The truth about switching from a gas carb to E85 or Ethanol: PRIMARY JETS 1. Isolate the primary system by wiring the secondary throttle plates firmly closed. If you don't have vacuum operated secondaries, you must disconnect the secondaries and wire firmly shut. 2. If you have an Wide Band, operate the engine in the range of 2000 to 4000 RPM at a steady speed looking for approximately 14:1 air/fuel, changing primary jets to get this. This will get you a close approximation. 3. Now run the car on a straight and level road. Keep going to a smaller jet until you get a "Lean Surge". This is a feeling of the car surging back and forth while the accelerator is held steady. Richen back up (larger jet) until lean surge is just gone. Write this jet number down. This will be your primary jet eventually. POWER VALVE 1. Now put in the next larger number primary jet, temporarily. The power valve on the Holley is replaceable, but only effects when the valve opens, not how much is flowed (assuming it doesn't restrict the flow). The actual flow is determined by the Power Valve Channel Restricters (PVCRs). Unfortunately, the PVCRs are not interchangeable jets, so they must be drilled out, or modified for using replacable air bleeds in them. This is why I told you to put one set richer primary jets in temporarily. 2. Make full throttle acceleration runs up to about 4000 RPM and drill out the PVCRs until you can determine no more improvement. Since you will go "too far" by perceiving no more improvement, you should be "right on" by going back to your "right" PRIMARY JETS. (BE CAREFUL! Over-drilled holes "can" be plugged up with lead in the event of a mistake and re-drilled, but it is a very poor fix.) This is why, for real performance use, it is better to drill, and thread them for the bleeds. 3. Put your correct PRIMARY JETS back in the carburetor. SECONDARY JETS 1. Now, you can un-wire your secondaries, and change the secondary jets to get best acceleration overall, paying most attention to over 2000 RPM. The above will give you your "cake and eat it". Most procedures have you change primary jets for power. This is wrong unless you are interested in race-only performance with no interest in economy. This is a long procedure but if used can give you the best performance , with fuel economy in the range of twenty or more miles per gallon (assuming you aren't using too big of a carburetor). 1. Holley jets all of their carbs to run just right at sea level (0', mean sea level.) 2. Use the butt end of a good set of number drills (very gently) to gauge the actual diameter of any jets or orifices which are not labeled. Keep notes for reference. 3. Main jet diameter varies proportionally to venturi diameter to get the same mixture ratio with all other factors constant. 4. Always go to the jet size tables, and use actual jet diameters for the calculations describe herein. Only convert your calculated jet diameters back to jet numbers using the tables just before selecting and installing actual jets. 5. At high altitudes (actually at any altitude above 0' msl.), the diameter of the main jets varies proportionally with the fourth root of the air density ratio at a particular altitude in order to maintain a constant mixture ratio at that altitude. For instance, if Holley used a .100" diameter main jet for a standard (sea level) setting, and your local density ratio is .8, you should use a .946" diameter main jet in order to maintain the correct mixture ratio. 6. The two little holes in the metering block which are hidden behind the power valve are part and parcel of the main jet setting. 7. If you want to set a carb up to cruise at a stochiometric fuel-air ratio (high vacuum, power valve closed, best fuel mileage), and have the ideal mixture for maximum power at wide open throttle (power valve open), these little "power valve metering orifices" should be exactly one half the diameter of your main jet orifices when you are all done jetting. This ratio of orifice size to jet size will give you a 25% increase in fuel flow This 25% increase is exactly the difference in fuel flow required to make the difference between a stochiometric and a best power fuel air mixture. 8. Older Holley's generally made the PVCR's on its general application carbs WAY bigger than what would be indicated by this 25% rule. I've even seen some that are as big, or bigger, in diameter than the holes in the main jets! No wonder the gas gauge jumps when you mash the throttle! And no wonder your rings, piston skirts, and bores wear out so quickly! 9. On the other hand, if you check out the stock jetting on a carb like a 4150G on a heavy truck, you will find that Holley applies the 25% rule almost without exception in these very demanding applications! 10. The best way to get the oversized PVCR's back to what you need on a carb like a 1850, a 3310, or a double pumper is like menthoned earlier, and install replacable air bleeds in these passages. 