The Ford Barn

36tudordeluxe · 10-05-2016, 06:19 PM

Does 13" of vacuum sound about right?

40 Deluxe · 10-05-2016, 09:21 PM

What is your idle RPM? That affects the vacuum reading.

Ol' Ron · 10-05-2016, 09:33 PM

13 is alittle low, but not much. The last one I checked was 15. I can ask My friend Rob what his 294 is.

Talkwrench · 10-05-2016, 09:40 PM

Twin carbs or single ?

40cpe · 10-05-2016, 09:45 PM

Quote:

Originally Posted by 40 Deluxe

What is your idle RPM? That affects the vacuum reading.

and initial timing

36tudordeluxe · 10-05-2016, 10:01 PM

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Idle was at 600 RPM, will try at 750RPM, single 4 barrel with air cleaner on and initial advance not sure about, just set it so it would fire right up.

Talkwrench · 10-05-2016, 10:47 PM

Try advancing until you get your highest reading then back it off about 1 1/2Hg [1.5Hg] then see what it is. Shouldn't need to idle that high ..

36tudordeluxe · 10-05-2016, 11:43 PM

Quote:

Originally Posted by Talkwrench

Try advancing until you get your highest reading then back it off about 1 1/2Hg [1.5Hg] then see what it is. Shouldn't need to idle that high ..

I'll give it a go tomorrow at 600 RPM and see what I get.

40 Deluxe · 10-06-2016, 02:29 AM

Altitude and compression ratio also factor in.Vegas is about 2,000 ft., I think. So the effect should ber relatively small. But the lower the compression, the quicker altitude affects the vacuum reading, and performance.

Ol' Ron · 10-06-2016, 08:03 AM

Initial advance is not that important, as long as the engine starts. Then the Vac adv will add enough advance for idle. However that's part of the tuning process. setting the AF and ign curves. Done right you'll have a fine running engine with good power and economy. A good starting point is: 2-4 initial. 16 mechanical all in by2000. and 8 vacuum.
With the right AF in the carb youll be in the ballpark for most engine combinations.

36tudordeluxe · 10-06-2016, 10:14 AM

Compression ratio is about 8.2:1. Am only getting about 9 MPH, don't have a 5th gear, running a 3.55 in the rear and large diameter tires. Currently have setup #11 in the EDELBROCK manual, am going to try #10 with different metering rods but same jets.

40 Deluxe · 10-06-2016, 04:55 PM

Quote:

Originally Posted by 36tudordeluxe

Compression ratio is about 8.2:1. Am only getting about 9 MPH, don't have a 5th gear, running a 3.55 in the rear and large diameter tires. Currently have setup #11 in the EDELBROCK manual, am going to try #10 with different metering rods but same jets.

Changing main jets and/or metering rods will not affect idle mixture nor vacuum readings unless the throttle opening is so large that fuel is being pulled from the venturiis. At idle only the idle circuit should be feeding the engine. I think your Edelbrock manual has diagrams showing this.
Only 9 MPG means you have other problems than idle vacuum.

Ol' Ron · 10-06-2016, 05:24 PM

Set that up on #8 and give it a try

36tudordeluxe · 10-06-2016, 05:48 PM

Quote:

Originally Posted by 40 Deluxe

Changing main jets and/or metering rods will not affect idle mixture nor vacuum readings unless the throttle opening is so large that fuel is being pulled from the venturiis. At idle only the idle circuit should be feeding the engine. I think your Edelbrock manual has diagrams showing this.
Only 9 MPG means you have other problems than idle vacuum.

Jets and rods are for the bad MPG, knew it wouldn't solve low vacuum.

36tudordeluxe · 10-06-2016, 05:49 PM

Quote:

Originally Posted by Ol' Ron

Set that up on #8 and give it a try

Will try it. BTW, the needles isn't a steady 13, it bounces around between 11 & 13.

Ol' Ron · 10-06-2016, 10:01 PM

You might waht totake a compression check, you might have a bad cylinder.

36tudordeluxe · 10-07-2016, 12:01 AM

Quote:

Originally Posted by Ol' Ron

You might waht totake a compression check, you might have a bad cylinder.

Going to do that first thing in the morning.
Last time I checked cold was 1- 150 2 -150 3 -145 4 -150 5-154 6-140 7-142
8--135

37don · 10-07-2016, 12:24 PM

If you are testing vacuum with a piece of hose on your gauge just bend the hose to restrict the line and the needle will settle down. iI have between 14 & 15 with my 276 and l 100.
Regards, Don.

40 Deluxe · 10-07-2016, 12:29 PM

Quote:

Originally Posted by 37don

If you are testing vacuum with a piece of hose on your gauge just bend the hose to restrict the line and the needle will settle down. iI have between 14 & 15 with my 276 and l 100.
Regards, Don.

14 or 15 at sea level in Rhode Island would easily drop to 13" in Las Vegas at 2,000 ft. + above sea level.

