is nothing wrong w/ the bike,.....as to the low vacuum. I still hqave to road test it yet.
Charon wrote on 03/19/10 at 06:01:31:

I am going to make a guess, here. I am guessing your vacuum gauge is "averaging" or "integrating" the vacuum in the manifold. During the intake stroke, about 180 degrees, there is a pressure reduction or vacuum in the manifold. During the other strokes, about 540 degrees, the pressure is near atmospheric. So vacuum is present only about 25% of the time. The restrictor in the vacuum hose (or in the gauge) "damps" the gauge response so the needle responds more slowly, and you see the average vacuum instead of the instantaneous vacuum. I expect this phenomenon would exist in the manifold of almost any multi-cylinder engine with individual carburetors and manifolds, and no balance plumbing.

I have to wonder whether this very pulsatile flow and vacuum makes setting carburetors more difficult. I wonder whether the throttle slide on CV carburetors is constantly jittering in response to it.

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

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Routy

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Re: Vacumn Gage or Tach ?
Reply #21 - 03/19/10 at 16:11:43

I machined a round pc of plastic 3/8 " long to the same diameter as the "T". Then I drilled it w/ a number drill at .020 then I used the T to push it into the hose. And It is 100% stable at all speeds.

jabman wrote on 03/19/10 at 05:35:39:

hey my vac gauge goes from 0-30 like that one what did yer do to make it work?

does it need blocking of with a 0.5mm hole in the middle?

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

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miker Junior Member Offline SuzukiSavage.com Rocks! Posts: 53 Texas, USA Gender:	Re: Vacumn Gage or Tach ? Reply #22 - 03/20/10 at 07:10:29 If you need a restrictor, find a friend in the commercial Air Conditioning business. A restrictor costs about $0.30, and is available in many sizes, and you can get restrictor tee fittings as well.
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T Mack 1 - FSO Serious Thumper Alliance Member Offline sold 2001 LS650 for a 1986 XLH1100 Posts: 2919 Emmaus,Pa Gender:	Re: Vacumn Gage or Tach ? Reply #23 - 03/20/10 at 07:21:31 A nice ananlog (dial) tach from Drag Specialties, Around $80 with the mounts. Then you have something to check the idle RPM to keep it above 1000 rpms. Heck, after a while I started to use the tach as a Speedo since it was higher and easier to look at.
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