Offroading Subarus

Where we modify and drive flat fours

Modify your Stock 2BBL Hitachi Carburetor (ea81)

Written by TheSubaruJunkie

I’ve done this modification to my carburetor with great results in acceleration and highway speed’s. This modification may impact emissions results so if you need to pass emission tests in the future you might want to get a spare carburetor from the Junk Yard to perform this operation on. NOTE: This modification will only work on the EA81 series Hitachi’s. Although the same modification is possible for the EA82 Hitachi’s, I have not performed it, or do I have images available for the modification.

Just a little background about this modification and the reason why I did this. The Hitachi carburetor has 2 barrels, but only the primary barrel will open under acceleration. It is not until the gas peddle is fully depressed and a certain amount of vacuum is created in the intake manifold that the 2nd barrel will open up. This modification will bypass the vacuum actuator on the hitachi and force the 2nd barrel to open when the 1st barrel reaches 1/3 throttle.

Lets Get started shall we? Here are some diagrams of the part of the carburetor we will need to play with. You will not have to disassemble the carburetor at all, so almost anyone should be able to do this mod.


Here in this figure we see the diaphragm that will need to be removed. It is held on by 3 screws (#2 in the diagram) and is also held on by the snap ring at the end of the diaphragm arm. You will want to plug the hole in the carburetor that the diaphragm connects to.

After you have the diaphragm removed, play around with the carburetor a little and notice how there is a lever for the primary and the secondary barrel.


Here is a close up of the moving parts that we will play with. #3 in the diagram is the actual throttle lever that connects to the throttle cable. #4 is the secondary lever that we need to make move. I’ve put red arrow’s on the contact point where we need to attach the primary and secondary plates. I have heard of people welding it together right there, but I don’t have a welder, nore do I like that idea all too much.
I took a piece of coat hanger and cut off a piece about 4″ long and bent it to the desired shape.


Here you can see how the wire should go. It might take a little time in order to get it just right. Here are some pictures of the actual modification on my carburetor:


And here are some short movie clips of the modification in action:

[ Movie #1 ] [ Movie #2 ]

Both movies are under 500k in file size, so it wont take long to download them.

— Additional Info:
Throttle response is iffy. It actually creates a huge dead spot when you step on it. Because you are forcing the secondary open, the jets arent primed and you end up sucking in alot of air, with no fuel. Only until the jet for the secondary gets fuel, then everything’s a go. Power is felt past 1/3 throttle when you step on that. If done right, you can rev the engine a little and get the secondary to open up, force the jet to prime. Then when the light turns green dump the clutch and romp on it… seems to accelerate alot better than stock. But if your just cruisin everyday driving, the dead spot can suck if your not expecting it.

I suggest doing this to a spare carburetor. I did it to a junkyard carb and swapped back and forth between the 2.



I bought my first Subaru back in 2005, it was a 89 Brumby, flair red. I lifted it, fitted Kumho 27″ MT’s. After a while I swapped the dual carb EA81 it had with an EJ22 bolted on a custom gearbox which used EJ D/R casing, EA82 5sp low range and an RX centre locking diff. Once I sold the Brumby I got a 83 Leone. Converted it to 4WD, put the Kumho’s on it, added a 5sp and drove it like I stole it. I then upgraded to a 99 Outback. It was hail damaged so I repaired it myself. I fitted it out with some storage and a mattress. I now have a 87 Brumby that I’ve resprayed with two pack urethane in Waratah Red. I am planning to fit an EJ with PT gearbox and a little bit of lift. It’s another project in progress.

Phizinza – who has written posts on Offroading Subarus.

July 27th, 2008 by Phizinza
Posted in Modifications