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Carburetor Problems On Older Cars

Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
This forum is for discussing the care and feeding (and fixing) of problems related to carburetors, those primitive and extinct devices found on most cars 15 years or older.

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  • div2div2 Posts: 2,580
    I rebuilt a mid-seventies Quadrajet a couple of months ago. The Q-jet is actually a very elegant design; you can calibrate cruise, mid-range, and full throttle mixture to a very precise degree. The people who bad mouth them simply don't understand how and why the Q-jet operates the way it does.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    Carburetors work quite well when properly set up and adjusted, which is like HARDLY EVER....congratulations on getting it right. I think the big fuel dragsters all use carbs don't they?

    Many the reason they were abandoned is that a computer can't control them very well---you have to use mechanico-electrico-vacuumo devices and these get all whacked out--not stable enough for emissions requirements.

    Remember those GM combo carbs, "throttle body injection" I think they were called? Or Jeep also had a electronic carb that was a nightmare.

    The best carbs are pre-emission types. British SU carbs are also brilliant if you understand them, and not at all troublesome.

    Old German Solexes and Zeniths however can be diabolical when used in tandem.

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  • isellhondasisellhondas Issaquah WashingtonPosts: 19,552
    When I realize the average mechanic/technician today hardly knows what a carburator even is!

    Quadrajets came out in 1966 and I can remember how they were bad mouthed by a lot of "mechanics" who didn't understand them. Like div says, they were really well designed. The worst were Ford's Varible Venturi carbs and Chrysler's Thermo Quads.

    I used to enjoy watching a good "carburator guy" tear one apart and restore it to new.

    These guys are a disappearing breed.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    What's even worse is many times people without experience will attempt to modify their carburetor systems without much forethought. You just can't bolt on a bigger carb without doing other things as well, like a good intake system.

    We were just working on a Porsche 914 that someone had stuffed a 3.0 liter carbed engine in. Ran like crap---had larger venturi carbs on it but nothing else added. So we switched to stock venturis, tuned the car and it ran about twice as well. So much money spent and wasted!!

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  • isellhondasisellhondas Issaquah WashingtonPosts: 19,552
    There used to be a BLIND tune up guy at a Chevy dealer in So. Calif. A lot attendant would pull the cars in and out for him. He could overhaul a Quadrajet in record time.

    I refused to believe it until I saw him at work one day!
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    A lot of carb adjustments are done with a feeler gauge, so you don't need your eyes for that. Still, quite an achievement!

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  • isellhondasisellhondas Issaquah WashingtonPosts: 19,552
    Think of the balls and springs etc he had to deal with and be sure not to lose.

    He had to ask somone to read the scope pattern for him if he couldn't figure out a miss or something. He was incredible!

    Remember Sun scopes? Talk about a thing of the past!
  • jsylvesterjsylvester Posts: 572
    I'm getting the carb on my 67 Galaxie worked on this summer. Let me tell you, finding a good carburator guy who is not charging an arm and a leg because most of his customers are wealthy musle-car owners is not so easy anymore.

    I use my mechanic mainly because his father is semi-retired, but does come in to do any of the carburator work they get. I've never seen top shelf older cars, but I've seen them working on 6 cylinder Mustangs, MGB's, Buicks, etc.
  • isellhondasisellhondas Issaquah WashingtonPosts: 19,552
    Trouble is, today's mechanics/technicians don't like to rebuild things. They just replace components in many cases.

    An old school guy would NEVER put an assembly line "rebuilt" carburetor, starter, alternator or anything else on a car. They wouldn't stake their reputation on the unknown quaity of a so called "rebuilt" part.

    Instead, they would carefully disassemble the part and with a great deal of pride, overhaul it to as new condition.

    I guess today's labor rates forbid this now?
  • stinkpot1stinkpot1 Posts: 11
    I have a 68 Ford Mustang w/289 2 bbl. mechanical fuel pump. It has recently developed an issue with fuel bubbling out of the carb all over the intake manifold. enough that it fills the valleys on the manifold. The fuel is coming out of the two upright tubes in front of the butterfly. It does not do this all the time, usually after you drive it a while, stop, and then go to start it back up. It has sat for 2-3 hours after driving and had this problem but shorter times also. It did this with both the replaced carb and the new one.

    I have replaced the carb. I have checked the float level, its ok. I have flushed out the radiator and engine. I have inslulated the fuel line from fuel pump to carb. I have changed the fuel filter. The fuel tank is not pressurizing. I am at a loss for what else it might be.

    The only engine work done recently was a mechanic attempted to adjust one of the hydraulic lifters due to a small tap.

    Can the mechanical fuel pump be overpresurizing? occasionally?
    What esle might be going on?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    I suppose you could add a fuel pressure regulator and see what happens...the pressure could be enough to defeat the float valve.

