I recently replaced my fuel pump with a carter pump and swtiched to running premix (MMO, 1oz per gallon) and now my car is acting wierd. It wont idle (and its set to idle at 1.5k ), it dosent pull very much at all, and when I engine break it backfires like crazy (never did this before)

Just after I got the new fuel pump I checked the spark and it was yellow, not blue. I figure I need new plugs, but I cant get them untill I get paid next. Also, I have a vaccume leak somewhere (why it was set to idle at 1.5k).

would having crappy plugs and a vac leak make my car run this bad, or do I have other issues to deal with?

Note: the car ran fine (if idling at 1.5k is fine) and plenty of power before the new pump and premix, but the plugs were sparking good then

 

fuel pump might not be flowing enough, or filter might be clogged, clean ur plugs and retry, try running not premix

 

Do you have a fuel pressure regulator for your pump? Do you have a fuel pressure gauge? Sounds like you are running really rich. you could be overpowering the floats and overfilling the bowls. You might have fouled your plugs because of running rich also.

-Marques

 

well the plugs went bad before i ever ran the car with the new fuel pump, and I tried cleaning them (I have cleaned them many times before with a wire brush, I think they are dead ).

the pump is a carter 4 psi pump, that should work, shouldnt it? I have to run premix, my OMP stoped working and I cant afford to replace it.

I was thinking maybe the plugs arent burning all the fuel before it is sent out the exhaust. is that possible?

I also noticed that if I let it idle for ~30 sec before I shut it off I get a poof noise from the exhaust. kinda like a half-assed back fire. It is exactly 3 sec (i count to 3 every time ) after I shut it down.

Edit: oh, and I dont have a fuel pressure guage or regulator, new filter came with the pump.

WOOOHOO! 100 posts!! go me!

 

I would get the vaccum leak fixed first. Have you check the anti-afterburn hose yet? That's the first place I'd look. Good luck!

 

Yeah, the vaccume leak is on the top of my list. where is the anti-afterburn hose at? or should I just remove the whole rats nest alltogether? the cats and air pump are gone so I dont really need the rats nest, do i?

 

Always make sure everything works before doing anything to your car. Unless you are sure that the rats nest is the thing giving you problems, do not remove it. If you do you can compound your problems and not sure what is fixing what.

-Marques

 

all rotary engines have this problem

 

i thought i read somewhere that the stock fuel pump ran 6psi.

 

"Fuel pressure should be 3.7 to 4.7 lb/in"
-Haynes Manual, page 66

is it possible that my 4 psi carter pump is running at more than 4.7 psi? I didnt think they were that inaccurate.

It might also have something to do with how my carb is tuned? It worked ok with the old pump, wich im sure in its age had pretty low pressure. unfortunatly I have no idea how to tune the carb, I couldnt even find the screw

 

OEM 12A fuel pressure per Mazda 1985 workshop manual is: 2.8 - 3.6 psi & what happens at high RPM the OEM pump continues at the same psi except that the motor is using considerable more fuel therefore the stated psi drops & is around 2 psi + or - some at higher RPM's.

Have Fun
David

 

That "poof" is the magic of the wankel escaping.