Just Plug It! Taking some of the mystery out of your Hitachi

[ihscout54]

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...

Edited June 26, 2015 by ihscout54

[tweety]

Yes, keep it going. It's always good to document this stuff. And these vehicle are entering an age whereby some owners will consider taking their cars back to original. It's the sort of thread that if it helps one person fix the running of their Hitachi and save a few dollars it's worth it.

 

Well done.

 

[Loyale 2.7 Turbo]

... If there is real interest in this thread I have more to add ...

 

I believe that you did a great work here, and it worth be completed AND saved at the USRM section.

 

Kind Regards.

[Sapper 157]

This forum is a gold mine for those of us which wish to keep the original carb. Keep up the good work.

[ferox]

Nice work, I like the attitude.  I would like to see similar treatment with the great graphics on the other components (vacuum solenoids and such) that newcomers are afraid to deal with.  

 

With all due respect I will say that I have run my Hitachi for 10 years without a VCV, VSV, or thermal vacuum valves.  I don't consider them "crap"...that would be ignorant, but for me I wanted dependability and when those components fail or the users reading this post have already failed parts, they are expensive to replace if it's even possible and will required delivery.  I'm not trying to undermine your efforts, but I just want to note that those components can be removed without issue.  It is nice to see such a nice explanation, so members can decide for themselves which route they want to take. 

[ihscout54]

Thanks for the feedback! This is not my thread, its our thread. Just because I started it does not mean others cannot add too it. Admittedly 4 out of 6 EA81s ive owned were factory feedback. I live near CA so most of the cars Ive seen would be CA emissions. My new hatch is not. I will repeat that I have never seen a car with these ports plugged. And I will add that my feeling the car runs better with these ports unplugged could be placebo affect. Does anyone know if there is a factory calibration with the air passage ports plugged?

One thing I didnt mention in my post is the 4th (air passage?) port that some of the later carbs had. It was furthest to the rear of the carb and sometimes was pointed towards the passenger side. One of my feedback cars had it, but plugged. I do not know what this was for, and since the car Im using for this Info is not equipped with it I cannot add anything about it. IIRC reading that it was a high altitude calibration feature? If someone knows I feel it needs to be In this thread.

 

Ferox - YOU need to post the link to your delete in this thread. Im going to try to post about the thermo switches this weekend.

[rdweninger]

Yes, Ferox.   Could you please post link (if written) to your delete mods on the Hitachi?   Like what is hooked up and everything else is deleted?    Thank you.    Awesome graphics ihscout54.   What software did you use to create that.... and did you post it as an image filetype?   Great job.

[ferox]

I'll see what I can do.  I am prepping my house for sale and planning a move to Eugene (job search, etc..)  I have to rebuild the Hitachi one last time before I move and was planning to post a step by step of my method.  I can probably make it more comprehensive and go through the deletes.  I don't have any of those old components anymore so it might consist of mostly photos.

[ihscout54]

I mentioned Ide cover the thermo vacuum valves, so here we go.

The first one (Thermo Vacuum Valve II) is the black 2 port thermo valve near the distributor. The top port on the valve is to the air cleaner, the bottom is to the choke pull off. While the coolant is below 70ish degrees this valve is normally open. From the looks of it, this reduces the strength of the choke pulloff until the car has warmed up sufficiently (and the valve closes). In effect its one stage of the choke/warm-up operation. This is not quite an emissions device, but more a device of cold drive-ability. Ide prefer to have this one working over deleting it. Unfortunately, if it even worked, the top port is often snapped off due to it being over looked during air cleaner removal. If you delete you will have to decide whether you like the port on the pull off open to the air cleaner or plugged. Ide leave its carcass in place, as its the cheapest way to plug the hole it would leave behind.

I dont think all calibrations have this one. Specifically the later carbs with the dual pull off setup. -please correct me if wrong.

