johnwest

Hey guys,

I let my car sit for the weekend - untouched. I went out to use it this morning. Temps were up today about 5C and rainy. It started and ran fine for a few kms. Choke still on, I giv'er about 60% throttle at 3k rpm and it stutters and sort of sounds like it is farting. It eventually went away after properly warming up. Is this misfiring? It didn't feel like the bog down from running rich.

RX-7 Chris

iTrader: (19)

could be either. check the plugs.

j9fd3s

iTrader: (3)

if you're a little lean or rich it feels different, but if you're way off in either direction it feels the same

with the choke on, its prolly rich, and if the choke pull offs arent working, its not getting any airflow either

johnwest

What would I be looking for? I'm hoping this was an isolated incident, but is probably telling me something will eventually happen. Are there tell tale signs of what may have happened if this is not a recurring problem?

RX-7 Chris

iTrader: (19)

Pull the plugs and see it they are black (rich), white or rainbow (lean). I bet j9fd3s is right though and it is running rich because of the choke.

johnwest

Any reason why it did this out of nowhere...other than being a rotary blessing?

The temps were about -10C for the last week, it is now about +8C.

85rx

well this brings up my question I'm up hear in Wisconsin and my car has a problem revin passed 5000rpm when I'm in 3rd gear and on up through 5th...this happens if the car is choked or not...and it sometimes back fires in 3rd in higher rpm range...what might be the problem?

BeenJaminJames

Greetings 85, I would check my spark and timing. Make sure you have the leading and trailing wires all going in the right places. Check your dizzy cap and rotor. A weak or mis-timed spark can cause serious lagging in the rpm's. Also make sure your vacuum advance is working, all the lines are hooked up, and nothing's leaking. If you doubt the advance, hook up your timing light and advance the whole distributor a couple degrees. Keep in mind though that advanced timing can make starting harder in the cold.

JohnWest, I agree with j9fd3s, check that choke and make sure you're getting good mixture with a warm engine. Other than that I wouldnt worry too much though unless it does it again with a warmed-up engine. When a rotary is cold, it can be very temperamental.

1979mazdarx7

If the lead and trail wires are backward, would the car even start?

BeenJaminJames

Yes, I crossed my lead/trail plug wires once and drove the car about 50 miles before I figured it out, wondering the whole time why she wouldnt run right. Granted, its hard to do with stock wires as they are all different lengths, but when you get in a hurry plugging them in, anything's possible.

BeenJaminJames

The trailing spark is usually strong enough to ignite a good fuel/air mixture at low rpm. And the trailing timing is usualy 18-20 degrees atdc, remembering that the e-shaft turns 120 degrees during the combustion phase as compared to 90 on a piston engine. This difference effectively shrinks the 18-20* retard to about 13-15* retard. And considering that the rotor apex seal doesn't block off the leading plugs untill 45* (I think its 45) atdc, then you certainly can make the engine run on trailing spark alone. Of course, all of what I just said assumes you have a proper mixture, and that you are turning low enough rpms to allow the flame front to burn enough fuel to compensate for resistance. As you gear down to higher rpms, you are giving less time for combustion to take place before the exhaust phase, so you wind up with increasingly less torque, as well as lots of unburned fuel vapor in the exhaust which can make for some pretty awfull backfire issues.

Food for thought

1979mazdarx7

interesting cause when I was trying to start mine the other day it didn't want to fire right. Then I flipped them and it sounded like she wanted to start. My assumption is the 1-gallon gas tank I stuck a the gas lines into didn't have good enough fuel pick up.(my gas tank had rust in it, now I'm in the process of putting it back together)

BeenJaminJames

Yeah the leading plugs are on the bottom and the trailing are on the top. When looking at the engine from the front, the rotors spin clockwise, but the rotor passes the trailing plug before it passes the leading plug. Crazy, huh? I have heard a few people say that the trailing spark builds up pressure in the trailing side of the chamber so that the flame front does'nt travel across and slam into the apex seal. I don't know if that's why or not, but if anyone has another explanation, I would love to know. (Of course I assume you changed the fuel filter, flushed the lines and pulled the air horn to make sure your carb float bowls were clean, right?)

j9fd3s

iTrader: (3)

18C temp swing is big, especially when its that cold!

j9fd3s

iTrader: (3)

first thing to check is the fuel filter, next would be to test the fuel pump

mjm4jc

It could very well just be condensation in the distributor cap that worked its way out after warm up. Don't worry unless it happens again. Take note to see if it only happens on damp, rainy days.

Mike

1979mazdarx7

Well the previous owner did it because the car wasn't starting at all and wasn't getting enough gas to the carb. So he thought that the lines at the tank were clogged and took off the original tank, and put on another one from another car that didn't even fit on the car the right way. The reason it wasn't firing and getting gas was because the fusible link wasn't attached to the battery at all, and he had a wire that looked like it came off of a lamp running directly to the fuse box which is the only reason the car had any power at all. and yes i did flush the lines and change the filter tested the pump. And I haven't cleaned the carb yet but I'm working on it, money is tight for me now.