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Technical Carburetor Jetting The Old School Way

Discussion in 'The Hokey Ass Message Board' started by Truck64, Nov 30, 2016.

  1. If your area's population got together and boycotted ethanol blend fuel with demands for pure gas to be available y'all might make it happen.

    I mean look at what happened when y'all bitched about pure gas- the whole damn country got ethanol.
     
  2. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Ethanol came about in part because MTBE (methyl-tertiary-blahblahah) was banned, ending up in groundwater supplies. I support agriculture and Farmers 100% but it doesn't belong in our soda or fuel. Corn is just feed that hasn't been turned into steaks yet.

    I did run two sizes smaller jets - #46 - for a little bit on a short highway run. It seemed to run "ragged", though no surging at steady cruise. Maybe I just needed to back off the timing a little bit? On account of the fact leaner mixtures are harder to ignite. Reinstalled plugs, gapped back down to factory .035"
     
  3. So totally off topic but knowing the truth helps figure out your tuning issue.

    Henry ford had cars running on straight ethanol in 1907, and it's been around ever since. Anyone with a still could grow and produce their own fuel- self reliant and renewable. The oil companies saw the impact the automobile would make and decided that cars should run on gasoline, a once discarded byproduct of refining oil. The oil companies made out selling the garbage by-product that they once had to pay to dispose of.

    Ethanol usage was mandated via politics in the 2005 renewable fuel standards program. By 2007 manufactures were mainstream producing flex fuel vehicles. The price of ethanol is fixed on a spread controlled by the oil companies who cried because of the MANDATE. It's their pumps, tanks and stations that provided the infrastructure to get ethanol into your tank. PLUS They have been selling garbage for 98 years. No matter what it costs to produce home grown ethanol the current pump price is set by the foreign oil companies and what it costs for foreign oil. There's no competition.
    Because of the MANDATE and political lobby power of the oil companies to be able to fix the price it costs just a tinech more per mile to go down the road on E85 than on gasoline. It should be cheaper, but if it were what would they do with gasoline since it wouldn't sell. Remove the mandate, eliminate the price fixing and let the competition be on a fair market. US farmers and refineries are currently producing 15 billion barrels on a laxidazical pace. Farmers are still getting paid not to grow. 1 small refinery with 28 employees can produce 15 million barrels operating at 1/2 of max capacity.

    Don't even get me started on the petrol dollar
     
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  4. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 2,314

    19Eddy30
    Member
    from VA

    Hear not to far from the Big White House , its geting to be more common ethanol Free in last year .
    But new formulated blend of fuel's ( off the pump ) is still hard to read By the plugs
     
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  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    That's never going to happen.
     
  6. southcross2631
    Joined: Jan 20, 2013
    Posts: 4,413

    southcross2631
    Member

    I sorta read through this whole thread and never once did I see that you had hooked dwell meter up to see if that was changing while you were driving. Old Ford distributors were famous for sloppy bushings which caused the points to close up under acceleration which retards the timing.
    I made extended leads for my Snap-On dwell meter which I still own . So I could lay it on the seat and go for a test drive to check dwell under load . That and a vacuum gauge taped to the windshield told a lot. If I missed where you had done that or converted to electronic ignition, sorry I am old.
    Worked in Ford dealerships when carbs and points where standard equipment. A Rotunda distributor machine was a handy tool if you knew how to use it.
    Play with carbs all you want ,but if you don't have good spark you are wasting your time.
     
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  7. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    As a matter of fact, yes, it has a remanufactured distributor with Pertronix points eliminator and Flamethrower coil. The dwell stays steady at 30.

    A new distributor was night and day! When they get old the mechanicals inside can stick, become erratic, vac advance can blow out etc.

    I spent a lot of money (for me) getting the engine rebuilt some years ago, and then cheaped out at the end with a junkbox carb and distributor with a gazillion miles on it. That was a big mistake. One of the reasons Pertronix has been so successful I think is in part because they aren't affected by a wallered out distributor. It ran better when I replaced the points, but it really ran solid after a new distributor! Then I learned to curve it for my application. A feller is better off getting Bubba or somebody to set them up a dizzy, but I can recommend to anybody to get a new dizzy in their rig ifn ya haven't already.

