gibsonguitar11

Hey guys, first time posting. After hours upon hours of searching, I can not figure out why my carb is running very rich.


Car is a 1985 Pontiac Trans Am with the LG4 with literally everything on it being stock.

I got the carb rebuilt after it still ran like crap after I tried rebuilding it. I admitted defeat and had it professionally rebuilt and cleaned.

I hooked everything up. No air leaks and no major problems of that regard, WITH THE AIR CLEANER OFF and it ran like a champ. I took it down the street and around the block WITH THE AIR CLEANER ON and it bogged and back fired like no one's business. I called the guy who rebuilt it and he suggested running the car without the air cleaner on. I ran it around the block again and it ran perfectly. I had the car sideways it had so much power to it.

I removed the charcoal filter to see if that was the reason it was bogging, no luck.

I figured out how to hook up a dwell meter (+ on green connection next to blower motor, - on - terminal on battery) and had it set up on 6cyl as requested on another thread. With the lid off the air cleaner, the dwell is dancing somewhere around 30*. With the lid on, it jumps up to 40-45*.

I'm scratching my head. Anyone who has any sort of clue to what's going on, please help

Apeiron

What kind of air cleaner and filter element are you using?

gibsonguitar11

The stock one

gibsonguitar11

update: turns out when the car is running, the "damn door" on the air cleaner is shut. That would explain a lot to me

gibsonguitar11

update2: clogged off the air line off the carb to the door on the air cleaner. Car runs like a champ, feel like an idiot for not noticing that sooner. (which may have been why the car was running rich all along?)

Anywho, hope this thread helps someone somewhere

gearhead141

Thanks for that info. I have the same year and model car. And mine is also completely unmolested. I rebuilt my carburetor and had no problems. Watching a YouTube video really helped me out. I am still trying out different rods and I may try a different hanger for the secondaries. Right now it has the stock "L" hanger. I'm curious what kind of fuel mileage you're getting? I drive mine over twenty miles to work. I typically have been getting solid 21mpg, and sometimes very close to 22. I do keep the rpm around 2000 which gives me a cruise speed around 68mph. I just wonder if there's anything else that could be done mechanically to get a little better mileage? When I bought the car a couple of years ago I had no idea that the 305 was such a great fuel miser. I am very happy with the economy this car routinely provides on regular grade fuel.

gibsonguitar11

Im not quite sure yet. It turns out after driving around a little bit Im still having issues with my carb. Its running better than it was before i fixed the air cleaner, but it still runs best with no lid on the air cleaner/the lid turned upside down. I cant figure out why it's starving for air.

I was getting 22 or 23 on the highway pre-professional-rebuild. Running around town and my "spirited" driving style i was getting 12 or 13

midias

May want to try upgrading to a K&N filter see if it helps.

gearhead141

Take it back to that "professional" and have it adjusted on the car. He should be willing to make it right.

gibsonguitar11

I will be stopping back up there tuesday. According to the guy who rebuilt it, theres a "mixture control solinoid tool" that fits in a section on top of the carb. Naturally, the guy at napa looked at me like I had 7 eyes when i asked for it and couldnt find the tool. The guy who rebuilt my carb is a man of his word, and will fix it when he's open. For now, my "ghetto engineering" has me driving with my air cleaner lid upsidedown.

I will update when all is said in done hoping this helps someone somewhere

83LG4

Hi Gibson
The tool you need is an OTC 7667 or Thexton THX362 or equivalent. I work at a NAPA store and got the OTC one a couple of years ago. Most people don't know anything about the CCC carbs or the tools to adjust them. I think it's been discontinued now though and they're getting pricey. You can search it on Google and still find them or other cheaper equivalents.
As for your problem, is your check engine light on? I had my carb rebuilt a few years ago and developed a problem kinda like you're describing that I didn't have before. The code (I can't remember which) was for an oxygen sensor reading low voltage or something like that but the guy who built the carb said it was my fuel pump. I replaced the pump but still had the problem. Just for kicks I put a new oxygen sensor on and it ran like it had fuel injection then. Hope this will help.

gibsonguitar11

Hey, oxygen sensor is less than a year old. I drove like an idiot when i first got the car and i literally blew the original one out of its socket...

The only check engine light i get is when the car is on high idle for choke or just sitting there with the throttle open for a little bit. I get code 24, relating to the VSS. Still have no idea why it throws that code. Have not replaced the sensor. It goes away when you drive for more than 10 seconds

gearhead141

I'm betting this is related to the mixture control Solenoid (MCS). All part throttle operation works from this device. If you can floor it and are running on secondaries and it's just fine, then there is nothing wrong with the secondary circuit. Too rich is either the O2 sensor, the ecm, or the MCS. When I rebuilt mine, I counted how many turns it took to bottom the MCS plunger. It only needs about an eighth of an inch of travel. Hopefully, the mechanic will make things right for you. Adjusting carbs is becoming a lost art!

83LG4

Did you replace or reset the TPS (throttle position sensor)? The TPS may be out of adjustment if it wasn't "set". That could possibly have something to do with your code 24 also.

gibsonguitar11

Both tps and mcs are brand new and should have been set to spec. How do i check the tps?

83LG4

The new TPS should've come with instructions on setting it. The easiest way is with a scan tool that will read "live" obd1 data. If your carb guy doesn't have one you can do it with a digital voltmeter. If you don't have the instructions I'll see if I can locate the ones I kept when I replaced mine and post them. You can prob find out by searching this site too. The mechanic that helped me with mine said it would be fine to just install it and go but it wasn't. I had to adjust it for it to run right.

gibsonguitar11

So I figured I'd give it a few days for everything to progress.

I drove the car out to the guy who rebuilt my carb, and he played with the MCS screw for a little bit. He claimed that it just wasn't getting enough air and recommended that I get a taller air filter so that the lid would stay open a little higher, and allow more air in.

I ended up going to my local speed shop and buying a new air cleaner and breather valve for the motor. The car starts up for me every time and the car still will tach up and down happily all day (even with fouled plugs that I haven't replaced yet...waiting on UPS)

Problem still: I smell gas after flooring it extensively and/or braking very hard.

I bought dye to put in the gas tank and drove it around for a day or two. There's a couple little yellow dots here and there I see around the connections from the fuel pump to the carb, but they're dry when I check it with the car running.

The carb and brand new air cleaner however.....is covered in dye.
Anyone's recommendations on this?

gibsonguitar11

more pictures of the carb

gearhead141

It appears that there is fuel sloshing up from inside the carb. If all the gaskets are good, and I assume they are, then my opinion is that the float is set incorrectly or the needle and seat are bad. In other words, there is nothing keeping fuel from overfilling the float bowl. Rochester carburetors have a fairly small float bowl in the first place, so it doesn't take much to overfill it. This would entail removing the carburetor and disassembling to the point where the float level could be checked. Have you showed these pics to the mechanic who performed the work?

gibsonguitar11

Not yet, I wanted to ask you guys so I have some sort of idea on whats going on