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hitachi carb - issues after partial rebuild


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27 replies to this topic

#1 belacane

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Posted 25 September 2013 - 08:42 AM

Hi all,

 

Recently partially rebuilt and cleaned out the hitachi carb on my '86 brat. Replaced the main gaskets and accelerator pump, which was leaking all over the place. 

 

Started her up again, and went around the block a few times. Everything was fine. 

 

Later that day, started driving to a destination about 12 miles away. Around the time that she reached operating temperature, she started bogging a little bit (at around 60mph). Within about 15 more minutes of driving, she was bogging and bucking like a bronco at a rodeo (while driving at around 30mph).

 

Any ideas what I might have done that caused this? 

 

I took out the emulsion tubes to clean, and suspect I might have put them in backwards. Would that cause these type of symptoms? 

 

Only other things I can think of that is that I possibly connected the hoses wrong when I hooked things back up.

 

Thanks in advance!

 

 



#2 ivans imports

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Posted 25 September 2013 - 09:55 AM

on the feul inlet line at carb inside is a small screen that gos' to the neddle and float likes to plugup and bypass the carb thru return line chek this screen if you pull inlet fitting off can look in with light and see take two minutes



#3 ferox

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Posted 25 September 2013 - 12:50 PM

Did you replace the fuel filter?



#4 belacane

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Posted 26 September 2013 - 09:54 PM

Thanks guys, I"m going to try both of these. I'll post the results.



#5 PA Grown

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Posted 27 September 2013 - 12:33 AM

Having the same problem let me know!!!

#6 ivans imports

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Posted 27 September 2013 - 09:14 AM

Oh i love my TBI ea81 !!



#7 methusalah

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Posted 27 September 2013 - 04:28 PM

So...I have a 81 dl 4wd wagon that needs the card rebuilt...the accelerator pump is leaking right around the little cone shaped bellows/shaft area. Where can I find the bits or a kit to rebuild it? I know the hitachi isn't the best but I'm unwilling to get a weber.

Thanks!



#8 belacane

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Posted 28 September 2013 - 04:31 PM

So...I have a 81 dl 4wd wagon that needs the card rebuilt...the accelerator pump is leaking right around the little cone shaped bellows/shaft area. Where can I find the bits or a kit to rebuild it? I know the hitachi isn't the best but I'm unwilling to get a weber.
Thanks!


Any Autozone, O'Reilly's...etc. will have a carb rebuild kit. They cost around $20.

#9 belacane

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Posted 28 September 2013 - 07:13 PM

ok, I did what both Ivan and Ferox suggested.

 

However, when I took off the fuel inlet, there was no fuel filter/ screen, and thus I could not see if anything was caught in it.

 

I noticed a few screws were slightly lose though, tightened them, and restarted and drove the car. 

 

Again, It ran fine until a few minutes after it reached operating temperature, but then started to bog and buck again.

 

The only thing I can think of is that what is malfunctioning must be temperature related. 

 

I haven't a clue where to start looking beyond this. Any hints would be much appreciated.


Edited by belacane, 28 September 2013 - 07:19 PM.


#10 Gloyale

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Posted 28 September 2013 - 07:44 PM

Check the hoses at the thermo vacuum valve are intact and hooked up correctly according to the sticker under hood or FSM



#11 belacane

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Posted 01 October 2013 - 08:34 PM

bump? Anyone have any more ideas on this I can try this weekend when I have some time?



#12 ferox

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Posted 01 October 2013 - 10:10 PM

Check the hoses at the thermo vacuum valve are intact and hooked up correctly according to the sticker under hood or FSM

+1 The thermo vacuum valve could be opening up at temperature and causing a vacuum leak or some other vacuum related issue if it's not hooked up correctly.  It could also be leaning out when the choke disengages I guess.  In your op you said it bogged at 30.  Is it still doing it at that speed or just when you put some throttle on it?

 

I would go for a full carb rebuild personally, making sure to replace the venturi o-rings, dial in the float, and getting plenty of cleaner and compressed air through the passages.  I would also recommend simplifying the vacuum system.  I pulled everything off mine except the choke pull-off, vac advance, brake booster, and charcoal canister lines.  It made diagnosis much easier and removed a lot of possible vacuum leaks and malfunctions.

 

What is your idle mixture screw set at and idle rpm? 



#13 ivans imports

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Posted 02 October 2013 - 10:26 AM

have you changed the rear feul fiilter ? and try bolwing some compressed air back thru the rear line into tank mabee sock intank is pluged carfull a little bitt of air is all or can damage tank and spray gas make shure cap is off and a rag loosly over filler hole. Is funny no screen must have been removed from carb



#14 ferox

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Posted 03 October 2013 - 02:13 PM

have you changed the rear feul fiilter ? and try bolwing some compressed air back thru the rear line into tank mabee sock intank is pluged carfull a little bitt of air is all or can damage tank and spray gas make shure cap is off and a rag loosly over filler hole. Is funny no screen must have been removed from carb

That's a good point Ivan.  I should have explained a little better...the fuel filter is located at the rear-underside of the vehicle.  On other ea81s it's just in front of the rear drivers side wheel on top of a little metal plate, I don't know for sure if Brats are the same way.  An '86 would also have a vapor separator in the engine compartment that has a filter element in it as well.  It's not uncommon for people to think that the vapor separator is the fuel filter and replace it only while the actual fuel filter continues to clog, resulting in behavior like you've been experiencing.  If you knew that already, sorry for the over-explanation, but I thought it was worth making sure.



