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EA71 Backfiring


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26 replies to this topic

#1 lvsarge

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Posted 03 March 2014 - 12:18 PM

Hey. Just wanted to pingpong around some ideas, again. My BRAT running an EA71, more often than not, will backfire when turned off. And just recently, after the car turns off, it actually cycled the engine (after it had been sitting) a few times. That scared the crap out of me when it happened.

 

So, obviously there's unburnt fuel. My question is, is it likely in the cylinders, or worse, would it be in the exhaust and the backpressure caused the engine to cycle through the exhaust valves? Doesn't sound likely, but then again this vehicle's been really odd to me.

 

Before, I wasn't able to get it started. This seemed to be attributed to tight valves. I adjusted the lash and she fired right up. Since then I've also slapped a new fuel filter in, and I adjusted the carberuator. It's running a dual-carb weber, and it is still idling very high. I have the idling screw backed out as far out as it will go (not touching the arm), and still my idle is close to 1300.

 

Doing some internet searching, some people are also suggesting that this scenario might also be caused from a lean condition in the engine? Fuel doesn't ignite in the cylinder, passes to the exhaust, when car shuts off exhaust creates a vaccuum, inducing air and then red-hot exhaust components causes the ignition of fuel. So I'm confused, and wanting to see if anyone has any idea. Rich or Lean? Or Leak?

 

Thanks in advance.



#2 RustyBrat

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Posted 04 March 2014 - 06:52 PM

i dont really know much, but im going to GUESS it could be a timing issue. a buddy's truck had a similar problem and after i got to looking at it i found out he had hooked up the plug wires in the wrong order, then advanced the timing all the way so it would kind of run, he's a dumbass needless to say. NOT that im saying you are, im just saying its something to double check! :)



#3 sjschlag

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Posted 04 March 2014 - 07:46 PM

check your timing, then check the fuel cut off solenoid on the carb. If the timing is off, that explains everything, if not, then the fuel solenoid isn't cutting off fuel to the engine when you shut it off, and the motor will either back fire, or "diesel" and run backwards!



#4 lvsarge

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Posted 05 March 2014 - 10:34 AM

Timing is something I've been putting off. I don't know why.

 

I will check that and report my findings here. Thanks for the input gentlemen.



#5 ivans imports

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Posted 05 March 2014 - 11:38 AM

Vacume leak exhaust leak idle to high timing to far advanced my 80 brat gives a pop when I shut it off. Vacume advance or mec advance sticking on idle should be 800-950. idle at 1300 with screw backed out sounds like vacume leak check hoses and intake gaskets



#6 1000 Pistes

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Posted 09 March 2014 - 06:56 AM

First take a look at the thin vacuum hose(from the advance regurator,on the dizzy,to the intake manifold) if it is broken,then you have to adjust the firing advance(by turning the dizzy left or right).

Good luck....



#7 lvsarge

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Posted 13 March 2014 - 06:00 AM

So I found a few vacuum plugs that were litterally crumbling away. I replaced them, cleaned the dizzy, and timed the motor. It was pretty far off. 8deg BTDC is the spec, and I was well past the last mark (20deg), probably closer to 30-35deg, if I had to guess.

 

It took some futzing with the carbuerator to get it so it wouldn't die in increments to get it down to the 8deg area. My idle is now down to around 900 rpm, which is good. Now, however, I have some pretty gnarly popping when I let go of the throttle. Idle sometimes feels a little sketchy, like it wants to die (doesn't though), but the exhaust is now my main concern. It does a rapid poppity-pop-pop-pop after every lift from throttle. Worse the higher rpm's it goes. I had to crank up the mixture just to keep idle alive, so I'm not sure if I'm too rich now under throttle?



#8 lvsarge

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Posted 13 March 2014 - 10:47 AM

I took a video... Here's the link:

 



#9 the sucker king

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Posted 14 March 2014 - 12:36 PM

"dual-carb weber" - do you mean two barrel carb, or are you running two webers? If the latter, I would love to see a pic. I want to do this, but seems like a TIGHT fit.



#10 1000 Pistes

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Posted 14 March 2014 - 12:47 PM

where I could find some intake manifold for twin WEBER carb?



#11 the sucker king

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Posted 14 March 2014 - 12:48 PM

where I could find some intake manifold for twin WEBER carb?

they turn up in the states from time to time. Post in the wanted section.



#12 lvsarge

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Posted 14 March 2014 - 01:27 PM

I meant twin barrel. My thoughts and my typing don't always coincide. Sorry.



#13 lvsarge

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Posted 17 March 2014 - 03:15 PM

Update:

 

I couldn't seem to time this thing right. It would be too lean or just barely rich enough to hold idle and act horrible on throttle response or be entirely too rich, unless timing was advanced far enough to compensate. So I decided to pull the plugs (which are maybe 200 miles old), and cyl 3 is fouled bad. Other plugs were showing a fairly lean to normal burn, but cyl 3 was completely black and the insulator was a very dark brown.

