backfiring

[blindrummer]

85 EA81 hitachi

146,000 miles

i'm having some backfiring woes

at cold idle when i press the throttle- there is a pause, drop in rpm's, then it kicks in with pat-dat-dat-dat

most times I let er warm up, but occasionally i have to start and go

this is when it really backfires, upon releasing the throttle to shift

once warm no backfiring at all

gas tank replaced year and half ago

fuel filter one year ago

air filter, sparks, plugs, and turned up the idle slightly one year ago

i was getting 25 mpg now i'm at 23 mpg but prob from the hills i'm mounting every day

please help

[opus]

Vacuum leak that has to do with the choke?

[Subarule]

 

85 EA81 hitachi

146,000 miles

i'm having some backfiring woes

at cold idle when i press the throttle- there is a pause, drop in rpm's, then it kicks in with pat-dat-dat-dat

most times I let er warm up, but occasionally i have to start and go

this is when it really backfires, upon releasing the throttle to shift

once warm no backfiring at all

gas tank replaced year and half ago

fuel filter one year ago

air filter, sparks, plugs, and turned up the idle slightly one year ago

i was getting 25 mpg now i'm at 23 mpg but prob from the hills i'm mounting every day

please help

 

The anti-backfire valve is shot? Distributor has a problem (like mositure in it)?

[blindrummer]

i'll check the distributor tommorrow

where is this anti-backfire valve

how can i check the choke

[Subarule]

 

 

where is this anti-backfire valve

 

I don't know. I just know that mine has needed replacing for a really long time. I get a backfire (not a big loud 'ka-pow' one) when the engine is still is still on the cold side and I first go through the gears. And when the engine is fully warmed up I get a backfire when shifting gears going up steep hills.

 

A new anti-backfire valve is expensive, which is why I haven't replaced mine. Don't think it would be a good idea to get one from a junkyard. They are also getting very hard to find new, so I guess I should buy the one I ran across recently.

[GeneralDisorder]

The "anti-backfire valve", for which the correct terminology is "anti-afterburn valve" is not your problem. It's sole purpose is to prevent the engine from sucking fuel through the carb on closed-throttle coasting. Even if it were not functioning (or removed as in the case of every one I've owned [they fail anyway]), it will not produce large backfireing. What it will do is allow the engine to ingest a small amount of fuel through the idle circuit on closed throttle coasting (down long, steep hills, etc). This will produce suttle popping - completely harmless and pretty standard for every car made prior to 1980.

 

No - your backfiring between shifts is due to exhaust leaks and possibly a rich mixture and/or poor ignition. The poor ignition/rich mixture is allowing an excessive amount of unburned fuel into the exhaust system - the exhaust leak is allowing in fresh air (oxygen) - they mix inside the exhaust and are spontaneously ignited by the high exhaust temps. Generally only leaks in the header (y-pipe) will cause backfireing as leaks farther down don't get hot enough to ignite.

 

Your leak is either at the heads, air suction valve(s)/piping, or in the y-pipe itself (they often like to crack at the junction to the cat - check under the heat sheilds). And you need to fix the source of the unburned fuel.

 

Sounds like you have quite a few problems. Perhaps you should go through the engine in general and give it a decent tune up.

 

For comparison - my '83 hatch, running a Weber, and with one cylinder running 20% lower comp. than the other's - I get 25 MPG daily, and I just ran out to the Beach with it ~ 250 miles. I pulled in 30.5 MPG on that tank and the first 65 miles was in town. Running properly in top condition, an EA81 4WD hatch can turn in 27/32 MPG figures easily. You definitely have issues.

 

GD

Edited September 16, 2009 by GeneralDisorder

[Twitch de la Brat]

I think we're on the right track with this one, but as was already mentioned,

they are spendy.

 

Another thing to check is for a leak in the exhaust.

This could be allowing for a proper air/fuel mixture for the hot exhaust pipe to

ignite the mix and cause the back fire.

