Anti-Backfire Valve?!

[RudyV]

my 620 that i got not long ago and it went bad... according to my old auto teacher, i believe him he owns a z himself. so now my question is can any one help me locate a new one? or used. whats inside these thingys? mine is i guess clogged because it wont let air threw so could i clean it up with some brake cleaner?

 

is there a diagram of how it works?

 

 

anyone have one  :poke:

 

thanks!

[h190]

anti diesel solenoid?  Spring, plunger, magneto.  Thats it.

[RudyV]

ahhh no i dont think so  :confused: this one, on mine is behind the carb with a hose to the air filter pan and 2 other places gosh i forgot to take pictures :(

im at work and well yeah

 

my teacher said it feeds the carb more air when you suddenly stop pressing gas (if i remember right :hmm: ) so it wont burn in the header and cause a backfire.

[bilzbobaggins]

idle cut solenoid?

[HRH]

It's the little round dingus that looks like a mini-egr.  You don't really need it unless you're using the stock system.  Throw a 32/36 on it and be done with it.

[RudyV]

It's the little round dingus that looks like a mini-egr.  You don't really need it unless you're using the stock system.  Throw a 32/36 on it and be done with it.

 

yes that ! well i am all stock. and well i dont have webber carb kind money  :blush:

 

has anyone had this problem before? do they get clogged or just completely go bust?

[bonvo]

i might have on floating around still but i would rather keep all my smog equipment together as a "kit" of sorts what year is the 620? you live in seaside im surprised there is any truck left my ex goes to school there and i could literally watch the surface rust form on my roof 

[RudyV]

i might have on floating around still but i would rather keep all my smog equipment together as a "kit" of sorts what year is the 620? you live in seaside im surprised there is any truck left my ex goes to school there and i could literally watch the surface rust form on my roof 

 

 

its a 78 L20 and well i think you may be referring to Seaside, Oregon

in from Seaside, Ca...unless...you mean my seaside

in that case...whoa haha

[bonvo]

yes i mean seaside cali its by montery she went to csumb

[RudyV]

yes i mean seaside cali its by montery she went to csumb

 

:hyper: oh my gaaaawd! haha whaaat

you've been around here?

 

i thought i was the only one..beside this 510 down my street and another 620 i just recently saw.  :hairy: civilization

haha

[datzenmike]

When you let off the throttle the intake air goes over rich and burns in the exhaust manifold and pops and backfires. To reduce this (and to save a little gas too) an anti backfire valve is installed. One side of the valve draws filtered air from the air cleaner. The outlet goes to the intake manifold. There is a smaller hose from the intake that sends a vacuum signal to the AB valve. When the vacuum suddenly rises above a pre determined amount when suddenly closing the throttle, the AB valve opens and dumps air into the intake to reduce the air/fuel ratio to something much leaner. It reduces hydrocarbon emissions out the tailpipe but actually save you gas too!

[bonvo]

for 2 years i was down there at least once a month for about 2 weeks car woulda looked like this when i was down there

 

if you like ill pull out my old smog stuff if your interested

[ggzilla]

Yes, Mike is right on track. I would only add that the AB valve is used with Air Pump (or passive Air Injection), which injects extra air into the exhaust system. It is not used nor needed for an engine that doesn't have this.

[RudyV]

When you let off the throttle the intake air goes over rich and burns in the exhaust manifold and pops and backfires. To reduce this (and to save a little gas too) an anti backfire valve is installed. One side of the valve draws filtered air from the air cleaner. The outlet goes to the intake manifold. There is a smaller hose from the intake that sends a vacuum signal to the AB valve. When the vacuum suddenly rises above a pre determined amount when suddenly closing the throttle, the AB valve opens and dumps air into the intake to reduce the air/fuel ratio to something much leaner. It reduces hydrocarbon emissions out the tailpipe but actually save you gas too!

 

 

Yes, Mike is right on track. I would only add that the AB valve is used with Air Pump (or passive Air Injection), which injects extra air into the exhaust system. It is not used nor needed for an engine that doesn't have this.

 

okay i understand now.

hmm so why do they brake? is it carbon?

[RudyV]

for 2 years i was down there at least once a month for about 2 weeks car woulda looked like this when i was down there

 

if you like ill pull out my old smog stuff if your interested

 

geez it looks so nice :thumbup:

and well i would just need that valve... i was thinking if it may be carbon that clogged it. i could probably just clean the inside with some brake cleaner??

[datzenmike]

Yours isn't working? Is there vacuum from the intake on the small hose going to it? Hose fell off/cracked and leaking?

 

Remove and put a small hose on it and apply vacuum from a borrowed hand pump. At some point the valve should open and you should be able to blow through one of the two larger hoses. I can't find the vacuum rating but it would have to be over 20 in, Hg or it would 'leak' at idle vacuum.

 

The valve may just be stuck, tap it on a piece of wood to try and dislodge. There is no way to service it only replace.

[RudyV]

Yours isn't working? Is there vacuum from the intake on the small hose going to it? Hose fell off/cracked and leaking?

