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Guest Message by DevFuse

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Carb experts - help please! EA81 Hitachi Q's *update - fixed*

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12 replies to this topic

#1 GeneralDisorder


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Posted 02 April 2004 - 01:13 AM

Ok - I've rebuilt the Hitachi on my Brat - it's a DCP306-26. It runs AWESOME most of the time. Idles right around 700-750 RPM's when warm, and revs right up with no flat spots or anything. However, when I take a sharp turn, or a very fast take off, it will start to run like crap. It will idle, but slower than normal, and when you try to give it more gas, it just dies, it will run over 3000 RPM's or so when it's doing this, but nothing in-between that, and idle (just dies). I suspect it could be a sticking power valve piston. What do you guys think? It will run like this till you shut it off and let it sit anywhere from a few minutes, to a few hours (overnight one time). After you let it sit a while, it will start up as if nothing happened, and drive away just fine. I have checked the float bowl vent - it is functioning normally. I've disconnected most of the vacuum lines that are not needed and plugged them off. I've checked very carefully for vac leaks all around the carb with spray carb cleaner, and since it idles very nice, I'm pretty sure there are none.

And no - the answer is not to put on a weber. I want this stupid thing to work. It's a matter of priciple. The Hitachi is not a bad carb, and this is a learning experience for me. I really want to know how to rebuild them properly, since I have a number of the things sitting around here. Free is a very good reason!


#2 Caboobaroo


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Posted 02 April 2004 - 01:18 AM

you also might want to check to see if you're vapor locking. It sounds like one of the symptoms you have might be from vapor lock. Just something to check:D

#3 GeneralDisorder


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Posted 02 April 2004 - 01:28 AM

Vapor lock is when a hot engine vaporizes the fuel in the fuel lines going into the carb, and is generally seen on cars with engine mounted mechanical pumps.... I don't think that's likely on a Subaru, and besides that it wouldn't run at any RPM's if that were the case. It will idle, and run over 3k RPM's just fine. Also - one time I waited nearly 3 hours, and when I tried to start it, it still was acting up.... I would think it would have been plenty cool at that point to make vapor lock all but impossible.

A good theory, but not the problem in this case I don't think.


#4 GeneralDisorder


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Posted 02 April 2004 - 04:00 AM

When I rebuilt the carb, I did check the float level, and it needed no adjustment at that time. And since the carb only acts up "sometimes" that leads me to believe the float level to be correct. What I'm trying to say is that the carb will "act up" when I take a hard turn or a fast take-off, but not 100% of the time when I do these things. Only sometimes. Thus the car is driveable, and just when I think I've got the problem licked, it comes back and bites me. Very intermittant, and thus difficult to troubleshoot. If it were the float, I would expect it to act up on every hard turn, or fast take-off, and then return to normal under regular driving..... which this does not. The only thing that will correct the problem is to shut it off, and walk away for a while.


#5 Mr. Carb

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Posted 02 April 2004 - 04:22 AM

Maybe the float is sticking anyway? I'd take a look at the float bowl and see if gas is in it when it runs like crap... Very weird problem though. Check yer fuel pump and fuel filter?

#6 Turbone


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Posted 02 April 2004 - 04:44 AM

When you rebuilt the carb, is there a gasket that seperates the 2 halfs? I ask because I've torn down other carbs, but not a Hitachi. It kind of sounds like there is fuel going somewhere where it shouldnt be when you slosh it inside. If there was a break/misalignment of some kind on the gasket, this might happen. Or maybe the screws that hold the halfs together are not tight. I've only had one Soob that had a Hitachi on it, the rest are Weber and FI.

#7 Guest_taprackready_*

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Posted 02 April 2004 - 12:33 PM

I can't remember, and I'm at work with no manual to look at. Were is the bowl vent? If it happens to be similar to other carbs I've worked on it may be situated in such a manner that when you corner hard, excess fuel dumps right down the throat of the carb. If thats the case then a baffle inside the bowl or a longer vent tube would help prevent this. Hollies have this problem and they have a plasitc baffle that goes inside the bowl.


#8 GeneralDisorder


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Posted 02 April 2004 - 01:38 PM

Fuel pump is fine - both filters are brand new (napa, WIX filters)

Yeah - I was thinking the same thing about the bowl vent. In the case of the Hitachi, the bowl vent's to the evap canistor. I was thinking that maybe the bowl vent was being clogged by liquid gas from the "slosh" effect. And one time it was running like this, I disconnected the bowl vent line, shook a little bit of liquid out, and then she started just fine. But when the problem came back a few hours later, the vent line was still disconnected, and I even blew into the line - nothing was blocking it, and it still wouldn't run.

The gasket that seperates the halves is new. I compared it to the original (really crappy), and couldn't see any differences that would matter. The gasket is properly aligned - I have had the carb apart three times now, and each time this problem has come back....

Does anyone know if my symptoms could be from a stuck open full-power valve in the float bowl? It's not technically a serviceable part of the carb, but it's only supposed to come on at very low manifold vacuum (like wide open throttle), and if it were stuck open, it would be letting fuel right out the bottom of the float bowl.... I think this would cause a pretty rich condition, and maybe the problems I'm seeing. Anyone have experience with that before?


#9 Goatboy


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Posted 02 April 2004 - 01:46 PM

Hey GD! Long time no talk. I have similar issues with my Hitachi on my EA82. I see it when I hit a bump pretty hard or a strong corner. And then it bogs and won't run. usually a restart will fix the problem but not always. So if you figure it out let me know beause I think whatever is causing your problem is causing mine too.



#10 soobme


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Posted 02 April 2004 - 04:58 PM

I'm NOT an expert @ carbs, but do have YEARS AND YEARS of ex. with them on and off road :rolleyes:
It sounds to me like U have somthing that made it into your float bowl and is geting sloshed into 1 of your jets, or your ac. pump(and into the squrter) from time to time. Then when it sits long enough it floats back out into the bowl. If that's what it is U would be looking for somthing like a fragment from one of the seals, tiny tiny rock ect.

Just my $.02

#11 brat86


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Posted 02 April 2004 - 05:55 PM

Measure the fuel flow (gph and psi). There's another filter in the tank on the pickup tube. Little plastic job like the glass screw together filter elements. Usually drops off at high rpm's and load though. Had to rebuild mine 3 times in two years from that and fuel line gunk in a two year period.

How's the float hinges? The little loops and pin? Could be a side load sticking the float.

The bowl vent goes to the evap canister which also gets engine vac. A bad canister could cause negative bowl pressure.

#12 GeneralDisorder


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Posted 03 April 2004 - 10:27 PM

Well - I think I figured it out:

Posted Image

That's a picture of the primary jet before I removed the miniscule shaving of wood or whatever it was. Seems to run fine for now..... but it's done that before. Hopefully this was the problem, and I've finally got it licked.

Tony - looks like you were right on this one. This carb has been through hell and back. I pulled it off an engine that blew a HG, and the carb was full of "milkshake", but it runs really nice. I just had to get it cleaned out completely.


#13 ariva


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Posted 10 March 2005 - 01:07 AM

Dear Mr Carb,

Need some advice, if you could help. What happens if i put in a 1.8 Carb onto a 1.6 engine. Will i face problems?

Hope to hear from you soon .

Thank you

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