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Old 05-08-2014, 02:26 PM   #1
G.M.
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Default V l 1 & 2-- 2

Getting good and hot down here. Had the 39 out for a 2 1/2 hour test run 3 times. First 2 days it was 89 out. Today it was 92, drove 30 miles to lunch driving at 65 to 70 MPH, water temp climbed to 182 slowed down for 4 or 5 miles to 45 to 50 and temp dropped to 178. Bob Shewman's 180 stats in the hoses. Ate lunch and after 30 minutes of sitting with the hood down in the hot sun on the black hood opened hood and the fuel in the carb fuel bowl viewing tube was right near the float line. No carb boiling with Shewman's 1/2" vented spacer. The boiling in the carb is what I call VL-1 and this isn't a problem with the vented spacer.
VL-2 is the fuel vaporizing in the fuel pump and causes the fuel pressure to drop to almost zero. When this happens the pump don't pump fuel. You have to be careful the fuel pump pressure is at least 3 lbs cold because as the pump temperature rises the fuel pressure drops. The large spring in the pump controls the pressure as long as the pump linkage and push rod are working properly. I installed a 3/16" steel brake line after the pump and dumping into the filler neck about 4"s from the top. I wound up with a .070 restrictor hole in the return line after the Airtex fuel pump valve. I tried a .100 hole and it let to much fuel return and the fuel pressure dropped to low. The .070 hole keeps the pressure at about 2 3/4 lbs depending on the temperature. After returning I had 1 3/4 to 2 lbs of fuel pressure. Engine ran perfect at all times. After lunch the soak temperature was up to 190 and it took 4 turns of the engine to start. I don't know why because the carb bowl was full. I have noticed this when hot and sitting for a while so I gave it a nudge of chock and it didn't help.
Have a diode in the starter to resister for a good voltage kick to start so I doubt it was spark. 4 turns isn't bad but I like them to fire on the first turn which it usually does. I have T in the carb line right after the fuel pump, the Airtex valve, the .070 restrictor, the return line back to a fitting brazed into the filler neck. Will try the same route tomorrow (special steak Day) for lunch, it's supposed to be over 93 and see what happens. I also noticed the other day the cold fuel pressure was down and put a little stronger spring in the pump which upped the pressure to a little over 3 lbs. going to look into better springs. G.M.
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Old 05-08-2014, 05:29 PM   #2
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Default Re: V l 1 & 2-- 2

For those that picked up on GM's typo regarding the diode, to be clear, GM has his diode connected to the output side of his resistor. The attached pdf describes the advantages of using a diode, and the wiring diagram.

(Sorry, I don't know how to convert the page to a smaller version for the upload. It's just one page, but too many pixels to upload directly.)
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File Type: pdf Quick Start4.jpg 1,390×1,800 pixels.pdf (464.7 KB, 98 views)
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Old 05-08-2014, 08:00 PM   #3
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Default Re: V l 1 & 2-- 2

Note that PDF has the diode drawn incorrectly for a positive ground car. See this link for an explanation of diode polarity. And the Top Hat diodes mentioned in the PDF are not very common now; most are in plastic axial lead packages. Here is the link:
http://www.allaboutcircuits.com/vol_3/chpt_3/1.html
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Old 05-08-2014, 09:35 PM   #4
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Default Re: V l 1 & 2-- 2

Bill, I see what you mean. I don't know a whit about electricity other than to be afraid of it, but... wouldn't that diagram be incorrect only in that the + is pictured at the diode rather than at the coil? The direction of - going through the diode to the coil?
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Old 05-08-2014, 10:05 PM   #5
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Default Re: V l 1 & 2-- 2

George,
Would the design of the vented cap be the basic problem? The cap vent valve was most likely designed for straight gas. The vapor pressure would have been higher than the E10. That may be why the old Fords are having issues in the heat. I am running a Tanks Inc. unit that does not use the cap vent. It seems to be OK so far. I'll post here if I have problems as the summer heat rises. Believe it or not we do get 100+ degreeF days in New England during the summer.
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Old 05-09-2014, 11:10 PM   #6
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Default Re: V l 1 & 2-- 2

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George,
Would the design of the vented cap be the basic problem? The cap vent valve was most likely designed for straight gas. The vapor pressure would have been higher than the E10. That may be why the old Fords are having issues in the heat. I am running a Tanks Inc. unit that does not use the cap vent. It seems to be OK so far. I'll post here if I have problems as the summer heat rises. Believe it or not we do get 100+ degreeF days in New England during the summer.
I'm not aware of a vent valve in the cap any I have seen have small vent holes with a baffle effect so gas wouldn't slosh out if it was full. If there was no vent there would be trouble pumping fuel from the sealed tank. G.M.
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Old 05-09-2014, 11:26 PM   #7
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Default Re: V l 1 & 2-- 2

Took the 39 out for another test ride today. Temperature was 93 and I didn't open the hood at lunch or any time during the ride. Same route as the other test rides. Did a little more city stop and go looking for any slight hickup but ran perfect the entire 2 3/4 hour time. I see no further need to do any testing other than normal driving. When it gets to a 100 I want to give it a final test. As I see it with the return line, check valve, good fuel pump pressure, the return line restricted with a .070 orfice it eliminates vapor lock. G.M.
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Old 05-10-2014, 02:40 AM   #8
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Default Re: V l 1 & 2-- 2

Thank you, G.M., for sharing the results of your testing. While I have personally never suffered from a vapor lock issue, I am finding your alternative to an electric pump interesting, and, in my opinion, as simple as a safe electric pump installation.
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Old 05-10-2014, 09:23 AM   #9
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Default Re: V l 1 & 2-- 2

Quote:
Originally Posted by s55mercury66 View Post
Thank you, G.M., for sharing the results of your testing. While I have personally never suffered from a vapor lock issue, I am finding your alternative to an electric pump interesting, and, in my opinion, as simple as a safe electric pump installation.
A lot of people have never suffered vapor lock. People that live in cooler areas, don't drive the car much and don't drive when temperature gets in the 90 degree range. I'm talking of driving for over an hour. If the engine runs much over 180 degrees this heat starts coming up from the floor boards, soaks through the fire wall and the hood gets so hot the air coming in the vent is hot. 33 years ago when I restored the 39 I added as much insulation as I could between the fire wall and the interior fire wall panel. I had to make new special "buttons" that were longer to hold the panel to the fire wall. On these 90 degree days with the engine running at 180 all the time as long as we are moving there is a cool feeling to the air coming in the vent and not getting super heated from the floor and fire wall it's comfortable on the legs. Ones that never had vapor lock and now use this new ethanol will start to see the vapor lock problem. G.M.
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Old 05-11-2014, 12:57 AM   #10
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Default Re: V l 1 & 2-- 2

So what causes a FH V8 vs an old Chevy/etc, to suffer the vapor lock issue?...is it the location of the fuel pump on a FH V8?
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Old 05-11-2014, 02:21 AM   #11
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Default Re: V l 1 & 2-- 2

Yes
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Old 05-11-2014, 08:19 AM   #12
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Default Re: V l 1 & 2-- 2

Yes, it's even worse on an aluminum intake manifold, the bottom of the pump almost touches the manifold. I made a 1" insulated spacer under the fuel pump stand with a longer push rod. This helped a little but didn't eliminate the problem. It just gets to hot in the area of the pump. The return fuel line cools the top of the pump and is the only thing other than a large high speed computer fan mounted over the pump with a funnel type duct blowing air on the pump. G.M.
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Old 05-11-2014, 11:43 AM   #13
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Default Re: V l 1 & 2-- 2

Thanks!
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