 

This is telling me oil is getting into the cyl one way or the other.. I cranked the engine with a flashlight in cyl 3 and sure enough the piston is completely covered in muck. So I'm thinking it's misfiring in cyl 3 (even though compression checked out ok...) ... I'm going to just pull the motor and look at everything under a microscope, especially on that side of the motor. Bad thing is I just put new sealant on the valve cover gaskets and those things are ON.

 

I was considering just seafoaming the motor and see how it goes, but I think this will be more thorough and tell me a bit about the motor in the process. Plus I've got some oil leaking from the oil pump and other miscellaneous odds and ends to clean up/fix while the engine is out.

 

Thanks to those who have given me some input. I'll post back again when I know more.



#14 spicypeanut

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Posted 17 March 2014 - 05:36 PM

I took a video... Here's the link:

 

th_WP_20140312_002_zps7e85d2af.jpg

Just wanted to say I'm loving this gauge cluster. Is that a cluster out of a different car? Ive never seen a brat with that cluster before.



#15 Leeroy

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Posted 18 March 2014 - 07:26 AM

That cluster came in the later Gen 1 'GL' Brats if I'm not mistaken.

#16 ivans imports

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Posted 18 March 2014 - 09:52 AM

My 81 brat has that one 81 year only. Anyway sounds lean and might have a broken piston ring land. Do a fuel volume check



#17 lvsarge

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Posted 20 March 2014 - 05:11 PM

Borrowing a friend's cherry picker tomorrow... Should have the motor out and taken apart in fairly short order.



#18 bertmann73

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Posted 25 March 2014 - 12:58 AM

ea71s are notoriouse for ring ridges cracking due to larger compression rings. My first subie tear down exposed a cracked compression ring and piston ridge. i was driving her like that for who knows how long and she did pop like hell on deceleration. I made a traffic cop reach for his peace once because i slowed down when i passed by and.. Poppedy-pop!!



#19 lvsarge

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Posted 25 March 2014 - 09:28 AM

Hey bertmann, you're kreepndeth on flat4, yeah? I should come pick your brain sometime.

 

Another question, not directly related to the cylinder (which is #2, not #3... I was thinking firing order, not cylinder layout):

 

I have the block pulled, and I've started the tear down. On top of the block is a hard tubing over each exhaust valve on both heads, which feeds back to my carb. I assume this is the factory PCV, book I was reading called it an air induction something-or-another. My valve covers also had a piece of tubing coming from the 1-3 cylinders to the same spot as the hard tubing via tee, and on the 2/4 cylinders valve cover a piece of tubing was coming in directly to a port on the intake manifold. Is that normal, and it is it necessary? I might be able to get a picture if needed..

 

I understand the ideal thing for emissions is to recirc the blowby back into the intake stream to be burned off, as is the point of a PCV system. But, why would I need the hard tubing on the cylinder heads and the valve covers recircing? Can I just throw breathers on the valve covers?



#20 bertmann73

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Posted 26 March 2014 - 12:36 AM

Yo Sarge. we gotta recruit more old schools here in vegas. I was Kreepndth on here too but during computer changes and forgetting passwords i got locked out and had to change ID. Really been here since 09



#21 lvsarge

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Posted 26 March 2014 - 12:44 PM

Nice. Yeah, I know another brat guy (2nd gen) but most everyone else is 98 and newer. It's kind of funny going to meets because half the kids don't even know what my truck is.



#22 bertmann73

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Posted 27 March 2014 - 01:54 AM

thats the guy with the 82 cyclopse right? also someone has an 86 turbo brat. when is the next meet? we gotta represent the roots brotha.



#23 lvsarge

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Posted 27 March 2014 - 09:08 AM

The 86 turbo brat, that's Jay. He's been around a long time. They meet every Friday, but I won't be out with my brat in a bit, nor this Friday in particular as I have a dinner I have to attend. In any case, I've got the motor on a stand, and the heads off. I plan to do some cleaning and painting with the motor out, so it'll be a bit before I take the brat out.. I have an 06 sti I drive also.

 

Anyway, as for this motor, there was quite a bit of carbon build up on the heads and valves. The #2 cyl looked worse, and more wet than #4... I pulled the intake valve on #2 only and checked the back of it, which had some considerable build up... But there was shiny metal around the back of the valve and in the seat.. Does it look normal-ish? I ask because this is my first engine tear down, and I'm not 100% confident on what to look for.

 

 

 



#24 ivans imports

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Posted 27 March 2014 - 10:55 AM

looks fine show us a pic of pistons on the problem holes little bit of oil burning is all I see



#25 lvsarge

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Posted 27 March 2014 - 11:25 AM

I only have a picture of the pistons in the cylinder right now... I'll post here. I haven't removed them yet.

 

Obviously cyl 2 is on the left.

 






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