    Point systems being mechanical, cannot tolerate sideplay in the distributor shaft. Have spent a lot of time trying to make sure the ignition is just as hot and reliable as possible with new cap, rotor and wires and good solid tight grounds and heavy gauge 1/0 wiring, charging system up to snuff etc.
     
    Last edited: Feb 5, 2017
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  8. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Today warmed up to around 45F so took it for a quick spin to check cruise AFR after jetting down to 46. On steady level ground at 50 to 60 mph it runs around 15.4. No surging or misfire, runs real good. Could maybe lean it out even more. And, overall, mixture will only get more fat at summertime temps.

    WOT though, runs about 14, too lean. Dropping from 48 to 46 jets dropped WOT afr a whole point! Looks like enlarging the PVCR is in order here to get things dialed in. One suggestion I read in another forum sez to enlarge PVCR by about .003" and I'll see it on the AFR. OK, but drill step sizes aren't normally supplied in those increments? The "next size" drill bit will be way too large right?

    Vacuum on level ground runs steady 15" to 20" depending on speed and drops to a low of around 11" on slight hills. A step up in power valve size would make it come in earlier, but it wouldn't change the overall AFR at wide open throttle?
     
    Last edited: Feb 6, 2017
  9. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

  10. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    So what I found was the stock 48 jets were running about 14.5 AFR at steady highway cruise. It would be interesting to know what Ford engineers tuned for. This engine is running lots of advance, and maybe drawing higher manifold vacuum somewhat. Also dual exhaust. The latter usually means stepping up the jets, though not always. I'm wondering if this would be the case here. It is a small stock carb, 1.02" venturies so it has a pretty good "pull". Anyway installing 46 jets brought the cruise AFR to 15.4, that is pretty good for economy I guess. 16.2 is supposedly best lean cruise. Also need to consider though that, A. Only reading half a bank of cylinders with the wideband, B. Not all cylinders will see the same fuel mixtures and C, Have to take into account a tank of bad gas and/or effects of Ethanol. I'm running these tests using pure gasoline - but on a road trip that won't be the case. So maybe we'll leave .5 or so on the table for a little cushion.

    On the other hand, it's only about 40°F, average AFR should richen out as things get warm this summer. I figure cooler temps make better baseline testing than say July, when fuel is boiling in the bowl. That's got to throw idle mixture way out, no?!

    WOT with the new jets was too lean, 14 AFR. Using numbered drill bit shanks I determined the PVCR size was #70 or .028" and hogged them out slightly. Luckily for me the WOT ratio dropped back to 12.5 - just about right for max power. I might try dropping one jet size to 45, it's supposed to be almost 60 degrees this weekend and give it a good run and see what's what.

    Getting a carb dialed in is real educational, truck runs better than ever with no flat spots. It seems like problems or bogs I thought were caused by being lean were really too rich, and vice versa. On slight grades and cruise it just seems to "float" and don't have to mash the pedal down all the time.
     
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  11. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 2,314

    19Eddy30
    Member
    from VA

    Truck64 , now imagine trying to tune without an O2 sensor ;):D
     
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  12. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Yeah, lots of variables I hadn't considered - temperature and ethanol for just a couple. Also whether a catalytic converter must be installed, they would get nuked running lean. I don't think those are required in any state, if the vehicle did not have one at the time of manufacture? Leaning out cruise fuel mixtures was the "lean burn" strategy, till NOX emissions were targeted, that ended that. If my state had emissions testing, it would fail NOX, I suppose. It's getting 50% better fuel economy than with the other carburetor, but what the hell. On the other hand "gas is cheaper than pistons" so I gotta be careful. But if it's true each jet size equals 4.5% flow difference, stepping down a few jet sizes should mean extending the range quite a bit on the highway. If I could get 300 miles on a tank of juice that would be something.
     
  13. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Today got up to 65°F, super nice day. Had #45 jets delivered as part of a Care package, jets installed let's take it on a test cruise! The warmer temps richened the mixture considerable. Back around stoich 14.7 at level cruise!

