How to convert your carburetor to E85

For Carbed engines, you need to up the size of the jets to flow about 20% more for the primary, and 35% more for the secondarys, and tune from there. The Power Valve circuit needs to have its flow increased also to bring the primary up to about 35% at WOT. This is done by increasing the Power Valve Channel Restriction (PVCR) passage size in the metering block. With 20 % increase in the primary jets, increased size of the PVCR, and 35 % increase in the secondarys, the engine will cruise in a efficient a/f range, and then richen up to the proper WOT range when the power valve operates. There are several passages in the metering blocks that should be re-sized for optimum performance. Quickfuel sells E85 metering blocks that are ready to go. They also have the needed floats, SS needle and seats, jets, and air bleeds to complete the conversion. A 750 CFM carb will need boosters with at least .150 size pins for WOT with E85. Most engines will need boosters in the .170-.180 range. Changing boosters requires special tools, and is beyond the abilities of most basic carb guys. You can get your boosters replaced by most carb builders like Quickfuel for around $100-125 including the cost of the boosters.





These are based on the flow area of the jets, not the jet number

So if you have 75 primary jets and 85 in the secondary, you need to use about 79-84s in the front, and 92-96 jets in the rear. These are for a 750 carb, with the proper size PVCR passages in the metering blocks for the power valve. This is only a starting point, but very close.


Here is a good starting point for a 750 DP Carb to E85. using Quickfuel's E85 Metering Blocks, which have custom sized internal passages to compensated for the increase in fuel demand of E85. They are also hard anodized to prevent any corrosion of the internal passages.

750cfm
squirters = Pri .042 Sec .042
accel pump = 30cc
Boosters = Primary 180, Secondary 180 
IAB = .065
HSAB = .028
Idle Feed Restriction = .046 
Emulsion holes = top down .028, blank, .028, blank           
PVCR = .094 (for boost) NA, about .076
Powervalve = 6.5, rear blocked
Needle & seat = .130 SS
fuel pressure = 6.5 psi
Primary jets = .080
secondary jets = 96 (for boost) 92 (for na)


When using E85 with EFI, there is little to no problem from moisture, since the fuel system is air tight. With a carb, the carb vents are open to outside air, and will allow the E85 absorb moisture. When Ethanol and water are mixed, it will form a mild acid in it. This is where the corrosion from using E85 comes from. Keep the moisture out, and you will not have corrosion problems.

If you are running a carb with E85, you need to take extra care if it is parked for over 2 or 3 weeks. The guys in the south east will be affected by the moisture much more than in the north, while the guys in the south west will have very little problem, if any.

1. Drain the carb when parked.

2. Fill the bowls with gas, start it, then pump the gas pedal a few times to get the gas into the accelerator pump circuits also. Top the bowls off.

When you start it the next time, just burn off the gas, and turn on the E85 pump.

Here is how mine was set up when NA.




The above diagram works fine when NA, but when using a SC, the added fuel pressure you get when under boost will be blocked after the check valve, and when you get out of it, the pressure will over ride the needle & seats, and flood the engine.







This shows what gauge drill to use to get your
desired size power valve channel restriction


Chart Showing Numbered Drill Bit Sizes


This is what the Replaceable PVCR look like installed


This shows the inner working of a typical
Holley type carb, and labels the passages.



This is a E85 high performance metering block from Quickfuel. It has several passages that are designed to enhance performance, and a completely tunable emulation circuit, and a special power valve circuit to make for smooth transition as the carb goes from idle, on up to WOT.




With some time, you can set up the carb to have perfect air fuel ratio from idle to WOT, and back to idle, and as smooth as EFI. This is done by starting will a good performance carburetor, then fine tuning it to your application. If you get a custom built carb, they can build the carb for your application, where all the work is already done.



The new 130 SS needle and seat on the
left and the old 120 Brass on the right

To remove the needle and seat, just loosen the screw as you would for adjusting the float level, then turn the nut down some to force the needle up a little. Slide the needle and seat out, then transfer the the nut and screw, along with the new washers onto the needle and seat and install.



Turn the float bowl upside down to see where the float is set for. This shows where to set the floats at after installing the new 130 SS Needle and seats You should also not be using brass floats, as they will reach to E85 over time. Setting the float this way will get it close. Make sure to check it while the fuel pump is on, and engine running when installed. QFT has any parts you need.



This shows where the Air Bleeds are.
Notice it has annular boosters to respond to load changes faster





The Tslot should be exposed slightly as shown. Not having any showing will cause a stumble as you apply the gas from it going lean. Having too much exposed will feed enough fuel to the engine at idle, to make adjusting the idle air fuel screws not have any effect, making it idle too rich. It is best to set the Tslot so the opening that is exposed is as long as it is wide, square. After doing this, make your idle speed adjustment using the secondary idle adjustment screw. If you are running a real radical cam, this may not be enough to control the idle. If that is the case, drilling small holes in the throttle blades may be required to provide enough air to the engine, while the blades are nearly closed. On some older carbs you may have to remove the secondary adjuster screw from the bottom of the base plate and put it in from the top to allow easy access. The Tslot controls the fuel delivery until between 2200 and 2800 rpms in most engines when the fuel starts feeding from the boosters. If you are rich or lean before that, it is most likely from a idle air adjustment, Tslot, or emulsion circuit that feeds the Tslot causing the problem.

TIP: The best way to test your carb, is to do the primary first by its self. This will prevent the flow of the secondaries from masking any lean spots that may be in the primary from too small of jets, or incorrect sizing of the PVCR passage. Disconnect the link on the linkage to the secondaries until you have the primary fuel curve correct. Having a Wide Band O2 meter installed before you start would be a great asset. You can use it, along with checking the spark plugs, to get a good safe fuel curve, that will perform great at the strip, and cruise with only a slight increase in consumption.



This shows where to disconnect the link so it only runs on the primarys .
Once the fuel curve is good on the primary, reconnect and check them together

Quickfuel has all the parts needed to convert your carb, and also will build you one that is set up for your engine for Normally Aspirated, or for E85 Blow Through.

CarCraft does some Performance Testing with E85
CarCraft E85 Test


Some good Carb tuning information here


This is my Quickfuel 750 Blow
Through Carb converted to E85

I converted it to E85 using Quickfuel's E85 blocks



Complete Carb Tuning


Advantages To Using E85

For you guys with that are into Drag Racing ,
click here for E85 Racing information



Getting it ready for the Strip

Full Project

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