 

Remove and put a small hose on it and apply vacuum from a borrowed hand pump. At some point the valve should open and you should be able to blow through one of the two larger hoses. I can't find the vacuum rating but it would have to be over 20 in, Hg or it would 'leak' at idle vacuum.

 

The valve may just be stuck, tap it on a piece of wood to try and dislodge. There is no way to service it only replace.

 

 

okay will try when i get home! 

 

yes there is a small hose it appeared fine,

 

ill post up what happens next  :hug:

[ggzilla]

They don't normally break. Most of them i would guess are still working.

[RudyV]

IM DONE!

i was playing around with the valve last night ;)

 

and it seem to let air threw so i hooked it up and yeah it worked for by separating the backfire

but then again with the loud firecrakers

 

so im done. weber in hitachi out. hitachi is pretty new so ill store it.

 

question will any 32/36 work or will a certain #? 

looking on ebay they have listings for jeep 32/36 mazda 32/36 yeah... is it because the adapter. thanks guys

[ggzilla]

Any 32/36 will work ...

 

But ... they are jetted slightly differently. The ones for L-series engines are jetted appropriately stock engines and will run quite well. A jeep one may not work very smoothly.

 

And they have different choke types. Electric choke works best.

 

 

Why do you want to change the carburetor? If you get the 32/36, you will need to disable (or fix) the Air Injection setup. The stock Datsun carb will work w/o a working Air Injection system.

[RudyV]

Any 32/36 will work ...

 

But ... they are jetted slightly differently. The ones for L-series engines are jetted appropriately stock engines and will run quite well. A jeep one may not work very smoothly.

 

And they have different choke types. Electric choke works best.

 

 

Why do you want to change the carburetor? If you get the 32/36, you will need to disable (or fix) the Air Injection setup. The stock Datsun carb will work w/o a working Air Injection system.

the anti backfire valve is killing me,

plus all that smog stuff :sick: all the lines are not good to begin with there all probably leaking and what not.

and air injection? on the weber?

[DanielC]

Here is a diagram from the Nissan service manual, emission control system, 1970-1971

The glup, or anti-backfire valve is normally closed.  When you suddenly close the throttle, the air stops flowing through the carb, and the fuel keeps going for a split second longer.  This causes a momentary rich condition, and not all the fuel burns in the cylinder, and sometimes it is so rich the cylinder actually misfires.  When this shot of over rich gas reaches the exhaust ports, where the air pump is injecting fresh air in to the exhaust system, it then burns, or explodes, commonly called a back fire.

The gulp valve dumps a shot of air into the intake manifold, and greatly reduces the over rich condition in the engine, when suddenly closing the throttle.

 

If you still have the air pump on your engine, you probably still need the gulp valve, no matter what carb you run.

[RudyV]

Here is a diagram from the Nissan service manual, emission control system, 1970-1971

The glup, or anti-backfire valve is normally closed.  When you suddenly close the throttle, the air stops flowing through the carb, and the fuel keeps going for a split second longer.  This causes a momentary rich condition, and not all the fuel burns in the cylinder, and sometimes it is so rich the cylinder actually misfires.  When this shot of over rich gas reaches the exhaust ports, where the air pump is injecting fresh air in to the exhaust system, it then burns, or explodes, commonly called a back fire.

The gulp valve dumps a shot of air into the intake manifold, and greatly reduces the over rich condition in the engine, when suddenly closing the throttle.

 

If you still have the air pump on your engine, you probably still need the gulp valve, no matter what carb you run.

 

hmm okay good to know, was going to jump in not knowing how deep the situation was.

 

could a vacuum leak also cause all this trouble??

 

 

 

and so how could i disable the air injection...nevermind found ittt 

 

im putting this l20 in a 521 in January so its just for future reference.

 

 

 

 

PS this is in a 78 620, body is rusted worse then the sheet metal on my 521 so im swapping the l20 into the 521 (smog exempt :thumbup: ) in January so i really could give less for anything smog related.

[bananahamuck]

If i had the option of keeping a stock Hitachi that was working correctly or switching it out for a weber ,,i would try to keep the Hitachi..We stripped almost all the smog stuff off my sons 78 wagon and kept the stock carb and he has had absolutly no problems when the weather changes and it was already tuned to the engine.. unlke almost every weber your going to buy... It was snowing last night 34 degrees and after sitting for a week ( because of traffic ticket punishment ) fired right up and idled and drove off.. not missing a beat...

 

A ton of engineering went into that carb and when working properly it shows,,,,something to think about if truck is daily driver.

[RudyV]

If i had the option of keeping a stock Hitachi that was working correctly or switching it out for a weber ,,i would try to keep the Hitachi..We stripped almost all the smog stuff off my sons 78 wagon and kept the stock carb and he has had absolutly no problems when the weather changes and it was already tuned to the engine.. unlke almost every weber your going to buy... It was snowing last night 34 degrees and after sitting for a week ( because of traffic ticket punishment ) fired right up and idled and drove off.. not missing a beat...

 

A ton of engineering went into that carb and when working properly it shows,,,,something to think about if truck is daily driver.

 

would taking all the smog stuff still cause the problem of backfiring...did you leave the air injection on?

  :confused: