Introduction and a question
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6th Gear
Joined: Mar 2025
Posts: 6
Likes: 1
[ZITAT=Patpät; 21522295]
Ich dachte dasselbe! Habe die Bilder sofort überprüft! Vergleichte die Details. Das muss doch dieser Truck sein, oder?
Tolle Geschichte!
:-Jammin[/ZITAT]
Yes, that's my truck.
I think it's very safe with the color combination and the rims.
Really incredible - very funny
Best regards Markus
Ich dachte dasselbe! Habe die Bilder sofort überprüft! Vergleichte die Details. Das muss doch dieser Truck sein, oder?Tolle Geschichte!
:-Jammin[/ZITAT]Yes, that's my truck.
I think it's very safe with the color combination and the rims.
Really incredible - very funny
Best regards Markus
Last edited by Whity_71; Mar 23, 2025 at 03:24 PM. Reason: wrong language
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6th Gear
Joined: Mar 2025
Posts: 6
Likes: 1
I would be very happy with 10 - 12 mpg!
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6th Gear
Joined: Mar 2025
Posts: 6
Likes: 1
The AFR at idle is a little rich, so might just need a slight adjustment on mixture screws, that's assuming the AFR of 12.5 is engine fully warmed up and choke completely open. Your AFR while driving looks good though considering 14.7 is "perfect" stociometric ratio so I wouldn't mess with carb too much.
Might check base and total timing, mine seems to run best around 12 degrees advanced at the base with a nice mechanical advance curve up to about 34 degrees advanced around 2500 RPM. I would make certain your vacuum advance is functioning to. That can help low load efficiency by adding a bunch of advance when cruising and throttle plates are barely open/manifold vacuum is high.
I noticed you mentioned you have 31 x 10.50 tires, stock tires were 235/75-15 which are around 28" tall, those extra few inches of tire height combined with 2.75:1 rear gears your engine may be struggling to get that weight moving. Those taller tires effectively changes your gear ratio to 2.48:1, great for highway speeds and keeping RPM down, but makes it more difficult to get truck moving thus using more fuel to do so.
Dropping down to a 28" tall tire or replacing rear gears with 3.00:1 might help.
Also, if the speedometer gear wasn't changed to account for change in tire size you might not be calculating your fuel consumption correctly since the speedometer is off and how many miles you actually traveled won't match what the odometer says you traveled.
All that said, 10 mpg give or take a couple points is the norm for these trucks in my experience.
Might check base and total timing, mine seems to run best around 12 degrees advanced at the base with a nice mechanical advance curve up to about 34 degrees advanced around 2500 RPM. I would make certain your vacuum advance is functioning to. That can help low load efficiency by adding a bunch of advance when cruising and throttle plates are barely open/manifold vacuum is high.
I noticed you mentioned you have 31 x 10.50 tires, stock tires were 235/75-15 which are around 28" tall, those extra few inches of tire height combined with 2.75:1 rear gears your engine may be struggling to get that weight moving. Those taller tires effectively changes your gear ratio to 2.48:1, great for highway speeds and keeping RPM down, but makes it more difficult to get truck moving thus using more fuel to do so.
Dropping down to a 28" tall tire or replacing rear gears with 3.00:1 might help.
Also, if the speedometer gear wasn't changed to account for change in tire size you might not be calculating your fuel consumption correctly since the speedometer is off and how many miles you actually traveled won't match what the odometer says you traveled.
All that said, 10 mpg give or take a couple points is the norm for these trucks in my experience.
I have checked the speedometer with GPS. The speedometer displays accurately.
I have set the ignition to 12° before TDC.
No improvement in fuel consumption.
Its Comin Right for us!
Joined: Feb 2005
Posts: 12,149
Likes: 2,633
From: GA
Another thought popped into my head, with current setup of tires and gears, at 65 mph you'll be sitting around 2000 RPM which is nice on engine wear, but the factory mechanical advance curve with stiff spring on the advance weight often keeps full mechanical advance from occurring until 3000 RPM or so. Since you'll be sitting around 2000 RPM at highway speed, you might not be getting much mechanical advance at all. Going to a lighter spring on the advance weight inside distributor will help reduce the RPM required to get full advance. It would be a good idea to check what RPM you have to hit to get full advance and make adjustments as needed. You can get lighter springs to "tune" the advance curve.
I don't have the website handy but @KubotaOrange76 I think is who provided me with a website that has pictures and instructions how to recurve your dizzy. Unless you want to shell some money and buy a custom curved dizzy. I have more time than money so I prefer DIY solutions whenever possible.
I don't have the website handy but @KubotaOrange76 I think is who provided me with a website that has pictures and instructions how to recurve your dizzy. Unless you want to shell some money and buy a custom curved dizzy. I have more time than money so I prefer DIY solutions whenever possible.
”The factory oem spring package in the duraspark distributors consists of one light and one heavy spring the heavy spring having an elongated hook on the end that hooks to the spring tab.
The factory ignition curve is two stage. The light spring controlling the early part of the curve allowing it to come on fairly quickly then near max mechanical advance the heavy spring comes into play and slows the last 4 to 6 degrees of timing. This of course is dependant on the application.
I typically utilise the light factory spring and one of the mr gasket 925D light springs for most curves the pull all of the centrifugal advance in by 2700 to 3000 rpm, fine tuning the rate by bending the spring perches. The amount of advance is dependant on slot width. (10l, 13l, 15l 18l and 21l are available) The slot designations are in dizzy degrees not crank degress so they must be doubled. For faster curves i utilise only the mr gasket springs. In some applications where towing or heavy vehicle weight with taller gearing are involved I will utilise a mr gasket spring and the factory heavy spring for a two stage curve to avoid detonation under heavy loading.
Most oem iron headed applications need 34 to 36 degrees total advance for best power. Some low compression applications or domed piston applications will like more advance for best power. 12 to 14 degrees initial is a good starting point. The more radical the cam timing the more initial advance is required for decent idle characteristics. You can bush the pin in the slot or weld the slot up to limit centrifugal advance and allow more initial timing.
After market heads like the scj / P-51 do not require as much total timing needing only 26 to 30 for best power.
Vacuum advance in oem state is set up for use with EGR and can be on the order of 25 additional degrees above the totals stated above. When EGR is not utilised and additional 10 to 15 degrees will suffice. Vacuum advance is necessary because at part throttle the engine is not ingesting a full breath of a/f and is usually somewhat lean. This mixture has a slower flame front propogation rate and requires more advance. Any street driven application will benefit from vacuum advance. It can be tuned in the duraspark by inserting a 1/8" allen wrench into the vacuum nipple and turning ccw for less advance and higher required vacuum depression. Conversely turning clock wise will allow more advance with less of a depression.
Most factory distributors have too much centrifugal advance and too slow an advance rate. The vacuum advance needs to be adjusted to application. In other words set up your dizzy for your particular application.
There are instructions on my website specific to the duraspark distributor...”
https://www.reincarnation-automotive...ons_index.html
Fleet Mechanic
Joined: Mar 2013
Posts: 1,661
Likes: 1,062
From: Montana
I am thinking a change to the tires or gears would help a lot. Changing tires is a lot easier and likely less expensive than rear gear swap. Unless you happen to have other gears laying around for a Ford 9 inch already. Going back to a 235/75R15 or if you like a bit wider tire 255/65R15 might help a lot. The narrower 235 might provide a bit better mileage due to less road friction compared to wider tires. The 255 about a half inch less in width than what you have on there currently.
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