    Hm. Decided to skip #44 jets and drop to #43, smallest I have on hand. Leaned out the idle mixture too where it ran good. The mixture screws are about 1/2 turn out. These 43s worked slick, at around 60 to 70 mph, it just touched on 16.0 at steady level cruise. Runs real good all around.

    Must have hogged out the PVCRs a little too far, but not by much, WOT stayed 12.0 to 12.5 under all heavy full throttle acceleration. Maybe a little rich, tho safe. The wideband takes all the guesswork out, that's for sure. We'll run with this for a while, to leave some "room" for fuels laced with Ethanol. It should also richen up more when temperatures get in the 80s or better.

    In theory 5 jet sizes difference should result in around 20% better economy in level cruise. The wideband will pay for itself the first long roadtrip, easy. Plus, it runs better than ever.
     
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  14. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Lean mixtures need more ignition advance right.. Harder to ignite. This is handled best by vacuum advance, because as the load levels off the mixture leans out, the manifold vacuum conveniently comes back up, and a lot of additional advance is added in.

    Is it possible though, that there could be a specific condition where engine knock at cruise is evident because there isn't enough ignition advance?? Need more coffee I think.
     
  15. caton462
    Joined: Jul 17, 2013
    Posts: 176

    caton462
    Member

    To a point. Limited by mechanical limits of the cylinder and valve timing. About the first third of the stroke is where you want to extract the fuels power. Remember the piston needs to slow to a stop at the bottom of the stroke, and cool a bit through the exhaust cycle before introducing new fuel to prevent fire in the intake.
     
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  16. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    So is that classic part throttle ping rattle a result of the timing coming down or going up? Also seems like the "adjustable" vac advance cans are just "when" not "how much". Measuring in neutral (no load) isn't so helpful.

    It might be useful to figure out what the total mechanical advance is in degrees at the typical cruise RPM of 60 or so, and then select or limit the vacuum advance to add enough on top for around 50° BTDC or so. Or maybe backing off the vac so it don't rattle is the same. Vacuum advance is weird because it's sort of hard to measure.
     
  17. caton462
    Joined: Jul 17, 2013
    Posts: 176

    caton462
    Member

    Getting spark knock-retard the timing until it is gone (rule of thumb). This is what your late model car does automatically with a computer tied to a knock sensor. 50 deg. is a lot by the way. We used to curve distributors to get a lot of advance early and limit the total advance to around 37 deg. depending on the build.
     
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  18. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    That's mechanical advance though in a race engine right? What kind of spark knock is the question. Full throttle knocking is bad stuff, that's too much initial or, mechanical. Part throttle knock at cruise when accelerating, that slight momentary rattle you hear is too much vacuum advance. Every now and then, that's considered acceptable, at least as I understand it. The very lean mixtures at level highway cruise need lots of extra advance that mechanical won't provide.

    Vacuum advance is different, it only comes into play at low load, steady cruise situations where manifold vacuum is high. This engine is low tech, compression is only 8-1, it will tolerate lots of advance without complaint on pump gas.

    One thing that isn't taken into account when talking timing, depending on gearing, typical street cruise RPM is going to be what, around 2400 RPM at say 60mph? So the mechanical advance will be at least somewhat less than the "all in" full throttle mechanical distributor timing., depending how heavy the springs are.

    A vacuum advance can will somewhere between 10° or 15° timing, but only in those low load conditions, where the fuel mixtures are very lean. My shop manual sez the distributor could have either a 13 or 18 slot, and the vacuuum advance would add 6.5°. They are talking distributor degrees, which are half of crankshaft degrees. Initial timing on these were listed anywhere from 3° to 6° BTDC, though they allowed that it could be increased by up to 5° more for increased performance and economy. So if you juggle the numbers around, they all add up to somewhere around 50° timing in certain lightly loaded situations.
     
    Last edited: Feb 19, 2017
  19. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    IMG_0310.PNG

    Well I picked up one of these today, complete with all the manuals and cables. Probably needs some power supply work by now, no big deal there, we'll git 'er done.

    You ready to decipher all those squiggly lines on parade fer me??
     

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