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  • bolivarbolivar Posts: 2,316
    -Any possibility some fool has added an electric fuel pump? And it is stuck 'on' all the time?

    -Does the fuel 'bubble' out when the car is running or stopped? If when running, even if you have a new carb, the float valve is not doing it's job. Have the carb rebuilt one more time, with new float valve and set the float to the right level.

    -I would think a 1968 would have a 'vented' fuel tank cap. Do you have the correct cap? If an unvented cap is on there, when the fuel heats up, the pressure might push through the carb when it is stopped.
  • stinkpot1stinkpot1 Posts: 11
    No electric fuel pump,
    It only bubbles out when running right after starting it up. It runs real rough. I have checked the float level and function several times now. It is fine.
    Fuel tank vent works fine.
    I noticed after shutting the car off the throat of the carb fills with vapor. So much that it looks like a witches cauldron.
    I had a thought on this tho. I may have gotten some fuel that had a high amount of alcohol. They are selling corn fuels here in Illinois and may have had a fuel mixup at the stations. That or some [non-permissible content removed] sugared me. Still have not ruled out the mechanical fuel pump.
  • bolivarbolivar Posts: 2,316
    Well, you are having fuel being pushed into the carb. The 'vapor' is just that, gasoline vapor. When it overflows the carb and goes down into the hot intake, it vaporizes and you see the vapor come back up through the carb to the outside.

    The float is either set too high, or the float valve is not shutting off the flow of fuel. I've never heard of a mechanical fuel pump overpowering the float valve. It might be happening, if someone put the wrong fuel pump on, one with a much higher pressure capability than the correct one. But I would think if the fuel pump is putting out that kind of pressure, the car would not run at idle or slow speeds, the fuel overflow, raw fuel running down into the intake, would flood it out.

    Alcohol might have eatten up the little rubber tip on the float valve that does all the work closing off the fuel. Take that carb off, turn it upside down, blow through the fuel line into the carb. If you can blow throught it, then the float valve is not working. (Holding it upside down should make the float close the valve.) If alcohol ate up something like the 'power piston' diaphram, I don't know what the symptoms would be. Tearing the carb down and looking is only way I know to find things 'eaten up'.
  • bolivarbolivar Posts: 2,316
    P.S. Sugar won't harm the car, other than stopping up fuel filters, etc. It doesn't dissolve to any entent in gasoline, it just sits there.

    Sugar in the gas is so old a tale it's not a urban ledgend, its an old wive's tale.
  • isellhondasisellhondas Issaquah WashingtonPosts: 19,552
    Do you mean the person in my frat house who sugared the motorcycle cop that night didn't do much damage? :)
  • warnywarny Posts: 1
    I had the exact same ploblem with a 66 Mustang 289. Totally rebuilt the carb but the problem remained. From a clue on another panel, I replaced the mechanical fuel pump and now no more problem. Seems that there was internal leakage that caused the pump to pump in spurts when starting from cold especially after setting for a couple of days. (When hot, it started fine.) Am guessing that the float was unable to cope with this pulsing action and the excess gas was blown out the relief hole.
  • oldharryoldharry Posts: 413
    There may be a clogged vent in the float bowl. If the air cannot get out, the float never rises, and the pump forces the fuel out where ever it can. The old Rochester 2 bbl's had a * TINY* notch below the cover gasket that vented into the ventry area.

  • Okay here is what I've got. I bought a 1965 Chevrolet Truck with a 327 corvette engine. It was running pretty good except for when you gave it gas it would sputter. It had the original Rochester carb on it (40 years old might I add). Anyway, I bought a new Edlebrock carb and put it on it. The only hookups on this truck to the carb is the throttle, gas line, and I guess the pcv valve is the big hose. The new carb has an electric choke so I hooked that up. The problem is the truck will not start. It will turn over but will not fire. I covered both the vacuum inlets in the front of the carb with the provided rubber stoppers. I also screwed in the hex head stopper screw into the hole in the back of the carb. As far as I can tell everything is hooked up correctly. I thought that I may have flooded it at first but, I waited for about 2 1/2 hours and then tried it again, but it still didn't crank. If anyone has any suggestions thanks.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    Try to start it and check for a spark.

    Got a fat blue spark? Okay, then.....

    If it still doesn't start pull a plug and smell/look for gas.

    It is rare---nearly IMPOSSIBLE---for a car not to start at all due to a bad carburetor. It may run BADLY but it should always run.

    However, it could be flooding, that is dumping too much raw gas in there, and that douses the plugs like it was water. (stuck float?)

    If the plugs are wet, AND you're sure you have a spark, put in fresh plugs, then try to start the truck with the gas pedal pushed down AND staying down, and see what happens. If it starts up but refuses to run and you have lots of black smoke out the tailpipe, you've got some internal carb problem.

