I've been working on figuring out why my Catalina seems to want to stall when it's idling, but it will race down the highway with no issues at all. My last really good drive I got 8 MPG. Haha. I was doing around 65 for 15 miles, and drove through town another 15. It seems like I should've gotten a bit better mileage than that.
Could something suddenly have caused it to start running too rich? I noticed when I started it the other day that sometimes I'll hear a popping sound coming from inside the air cleaner when it's cold. I was actually unscrewing the cover with the engine running and felt it. I believe that means it's backfiring a bit.
Once the car is hot, sometimes I have to press the gas pedal as I'm cranking it to get it going again. Other times it starts immediately when cranked.
hey how is it going with the catalina? I suggest you clean the fuel tank and filter.
What do your plugs look like? If you're running too rich the plugs will tell the tale. I'd expect to get around 15 mpg on that car, give or take depending on how it's driven. Likely it's time to rebuild the carb.
I'm not sure, but I'm going to check them Wednesday. I have a spare carburetor that I was told is the original. It doesn't have all of the vacuum ports for emissions crap. I thought about giving it a shot to try rebuilding one. Is it a hard thing to do?
If the spare carb doesn't have all the ports needed it can't be the original one, maybe an earlier pre-emission version of the same model. It's not too tough to rebuild most carbs, it's mostly replacing worn parts and cleaning jets and passages. Of course there are a lot of small parts to keep track of and numerous mechanical adjustments that need to be right. I assume it's a Rochester carb of some type. You may find a youtube video showing how to do it step by step. If you have a shop manual, that should include a carb teardown as well.
It's a Rochester Dualjet. I thought about replacing it with a Quadrajet but I don't feel like messing with replacing the intake manifold and I'm not sure what that extra power will do to an old engine. The older one is in the back seat and appears to be a much simpler model Dualjet than what's on the car right now.
Check out this video of overhauling the Dualjet carb on a 1981 Pontiac, should be pretty much the same as yours:
https://www.youtube.com/watch?v=h8Cl7ZantCA
Lots of things can cause a carb to go rich. A stuck or broken float, poorly adjusted accelerator pump diaphragm, clogged air correction jets and more. Also a badly or malfunctioning choke. When these occur, unless it's something minor, I will get a complete carb rebuild kit and do the whole thing with a thorough disassembly and cleaning.
Again a silly notion, but the air cleaner isn't clogged, is it?
Air filter is pretty much brand new. I've seen it more times than I can count after getting in that air cover a million times this summer to find vacuum leaks, haha.
That's a great idea except for the cost, about $2000. I would love to convert my old truck from carb to FI.
Fuel injection would kinda kill the old car vibe. I didn't grow up with them, though. Haha. Does that tailpipe look like it could he burning oil, or is that soot from unburned gas?
yeah, I have to agree on that one. It is a nice reminder of better built american iron. I'm not a mechanic but it looks like soot to me. This is going to sound crazy but,,,,,,,,, taste it. Or smell it.
Definitely looks like soot, which goes along with the carb running rich and excess fuel consumption. Of course that could also be caused by ignition problems as well, if misfiring you'll get similar symptoms. At least you don't have points and condenser to deal with. That car should have GM's high-energy electronic ignition which is actually quite good , but timing still needs to be set and it's possible ignition wires or other components have deteriorated and it's misfiring. A quick check is to hook a timing light up to each wire near the spark plug and see if it flashes consistently.
I could be feeling a misfire. My old lady's dad has a timing gun. Will that work for checking the ignition timing?
I changed the plugs when I first started messing with the car, and the wires aren't new with them. I was going to replace them with the distributor.
Yes, if that timing gun still works certainly it can be used to check the ignition timing. Check the shop manual since a lot of emission-controlled cars had a specific procedure to set timing. (Once it's on the factory settings and you get things sorted out you can work on modifying the timing for better power and mileage. Typically 1970s emission controls run the engine with retarded spark under at least some conditions.)
I don't use a vacuum gauge; I use a tachometer to turn the idle mixture screws in until the engine just starts to slow down, then out to the smoothest and highest rpm. I find the vacuum gauge needle just bounces around too much to get an accurate adjustment.
I may not need to actually pull a plug to figure this out. I took it out for a country drive this morning. It ran pretty bad initially, I noticed a gas smell when I popped the hood, but couldn't find leaks. when I got home, I noticed in my rear view mirror that black smoke comes out of the tailpipe when I rev the engine. My driveway has an incline and is gravel grown-over by grass, so I had to feather the throttle to get it to move without tearing up the surface or going into the door. That's what led to my noticing it. I took a picture of the tailpipe and I felt the inside of the opening. It's pretty carboned up, but it's not slimy like oil would be. It almost feels like the black surface of Kingsford charcoal and is very dry. I assume this is soot from burning excess fuel?
One thing I have not replaced is the distributor. I've not learned how to set timing yet and the one in the car seems to run fine, so I've more or less put it on the back burner for now.
I hate to mention this as I really like older cars but perhaps its time to lose the carb and switch over to throttle body fuel injection.
May ditch the distributor and go CDI too.
Just a thought.
I can't tell from the photograph but it does look like it is running quite rich. I would get that timing correctly set before doing any damage to the engine, ie too advanced.
I pulled all eight plugs this morning to see if any of them had oil fouling. I was greeted with good news, no slimy carbon was on any of the plugs. They are covered in a thin layer of hard carbon, they look like they've been powder coated, so the carburetor is indeed giving the motor too much gas. This was the #6 plug and is a good representation of the state of the other 7.
I did find something else happened. Two plugs were slightly loose on the right side, #2 and #4. They're both buried under the air conditioning equipment and I must not have torqued them enough when I changed them in April. 6 months of vibration slowly must have backed them off. I've added a few 3/8" U-joint sockets to my toolbox since April and tightened them down more firmly this morning. I started it up and it stopped acting like it wants to die right away. Those two loose plugs must have been causing misfires and leaking compression. Should I replace these plugs, or just give them a good spray down with carb cleaner? I heard a nice poof under the air filter again when I was manipulating the throttle.
I'm thinking about giving Scotty's old video a shot on adjusting the mixture screws this week. Should I try this adjusting by ear and see if the backfiring stops and the MPG improves, or do it with a vacuum gauge?
How To Adjust A Carburetor On Your Car - YouTube