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EA71 sputtering above idle


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6 replies to this topic

#1 talldude

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Posted 28 July 2013 - 12:45 AM

I just went through an experience tuning an EA71 and thought it might be helpful to discuss.  Resurrecting a long sitting engine in a 79 BRAT that really didn't run well.  Turns out all the engine wires were melted together near the carb, so I spent a day rewiring the harness and cleaning grounds, etc.  Next was all new vacuum hoses, routed per the underhood diagram (this is sunny CA and I don't want to go to prison).  Then a basic hitachi carb clean and rebuild, new accelerator pump, float level set, choke adjusted.    Next, adjusted the valves, new plugs, wires, cap and rotor, air gap set on disty pickup coil (transistor system, not points),  even new battery cables. Fired right up  and the choke opened up as she warmed up.  Set ignition timing, idle speed and mixture.  

Now the fun:  Any RPM above idle was erratic, engine would not take throttle and backfiring out the exhaust. It acted as though the accelerator pump wasn't working and the carb wasn't delivering fuel except in the idle circuit.  Except the accelerator pump WAS working and you could see a little fuel entering the venturi, and the fuel level never dropped in the float bowl sight glass when it was running.  Maybe it somehow wasn't enough fuel, so new fuel filter, fuel pump ops check good, lines cleared back to tank with a little air pressure and the gas cap off.  No change.  Next, cleaned EGR ports and valve.  EGR valve tested good. No change.  Anything above idle still is erratic with lots of popping out the exhaust, will not take throttle.  Sometimes I could get rpm to come up slowly, as if vacuum advance wasn't working.  Checked vacuum advance and retard on the distributor with a vacuum pump  and vacuum signals from the base of the carb with a vacuum guage.  Everything checked out good.  Cleaned the carb again to make sure I didn't miss something there.

  Then I noticed the timing light was intermittent when the engine stumbled.  Ignition coil resistance was normal both primary and secondary, so naturally I replaced it anyway for good measure.  A small improvement but not enough.  Took the cover off the ignition control unit and checked for broken wires, corrosion, broken solder joints, anything.  It looked perfect so that went back together.  No change, so at least I didn't make it worse...

Last stop distributor pickup coil, the one inside the distributor that has the air gap adjustment.  Per my Chilton's manual this coil should show 130-190 ohms resistance.   It measured 180 ohms but I could get a small fluctuation when I gently wiggled the wires, but still in limits.  Put it back in and reset air gap.  No change.  I was running out of ideas fast.  Finally dug in my scrounge and found a new pickup coil.  Measured 160 ohms, so I installed it and voila, problem solved!  

 

Sorry for the long wind and  but hopefully this will help others.  My first impression was it was definitely a fuel/carb problem.  I would have bet on it, mainly because of the bad rap Hitachis have gotten.  I'm willing to bet  more than a few problems get blamed on these carbs when it is something else.  Also, a multimeter doesn't always tell you what you need to know, because it doesn't simulate the actual voltage/current/temperature through a circuit. Also, if it's 35 years old, it's probably tired or worn out!  For what it's worth...



#2 moosens

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Posted 28 July 2013 - 10:58 AM

Thanks!

Did Ahnold legislate doing time for emissions offenders? Death camp for oil leakers? Lol

Seen those pickup units on eBay around $13 FYI to all.

#3 ferox

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Posted 28 July 2013 - 11:36 AM

Adjust your valve lash to spec and see if that helps.  It probably needs to be done regardless of whether it's the problem.



#4 bertmann73

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Posted 19 August 2013 - 11:42 PM

I had the same problem on my brat...mine turned out to be the points condensor .........of course after replacing the points, coil and not to mention a couple days of headache and trouble shooting.

 

Another FYI....When the alternator or voltage regulator goes the car dies after a few minutes as the light pops on. most cars i have ever owned will run off the battery if these go, but not the old soobs.....after thinking it was the alternator and being stranded again.....i replaced the regulator and all was well



#5 bonvo

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Posted 19 September 2013 - 08:17 PM

sounds like what im dealing with i have a dead spot in the throttle i know its the accel pump though cause the entire ignition system is new the fuel system has been gone threw and the carb rebuilt it these carbs are not good they have a bad rap for a reason there just isnt enough accel pump to make it happy though im gonna try adjusting my voltage regulator my charge light is dimly lit it has enough voltage to keep the battery charged though



#6 talldude

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Posted 22 September 2013 - 10:42 PM

On a related note,  I wanted to mention I just installed an MSD Streetfire igniter control unit and coil in my '78 BRAT, which mostly ran well but I felt could have better driveability.  It also got  a new distributor pickup coil  at the same time.   Now it runs like a different truck:  smooth starting every time, idle is rock solid whether it is cold or hot, smoother running, and I can now hold 65 mph up every grade from Sacramento through 4000 feet where I live, and no detonation.  I left the timing set stock, and the timing light does not wander on the mark like it did before.  I can already see improvements in mileage, too.  So far very happy with this mod.



#7 moosens

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Posted 23 September 2013 - 01:25 AM

Can't tell ya how many times I see one on eBay and say "ah, I'll get it another time."

Thanks for the post. On my list NOW. :)




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