11. A 4150 with no power valve in the secondary metering block will want what appear to be oversized main jets compared to the primaries at wide open throttle (full power) because there are no PVCRs to flow part of the fuel. In fact, the math works out that the diameter of a secondary jet with no power valve should be 1.118 times the diameter of a primary jet with a properly sized PVCR, provided that the venturi sizes are the same. 12. The primary factor other than venturi size which will affect the relative size of the main jets from the primaries to the secondaries is the main air correction orifice. These are the little brass orifices which can be seen looking down the top of the air horn. There are two orifices in this location for each barrel. The other one is the idle air corrector orifice. At any rate, and in general terms, a .006" smaller diameter main air corrector orifice will require a .002" smaller diameter main jet diameter in order to get the same fuel-air ratio with all other things remaining constant. Use this rule to determine whether your carb is giving the same mixture ratio from the primaries as from the secondaries. 13. You can get quite accurate results by multiplying the various adjustment ratios described above together. 14. Always use a power valve with a setting number (the number is the amount of vacuum in inches which is required to hold the valve closed, for example: 5.0=5.0 inches of vacuum) which is at least 2 less than the amount of vacuum which your engine will maintain at idle. Always take this vacuum reading AT YOUR OPERATING ALTITUDE! 15. On an engine with a well designed, two-plane, equal length runner, intake manifold, with symmetrically located intake ports, it is rarely necessary to bias the jet settings from front to back or from side. Occasionally, if you are really picky, the side of the carb over the side of the manifold which has longer runners from the carb down to the plenum will want one size bigger jets, both in the primary and secondary barrels. 16. A good way to avoid too much nonsense with the size of the PVCR's during the jetting process is to install a power valve plug in the primary metering block (and suitably bigger main jets) while doing your timed runs, runs up your favorite grade, dyno runs, full throttle plug cuts, or whatever else you do. After arriving at ideal maximum power main jet sizes with the (primary side) power valve blocked, just install primary main jets which are 0.894 times the diameter of the main jets which were right with the power valve blocked out, make the PVCR's 1/2 of that diameter, and install the right power valve. Air Density Ratio Chart If you are going the dyno tune route, disable the secondaries, put a plug in the power valve, and figure out the leanest primary main jet size that will make it butter smooth on the street before going to the dyno. Stay with this main jet size when you are all done, just adjust the primary PVCR size based on what the dyno indicates is the best for power. This will make it drive like an absolute sweetheart, plus get great gas mileage. Another thing which will help street manners AND fuel mileage a BUNCH is putting one of the Crane adjustable vacuum advance pots on the distributor and fiddling with things until just right! Pipe FULL manifold vacuum (not ported vacuum) to its pot, and use one of the Crane adjustable pots on it. Adding vacuum advance to a mid sixties hi-po or fuelie Vette used to be worth 2.5 to 3.5 mpg on the highway, plus much more polite street manners, and much cooler running around town. Well worth it! Having the vacuum advance will probably let you go a jet or two, maybe even three, leaner on the primaries and still get good behavior. If your engine is a wee bit cammy. One of these days, I'll have to explain how one goes about drilling little holes in the primary AND secondary throttle plates, on the side of the plates opposite the idle mixture feed holes and slots, so as to get the tip in of the transition slots to happen EXACTLY right when coming off of idle. There is a whole 'nother WORLD of insanely quick, sharp throttle response in this little fangle!! Among other things, it lets you avoid the need for SOGGY rich pump cams and squirters! Would not be surprised if the stumble you have when opening the secondaries is coming from the throttle stop for the secondaries being mal-adjusted! Power valve might be opening a tad too soon but vacuum just doesn't seem to vary that much between idle and WOT. ???? Try the lightest secondary actuator diaphragm spring you can find --you might be in for a BIG surprise!! You may not be drawing enough air to open things up wide before you are at a bazillion rpm. Also--might check SECONDARY idle air bleeds for blockages--mosquitos or such. Primary idle and main air bleeds too. Mains should be just big enough for it to drive smoothly (but not good power) with a PLUG in the power valve hole and secondaries disabled. Then get the PCVR to 50% of main jet diam. Then play with main jet, 1 leaner, two richer, to see if it is just right for power