Hey everyone, I just bought a mostly original 1984 F41 sports coupe with the 305. The car had been in storage for the last two years, with maybe only 15 min of run time over that whole time. It has 154000km on the odom. I picked her up yesterday for a steal at $5000.00, super solid and clean.

My questions are related to the tune up. I have never owned a carbed car, and barely ever worked on one. I am a injection guy so this is all new to me. The car runs fairly well considering it's last tune up was in 2005. It is pretty low on power and has a misfire while under load. Other than the basic plugs, wires, cap and rotor, and fuel filter, what should I be looking for? Does the valve lash need to be adjusted on this generation of 305? What about the carb? any special checks should I do there? Also, I noticed what looks like a DLC connector under the dash, does this car have some sort of basic ECM?

Believe it or not, I am a licensed mechanic, however you just don't see carbed cars running around much on a day to day basis. Any time a carbed car comes in to work my senior tech gets the job despite my requests to learn. All that was said about carbs in trade school was "They "suck", and you'll never see them". I am from a generation of scan tools and labscopes, and really want to learn the tricks of the carbed engine.

Thanks!

 

Just thought I'd better clarify the "carbs suck" comment. Our Fuel and timing teacher used that saying as a description of their function, using vacuum or "sucking", where as injection "blows", using pressure. I certainly don't think carbs actually suck.

 

I would start with those basic tune up items, as that sounds like one of those components may have failed.

While you dont see carbs around much anymore because of this whole environmental awareness thing, they're still prominent. I'm not sure why a teacher would say they suck, because quite frankly, they are way easier than fuel injection to repair things and make more power or simple adjustments. I love working on my friends old Chevy because the carb. Much simplier.

The ALDL connection goes to an OBD 1 system in your car. OBD 1 is a very simple system that runs on a hand full of sensors to ensure the engine is running correctly. Much more simple than the OBD 2 system in cars now a days that are more emissions than anything

 

The computer controlled carb adjusts the primary mixture based on throttle position, vacuum sensor reading and O2 voltage. It varies the dwell of the needles in the jets in order to attempt to maintain a stoich mixture. The Mixture Control Solenoid (MCS) will cycle 10 times a second and the amount of time down (needles in jets-restricting fuel) will be varied and can be read with an old school dwell meter or a scan tool for the ALDL connector. There's a bit more the ECM does but that's the simple basics.

The secondary bores of the carb are not computer controlled and function mechanically, same as any other qjet.

Tune up should consist of plugs, wire, cap, dist and O2 sensor (if age of sensor is unknown). Verify that the CEL lamp works and no trouble codes are present.

Being new to you, I'd also connect a scanner or dwell meter up and verify that the dwell with engine warm and at idle is near 50% or 30 degrees on the six cylinder scale. If the tamper proof plugs are still on the carb and it is relatively clean and running well, I wouldn't tinker with it much.

Getting 20+ mpg is an good indication that the system is functioning correctly.

If you actually have the desire to learn more about the system, post back and we can provide tons of info.

 

You misunderstood the meaning behind that. Carbs use engine vacuum to distribute fuel so by definition they "suck", injection uses pressurized fuel distributed through injectors that "blow" the fuel in. It was just a funny way for the students to remember the basics of the systems.

 

Thanks for the info, I am quite familiar with OBD 1 systems, as my '86 obviously has that system, but I was unaware that this 84 used a computer controlled carb. The basics are definitely going to be done because it has a misfire, and I will prob do the 02, and the coolant temp sensor as well for good measure.

It looks like the tamper proof plugs are still there, and it looks fairly clean, although there is some residue on the body, not sure if its just normal road grime or if something is leaking. Is there is anything I should be checking first on a carb that has sat for a few years? All the vacuum lines look ok.
It does seem to have some trouble starting cold, you have to keep your foot on the gas for a few min before it will idle. If you don't it will idle around 500rpm then stumble and die, I'm thinking the electric choke isn't working

 

That is an awesome steal, I wont lie, while i went to trade school for cars and love to build engines, i am horrible at diagnosing issues beyond minor stuff, im not sure if it would help, however when i did a swap with a friend on his old 87 Trans Am, it started misfiring going on slight inclines, and it turned out there were 2, relatively small issues, we later found, 1) the timing was a single tooth out, and 2) the catalytic converter was clogged and the car was backfiring from the pressure it was taking from the heat and the timing, not sure if any of this could be relevent to the issues that youre having, but it had similar issues, and while its not necessary, i would always pull, clean, and rebuild an engine that sat like that, as well as modify with performance parts, and as far as carburetors, i personally swear by them. i love them, and am using a 4 barrel carb on my 82 Camaro project car and i love it. the big thing with carburetors are they can be quite annoying because they need adjusted from time to time. its not a difficult thing to learn, just a rather time consuming thing to practice. i personally found that carburetion gives the better raw horse power and can be very reliable and fuel efficient, however fuel injection is quicker for starting and throttle response. its honestly a pick what you want kind of thing, and truthfully pointless to argue that one is indecisively better than the other. Hope this helped!

 

Replace all your ignition tune up parts before going any further. A mis-fire on old wires/plugs/etc. is very common and can further confuse the O2 sensor.

 

Oh, and spray down the outside of the carb and choke assembly with carb cleaner. Very common for the choke linkage to get gummed up.

 

LOVE IT!!! My professor says the same thing. There is only pressure differential... no such thing as suction. Also, He hates pipe for conduit so we always say "pipe sucks"

 

Thanks everyone, It sounds like you are all mostly saying to leave the carb more or less alone other than a spray down. Like I said a full ignition tune up is happening tomorrow, I just wanted to make sure there wasn't anything special I needed to do to the carb. I'm really interested in hooking up my scanner at work to check out what kind of data I can get from a OBD1 carbed car. If it shows similar data to a OBD1 fuel injected car, then that will make my transition from injection to carbs much easier.
I'll try to snap some pics of the car today to show off my new ride.

Thanks!