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TBI Carburetor Adaptor Tech Tips

 Before ordering your Howell TBI conversion kit, there are a few important things to check on your vehicle to ensure proper installation and function.

 Inlet manifold carburetor flange – Due to the many variations in design between carburetor manufacturers and vehicle models and options, there are several factory applications that will not work for converting to our TBI kits.

 The first thing to look for before ordering is a 4-hole, 4-barrel factory inlet manifold flange. (photo 1)

(Square flange vs. spread bore flange differences discussed further down.) When the adapter plate for the 2-barrel TBI unit is placed over the stock carburetor flange, the bolt pattern may be the same, but the placement of the throttle bores is in the center of the flange, creating an obviously unusable restriction. (photo 2)

 The easiest cure for this problem is either to find a factory 2-barrel inlet manifold to use, or an aftermarket 4-barrel manifold with a divided, 2-section carburetor flange. (photo 3)

 This will allow for the proper air/fuel distribution into the manifold, and unrestricted airflow. 

 If you’re running a stock engine, going from a 4-barrel to 2-barrel manifold won’t usually affect performance in normal street or off-road driving. If you plan to run at higher rpm and power levels, an aftermarket aluminum 4-barrel inlet manifold is probably the better choice. You can closely match the cfm rating of the original carburetor by choosing a similarly rated TBI unit for your kit.

 Another potential issue with using an aftermarket inlet manifold is the thickness of the flange/carburetor pad walls. On some manifolds, the thickness of the casting surrounding the carburetor pad is barely enough to allow the plate-to-manifold gasket to seal. (photo 4) 

The material thickness varies between manufacturers, so you will need to check yours to be sure it has enough material to work with.  On some manifolds, minor blending may be needed inside the bores to eliminate the step below the adapter plate into the plenum, as shown in photo.

Rochester 2G/Carter BBD 2-barrel carburetor conversions

There are 2 different sizes of Rochester 2G carburetors, referred to as ‘small bore’ and ‘big bore’. As of this writing, we have adapter plates available for the small bore version (and Carter BBD) only. To determine which version you have, use the small bore illustration below for measurements – 

The material thickness varies between manufacturers, so you will need to check yours to be sure it has enough material to work with. On some manifolds, minor blending may be needed inside the bores to eliminate the step below the adapter plate into the plenum, as shown in photo.

Rochester 2BBL

Spread-bore 4-barrel carburetors

We currently only offer a spread-bore adapter plate for Rochester QuadraJet, Carter Thermo-quad, and Holley 4165 carburetors. (See illustration below for specs.) Other spread-bores, such as the Ford/Motorcraft/Autolite 4350 have a different bolt pattern, and also different throttle bore spacing measurements. We do not currently offer an adapter plate for these carbs. Most spread-bore kits are supplied with a Holley 670 TBI unit with 2” bores, though adapters are available for use with standard GM/Rochester TBI unit with 1.68” bores.


Unlike the adapter plates for standard square-bore carburetors, the spread-bore adapter plate locates the throttle plates of the TBI unit over the secondary bores on the manifold, blocking off the smaller primary bores completely.

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One Size Does Not Fit All

A custom wiring harness and kit are the only way to go with Electronic Fuel Injection conversions.

Not all vehicle builds are the same. That’s why they call them customizers, right?

The fact is that when converting an originally carbureted engine over to fuel injection, there are man upgrades that are required to make it work properly. Electric radiator with thermostatic controls, fuel pump relocation to the gas tank and exhaust oxygen sensors required to make the fuel injection operational all require a custom wiring harness with the right fittings and the proper length wiring to connect it all together. No “cookie cutter” conversions kits could possibly do the job.

“We see a lot of online conversions kits that claim to be a one size fit all solution for folks converting their cars to electronic fuel injection,” said Matt Howell, President of Howell EFI.  “But the fact is that these are very complex systems that need special attention to the layout of the wiring harness and the right matching components. We spend a considerable amount of time on the phone during the order process to make certain every piece of the kit is better than OE spec.”

Howell wiring looms utilize better than original equipment wire. The individual connectors used are exactly the same as those used by the original manufacture to ensure perfect attachment to the assigned component each one labeled with white tags to make for trouble-free installation. Best of all, when ordering a Howell EFI conversion kit, everything is included. Case in point for the classic Jeep carb to EFI change out, the kit features components like a new Throttle Body and computer module specifically programmed by Howell to the requests of the consumer. It is literally turn key!

