Ok so after 2 years of sitting i finally got motivated (well always been motivated, just finally decided to start spending money i don't have) on fixing my IROC and getting it running again.

first problem fuel pump was bad. i replaced it, and ran it from a mason jar filled with gas to make sure it would run properly. well running on the mason jar after the new fuel pump it fired up and ran beautifully. shut it down (well it ran out of gas or so i thought) reconnected the fuel lines, and waited to get a gas cap and battery before i filled it with gas. that was a week ago.

this weekend i went got a new gas cap and battery filled the car with about 4 gallons of gas and tried starting. after a couple of cranks the fuel pump got the fuel to the carb and it fired up.... though it was short lived. it stumbled to run like it alwasy does and started sounding like it was getting stronger and steady when it then acted as though it was starved for fuel and stalled out.

i figured it just ran out of gas in the bowl so i primed the carb and tried again. it then acted like it was flooded so i left it wide open to clear it and tried again. nothing. if i continue to try to run it wide open it will eventually sound like it is trying to start but then stalls out again eventually, sometimes quickly sometimes it runs for a little bit though it sounds like it's only running on a couple of cylinders. figured ok.... lets go back to the basics check fuel, air and spark. well the air cleaner was off, so air, check. i disconnected the fuel lines and fuel gushed everywhere... inside the carb looked wet as well so fuel, check. i then checked the plugs. all 8 looked as though there were soaked in oil/gas. thinking this was strange given how it ran the week before i decided whatever and changed out the plugs with used ones that were working well from my last tune up to my 91 Z. i then tested for spark, check. so i have air, fuel, and spark but it won't run. i then tried some engine starter fluid. tried to run it from the mason jar again since it worked before, and all yielded no prize for me. at this point i am questioning the carb.

i think it is just gushing fuel into the cylinders because when it does "run" it belches tons of smoke (way more than usual), puffs "smoke" from the primary carb barrels, and only seems to fire at WOT indicating it is flooded.

now that the situation has been presented, let me add an additional thought. last week before it died (i had just though it ran out of fuel from the mason jar and dismissed it at that) it made two backfires from the tailpipes that were out of the norm. the car has always backfired to an extent but these were different, bigger louder, nastier sounding.

i know with certain carbs there are backfire valves which if you run too lean will cause the motor to back fire and render the carb useless until the value is replaced. do the Q-jets have this and would this be a possibility given my unusual backfires? any ideas what may be the cause?

as an added comment.... this is not a stock L69 motor. it does not have the stock computer controlled Q-Jet on it. it has an 800CFM Q-Jet from a 425 Caddy Big Block (this was not done by me, but the car always ran fine so i left it alone) it is electric choke, and the choke was off due to outside temp.

appreciate the help.

Rick
85 IROC-Z "G"-car 305HO 5 speed
91 Z28 305 5 Speed

 

Q-jets don't have the back-fire damage problem that Holleys have.

What distributor are you using?

 

I'm using the stock factory HEI. i checked to make sure it wasn't wobbly or lose and everything is good and tight.

 

Q-jets do have a backfire problem. On the bottom side of the carb there is a composite material cam that lifts the secondary metering rods. With a serious backfire, this cam can be damaged/melted. Them what happens is that the secondaries start to open, and the secondary metering rods don't likewise open. Instant huge bog.

Second, there are a couple of lead plugs on the bottom that can be melted out causing huge vacuum leaks. JB weld will fix these...you just have to trim it after it sets so the carb will sit properly on the manifold.

 

With or without vacuum advance?

If without (like the computer carb used), then you aren't getting enough advance out of the distributor. That won't cause the dieing problem, but it won't run right.

 

I had the EXACT problem it acted just like that and i got several oppinions no one could figure it out, someone said it acted like the cat was bad so i sad "i will cut that bitch off right now!" i did... she fired right up and ran... still dont have a cat connected lol but she starts whenever i want her to

 

Check the fuel pressure too since you just replaced your pump. When I replaced my fuel pump with a factory chevrolet part I thought I was getting an L69 mechanical pump. Turned out to be the LG4 pump and fuel pressure was way high. Gas was constantly trickling out while idling. I installed a regulator and cured it.

 

Fleetmgr - not saying those might not have opened but i bought the carb through carbsdirect and all the J B welding was already done. but i will look into it anyway. i would prefer to stay with a Q-Jet so anything is an option at this point.

Five7Kid - yeah there's no computer left anywhere on this car except the gauge cluster speedo circuit and flex circuit. there's not even a radio in it. and the Distributor is a vacuum advance, sorry didn't know that's what you were looking for.

FlippindaBird - Cats have been off this car for a looooooooong time... Florida doesn't do emissions checks so this car has not had any of the emissions equipment on it for the last 15 years. it currently runs true dual straight pipes with cherry bomb resonators.

PeteZ28 - the fuel pressure thing is something I've heard from a handful of people. based on how you have to Wide Open Throttle it to get it to even seem like it will fire that screams flooded motor to me. and fuel pressure has crossed my mind and been suggested before. i don't currently have a fuel pressure regulator on the car nor has one ever been on it, but much like you said the newer mechanical fuel pumps (even the cheaper ones) are producing much higher pressures than the old ones. the car only needs about 7 PSI of fuel pressure and most new mechanical fuel pumps will run around 12. my guess is i'm running too high and blowing the fuel past the needle and seat right into the carb flooding it, hence it acts like it's flooded and is fouling my plugs.

 

Before you install a regulator I'd recommend opening the carb and checking the needle, seat and float. If it's flooding then IMO it's more likely an issue with the carb, either a sinking float or trash interfering with the operation of the needle and seat. Or it's just stuck. It did sit for 4 years, right?

 

naf is right, check in that you should check the carb too. If you have a gage to check fuel pressure, that would resolve if pressure is too high.

 

FLA NO EMISSIONS HUH? VERY COOL