Jump to content

Search the Community

Showing results for tags 'hitachi feedback air bleed'.

More search options

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


  • Welcome to the USMB!
    • Meet n' Greet. Your USMB Welcome Center
    • Members Rides
  • Older Generations of Subaru's 1960-1994 Except Legacy and Impreza
    • Historic Subaru Forum: 50's thru 70's
    • Old Gen.: 80's GL/DL/XT/Loyales...
  • Newer Generations of Subaru discussion
    • 1990 to Present Legacy, Impreza, Outback, Forester, Baja, WRX&WrxSTI, SVX
    • BRZ and its Sister the Scion FRS/Toyota GT86
    • Crosstrek "XV"
  • Marketplace
    • Ultimate Subaru Store
    • Products for your Subaru
  • Upgrading and Racing Discussion
    • Performance Tech Forums
    • Subaru Modifications
    • Subaru MotorSports
  • Ultimate Subaru Repair Manual-The Knowledge Base of USMB. Complied posts and writeups to common problems and projects.
    • Submit a Tip or Mod to the USRM
    • Product Links and References
    • The old Ultimate Subaru Repair Manual
    • Engine
    • Engine Electrical
    • Transmission, Axle, and Brakes
    • Heating and Cooling systems
    • Body Exterior
    • Interior / Body Electrical
    • Stereo tips and tricks
    • Offroad Modifications
    • Suspension and Steering
  • Off Topic Areas
    • Shop Talk
    • Alternative Vehicles (non soob)

Product Groups

  • Member Accounts
  • Ultimate Subaru Decals
  • Subaru Parts
    • Weber Carbs and Parts
    • Used Subaru Parts

Find results in...

Find results that contain...

Date Created

  • Start


Last Updated

  • Start


Filter by number of...