“We have people who call in thinking this is a simple process because they have done some research online or actually bought a cut-rate conversion kit thinking that they had everything they need for the job,” said Troy Brown, Howell EFI Tech Director. “But it becomes painfully obvious that without attention to these details, the system will either not run at all or it will start but not deliver the performance they expect. We get too many customers who spend good money only to find out that the discount system was a total waste of time. We spend a lot of time to get it right and an equal amount of time researching new and updated systems either to enhance our existing systems or expand out coverage to include new models.

To learn more or to order your conversion kit or harness contact Howell EFI at or call (810) 765-5100.

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Jeep EFI Upgrade Tips

#K247JPV8W401 - TBI Kit - Jeep Wagoneer 401

Howell EFI Conversion Kit Helps Kick The Carb!

No vehicle on the road  (or off road) benefits more from swapping from a classic carburetor to electronic fuel injection than a Jeep After all, eliminating those angle sensitive float bowls that can starve an engine for fuel and creating an engine system that can adjust to the altitude of the climb by richening and leaning out the fuel delivery is every Jeep lover’s dream.

Howell EFI offers eight different kits for most Jeeps built between 1982 and 1993 that originally came with carburetors. Best of all, for the street-driven Jeeps, the conversion kits include full emission compliance within strict Air Resources Board mandates. That means owners will never have a problem with the local regulators when checking emissions compliance.

“The Howell EFI conversion kit integrates the critical charcoal canister and the EGR systems and eliminates the need for the air pump and other engine cluttering components,” stated Troy Brown, Howell EFI Tech Director. “What we do recommend is that owners who install this kit go on our website and print out Air Resource Board Executive order D452 and keep this two-page document in their Jeep. This document shows that our system is emissions complaint and should handle any issues they encounter.”

Installation Tips

The Howell EFI conversion kit includes everything you need to install the kit including the GM Throttle Body, reprogramed computer, high flow electric fuel pump, fuel filter, MAP sensor, all hardware, clips, mounts and most importantly, the custom factory-look wiring harness that uses better-than-factory components and wiring. Howell estimates that most of their Jeep conversion kits will take between 8 and 10 hours to install depending on your level of skill and the condition of your Jeep.

Key points to the installation include modification of the fuel system. Fuel injection systems require both a fuel delivery line and a return line, both running the length of the vehicle from the fuel tank to the engine. The recommendation is that this line be 5/16-inch diameter line, either braided steel or hard line. Rubber fuel line or steel line, if so desired, should be used but when using steel line, small sections of rubber hose are allowable around the new fuel filter and fuel pump to make them easy to service when needed. Many owners choose to mount these parts inside the transmission protection pan to avoid the buzzing noise notoriously emitted by electric pumps. Mounting the pump with some kind of rubber foam spacer where it touches the pan will keep the noise to a minimum.

The MAP (Mass Air Pressure) sensor supplied with the kit is a key component to proper operation. Howell EFI offers two types; one that can be simply installed off the TBI unit with a stiff piece of rubber hose or a second type that must be mounted in a downward facing angle with vacuum pointing towards the ground and the sensor mounted above the TBI unit itself on a bracket or the firewall. When reviewing your instructions, the MAP mount for your component will be noted.

Your Jeep’s computer is located within the interior behind the glove box.  The dashboard on the passenger side must be loosened to allow for removal of the glove box. Once it is removed, the computer is easily located. Two nuts located on the engine side of the firewall must be removed to release the computer. Once it is free, gently remove the original equipment wiring harness junction from the computer.

The CTO (Coolant Temperature Override) switch is mounted on the engine block just below the intake manifold. It will be retained for any conversion and must be working properly. These switches are notorious for leakage, so if yours is showing its age it must be replaced. In addition, the original engine block mounted mechanical fuel pump will be removed and replaced by the block off plate supplied with the Howell EFI kit. The original pump rod stays in the block or the engine or oil pressure will not be correct. Make sure that the Howell plate is well sealed or oil leaks will occur.

For those looking for an overview of the system and owner experiences, YouTube-based instructional videos are readily available. “We have Jeep owners who go the full route and take out all of the original wiring loom and those that just tuck the unused original wiring away in the dashboard after heat shrinking the powered wires so they don’t ground out,” said Troy. “It is at the discretion of the builder as to how much or little they want to do – as with any vehicle modification. We honestly estimate the total install to not be longer than 10 hours from start to finish. The key is to study the schematic supplied with the kit and call our tech line if there are any questions.”

To learn more or to order contact Howell EFI at or call (810) 765-5100.