 

Does it rumble when you let off the gas or when you downshift?

 

But I say if its not an easy fix, just learn to live with it, enjoy it even.

To me its just another quirk about my beloved Subaru BRAT.

It makes it easier to be noticed and not get run over :-p

 

Twitch

[GeneralDisorder]

But I say if its not an easy fix, just learn to live with it, enjoy it even.

 

Not a good idea. It WILL get worse over time, and ultimately you WILL blow soft-ball sized holes in the muffler. Don't ask how I know this.

 

It's relatively easy to fix if you know what you are looking for, and it is indicative of problems that are robbing power and economy from your ride - plus it attracts *unwanted* attention from the authorities who (trust me) have nothing better to do than hassle the guy with the weird, old Subaru. Don't ask how I know that either .

 

GD

[Twitch de la Brat]

Not a good idea. It WILL get worse over time, and ultimately you WILL blow soft-ball sized holes in the muffler. Don't ask how I know this.

 

It's relatively easy to fix if you know what you are looking for, and it is indicative of problems that are robbing power and economy from your ride - plus it attracts *unwanted* attention from the authorities who (trust me) have nothing better to do than hassle the guy with the weird, old Subaru. Don't ask how I know that either .

 

GD

 

Don't worry GD, I'm gonna replace the whole exhaust with a 2" or 2.25"

Flowmaster and make sure every leak is sealed completely when its done.

 

And the authorities just point and wave or shake their heads around here.

They are much more after the "BWAAAAAP" of ricers, than the rumbling growl

of an old sube.

 

And I hope you learned your lesson :-p

I've never seen a problem with a small backfire, so I'm not knocking your

advise, but I wouldn't worry about it, personally.

 

Twitch

[Subarule]

The "anti-backfire valve", for which the correct terminology is "anti-afterburn valve" is not your problem. It's sole purpose is to prevent the engine from sucking fuel through the carb on closed-throttle coasting. Even if it were not functioning (or removed as in the case of every one I've owned [they fail anyway]), it will not produce large backfireing. What it will do is allow the engine to ingest a small amount of fuel through the idle circuit on closed throttle coasting (down long, steep hills, etc). This will produce suttle popping - completely harmless and pretty standard for every car made prior to 1980.

 

No - your backfiring between shifts is due to exhaust leaks and possibly a rich mixture and/or poor ignition. The poor ignition/rich mixture is allowing an excessive amount of unburned fuel into the exhaust system - the exhaust leak is allowing in fresh air (oxygen) - they mix inside the exhaust and are spontaneously ignited by the high exhaust temps. Generally only leaks in the header (y-pipe) will cause backfireing as leaks farther down don't get hot enough to ignite.

 

Your leak is either at the heads, air suction valve(s)/piping, or in the y-pipe itself (they often like to crack at the junction to the cat - check under the heat sheilds). And you need to fix the source of the unburned fuel.

 

Sounds like you have quite a few problems. Perhaps you should go through the engine in general and give it a decent tune up.

 

For comparison - my '83 hatch, running a Weber, and with one cylinder running 20% lower comp. than the other's - I get 25 MPG daily, and I just ran out to the Beach with it ~ 250 miles. I pulled in 30.5 MPG on that tank and the first 65 miles was in town. Running properly in top condition, an EA81 4WD hatch can turn in 27/32 MPG figures easily. You definitely have issues.

 

GD

 

I've read elsewhere online, on auto parts sites and auto forums, that the correct term is "anti-backfire valve". And that's the way it's listed in parts suppliers catalogs. That's what my local Subaru dealer calls it and that's what my mechanic's shop calls it when they search for one. If you do a Google search for anti-backfire valve you come with lots of hits, even one that defines it as the correct name instead of "after-burn valve".

