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Guest Message by DevFuse
 

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You and your Hitachi. A sordid tale of love, hate, and vacuum valves.


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28 replies to this topic

#1 GeneralDisorder

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Posted 08 March 2008 - 11:00 PM

I'm working on a write up of my experiences with the stock Hitachi carbs. Non-feedback of course, and mostly on the EA81 side - although most of the concepts are basically the same for the EA82 - things are just layed out slightly differently.

So this '83 Hatch followed me home. We have been bonding lately. I have plans to install the SPFI on it of course, but for the benefit of the community I've decided to use all my knowledge and experience relating the stock Hitachi's in a last-ditch throw down to make it run as good as possible before ripping it off.... I'm getting close.

There's a lot of confusion about the stock system. People find it overly complex, and that's not without merit as opinions go. It is of fairly high complexity. But if you really look at the design, it's all there to make the thing more "drivable" or for economy. There's very little that is there strictly for emmisions, although there are a few sub-systems which serve no other purpose.

This will all turn into a write up on my own web hosting, but for now there's a few things I would like to disburse in order to get the information out there and be able to reference something in other posts, ect.

The first step that's got to be done is to remove the roll-pin at the front of the carb base that prevents access to the idle mixture adjusting screw. As things are removed, or changed this is a critical adjustment that will come in handy for offseting the effects of changes made to hose routings, leaks that are fixed, and components that are removed. At each step of the process - as you complete a modification ect - you will want to readjust the idle speed, and idle mixture to a "lean best idle". You do this as a balancing act with both the mixture needle and "speed adjustment" throttle stop bolt. Make sure your timing is around 8 degrees at 750 RPM, and then adjust the speed screw till the speed settles at 750. You then adjust the mixture - screw the needle in to lean out the mixture till you get a slight stumble, and then back it out just till the enging runs smooth again - usually 1/4 turn out from slight stumble.

You want to do this regularly as you make changes.

Now that I've addressed the carb adjustments, I would like to bring your attention to the EGR valve, and it's partner in crime - the "anti-afterburn valve" (AAV). Below you can see the EGR valve, as well as the "hard line" that goes between the valve and the AAV. The second picture is of the AAV itself.

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This system is in place to prevent condensed fuel droplets on the inside of the intake manifold from being sucked into the engine under "rapid deceleration" conditions.

Basically that means you don't need it. It doesn't buy you anything but added complexity, and a bunch of expensive, likely already failed components. In fact you can't even tell it's not there once it's removed. And check out the usual condition of the hose from the EGR to the hard line:

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That's a NASTY hose, and a vacuum leak that will cause problems.

Removal is simple - remove the valve, and the EGR. Replace the EGR with one from an SPFI manifold or one from an older EA71/EA81 - 1980/1981 didn't have the AAV (which is another point indicating you don't need it - it didn't come on early models).

Here's some shots of it removed. Note the ground connection on one of the AAV mounting studs - don't forget to replace the bolt to insure the ground wire is properly attached. And put a bolt in the vacuum line that ran to the AAV - I like to cut it short (about 1.5") and put a bolt in it so I don't have long vacuum lines running around that do nothing.

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Next up on the list of bad stuff we can toss is a little valve known as a "thermo-vacuum valve". This guy's job is to NOT allow manifold vacuum to reach two vacuum control valves (more on these in a minute) until the engine bay hits 81 degrees F. It's basically a different form of choke - but since the carb already has a choke - I see little value in this device. Maybe if you live in a VERY cold environment you would want to consider replaceing this. Anyway - in testing I found that the valve did in fact open - but at a much higher temp than it was supposed to. Here's the valve:

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It's located on top of the bracket that holds the hard line for that AAV we removed above. Here's it's hideout on the drivers side of the manifold - under the air cleaner:

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It controls vacuum to these two air control valves that control air mixing ports on the carb:

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You can remove the thermo-vacuum valve, and supply those two valves with plain old manifold vacuum all the time. Just run the manifold supply vacuum that went to the thermo-valve to a T (such as the one that supplied the AAV) and supply both of these air control valves with it. This lets the choke set the cold mixture, and the mixing ports have filtered air at all times.

That's all I have for now - if anyone wants to give these two mods a try and give me some feedback as to how they worked for you that would be great. My experience has been good thus far - I plan to actually rebuild the carb, and modify the linkage for progressive throttle plate openeing as well as remove a few other uneccesary components. All of this will go to a write up layed out better than this of course.

GD

#2 bratsrus1

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Posted 08 March 2008 - 11:45 PM

Hey GD This is Jerry, i just removed that junk a week ago on my 86 hatch. I had a bad vacume leak found it, your parts look good compaired to what i took off of my hatch. My mileage is better now back up to 31 miles per gallon again. Thanks Jerry

#3 GeneralDisorder

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Posted 09 March 2008 - 12:17 AM

Hey GD This is Jerry, i just removed that junk a week ago on my 86 hatch. I had a bad vacume leak found it, your parts look good compaired to what i took off of my hatch. My mileage is better now back up to 31 miles per gallon again. Thanks Jerry


Definitely.