with the primary power valve in. If you end up going richer to get best power on the primaries, go back to the main jets that just made it driveable and smooth with the plug in the power valve, and enlarge the PCVR's one number drill size at a time until the full power mixture is right. If you have mechanical secondaries with a power valve on both primary and secondary sides, you need to run a plug in the secondary power valve hole if the car is quick enough for acceleration to uncover the power valve (by fuel slosh) and starve the secondaries. So, once the primaries are right, re-enable the secondaries, and play with the secondary main jets until you have the mix right for best power . Leave the primaries alone during this part--they are already right. Holley had a funny habit of putting sewer size holes in for PCVR's on hipo carbs. I think they figured they were saving hot-rodders from burning pistons at full power when the got the mains too lean!! (But assumed that most hot rodders had no clue what the PCVR's were for!!) I have seen some PCVR's that were actually bigger than the main jets--an absolute joke for what they are supposed to do!! Also, after '67 or '68 crude emissions controls were a reality. So they tried to lean things out at part throttle, and then use enormous pcvr's to get some of the fuel back under load. Basically if you set the mains so the carb gives a decently smooth and driveable mixture at light loads, it will be STEEENKING rich at full power. Also some carbs from that vintage came those godawful two stage power valves--another abortion from that vintage of emission controls! Every 4150 I have ever looked at from a gas motor from a heavier truck--things like Mopar 413's, Ford 391's, 370/429's, and 534's, and IH 304/345/392's, 404/446's,401/461/478/549's, and 537/605's---ALL had pvcr's about 50% of the diameter of the main jets in their Holley's !!! I think that this is telling us something!! (Along with the fact that in going from best cruise mixture to best power mixture, you want about a 25% increase in fuel flow!) (50% of diameter = 25% of area.) High flow power valve good, 2 stage bad. 10.5 probably wants to be an 8.5, if you are at sea level but that's later. Carburator - Tuneup 1) First thing, adjust the fuel pressure! On carburetors, proceed to set the float levels too. Everything is relative to the float level / fuel pressure. If you change that, you start over. 2) Adjust idle to get maximum vacuum in gear (autos)(Note1) or in neutral (man). You will have to play with idle speed and richness settings, because they are interdependent, and when you change one, you change the other. Divide that number by two, and use that number for power valve selection (or enrichment activation). If the idle screws have no effect, or a perfect tune causes more than a 300 RPM drop in RPM when shifted into gear (note 2,4), remove the carburetor and turn over. Where are the throttle plates? There should be an idle discharge hole, and a transfer slot. If there is more than .020 showing of the transfer slot (Note 3), you need to drill a hole in each throttle bore on the transfer slot side, near the center. Start really small (1/32) and work your way up in size until the idle screws work again and you can idle properly. 3) Adjust accelerator pump so you have the shortest duration and volume that won't cause a bog under normal acceleration (no secondaries and normal throttle action). You should not be able to tell when the pump shot ends and the mains come on line. If the car bogs then goes, you need to increase the squirter size. If it goes, bogs, then goes again, you need to either decrease squirter size or increase pump capacity, possibly both. On FI, move the dial or map, on a carb, change the squirter or pump cam. 4) Adjust the secondary jets to give maximum acceleration or highest MPH in the 1/4 mile. Sometimes the secondaries will be leaner than the mains, if a secondary PV is used. On carbs without secondaries, try a high flow PV if lean. 4160 Holleys, and other carbs with non-adjustable secondary jets, as you will have to tune using a high flow / low flow / two stage power valve and main jets. 5) Adjust the secondary accelerator pump / diaphragm spring / air door to give the quickest 60 foot time (also without bog or hesitation). Sometimes, it requires a lot of fuel to cover up the lean pump shot on the primaries. On Holley vacuum secondary carbs, the spring will also affect mileage, lighter the spring, the more performance and lower mileage you will get. 6) Note vacuum on top end at full throttle. If carb is way too small, the vacuum will climb above the number you got in step number three. If this happens, take the highest reading you have, and add one. Replace (or add) the secondary power valve with this number, and go to step 5. 