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Tuning the Carb


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5 replies to this topic

#1 glwagonman

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Posted 28 September 2009 - 09:41 PM

whats the best way for tuning the carb? i just got my wagon back together and my manual does not have very good info on tuning it?

Thanks in advance:banana:

#2 ferox

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Posted 28 September 2009 - 10:34 PM

Well now, that involves more questions and answers.

I don't work on ea82s, so I probably won't ask all the pertinent questions but I'll get you started.

Is it a Hitachi or Weber carb? I'll assume Hitachi.

What did you do to your engine, and did you rebuild the carb?

Is it a feeback carb? Probably easiest to post a picture of it.

Basic carb tuning is pretty straightforward and readily available on the internet [check into it for lean best idle procedure], but a Hitachi...especially a Hitachi in need of a rebuild is a a different story.

To get you started, make sure the timing is correct. IIRC on the ea81 I usually start with the idle mixture screw between 2-2.5 turns out, the ea82 is probably similar. Adjust/check timing, idle mixture, then air/fuel mixture, then repeat that procedure in that order until all those things line up with spec. Then go drive it and check it all over again, then do it again a few times, and if you have done extensive work on your engine you will probably have to do go through the procedure several more times.

There are good write-ups if you search for them. And other members (GD if he has time) can give you more specific instructions, but that should get you going.

If you carb hasn't been rebuilt within the last 2-4 years, you really should just do it. It's not that hard if you are methodical about it, and carb kits are like $30. Just take your time with the float adjustment. It's totally worth it, and your carb may never even get close to tuned without it. My '81 hatch just turned 270k, smooth as silk, great power, 29-31 mpg, rebuilt Hitachi carb. It's patient work though. It's all about the iterations. Good Luck

#3 GeneralDisorder

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Posted 28 September 2009 - 10:39 PM

Best way, by far, is with a wide-band O2 sensor.

If you mean how do you tune the thing without that level of sophistication - then you are limited to adjusting the idle speed, idle mixture, and timing. If you problem isn't at idle or transitioning from idle - then no amount of "tuning" will correct it - if that's the case then there is a problem and it needs to be "fixed" not tuned.

GD

#4 glwagonman

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Posted 29 September 2009 - 10:27 AM

its a hitachi carb non feedback and to my knowledge it has never been rebuilt so i think i will start with that

thanks guys

#5 torxxx

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Posted 29 September 2009 - 10:32 PM

I've rebuilt a few of these and tuned many. Words of Advice. When you go to change the needle/seat the seat wont want to unscrew out of the housing. its made of very soft brass and the head strips easily. the safest way to get it out his light heat with a propane torch and spray pb blaster on it when its hot. the heat will suck the pb blaster into the threads and break the rust/corrosion loose.
Set Idle speed to 750-850 RPMS and make sure engine is warm before making adjustments

As far as tuning it, unless you are rejetting a hitachi you wont need to do much. basically setting the idle mixture screw will be it. You will need a want to have a vacumn gauge on hand. Once you have the carb reinstalled, put the vacumn gauge on a constant vac supply (not a ported supply) Make sure you are somewhere between 20-25 Kpa ( I think its measured in KPA cant remember)

after you verify you dont have any vac leaks and are getting correct vacumn start playing with the mixture screw (its capped off from the factory so you'll need to drill out the housing to expose the screw) its located directed in the front middle of the carb and has a cap about the size of a dime on it. Turn the mixture screw either way. What your trying to do is get the engine to not idle up or down when you create a vacumn leak. your mixture will be set correctly when you can unplug a constant supplied vacumn line and the idle stays the same.

Good luck with it. sucks there isnt really any other adjustments that can be made. Make sure you clean out the air bleeds good when ur rebuilding.. They get plugged up and make the primary air bleed drip fuel into the throttle plate when the engine is idling

#6 GeneralDisorder

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Posted 29 September 2009 - 11:14 PM

Make sure you are somewhere between 20-25 Kpa ( I think its measured in KPA cant remember)


Typically in the US it's either plain old PSI(G) or inHg (Inches of Mercury Column). For smaller vacuum measurement it's inH20 (Inches of Water Column). And for even smaller measurement it's Torr and Micron..... but there are a LOT of vacuum measurement scales and different industries and applications neccesarily use different scales

But for a gasoline, 4 stroke engine, you would be looking for around 20 to 25 inHG

GD




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