36tudordeluxe · 10-07-2016, 02:18 PM

I was being too optimistic about my 13" reading, more like 11-12. At my location in the valley here am about 2500' ft. ASL

UPDATE: Have run cold compression test and have lost about 5lb. on average on all cylinders except cyl. #5 which lost 25lb. from 140lb to 115lb. The other cylinders in the 130lb.-145lb. range. Would the low vacuum be explained by the one weaker cylinder? Am going to put in a little more advance at idle and see if this helps.

10-05-2016, 09:21 PM	#2
40 Deluxe Senior Member Join Date: May 2010 Location: now Kuna, Idaho Posts: 3,818	Re: Vacuum reading 276 L-100 cam? What is your idle RPM? That affects the vacuum reading.

10-05-2016, 09:33 PM	#3
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Vacuum reading 276 L-100 cam? 13 is alittle low, but not much. The last one I checked was 15. I can ask My friend Rob what his 294 is.

10-05-2016, 09:40 PM	#4
Talkwrench Senior Member Join Date: Aug 2012 Location: Perth, Western Australia Posts: 2,706	Re: Vacuum reading 276 L-100 cam? Twin carbs or single ? __________________ *"Came too close to dying to stop living now!"*

10-05-2016, 10:01 PM	#6
36tudordeluxe Senior Member Join Date: Feb 2012 Location: Las Vegas, NV Posts: 1,260	Re: Vacuum reading 276 L-100 cam? Sponsored Links (Register now to hide all advertisements) Idle was at 600 RPM, will try at 750RPM, single 4 barrel with air cleaner on and initial advance not sure about, just set it so it would fire right up. Last edited by 36tudordeluxe; 10-05-2016 at 10:17 PM.

10-05-2016, 10:47 PM	#7
Talkwrench Senior Member Join Date: Aug 2012 Location: Perth, Western Australia Posts: 2,706	Re: Vacuum reading 276 L-100 cam? Try advancing until you get your highest reading then back it off about 1 1/2Hg [1.5Hg] then see what it is. Shouldn't need to idle that high .. __________________ *"Came too close to dying to stop living now!"*

10-05-2016, 06:19 PM	#1
36tudordeluxe Senior Member Join Date: Feb 2012 Location: Las Vegas, NV Posts: 1,260	Vacuum reading 276 L-100 cam? Does 13" of vacuum sound about right?

10-06-2016, 02:29 AM	#9
40 Deluxe Senior Member Join Date: May 2010 Location: now Kuna, Idaho Posts: 3,818	Re: Vacuum reading 276 L-100 cam? Altitude and compression ratio also factor in.Vegas is about 2,000 ft., I think. So the effect should ber relatively small. But the lower the compression, the quicker altitude affects the vacuum reading, and performance.

10-06-2016, 08:03 AM	#10
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Vacuum reading 276 L-100 cam? Initial advance is not that important, as long as the engine starts. Then the Vac adv will add enough advance for idle. However that's part of the tuning process. setting the AF and ign curves. Done right you'll have a fine running engine with good power and economy. A good starting point is: 2-4 initial. 16 mechanical all in by2000. and 8 vacuum. With the right AF in the carb youll be in the ballpark for most engine combinations.

10-06-2016, 10:14 AM	#11
36tudordeluxe Senior Member Join Date: Feb 2012 Location: Las Vegas, NV Posts: 1,260	Re: Vacuum reading 276 L-100 cam? Compression ratio is about 8.2:1. Am only getting about 9 MPH, don't have a 5th gear, running a 3.55 in the rear and large diameter tires. Currently have setup #11 in the EDELBROCK manual, am going to try #10 with different metering rods but same jets.

10-06-2016, 05:24 PM	#13
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Vacuum reading 276 L-100 cam? Set that up on #8 and give it a try

10-06-2016, 10:01 PM	#16
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,985	Re: Vacuum reading 276 L-100 cam? You might waht totake a compression check, you might have a bad cylinder.

10-07-2016, 12:24 PM	#18
37don Senior Member Join Date: May 2010 Location: South Kingstown, R.I. Posts: 262	Re: Vacuum reading 276 L-100 cam? If you are testing vacuum with a piece of hose on your gauge just bend the hose to restrict the line and the needle will settle down. iI have between 14 & 15 with my 276 and l 100. Regards, Don.

10-07-2016, 02:18 PM	#20
36tudordeluxe Senior Member Join Date: Feb 2012 Location: Las Vegas, NV Posts: 1,260	Re: Vacuum reading 276 L-100 cam? I was being too optimistic about my 13" reading, more like 11-12. At my location in the valley here am about 2500' ft. ASL UPDATE: Have run cold compression test and have lost about 5lb. on average on all cylinders except cyl. #5 which lost 25lb. from 140lb to 115lb. The other cylinders in the 130lb.-145lb. range. Would the low vacuum be explained by the one weaker cylinder? Am going to put in a little more advance at idle and see if this helps. Last edited by 36tudordeluxe; 10-07-2016 at 04:03 PM.