[GeneralDisorder]

I've read elsewhere online, on auto parts sites and auto forums, that the correct term is "anti-backfire valve". And that's the way it's listed in parts suppliers catalogs. That's what my local Subaru dealer calls it and that's what my mechanic's shop calls it when they search for one. If you do a Google search for anti-backfire valve you come with lots of hits, even one that defines it as the correct name instead of "after-burn valve".

 

That's nice and all, but all your sources are wrong. 1984 Factory Service Manual:

 

 

At any rate this valve is NOT the cause of major backfireing. As I said this is only to prevent the small pops durring closed throttle coasting. I don't have a single one of these currently installed and I don't have any backfireing either.

 

GD

[Subarule]

 

That's nice and all, but all your sources are wrong. 1984 Factory Service Manual:

 

 

At any rate this valve is NOT the cause of major backfireing. As I said this is only to prevent the small pops durring closed throttle coasting. I don't have a single one of these currently installed and I don't have any backfireing either.

 

GD

 

 

You won't find it listed anywhere as an after-burner if you go to buy one.

 

I was only offering it as a suggestion for backfiring. I get those "pops" and they're annoying as well as embarrassing if other drivers are close enough to hear them.

[robm]

With the drop in fuel mileage, it looks like a rich mix is a big part of the problem. Exhaust leaks may allow it to ignite, but there shouldn't be anything there to ignite at all. lt happens when it is cold, but not when it is warm. I suspect a rich mix, with poor vapourization when cold allows lots of fuel into the exhaust. When warm, enough burns in the cylinder that it won't explode. Maybe the choke is set a little too rich? Maybe the carb needs a good overhaul, as one of the emulsion tubes is crudded up so more gas than required is flowing into the venturi?

 

Is the exhaust pipe black and sooty?

[GeneralDisorder]

I get those "pops" and they're annoying as well as embarrassing if other drivers are close enough to hear them.

 

If they are loud enough to annoy you then they aren't being caused by a faulty anti-afterburn valve. That was my point. I haven't a single one of them installed and you have to know what you are listening for to even hear the difference. It's more of an economy device to appease the EPA than anything. Cars didn't have these for 75 years - it wasn't until the 80's that stuff like this caught on.

 

GD

[Subarule]

 

If they are loud enough to annoy you then they aren't being caused by a faulty anti-afterburn valve. That was my point. I haven't a single one of them installed and you have to know what you are listening for to even hear the difference. It's more of an economy device to appease the EPA than anything. Cars didn't have these for 75 years - it wasn't until the 80's that stuff like this caught on.

 

GD

 

"Pops, popping" doesn't describe the sound properly. When I'm negotiating a steep hill it definitely backfires. Old Subraus just don't like steep hills. When the engine is cold and I go through the gears then it's more like a clattering sound. Something in the emission or the exhaust system, I imagine.

 

I'm keeping the car stock and I would love to get rid of those noises.

[GeneralDisorder]

Leaks in the exhaust or the ASV's, and unburned fuel will cause backfireing. Generally speaking, a good running (street) engine that's properly tuned will not backfire. Race engines are a horse of a totally different color and backfireing is generally unavoidable.

 

GD

[Subarule]

 

Leaks in the exhaust or the ASV's, and unburned fuel will cause backfireing. Generally speaking, a good running (street) engine that's properly tuned will not backfire. Race engines are a horse of a totally different color and backfireing is generally unavoidable.

 

GD

 

I'm sure it needs some tweaking. I have a bunch of new (and used) parts* that I've bought over the past year that I intend to have installed all at once so that will be the time to do the tune-up. I was thinking that when we get into the bad weather part of the year would be a good time to be w/out my wheels for a few days while it's being worked on.

 

*

trunk struts

stabilizer bars

headlights, sidelights

front bumper

rebuilt Hitachi carb

evaporative canister (or whatever that thing is called)

some miscellany

[blindrummer]

 

Is the exhaust pipe black and sooty?