#15 Dinky26

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Posted 04 October 2013 - 10:08 PM

That's a good point Ivan.  I should have explained a little better...the fuel filter is located at the rear-underside of the vehicle.  On other ea81s it's just in front of the rear drivers side wheel on top of a little metal plate, I don't know for sure if Brats are the same way.  An '86 would also have a vapor separator in the engine compartment that has a filter element in it as well.


I can say for sure that the filter underneath holds true on the Brat, at least for the 86' anyway.

I have been thinking there was a filter in the engine compartment, apparently I have been deceived on that.

#16 belacane

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Posted 05 October 2013 - 02:42 PM

I can say for sure that the filter underneath holds true on the Brat, at least for the 86' anyway.

I have been thinking there was a filter in the engine compartment, apparently I have been deceived on that.

 

+1 The thermo vacuum valve could be opening up at temperature and causing a vacuum leak or some other vacuum related issue if it's not hooked up correctly.  It could also be leaning out when the choke disengages I guess.  In your op you said it bogged at 30.  Is it still doing it at that speed or just when you put some throttle on it?

 

I would go for a full carb rebuild personally, making sure to replace the venturi o-rings, dial in the float, and getting plenty of cleaner and compressed air through the passages.  I would also recommend simplifying the vacuum system.  I pulled everything off mine except the choke pull-off, vac advance, brake booster, and charcoal canister lines.  It made diagnosis much easier and removed a lot of possible vacuum leaks and malfunctions.

 

What is your idle mixture screw set at and idle rpm? 

 

 

Idle mixture is at about 1k rpms.

 

It bogs when I put throttle on.



#17 ferox

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Posted 05 October 2013 - 03:12 PM

How many turns out from seated is the idle mixture screw?  

 

Does the idle speed respond to changes in the idle mixture screw?



#18 jonas

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Posted 05 October 2013 - 03:52 PM

Use that rear disc conversion monies and get yourself a Weber! :brow:



#19 belacane

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Posted 05 October 2013 - 04:35 PM

How many turns out from seated is the idle mixture screw?  

 

Does the idle speed respond to changes in the idle mixture screw?

 

I don't know how many turns as of recently, because I was the one sitting in the car watch the tach the last time the idle was adjusted. 

 

It does respond to the changes in the idle screw.



#20 belacane

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Posted 05 October 2013 - 04:35 PM

Use that rear disc conversion monies and get yourself a Weber! :brow:

 

 

I'll be using that to pay my rent :\



#21 jono

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Posted 05 October 2013 - 05:04 PM

Well, where things happen differently 'down under' , I had this bucking, engine dying thing resolved only after a carb rebuild, full tune up parts replacement, ( dizzy 'rebuild' by previous owner :) think why they sold it) under tray fuel filter, under bonnet fuel filter and finally bought a new fuel pump and even that did not fix it. A blow through metal lines with all filters and pump disconnected, so was blowing air through sections at a time only when blowing the line from fuel pump to tank did I hear a thonk as crud hit the near dry floor of the tank , and I had the sender removed to see how clean and shiny the tank was until this rusty crud hit the floor of the tank ! Once cleaned out never given any problems since 1999 ! BUT, my problems of bucking were exact opposite on start up when temps were cooler - late night, early morning start ups going home on shift, usually never when I had the time to chase it !



#22 ferox

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Posted 06 October 2013 - 02:19 AM

I don't know how many turns as of recently, because I was the one sitting in the car watch the tach the last time the idle was adjusted. 

 

It does respond to the changes in the idle screw.

 

Ok so since it responds to changes in the idle mixture screw that means you're not bypassing the idle circuit.  The idle at 1000 is a little high. It should turn smoothly at 700-800, but that's a finer point to deal with later.

 

Here's the deal.  These symptoms are most likely fuel starvation of some kind.  The usual suspect is the fuel filter, but if you have replaced the fuel filter and the vapor separator then that leaves the fuel uptake sock in the tank, the fuel lines, or the carb.  The carb is obviously more complex than the other components so it's got more possibilities for clogging or mis-adjustment.  If you are going to run a carbed car these days you pretty much have to learn how to deal with it one way or another because most mechanics don't know spoob about carbs.  I guarantee that most of these old Subes went to the junkyard because of the carb.

 

Everyone has given good suggestions, but we're just kind of shooting in the dark with the remote diagnosis unless we can rule out the carb. The Haynes manual pulled the carb rebuild section straight from the Subaru Factory Service Manual (FSM), so you can easily do a full rebuild with the manual if you follow the instructions carefully.  I get my Beck & Arnley rebuild kits from Autozone for around $30.  I use aerosol solvent, compressed air, fine wire, and a wire brush for cleaning.  The rebuild kit comes with a little scale for adjusting the float.  Just be meticulous.

 

Jonas mentioned a Weber upgrade...always a good option if you can afford it.  It will need to be tuned...again it's just a matter of following the instructions.

 

It's possible that you have a vacuum leak that is leaning out the fuel mixture too much after the choke disengages, but that is difficult to fully diagnose without being able to eliminate the carb as the source of the issue.  Ultimately, your car is completely dependent on the state of the carb, so I highly recommend you dig in.  It's not as hard as it seems.  Once you do it you'll realize it's not that difficult.  I rebuild my Hitachi about every two years and it runs great.  It's just a fact of life with a carbed car.



#23 belacane

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Posted 19 October 2013 - 03:50 PM

so, does anyone have a good description or, even better,  picture of where the thermo vacuum valve is located??



#24 naru

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Posted 23 October 2013 - 12:11 PM

2 of them on the intake.One right side,one just left of the carb.



#25 ivans imports

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Posted 24 October 2013 - 09:26 AM

oh I love my TBI ea81 !






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