Next one (Thermo Vacuum Valve I) is the white manifold temp switch called "wall temp". Befor I go into my theory of what this does im going to contradict myself by saying, "pretty classic emissions crap". I feel this has little to do with drive-ability. It can go, in fact it isnt even needed to plug a hole. Its likely removal wouldnt interfere with emissions testing either. If what I just said is all you need to hear you neednt bother reading my thoughts on what its intention was. 

My best guess is their goal with this was to reduce emissions during part choke cold driving conditions. This was an archaic attempt at best. I spent very little time examining this after reading the shy-sty description of its function. It was clear it was silly. If you can wrap your head around these diagrams youd see that when cool, but I guess not cold the vac advance function is partially reduced. Its temporarily vented and controlled by the EGRs vacuum system. Genius/pointless. Cant say how many carbon toe nails this really trimmed and Im sure they didnt do this because they wanted too. One thing that has caught my eye in the diagram is the EGR setup. I looked in my hoses after removing them and was unable to locate the pictured orifice. I have the EGR plumed directly to a ported source on the carb. Will I end up with a drive-ability issue from incorrect EGR function? I havent noticed any, guess Ill keep the stereo volume down and pay attention for the next couple drives.

To truly delete this device I personally feel one should remove the steel lines under the manifold as well. The best way to remove these lines is when changing intake manifold gaskets or whenever you plan to have the manifold off. I did these right after buying the car and I thought I may try to restore the emissions system. So basically I left it to be removed later. Dont bother trying to yank this out in one piece.

Theres 3 bolts that hold the mess in, one of which is on the bottom of the manifold near the EGR. A real pain to get too! It only has the EGR line attached to it so I elected to cut it at the bolt under the front of the carb. I left the single steel line to feed the EGR valve. Look at the pic you can see the saw blade starting its cut. If you choose to do the same you must cover the carb, disconnect the rubber hose from the EGR, and blow the line out. It will be full of metal shavings.

Your goal is to end up with something like this.

Ill cover the evap routing next I suppose

Edited June 27, 2015 by ihscout54

[ihscout54]

 

Awesome graphics ihscout54.   What software did you use to create that.... and did you post it as an image filetype?   Great job.

Thank you for noticing, my skills are pretty rusty. Its been years since Ive been in the biz. I think the work gets the ideas across to you guys. Software used: Inksacpe and Adobe Image Ready. Files compressed as gif or jpeg formats.

[turfman454]

man thanks for the info and the graphics. Im getting ready to replace all the 4 miles of vacuum hoses on my 84 brat.At least i know what they do now!!! great write up

[bratbro]

Really good information. I replaced the EGR thinking it'll help with mpg. When I pulled the stock EGR it was full of corrosion to the point where I don't think it even works. So. I installed the new one anyway and nothing changed. Figure if my PCV works that's good enough.

Great write up very useful information. Thanks!!

[jonas]

Well done sir!  

[BulldogBlitz]

So very helpful.

[CoolDork87]

Im in love with this thread. The info youve posted has given me hope of repairing my brat to a proper running state. Please please keep it going I'd love to learn more

[Sapper 157]

Wasn't sure where else to put this but I found this helpful PDF on the web the other day and wanted to share it with you all to get opinions, as well as help us who strive to keep these unbearably picky carbs on our cars. Figured that it might be helpful for future rebuilds:

 http://mastertechmag.com/pdf/1987/12dec/198712IS_Hitachi2Barrel.pdf

Edited May 12, 2016 by Sapper 157

[soobenthusiast]

Wanted to provide an update on this. I was converting my car from a Carter-Weber to Hitachi 2-barrel, so I didn't have all the factory parts. I've tuned it with a wideband so I have some idea what's going on.

 

 

I essentially ended up with this setup, but my lines are simply Tee'd together instead of using a VCV. I made some .035" orifices by melting plastic vacuum tees and using a small metal rod. It works fairly well, and I don't have any doohickeys that can fail. Long term I'll probably tweak the orifice size a bit more, but it's fairly good, for a carb. 

I do have a lean flat spot just off idle, which may be related to these extra things I've removed. 