7) Adjust choke so under startup, no black smoke pours out, but no bog occurs either. All out drag tuning requires all jets to be equal on squarebore carbs, jetted for best MPH, and the accelerator pumps tuned for fastest 60-foot times. Chokes and air horns are normally removed. Sometimes the PV is (mistakenly) removed. If the PV is removed, the car will load up in the pits, because jet sizes need to come up about 10, causing an overrich condition at part throttle. General thoughts on the matter: Increasing cam duration requires more jet. A dual plane manifold can use a much bigger carb. If you decrease the metering signal, you need to increase the jet (as you do when converting from a dual plane to a single plane manifold). A blown power valve will have the greatest effect at idle and low RPM. You can check the carb by unbolting it from the manifold, putting the nuts back on the studs, and plopping the carb onto the studs. If you have an electric pump, turn it on. For a mechanical pump, completely remove the coil wire, and crank for about 15-30 seconds. The manifold and carb will be separated by a 1/2 inch or so, enough to see if any gas drips into the plenum when the engine is off (Don't try to start it!). If gas is present, check where it is coming from. There is a hole near the throttle plate that leads to the PV chamber. A blown PV will cause gas to drip from this hole(s). If it is dripping from the bores, the float level may be too high, or your carb has a crack. The biggest city mileage killer is the accelerator pump. A bigger jet requires less accelerator pump, a smaller more. A dogleg style booster requires the most pump shot; the annular style the least. The higher the velocity through the barrel, the better the atomization is. Better atomization means more efficiency (more MPG and Power). That's why dual planes typically give better MPG and performance up to the point where they start to choke off the upper CFM (and HP). If you have a 600 CFM 4BBl carb on a true dual plane, the most any one cylinder can draw through the carb is 300CFM, where a single plane allows it to draw 600 (At its rated in. Hg, that is). Note 1: This usually causes the idle circuit on auto transmissions to be slightly richer than need be when unloaded, but causes it to be perfect when you are actually driving it. Note 2: A lean idle circuit causes automatics to drop an excessive amount of RPM when put into gear and stopped, and may cause stalling. A richer idle is what is called for, unless you see black smoke pouring out the tailpipe. Note 3: The transfer slot must show, or you will get a really bad off idle hesitation. For the best results, the transfer slot will look very close to a square hole. If not, set it that way, then adjust the idle speed with the rear adjuster. On engines with very radical cams, you may have to drill a small hole in each of the front throttle blades to give the engine enough air with the blades closed this far. If these don't work, you really shouldn't be running a 1050 Dominator on your 2-liter motor anyway. Note 4: Sometimes, a really tight converter and a really big cam will do the same thing, there may not be much you can do.
Nothing wrong with that. But, it sure is cheaper to do it that way. Plus, the knowledge you can get from doing it yourself is worth more in the long run.
i do my own tunes on the dyno......and carbs are not a mystery to me but in the case of starting from scratch i do not mind spending a few extra bucks and getting a new carb that is generally a good starting point.
it is a really great writeup by Paul, as always. Bryant and I have discussed me going on E85 with the supercharger, I'm gonna stay tuned on this, might be the way to go.
I couldn't put all the information into the post above so here is the rest of it: You do not have to replace any neoprene hoses with E85. You will have to replace the in-tank filter sock on the sender with a piece of hose and install a metal cased filter in-line. Throw your plastic in-line filter away - it will dissolve. You might have to switch to an electric fuel pump unless you have installed new pump rated for the new fuels. The older diaphragm and valves are sensitive to the alcohol. You should not try to modify your carburetor unless you are knowledgeable enough to feel confident in making mods that can ruin your carb. Do not use an aluminum carb with ethanol or E85. Do a lot of research before you decide to use a carburetor with ethanol - there is a lot of mis-information on this topic.
Don't take this the wrong way Paul, I am not sure where you got that information but it is filled with misinformation. Some parts of it have some merit when using Methanol but certainly not Ethanol.
ive had e85 in mine for 4 yrs my cheveele and i didnt change anything ,it has a holley mech pump that is it , i built my own carb,its very simple if your running a holley , people are finding out now that the e85 wasnt as bad as thought, i have even had rubber in my lines for 4 yrs ,have inspected it reguraly, and never noticed any problems, and now were running it in our street strip maverick 351w ,no special stuff but a redone holley carb and a blue holley pump , with stock tank and lines
