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EA81 dual carb intake reassembly


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12 replies to this topic

#1 Psyko

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Posted 06 March 2009 - 12:01 AM

I've got a dual carb intake that had been sitting a while, so everything needed a lot of cleaning. Well, I've finally finished rebuilding the carbs (I hope they work :o) and now would like to get them mounted on the intake. I took a billion pictures before, so I know hose locations and all. Instead, I'm wondering about screw settings and the base gaskets, for starters. I set the floats using numbers in the rebuild kit, but don't have clear info for the screws.

Screw settings:
I have no idea what is adjusted before it's put in and what is adjusted for tuning. Help...
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Base gaskets:
There is a thick hard piece that is sandwiched between gaskets (intake > thin gasket > hard thing > thin gasket > carb) that raised questions for me. I got a gasket with each rebuild kit, but the water preheat hole is wider than on the hard piece.
What is the point of the hard piece?
Do I need gaskets that match it exactly? (Need two more gaskets anyway.)
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Clean carbs. :)
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#2 monstaru

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Posted 06 March 2009 - 12:04 AM

appears to me that the screws would be for idle adjustment.....usually in all the way seated (softly)...then backed out 2-4 turns.

the regular ea81 carbs gets 4 turns out.

cheers, brian

#3 Jerry DeMoss

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Posted 06 March 2009 - 12:04 AM

I have a complete dual carb setup like yours in my garage. I will have to see what some of the adjustment screws are set at. The plastic spacer is just to prevent heat soak up to the carbs themselves.(as far as I know) Your carb gaskets look good to me actually. They don't have to match up perfectly to do the job.

#4 Frank B

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Posted 06 March 2009 - 03:16 AM

It's going to be hard to do with two carbs, but you start with 2 1/2 turns out, start the engine and let it warm up. Set idle speed, then adjust the idle mixture with tthe screws in question by turning in untill the engine stumbles, then out untill it smoothes out. Usually settling 1/4 to 1/2 turn farther out then that. All that with a single carb, so you may want to start with 1 1/2 turns out. You may be able to use an infared thermometer on the exhaust to balance them.

#5 Psyko

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Posted 06 March 2009 - 09:12 AM

Looks like I've got plenty of places to start for the IAC adjustment. What about the left adjustment screw, for the butterfly valve? I made note of what the gap was, when I took everything off to clean, but each carb was set differently and I just said screw it and figured I could get a better answer on here. Right now I just have the screws set so the valves are completely closed, which won't fly.

Thanks for the comments guys.

#6 mudman

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Posted 06 March 2009 - 09:30 AM

If you want to set the carb before you put it on, turn the air/fuel mixture out 2 1/2 turns. (not sure about your carbs, but that is the normal setting.) You really don't have to play with the idle setting because you can up the idle if its too low after it's on already. Once you get the ilde set to the RPM that you want (I would like about 800 rpm) you can begin to lean it out. Do not adjust the idle screw while you are adjusting the air/fuel mix. You turn the air/fuel screw in to have more air/less fuel. In = lean Out=rich. Once the engine starts to bog down, turn the air fuel screw out about 1/4 turn. Hit the gas and check for flat spots. If you find a flat spot/you will need to adjust fuel/air mix, probably by letting in more fuel. Once you get it where you think it's right, run the engine for a while. Pull the plugs and check to see if you're too rich or too lean. Adjust the screws accordingly.

#7 backinbrat

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Posted 06 March 2009 - 11:15 AM

this is a proper smart looking rebuild, good job fella, im guessing that you set the carbs exactly the same on the screws, up to mid temperature, and do as said above, for idle, use your ear against each carb and listen for suction amount, and use your hands over each carb carefully to give a good approximate for as to idle balance, mixture i guess you could do either by plug condition, exhuast probe, bung in the exhaust, and get the overall exhaust to 3.0/.1 % for optimum power, and any lower than that for your economy

this is only what i would do! dont nessercarily follow it bibically :P

#8 naru

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Posted 06 March 2009 - 02:47 PM

Looks like I've got plenty of places to start for the IAC adjustment. What about the left adjustment screw, for the butterfly valve? I made note of what the gap was, when I took everything off to clean, but each carb was set differently and I just said screw it and figured I could get a better answer on here. Right now I just have the screws set so the valves are completely closed, which won't fly.

Thanks for the comments guys.


Set the throttle valves so that they are open exactly equal-Use a wire gauge.Precise setting not so important at this stage,equality is.You want them open a bit,but,not enough to uncover the transition ports.Once running,adjust idle speed by turning these screws identically to preserve synchronization.

2 turns out on the mixture screws should get you running.Adjust these idependently thereafter.Might need to redo one after the other a couple of times.

Suggest tyou check part throttle synchonization once everything is together.

Lookin good!

#9 Phizinza

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Posted 06 March 2009 - 07:54 PM

You can adjust both those screws on both carbs easily while they are on the car. The onr on the right in the carbs casting is the idle mixture screw. Set this to 1.5 turns out. Set the idle screw (other one in that pic) the same. Get the car running and warm, you might need to adjust the idle screw on both cars (do this exactly the same on both). Once it idles (or close too) while warm adjust the idle mixture screw on both carbs until they are running smooth (go out until it gets rough, go in until it gets rough and then set it in between. Both of mine had to be set an eigth of a turn out of sync with each other to both run steady and smooth. Now hold a hose to your ear and to the top of one carby, then to the other. Go back and forth between then slowly adjusting the idle speed screws until the car is idling right. If they don't sound the same through the pipe no matter where you set the idle speed screws adjust the mixture ones until it does.

There are better ways, but they involve buying expensive tools.


As for those thick pieces. I believe they are there to stop vapour lock from heat in the carb. The water passages don't matter, they don't even go far into the carbs. The gaskets don't need to be exact for the water side but best if they are for the air for obvious reasons.
And yes, you need a gasket on each side of the piece.
I ended up having to take my carbs off again and ended up just making gaskets out of the appropriate material because it was 10x cheaper then buying more gaskets.

#10 hatchsub

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Posted 07 March 2009 - 09:42 AM

Or you can just ship me the whole motor briggs. I swear i will get it running. LOL Not sure it will get shipped back though :lol:

#11 Psyko

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Posted 07 March 2009 - 10:01 AM

Thank's for the input everybody. Not sure when I'll get around to actually tuning them though, since the block they go on is currently quasi split (getting a second hot stock cam made up for possible future uses) and rebuilding is going slow. Might just shove them on my current engine for pre-tuning...

Steve. Hold onto that dream. As soon as you start to think it will come true, you'll be sorely disappointed. :-p

#12 hatchsub

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Posted 07 March 2009 - 11:42 AM

Steve. Hold onto that dream. As soon as you start to think it will come true, you'll be sorely disappointed. :-p


LMAO :lol:

#13 DR DLEX

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Posted 07 March 2009 - 04:20 PM

wait on any screw adjutments until the intake is assembled.loosen the throttle screws all the way(plates CLOSED) when you set these up do it on an assembled engine(bench core).this way you can set the throttle rod in position .first set the drivers side carb(there swapped in the pics),adjust linkage w/ screw-rod(throttle plates CLOSED),then pass side, adjust linkage rod so they both have the same open time for both primaries and secondaries.this will save countless hours of tinker-tuning.also,if possible tune these on a running engine,not a "new" rebuild.these older hitachi's are seeing their years and when you have 2 one will hide problems of the other...i.e..clogged slow jet,dead power valve,acc pump.

been tinkering with my duel hat.-1600 for years


just sharing braincells......have fun




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