Theoretically - all that suff shouldn't impact mileage and performance. But being 25 years old means it generally isn't working, and is a detriment all around. If people could afford to replace this stuff then they might as well install a Weber.... so if I can help a few folks to get their Hitachi back working as it should then maybe I can keep a few more older cars on the road.

GD

#4 TeamCF

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Posted 09 March 2008 - 12:44 AM

This info will prove to be useful.

Thank you GD! :)

So I'm thinking those EGRs without the AAV connection are easly found at the JY?
Also could the port on the EGR I have with the connection have the connection plugged? (like with a short new hose and bolt or something like that. Just in case one wanted to go for this and can't get to the JY right away.

I know the right way is to get the other EGR, just wondering if blocking the connector would also work fine.

#5 GeneralDisorder

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Posted 09 March 2008 - 12:51 AM

This info will prove to be useful.

Thank you GD! :)

So I'm thinking those EGRs without the AAV connection are easly found at the JY?


Yes - any SPFI EA82. Tons and tons of them at our yards.

Also could the port on the EGR I have with the connection have the connection plugged? (like with a short new hose and bolt or something like that. Just in case one wanted to go for this and can't get to the JY right away.

I know the right way is to get the other EGR, just wondering if blocking the connector would also work fine.


Yeah - you can do that - would have to be like a 1/2" bolt and a hose clamp. You can cut the tube to the AAV off and weld the hole up if you really want to also. But the SPFI EGR is the easy $5 junk yard way.

GD

#6 TeamCF

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Posted 09 March 2008 - 12:57 AM

Yes - any SPFI EA82. Tons and tons of them at our yards.



Yeah - you can do that - would have to be like a 1/2" bolt and a hose clamp. You can cut the tube to the AAV off and weld the hole up if you really want to also. But the SPFI EGR is the easy $5 junk yard way.

GD



Cool thanks.
Maybe I can make a run out to the damascus yard tomarrow. :)

#7 IdahoJak

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Posted 09 March 2008 - 11:18 AM

Great info GD, my '86 Hatch is currently running great, but I may do these mods anyway. If I do, I'll let you know how it turns out.
Thanks,
Jack

#8 Cougar

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Posted 09 March 2008 - 01:07 PM

Good write-up GD.

#9 woundedbrat

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Posted 09 March 2008 - 11:18 PM

Adjusted the mixture on my carb today and its all thanks to this thread. I had looked for the adjusting screw once before but couldn't find it. I wonder why they hid it behind that stupid roll pin maybe job security for suby mech/dealerships anyhow the hardest part was removing that roll pin, had to push it down and cut it off with my dremel repeat until it was out of the way. runs a lot better now turned the screw almost an entire rotation towards lean used to hesitate a bit going from idle to throttle but not any longer.Any how great thread thanks and keep em comming.:clap:

#10 smelly_cat

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Posted 10 March 2008 - 06:44 PM

Im unclear what a roll pin is? I am sure with all my hitachi gremlins this would be good start. SC

#11 GeneralDisorder

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Posted 10 March 2008 - 06:59 PM

Google image search....

http://www.nuttybolt...RO-Roll Pin.jpg

GD

#12 smelly_cat

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Posted 24 May 2008 - 06:59 AM

I finally found the roll pin blocking 2 openings in the front of the carb near the base, After 3 days, I worked the pin out, I now have tired plyer squeezing fingers,

Is the mixture screw in the Hole on top? I don't seem to catch anything when I spin a screwdriver in there

The bootom hole does have a screw in there, It only turns about 180 degrees before I hit a stop, And the engine does not stumble or speed up , Should I force the screw? Usually mix screws can go all the way in and all the way out.

Just checking before I decide to get angry and break something. SC

#13 GeneralDisorder

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Posted 24 May 2008 - 10:44 AM

Yeah - the one you want is the bottom one. There could be corrosion keeping it from comming out as the base is cast iron. If you have a mechanic's mirror ($1 at the parts counter usually) that will help you see what you are up against better.

I suppose I should update this post huh?

GD

#14 subyrally

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Posted 24 May 2008 - 01:35 PM

thanks for the write up GD.

#15 GeneralDisorder

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Posted 30 July 2008 - 12:31 AM

Bumping this for an update.

In frustration of trying to figure out the mileage issues I was having on the hatch (23 or so), I pulled off the metering port vacuum control valves and capped the metering ports. This made no difference at all so we can safely assume they are of little importance. At the end I was running all the mods in my first post as well as no metering ports or associated plumbing.