I also haven't gotten my choke to work well without the Thermo Valve. If I don't hook up the choke pulloff at all it runs super rich for a few minutes, or I have no choke...

 

Hope this provides another useful data point for others trying to follow this path!

[skishop69]

Funny this post comes back now. I just bought and rebuilt a second carb after doing the original one. I ended up with a total lack of power from off idle to basically 3/4 throttle.I monkey'd with it for quite sometime before concluding something was wrong with the power valve or the power valve plunger. Idled great and ran like a scalded dog wide open, but no so much for general cruising. I could get in and drive freeway speeds or regular roads fine as long as it was not stop and go. 5 or so minutes of stop and go and the whole midrange would go away. Put the freshly overhauled carb on and the same thing was happening.I finally started looking at the emissions/vacuum lines trying to figure out what had gone wrong. The high speed air passage and the atmospheric float vent are not that close, but have the exact same size and length hose with the same dog leg bend in them and come out of the same bundle of lines. I had switched them accidentally (actually more than once during the course of messing with this thing as the problem came and went). When the wall temp valve opened, it was applying vacuum to the high speed passage (instead of the bowl vent) which I assume is internally plumbed to the power valve plunger circuit and basically shut down the power valve.

[ihscout54]

I do have a lean flat spot just off idle, which may be related to these extra things I've removed

You seem savvy, and I have no idea just where your at with your car. Ill share my thoughts on this anyways; accel pump, power valve, small vac leak. Ide start with a check for leaks in ported vacuum circuits. The Vacuum advance would be a double whammy if the diaphragm is ruptured. If its slight, you could try to soothe this condition with a richer idle and or more timing advance. Does it disappear with the low speed port plugged?

I also haven't gotten my choke to work well without the Thermo Valve. If I don't hook up the choke pulloff at all it runs super rich for a few minutes, or I have no choke..

There are a few things I want to add and update to my original thread. I just dont have the time right now. I will briefly touch on a fix for this. I have been running a setup on my car that has replaced these old wax pellet type valves. Been strong for about 8 months. My cold starts and drive ability are fuel injection-esc. For your issue the simplest solution would be to find a working valve. It doesnt have to be the exact one, just close. Ideally, it would fit the hole

 

 

Memory of the setup is fuzzy and I dont have time for pix or wiring digrams right now but Ill give you a description and hope it gives inspiration.

What we have here is a temp switch (90 F) a 5 pin relay and a vacuum solenoid. The switches came in a pack of 5 for like 4 bux off ebay, and the one I installed has really held up great. I have 2 solenoids In use, one for the stove pipe control and one for the thermo valve that controls the VCV. You could easily adapt this to replace your "Thermo Vacuum Valve II" and regain a close proper choke function, OR replace all of the thermo valves. The 2 solenoids I used were old ones I had in a box. The one in the above pic is from a Toyota. In your case pretty much any one will do. It doesnt have to be the vented type, if its only going to be for your choke. You need your solenoid to close once warm or be open only when cold. Yes sounds wacky but its not. You can use the old solenoids from your car or go to the j-yard. remember tho youll have to solve the N/O N/C riddle. Example: youre solenoid Is normally closed. One wire for it would go to an ignition hot, the other to the thermo switch thats controlling ground. That switch is normally closed as well and opens at 100F. So the solenoid is on/open with the IGN and then closes when the thermo switch opens at 100 degrees. The solenoids and switches can be found in both configurations so.... I hope you get the idea.

 

IIRC my temp switch closes at 90 degrees triggering the relays coil ground (you may not even need the relay) energizing one solenoid, and shutting off the other. On my setup one solenoid Is normally open and one normally closed. Thats why I used a 5 pin relay it allows me to use only one thermo switch. The switch is attached to the intake manifold close to the block with some bailing wire. Ive not bothered updating this thread with this trick since I figured no one would be interested In such a semi-complex solution for gizmos they could possibly live without. If anyone can wrap their heads around all of this and has a desire for using it Im not opposed to sharing more on how Ive done this.

Edited October 8, 2016 by ihscout54