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  • bolivarbolivar Posts: 2,316
    "It was running pretty good except for when you gave it gas it would sputter."

    Symptoms of a bad 'power piston'.

    Rebuild the Rochester. If you can find the carb number, so you can get the correct 'kit'. There should be a small 'tab' under one of the screws on the top of the carb. This tab has a number on it. This is the carb number. Get the correct kit. The kit comes with general instructions that should be enough to do a rebuild.

    Replacing the power piston might be all that is needed. But a rebuild really isn't much.

    I think these are one of the most simple carbs around. Don't change any of the 'bendable' settings. Take the thing apart.

    For any 'adjustable' screw, turn the screw in until it bottoms, counting how many turns and partial turns this is. WRITE THIS DOWN. Then remove the screw. When you reassemble, turn the screw in until it bottoms, then back it out the number of turns you had written down. I have a roll of picture hanging wire. The kind that has several fine threads that make up the wire. Unwind a single thread of this fine wire. Tie screws and springs that 'go together' together with this wire. Tie jets and steel/copper washers together. Tie all these small parts together in one mess. Then put this into the carb cleaner. Otherwise, it will be hell getting these little things out of the carb cleaner. Look closely at washers, some are not metal, are composite material and should NOT go into carb cleaner. Put nothing plastic or nylon into carb cleaner. Look for the small steel balls. These sometimes do not come in a kit, and sometimes are of different size if there are more than one. Get them back where they came from. These may be under jets and come out of passages when you separate the carb body from the 'throat'. No need to put a steel ball through carb cleaner, it doesn't have any crannys for gunk to stick to. Look at the parts in the new kit before you start and as you are dis-assembling to see what will be replaced from the kit. No need to clean old parts being replaced.

    For rods that must be removed from holes, get a knife or small screwdriver. Scratch small marks on corresponding holes and rod ends. Magic marker doesn't work, it vanishes in carb cleaner. Look closely at things like this. Remember if the rod end goes up or down through the hole. Remember. It is best to not drink beer when rebuilding a carb.

    (Note: Kits will have MORE parts than you will need! There may be gaskets, etc that do not fit 'your' carb. The kit will probably be for multiple versions of the carb. Likewise, the instructions WILL NOT exactly fit your carb. Just use your brain, and work with what you have. If you have the right kit, it will all work out.)

    Buy a 1 gallon bucket of carb cleaner, put all metal parts thru the cleaner for a few hours. You might have to do more than one shift to get it all thru there. 'Turn' the parts to remove air pockets, so the cleaner gets to everything.

    Don't get the carb cleaner on you. Even small drops are almost like acid to human skin. (It's actually not as bad as acid. You WILL get some on you. And you will know where it hits your skin. Keep it out of your eyes. This is another reason to clean with hot water.) Use pliers to 'handle' the card parts with cleaner on them - to pull them out of the carb cleaner bucket, etc.

    Get an old 2 gallon bucket. Fill the bucket with the hottest water you can get out of your hot water faucet. Put a few drops of dishsoap into the hot water.

    Pull the metal parts of the carb out of the cleaner and dunk all of them in the bucket of hot water. This will remove most of the carb cleaner. Leave the parts in there long enough to get hot. Get your eye protection on now. Start pulling the parts out and use compressed air to blow the hot water off the part. Blow air throught EVERY hole you can see in the carb. This removes carb cleaner, water (since it is hot, the water will evaporate quickly also) and gunk the cleaner might not have dissolved. CLEANING the carb is the MOST IMPORTANT PART of rebuilding a carb. (Oh. If you don't have compressed air, you probably should not attempt a carb rebuild....)

    I absolutely swear hot water wil not harm anything in a carb. It is made of 'pot metal', which does not rust. Everything else is stainless or hardened steel. Plus, if you get it hot and then blow it off with compressed air, it will be completely dry in 5 minutes.

    Reassemble. Unless some idiot has attempted to 'adjust' the carb, none of the 'bendable' settings should be changed. I don't think I've ever changed one. If the carb was running at all, it should be ok. The float arm might have to be slightly bent, because the float valve from the kit may be a different length. Otherwise, the choke unloader, secondary linkage, etc should be ok. You can check it with the specs in the kit, but if it is close, leave it alone.

    You are mainly removing gunk from the small passages. And replacing something like the 'power piston' which has a rubber diaphram which does wear out. Clean. Replace. A carb is then rebuilt. Adjusting is usually minor.

    Cut and paste this message into Word or Notepad. Print it out. Save it. Then, even you can rebuild a carb.
  • bolivarbolivar Posts: 2,316
    One more item.