 

yes the exhaust is black and sooty

its a new muffler so its easy to tell

[blindrummer]

well there is an exhaust leak at the catalytic converter

after the y-pipe

its pushing air forward towards the engine

should i replace the catalytic converter???

and how do i adjust the fuel mixture???

[GeneralDisorder]

You need to start by welding up that leak - that is the major source of the backfires.

 

As for the mixture... with the Hitachi it's not such a simple question to answer. There aren't any adjustments except for idle and that's not your problem. A rich exhaust is generally a condition caused by poor engine tune in general. You start the process at the begining - check your compression. If you don't have good comp. it's going to be rough to tune out all the harsh running and idle misses, etc.

 

From there you need to verify good ignition - check your spark color. Gap/clean your plugs, etc. Set your timing and check for proper advance.

 

Get a vacuum gauge and check your readings - check for leaks.

 

Verify proper spray pattern from the carb nozzles.

 

If you haven't found the solution after that you may have to tear the carb down for a clean and rebuild.

 

GD

[blindrummer]

i just replaced the PCV, fuel separator, had em here figured couln't hurt

pulled one plug and looks normal, i have everything to check compression just have some ???

 

O.K. compression test- do i need to disconnect the fuel supply???

and what should i do to stop the spark???

should i remove all plugs or one at a time???

 

how do i check the spark color???

 

What does this mean .)

Set your timing and check for proper advance.

GD

thanks GD

[blindrummer]

GD i just found your (you and your hitachi) thread

where is this roll pin to access the idle fuel/air mixture

could this be the solution for rich fuel

[GeneralDisorder]

O.K. compression test- do i need to disconnect the fuel supply???

 

Yes - disconnect the fuel pump - it's under the car.

 

and what should i do to stop the spark???

 

Just pull the wire going from the coil to distributor cap.

 

should i remove all plugs or one at a time???

 

All of them, and crank with the gas pedal fully depressed.

 

how do i check the spark color???

 

Pull the plug and ground the electrode to the block while you have someone crank the engine over. Color should be white with tinges of blue. Orange or red spark = weak spark.

 

What does this mean .)

thanks GD

 

You need a timing light to check the ignition timing - get one and follow the directions if you don't have one. #1 cylinder is the closest to the front of the car on the passenger side - that is the one you use for checking/setting the ignition timing.

 

While you are checking the timing, rev the engine and see that the timing increases with increased engine speed. Also check the vacuum advance pot on the distributor by sucking on the line - the advance mechanism inside the distributor should move and stay there till you release the vacuum.

 

GD

[GeneralDisorder]

GD i just found your (you and your hitachi) thread

where is this roll pin to access the idle fuel/air mixture

could this be the solution for rich fuel

 

Bottom front of the carb - look for a mixture adjustment screw blocked by a vertical roll pin.

 

It's probably not the issue if it's still got the pin in it - if not then someone may have mucked with it.

 

It's not the solution for anything other than a rich IDLE. If it's rich at anything other than idle then it's not your problem.

 

GD

[Brock Samson]

Thank you General Disorder! I unknowingly had an anti-afterburn valve that worked only some of the time. So naturally I took apart the carburetor hundreds of times. losing the original settings while re-adjusting it each time the anti-afterburn valve got stuck in a different place.

 

After removing the valve all sporadic symptoms went away. Back fires a whole lot more now on account of the exhaust system ending 3 inches past the catalytic converter. I call it an audible oxygen sensor, allowing me to further tune it till it doesn't burn so rich. once warmed up it purrs nicely now. at one point it got almost 29 mpg before i messed with anything. now it gets 15 to 19mpg.

 

Any tips on fine tuning the Hitachi DCJ306-15?

 

or anyone have one setup just right already? Choke set at? air screw? fuel mix screw? how many turns and such?

 

or.... now that it can be relied on to bolt through intersections with reliable acceleration, I am just burning that much more gas by hot rodding it around??