 How much vacuum @ what RPM???, Checking my new MPS |
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| TJB/914 |
 Aug 19 2003, 08:33 AM
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#1
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Mid-Engn.  Group: Members Posts: 4,330 Joined: 24-February 03 From: Plymouth & Petoskey, MI Member No.: 346 Region Association: Upper MidWest 
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Bought a new MPS and my 1974 2.0 liter (Modified) F.I. Spliced a vacuum gauge into the hose connecting the MPS and got the following readings.
500 RPM @ 5" Vacuum 1200 RPM @ 10" Vacuum 2000 RPM & above over 15" Vacuum. I adjusted everything and it runs great without the past idle problem being to low. My question to the experts what is the correct vacuum pressure supposed to be with a stock cam?? and at what RPM?? I have a modified cam & I believe my vacuum reading is a little low but it runs ok with my latest adjustments. Tom |
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Replies(1 - 2)
| Bleyseng |
Aug 19 2003, 08:44 AM
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Aircooled Baby! Group: Members Posts: 13,034 Joined: 27-December 02 From: Seattle, Washington (for now) Member No.: 24 Region Association: Pacific Northwest |
At idle you should have 15-17 inches of Vacuum with a steady needle.
WOT (wide open throttle) O for a sec then whatever. At idle is the key on a Djet car since that sets the range the MPS reads. Old motors lose vacuum at idle so low vacuum screws with the MPS's ability to set the mix right. New motors with cams that have non stock vacuum signitures also are a problem. To test a MPS, use a vacuum pump with a gauge and pump it to 15hg and let it sit for 5 minutes. If it holds the vacuum its a excellent unit, if it s l o w ly leaks down a few pounds if ok. If it drops like a rock its junk. Geoff |
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| KenH |
Aug 19 2003, 09:15 AM
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Senior Member Group: Members Posts: 680 Joined: 16-January 03 From: Gilroy, CA Member No.: 156 |
The vacuum needs to be measured with the engine under load. The throttle position for an unloaded engine @ 5000 rpm is a lot different than the position it will be in going down the road at 100 mph.
Ken |
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