I posted earlier that my muffler exploded. I think it might have just been a really huge backfire. My car seems to backfire a lot, mainly small ones, but they are very frequent anytime the rpm's are dropping. I just dont want this to happen to my new muffler and was wondering if I should worry about it. I'm putting on an Apexi N1. I've heard good and bad things about them on rotaries, but I got it for much cheaper than I could get even a stock one for so it seemed like a good choice. My exhaust doesn't have any leaks I can find, I put all new gaskets on a month ago and made sure all connections were tight. What else makes it backfire this much. Would it be a good idea to remove the rats nest?

 

Is your shutter valve working? I understand that can cause backfiring if its not.

 

hmmm, no clue, should I yank it or replace it if its not?

 

The shutter valve is also called an anti backfire valve. It's hard to get to without pulling the carb, but if the large hose connecting to the airbox on the passenger side is sucking air at idle, the valve's bad. Also, do a search on shutter valves, it's been discussed a lot here. Some say 'plug it and forget it', my mechanic who worked for mazda for 14 years, says replace it because it helps cool the rear rotor during deceleration.
Do the search. Good Luck!

 

if you have no cat or gutted it jill the air pump. i have the thermal reactor and had your problem. took the air pump belt off and voila, no more air to let the extra fuel go boom.

 

yep, gutted the cats, and still have the air pump, i'll get rid of all that and the broken a/c this weekend.

 

dude!!!! your a/c weighs a ton. just the cast iron bracket weighs a ton.

 

yeah, thats why it wont be there very much longer I know that I also have to either run an extra belt or get a double alt. pulley if i dont want squeaking belts when i remove the air pump. I remember someone on here talking about running a "yoohoo belt" that was just a small belt instead of getting a double pulley. what size belt is it and what do i put it on?

 

i have no clue. mine just squeals past like 5k. i was going to try the sand paper trick but i haven't got around to it yet.

 

The small belt is a 3L220. It fits over the main / water pump pulley - you need to pull the fan to get it on. Obviously, there's no way to tighten it but it seems to work fine for me. Cheap alternative.

 

ok, so i can just go to an auto store and ask for a 3L220 belt and they wont look at me like i'm on crack? I have no clue how they size belts. But i'll be doing that this weekend, thanks.

 

I have streetport headers with a Bomz muffler (n1 copy)
it backfires exactly like yours. I havent had a problem, + with the big ones you get a cool blue flame out the tip. Looks tight as hell.

 

If it backfires, something is wrong. It might look cool, but it's not right.

Make sure you get a 3L220 belt rated for high hp applications (ie: cars). If not, you'll end up with a 1/2 hp belt that will snap the 1st day you put it on.

 

hell yeah somethings wrong. my gas mileage coming out the tailpipe. now the question is why? is the fuel not cutting off fast enough when i get off the throttle? is the car running to rich? how exactly do you adjust the carb for it?

 

A 3L220 belt is defined as follows: the "3" means 3/8" top width. The "L" stands for light duty. 220 means 22" long. This belt is meant for small blower fans and by definition is fractional horsepower belt. You may or may not be able to get these at an auto parts store. If not go to a bearing house or an industrial supply house or an industrial A/C supply house. Industrial belts have slightly different angles of the "V" but there is no reason it wont work. Try to get a good U.S. brand like Dayco, Woods or Gates. The Gates part number is 1220.

 

Interesting... I've never looked up the definition of the "L". Strangely enough though, the power rated belt I'm using now still has the 3L220 designation.

 

i got bored, so now i have no more a/c I'll go pick up one of those belts tomorrow probably so I can get rid of my air pump too.

 

hey..figured id comment on this...

heres the first thing...i have an 85 gsl with rb header and no airpump....bo cats etc....upon decelleration, mine will backfire so loudly sounds like a rifle is being shot off AND shoot a 3 foot flame out the back end (or so ive been told)

if you are going to remove the airpump..do yourself a favour and get an acv (air control valve) block off plate.and remove the whole acv...BEFORE REMOVING AIRPUMP!! or other emissions
or else as its been explained to me, you are injecting fresh air into the exhaust...i should be getting my acv blockoff plate soon and hopefully remove the backfires....


just my 2 cents

Paul

 

hehehe... paul.... I loved those flames coming home from teh muffler shop following you in my mom's van... looked like they were going to melt the bumper on the van .... does it still shoot flames with the presilencer on it now?

Jeff

 

**** mine shoots flames and it's normal...

 

Jeff, oh ya...still 3 feet or so

 

Ok i got a new motor, the block off plate, the rb header, and pretty much straight exhaust. And guess what put your foot into it and then let off and boooooom. Nice blue flame. I asked the guy who built my motor and he said it is normal and you cna play with timming and everything and it still won't change it. So i live with it. and the backfires are only slightly louder then the exhuast. And the flames are nice at night.

dan

 

As long as my apexi n1 can handle the flames without a problem, I dont have anything wrong with it. I should have it installed by wednesday. Anyone know how much a muffler place should charge to get it installed. It needs a funnel kind of pipe taking it from the stock 2'' pipe to the 2 1/2'' inlet on the muffler, welded on, and hung. I'm guessing it should be around $50-$75

 

I have an 84 GSL-SE that I just put a new Mazda Reman motor, Racing Beat Header and Power Pulse muffler. It accelerates great, but it does backfire on hard deceleration. My timming is set to stock and currently my cat is hollow. I modified the secondaries to be opened by the air pump as the back pressure from the new exhaust was too little. (They now open at about 3500) I was planing on going with a bonz cat, as I want to be able to pass emmisons. Do you think that when I replace the cat, the backfireing will go away, or should I look for an other solution?

 

I dont get flames and it pisses me off