84gsmcbane

I own an 84 gs 12a n/a. when started, as you rev in neutral, you can hear a distinct whistling. also, in decell in gear the bitch starts backfiring bad, not much smoke in general. and when you get on it it bogs in higher rpms... apex seal?? Have accel coil packs/plug wires, rb header with custom fabd collector into 3'' pipe into flowmaster super 40. running valvoline semi synthetic highmileage oil, and premixing with royal purple synth 2cycle oil 100:1

also is it possible to check compression with normal non mazda specific gauge???

thanks

DivinDriver

iTrader: (15)

If your intake is still stock, I'd be looking at your air control valve (ACV) and associated plumbing/blockoffs, or possibly a vacuum leak if you also have high-idle issues.

84gsmcbane

i had high idle issues when i first bought the car, but with a haynes manual and no experience to guide me, like a dumb ***, started adjusting the mixture screws and idle adj screw. I got the idle set to around 750/800 rpms. also, is the acv valve associated with the coasting valve, cuz i heard that if its sucking air all the time that its bad and thats why it backfires in decell. I checked it, it was sucking all the time, so I unhooked it and plugged the connect to the air cleaner and to the valve... im confused

84gsmcbane

possible to check compression with normal non mazda specific gauge???

henningmd

I just posted a question about not idling. If you adjusted the idle screw and the mixture screw you might have covered up a coasting valve/shutter valve problem. The whistling/horn like sound you hear may be due to the coasting valve. The only time the coasting valve should be open is when you are decelling just to prevent the backfiring you are describing. I found an excelent writeup on this circuit when I did a search on "no idle". It might be worth your effort to search for it. I coppied it and if you want I can send it to you. Just have to figure out how.

84gsmcbane

That would be great, and if you cant figure it out ill just search it... thanks

DivinDriver

iTrader: (15)

Coasting valve is not closely associated with the ACV; ACV is mainly an exhaust-side pollution control, coasting valve is intake-side.

You can get an estimation of rotary compression using a standard guage with the one-way valve disabled; you just have to watch for the peak values as the engine rotates, and remember that you have three peaks per rotor rotation. You have to mathematically compensate for RPM while testing, and the mechanical lag on the guage will likely make it read somewhat low.

84gsmcbane

2 dumb questions

1. mathematicaly compensate how??

2. how low are we talkin here? 5-10psi more?

84gsmcbane

ps,,, wow!!

DivinDriver

iTrader: (15)

1. There's a table in the field service manual that cross-references cranking RPM to expected compression. (FSM can be downloaded from the faq page)

2. hard to tell, as it varies by guage. Since it makes for a lower-than-actual reading, though, it's only a problem if your reading is considerably below nominal - - at which point, it's best to get it tested proper at a dealer.

jinxed4dub

iTrader: (7)

best thing to do for shutter valve issues. is remove the damn thing. My car occasionally backfires (1 big flame), only under 1 condition If I floor it to around 5 grand or more and let the motor decell in gear. then I get one healthy backfire it sounds kinda like a t shirt cannon. I do have 2gcdfis though, so cant say for stock ignition. when I got the car it backfired constantly people hitting the deck when I drove by, but no flames.

just remove the 2 screws on the butterfly, and fill the hole with J-B quick. let it sit for at least 4 hours to avoid sucking that into your engine. cap any vac hoses that go to it. including the air cleaner.

I'd also change your plugs, at very least sea foam, or mmo your engine, change your fuel filter, check your timing. check your leading igniter. don't just assume the worst. it may just need a good tune up. what kind of shape is your carb in?

Kentetsu

Whistling: coasting valve or vacuum leak.

Backfiring: Probably a leak in the exhaust system, but could also be related to timing.

Bogging: Change your fuel filter. If that doesn't help, you may have an internal blockage in the carb.

A great source for all things related to the stock Nikki carb: www.sterlingmetalworks.com


.

84gsmcbane

thanks a lot boys, got her all figured out. Turned out that the shutter valve was sucking air all the time, removed and plugged. This might make me sound like a dumbass but I really never expected my almost stock 7 to perform this well. I got on it a little down the highway and before I knew it I hit 125mph!!!! and the tach wasnt even in the red!!! I have said it before and will say it again, WANKEL IS GOD!!!!!! thanks again for all the help,
MITCH

DivinDriver

iTrader: (15)

Congrats; another satisfied highway missile monkey, heh!

84gsmcbane

I do have another question though, this 2nd gen 2GCDFIS mod for the ignition system? is it really worth the time you put in finding the coil from the second gen and installing it? especially if you have already spent a lot of money putting on accel direct fire coils in and they work well?

jinxed4dub

iTrader: (7)

you can do dlidfis if you have one of the stock coils, and a spare igniter. witch is just as good I'm told, but I like the 2g coil mod for its simplicity