I then couldn't handle the insanity any longer and installed my Weber (virtually brand new - bought from redline a few years ago for my wagon - less than 10k on it). Mileage actually got a little worse - dropped to about 21 or so.

My mileage issue turned out to be a clogged catalytic converter housing. The honeycomb disintegrated and left behind some metal straps and some wire mesh that surrounded and held the honeycomb in place. This got all wadded up in the cat discharge pipe. I removed that and the mileage immediately increased to 25.5 on the next tank with the Weber.

I have removed the muffler and mid-pipe and shook them but nothing dislodged. However I feel that there may still be pieces of the cat inside the muffler and once I fab a pipe to replace it it's going away as well. Straight pipe's on EA81's aren't all that loud anyway. I'll see if that helps. I know the Weber is capable of over 30 MPG in it's current jetting as I have achieved that with it on my wagon when it was 2WD. I expect around another 1.5 to 2 MPG increase by freeing up the exhaust. That should translate to very close to 30 MPG with the original Hitachi..... I haven't decided if I'll put it back on or not. SPFI is calling my name and my 91 SS will be on the road soon for daily driving duties.

GD

#16 McDave

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Posted 30 July 2008 - 09:48 AM

I got my best mileage yet with a gutted cat - 28mpg SPFI wagon A/C ON. Unfortunately the pipes were springing leaks faster than I could patch them so I had to put the original y-pipe/cat back on. I did take a good look inside the O2 sensor bung with a flashlight first. The honeycomb looked great. I hope it stays there for awhile and I get to keep the good mileage too. /dreaming

#17 daeron

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Posted 18 August 2008 - 08:47 AM

I like the gutted cat sound on my EA82 GL10.. I have a factory muffler in unkown condition, and a well ventilated exhaust pipe from head flange all the way back.. seafoam is an experience that should be done with lasers and pink floyd, smoke coming out from a billion tiny holes under the car... the sound is JUST right though, so I dont want to mess with it.

Just out of curiosity, have you checked the compression/leakdown on this motor? A leaking or down cylinder, or low comp numbers across the board might also be a culprit. Just an idea, probably a semi-useless task to perform as a rule-out, but it never hurts to know your combustion chambers are good and tight.

#18 Quidam

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Posted 18 August 2008 - 10:20 AM

I have a factory muffler in unkown condition, and a well ventilated exhaust pipe from head flange all the way back.. seafoam is an experience that should be done with lasers and pink floyd, smoke coming out from a billion tiny holes under the car...


Welcome to the Machine...real loud:)

#19 Big D

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Posted 01 February 2010 - 01:56 PM

GD/ Anyone,

Any new updates on this topic?

I'm going to try removing these items this week and cleaning the cat on my 84 Brat.

D

#20 GeneralDisorder

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Posted 01 February 2010 - 03:23 PM

I had a follow up post to this one - do a search it should come up.

Basically just cap off the metering ports. That seems to work the best as opposed to leaving them open or trying to use all the thermo-valves and vacuum valves to control them.

GD

#21 Petersubaru

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Posted 10 March 2010 - 06:21 PM

it was good that this thread was brought up to the surface again..EGR vac leak and rust made the old car run rough after winter..changed out the part and other alterations made this car run even better..very smooth..I can stand a nickel on end at 750rpm

#22 akc

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Posted 10 March 2010 - 08:56 PM

hey GD I had a vacuum lie snap off in my EA82 hatachi.. it is a small opening on the drivers hand side in the back under the air filter. We plugged it and ran and it sounded ok... but I wasn't sure if I could run it like that. Or would it be better to disconect the whole component Or should I ask what can you remove on the EA 82 Hatachi carb or is there a link for that.. thanks.... I LOVE your title.

#23 GeneralDisorder

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Posted 10 March 2010 - 10:52 PM

hey GD I had a vacuum lie snap off in my EA82 hatachi.. it is a small opening on the drivers hand side in the back under the air filter. We plugged it and ran and it sounded ok... but I wasn't sure if I could run it like that. Or would it be better to disconect the whole component Or should I ask what can you remove on the EA 82 Hatachi carb or is there a link for that.. thanks.... I LOVE your title.



Well - without pics of the port in question - I can't tell you for sure. Probably ok to disconnect it and cap it - only one way to know for sure though - try it or post a picture (start a new thread though) and we can try to ID it for you.

GD

#24 6 Star

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Posted 17 February 2012 - 03:27 AM

Hey GD, this thread is very helpful. Would it be possible to repost the pictures from the first post? They died. :(

#25 kabarakh

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Posted 29 February 2012 - 09:11 PM

Hey GD, this thread is very helpful. Would it be possible to repost the pictures from the first post? They died. :(


I second the motion!




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