Carb to TBI conversion kits offered by Howell EFI:



  • #K247JPV8W360 - TBI Kit - Jeep Wagoneer 360 CARB E.O. #D-452-2
    #K247JPV8W304 – TBI Kit – Jeep Wagoneer 304 CARB E.O. #D-452-2
  • #K247JW360 - TBI Kit - Jeep Wagoneer 360
    #K247JW304 – TBI Kit – Jeep Wagoneer 304
  • #K247JPV8W360 - TBI Kit - Jeep Wagoneer 360 CARB E.O. #D-452-2
    #K247JPV8W360 – TBI Kit – Jeep Wagoneer 360 CARB E.O. #D-452-2
  • #K247JPV8W401 - TBI Kit - Jeep Wagoneer 401
    #K247JPV8W401 – TBI Kit – Jeep Wagoneer 401 CARB E.O. #D-452-2
  • #K247JW401 - TBI Kit - Jeep Wagoneer 401
    #K247JW401 – TBI Kit – Jeep Wagoneer 401
  • #HJ283 283 CID I6 Jeep TBI Conversion Kit
    #HJ283 283 CID I6 Jeep TBI Conversion Kit
  • #HJ232 232 CID I6 Jeep TBI Conversion Kit
    #HJ232 232 CID I6 Jeep TBI Conversion Kit
  • #CJ258 - TBI KIT: 1972-80 CJ 4.2L Offroad
    #CJ258 – TBI KIT: 1972-80 CJ 4.2L Offroad
  • #CA/YJ258 - TBI KIT: JP1 Emission Legal Version CARB EO #D452 1987-91 YJ Wrangler 4.2L Emissions Legal
    #CA/YJ258 – TBI KIT: JP1 Emission Legal Version CARB EO #D452 1987-91 YJ Wrangler 4.2L Emissions Legal
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Drive By Wire Installation Tips

With many of their electronic fuel injection conversions, Howell EFI includes a drive-by-wire (DTW) pedal assembly that must be mounted in the new vehicle to control the throttle. DTW first appeared in Corvettes back in 1997 with the dawn of the C5 models delivering far improved throttle response than the previous cable-driven systems. By 2005-2007 almost GM vehicles switched to the DBW wire system, which delivered these benefits to all LS-powered vehicles in their line up.  The beauty of this system for enthusiasts is that they can place the throttle pedal in any position they like as long as the wiring harness has enough length to reach the new positioning. In addition, they can be combined with traction control and ABS completing a state-of-the-art vehicle control system.

Without most recent installation, removal of the original throttle pedal was a terrific move since the years of wear on the original parts meant their future was limited. After unbolting the original mount, it was clear that the new DBW pedal system would not mount cleanly to the flooring and allow the pedal to move and operate properly.

After a quick call to the Howell Tech line, it was clear that a custom pedestal is required to properly mount the pedal.  Researching the program further, a call to Steve Rupp, editor at Chevy High Performance Magazine netted his solution, which delivered not only proper pedal operation but excellent toe-heeling ergonomics. Bottom line, creating a plate to mount the DBW system is as unique as you want it to be. Here is an example of the solution used for Rupp’s Camaro – yours could be different.

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Howell Makes Ordering an EFI System Simple and Easy

Howell EFI, well respected in the industry for their plug and play EFI systems has earned that reputation for a reason. Their customer support team knows every question to ask to make certain that what ships out from Howell covers every possible base for a complete and easy to install system.

Here is a sample of a typical order taking conversation:

  • Wiring Harness was needed for 1971 Pontiac Firebird


  • Engine ?  GM Crate engine – LS3 with 525 horsepower
  • Transmission?  Rockland Standard Gear six speed
  • Manual or automatic? Centerforce twin disc hydraulic clutch
  • Any cam changes?

Key order taking questions:

  • Where does the battery mount – underhood or trunk?
  • What kind of cooling fan arrangement do you have – single or dual fans?
  • Any smog requirements?
  • Eliminate speed sensor?
  • Are we providing the computer?
  • Do you have a core on the computer?
  • Where do you want to mount the control module – under hood, in the interior?
  • With belt system does that put alternator on top or down low?
  • Does the alternator have a four or two pin connector?
  • What about mass air flow sensor? Are we supplying the front two oxygen sensors? Length of the harness from passenger harness to computer mounting point?
  • Fuel pump to mount in trunk – this is normal for fuel injection conversions
  • Gold or Silver Blade in the throttle Body – signifies engine type.


These engines require the drive by wire pedal – mounted on the firewall. Howell offers reprogramming of the computer control module if needed. Can be determined after the engine is up and running.

Each harness is well marked with each wire or component tagged to denote where it fits. The fittings are made to connect to the factory fittings so this is simply plug and play. Look to Howell EFI to make your order taking and conversion happen with ease. Link to video here.