  • Start





Website URL








Ezboard Name




Found 1 result

  1. Ive spent alot of time trying to salvage the stock fuel/emissions systems on the EA81 cars. In the end I found that the SPFI or weber swap was the only way to go. Unfortunately the the SPFI system is becoming scarce, and the weber kits are costly. I would still likely dump the Hitachi if it needed rebuilt, but my new hatch has a nice one bolted too the manifold. Ive decided to re-invest my energy into the non feedback Hitachi system. Much regarding the EA81 Hitachi carbs has been discussed on this forum. For some reason the vacuum system and its components still remain a little fuzzy. This may have to do with the vagueness of the service manual or the confusing difficult to follow steel vac lines. Subaru/Hitachi definitely over complicated this system and to add confusion theres numerous calibrations that vary per model year. During the 70s-80s automakers had to get pretty wacky to get cars to meet emissions standards. I suppose it was during this era that the "just rip it out, I hate emissions crap" ideals began. More often than not this gutting may have solved a problem by eliminating nothing more than a vacuum leak. Since these cars are so old and parts for this system are sorta unavailable we have no choice but to take this attitude. Thinning this system is much easier and will have greater benefit if its taken with some understanding of whats being removed. My time is limited and Im only going to post info that Ive seen members looking for lately. If there is interest I may add more at a later date. Alot of this info is opinion, based on my experience with these. My terminology may not match the FSM, and might be misspelled etc with poor grammar and broken sentences. Take it or leave it. Would be great for members to add (friendly) contradictions or contributions. Im going to start with the air cleaner: "Stove Pipe Control" - this is the thermostatic valve that controls vacuum to the carb preheat motor. This diverts air flow into the aircleaner/carb. When cold the valve is open causing hot air to be drawn from the exhaust pipe. This helps to speed up warm up time and prevent icing in the carb. They are great, except that mine had all failed in the open position. This is not doing you any favors in the summer time. I live in a mild climate with pretty warm summers so Ive elected to unhook this system (including the corrugated pipe) and plug its vacuum source. There are ways to get this working if needed. Ive used something like this in the past. "Thermo Valve Vents" - these ports are for the thermo valves. One is for the black water temp valve thats for the choke (the one by the disty). The other is for the white "wall" temp valve for the EGR valve, canister purge, and the vac advance. The origional vac hoses make it hard to mix these up, but I dont see it making any difference wich goes where. More on the valves another time. "Hot Idle Compensator" - pretty common gizmo from this era. Supposedly, some where around 150 F (air cleaner temp) this opens up to help prevent stalling. I suppose during long periods of idling in hot weather fuel in the carb can vaporize and richen the mixture. This valve would open and in effect raise the idle and lean out the mixture. Of corse in the real world (or least on my car) this gem failed the vac pump test. So it was just a filtered leak. I eliminated its tee and plugged the port on the air cleaner. I havent had any issues from this. "Air Bleed Ports" This is where the high speed/main and low speed air passages get their filtered air. Since this system is so poorly covered by the FSM Im going to share my opinions on it now. In a few posts Ive noticed members are simply plugging these ports. If you live in a cold climate and only drive short trips then you will notice very little difference in driveability with this mess removed and plugged. This system may be nothing more than an economizer. But I believe the Hitachi was designed to have these ports open in some fashion. These air passages arent like manifold vacuum ports. They are plumed directly into the mixing stage of the carburetor. Whether they were orifice'd straight to the air cleaner, temp controlled, or computer controlled, Im unaware of any factory calibration where they were plugged. As Ive said I live in a mild climate at hight altitude. I found the car runs fairly rich, and inconsistent, with the ports just plugged. On my car the mess of hoses were incorrectly routed, with one of the ports fed without the orifice in the circuit. Once I figured this out the carb no longer "needs a rebuild". Im unsure of how these were factory routed and tee'd. So, I found the car runs best with the passages directly routed to the vacuum control valve (VCV) with the orifce lines on the carb ports. You MUST have the orifi in place! On my configuration there were 3 total, 2 silver colored and one gold with a smaller hole. There may be dozens of different sizes, I cant say. It seems to run best with the gold one on the high speed port, and the silver on the low speed port. As mentioned these lines were ran directly to the VCV. I removed the the tees and loops. I tested the VCV with a vac pump, and the thermo vac valve with a lighter. They both checked out, so I kept them. Manifold vacuum is supplied to the thermo valve. IIRC it opens at 85 F and vacuum is then supplied to the VCV and VSV which causes them to open. What were they trying to do here? My guess is that under certain conditions the float chamber may end up under negative pressure. The VSV would open the chamber to the atmosphere, eliminating this issue. I have not experimented with capping this one yet since my VSV tested good. I did have to remove the VSV's cover and replace the air filter inside because it had turned to dust. I had a sheet of foam that is meant for window A/C's that I purchased at Lowes. A small cut circle of this foam was installed and the cap replaced. Years ago on a different car I removed the control part of the system. I used a tee and one orifice after the tee right before the port on the air cleaner. The VSV was also removed and the line from the float chamber was hooked directly to the unused connection on the air cleaner. This was in Vegas (hot) and I didnt run this setup long before going SPFI. But it worked. If you are missing an orifice or one of these components fails to operate correctly, there's no reason not to experiment with this setup. In fact the EA82 cars are setup similarly. If you are missing all the orifices you could try an experiment of your own by melting a tee closed at the third leg and poking a small hole in it. Im not sure how precisely engineered the orifices need to be. If there is real interest in this thread I have more to add. Not sure its really worth it, seriously, how many EA81 Hitachis are even left? You may also argue that its best to just eliminate all of this "crap" and plug everything. And I will say, Ive seen cars so stripped of this emissions "crap", even the PCV system had been disabled and plugged Why? Because they had a problem and didnt know how to diagnose it, or what any of this "crap" was for. Why delete it if you can get it working? Uh-oh Ive now been on the computer nearly 2 hours and my wife is getting suspicious so this is all I have for today...