    The choke valves and throttle valve. The things that close off the air that goes into the top of the carb. These valves are attached to the 'rod' that goes across the throat with screws. DO NOT ATTEMPT TO REMOVE THESE SCREWS! The throttle and choke valves screws are 'staked' in place. And cannot be removed. Just leave these together and throw the whole mess into the cleaner. If you attempt to remove these screws, you will probably bend the rod. The valves will never realign in the throat correctly. You've ruined the upper part of the carb.

    This advice comes from someone who did this. And got to buy a carb from a salvage to get the upper throttle and choke assembly.
  • bolivarbolivar Posts: 2,316
    P.P.S. "I bought a 1965 Chevrolet Truck with a 327 corvette engine."

    I doubt this. You might have a 327 that has the same general 327, heads, and/or carb as a Corvette. Millions of cars and trucks came with the 327, in all kinds of power configurations.

    But if you do have a 'Corvette' engine, removed from an actual 60's model Corvette, and it can be proved from casting marks on the engine and/or heads and carb number ------ just the motor would be worth more to a Corvette re-storer than what you paid for the entire truck.

    A high horsepower solid lifter or fuel injected block would be worth more.

    If you have any verifiable proof at all that your motor was pulled from a Corvette, you owe it to yourself to have a 'professional' investigate it. You might be setting on some decent money. I know a couple of people with this kind of knowledge if there is a possibility of this being true.

    'The guy that sold it to me told me.' isn't proof. Valve covers that say 'Corvette' isn't proof.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    I have all the ID #s if you need them.

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  • How do I check the engine to see if it is from a vette then. What numbers do I need? Thanks for the help guys.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    Two basic numbers are helpful. The series of numbers on a smooth pad in front of the right side (passenger side) cylinder head, and the large casting numbers on the very back of the engine, down low at the bell housing, left side in front of the steering wheel---you'll need a fender cover, a good flashlight and somebody to hold your feet maybe...I forget offhand but the casting numbers are all numbers, usually beginning with a 3 I think and maybe 7-8 numbers.

    The engine numbers on the cylinder head will have numbers and then a two letter suffix.

    If you have those two sets of numbers you can generally identify TYPE but not necessarily the year.

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  • gerngern Posts: 3
    I have a notorious bad starting 1979 Dodge 360 with a TQ 4bbl. It's a California/Canada set up model. It has been suggested that I connect a manual choke. I have a sneaking suspicion that it's more than just that. Would a rebuild and a manual choke solve or restrict my problems? It's tuned up with new wires and rotor and cap. Filters are all new along with PCV valve. It does have a monstrous 36 gallon tank and, wait for it, it's a Van Conversion to an RV. Any suggestions (and wrecking is not an option!)?
  • bolivarbolivar Posts: 2,316
    You can do some basic checks on the automatic chock.

    On a cold engine, take the top off the air cleaner so you can see the carb. If you can't get your hands on the linkage, take the entire air cleaner off.

    Manually open the throttle using the linkage on the carb. If the choke hasn't already closed, you should be able to see the choke drop closed. If the choke doesn't close on a cold engine, that is a problem. One that will cause hard starts.

    While you are under there, pull the throttle linkage to the full open position. You should see the choke open up some. This is the action where people (and the owners manual) tells you to 'hold the accelator to the floor if the carb is "flooded"'. This allows more air into the carb, helping to overcome a 'flooded' condition.

    On some carbs, you can look down the primary carb (you would have to hold the choke open), and when you pull the linkage to open the throttle you can actually see gasoline squirt into the carb throat. Sometimes you can't see it, but you can hear the squirt. This shows the 'power piston' inside the carb is working. But, on some carbs you will not be able to see or hear this.

    Other than these tips, I don't know much else to tell you to check on a carb for hard starting.

    Hard starts can be cause by so many other things.... With a 36 gallon tank, could it have 2,3,+ year old gasoline? Have you changed the fuel filter?

    By 1979, smog restrictions were in full effect, and Chrysler seemed to have more problems with them. My FIL had a ?1985? Dodge 4x4 with the 360 (called a 5.9L by then?) and this **** thing seemed to have TWO smog pumps on it. One had already been removed. If your engine has had smog stuff removed, vacuum hoses cut and/or plugged - well, good luck.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,347
    You know, a carburator has to be outrageously messed up to prevent a car from starting altogether; however, if it runs well warm then the choke could be an issue.

    If you are going to check anything with the air filter off, don't be sticking your nose down the carburator when the engine is cranking. You won't look good without eyebrows.

    You could also take off the air cleaner and squirt one/two bursts of starting fluid in the carb (not TOO MUCH) and see if the engine kicks off right away.

    If it wont' fire immediately on starting ether, you have an ignition or compression issue I think.

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  • gerngern Posts: 3
    OK, so let give you more info: Following the instructions on the visor, one pump and a little gas for cold starts (and the air cleaner cover off) I see the choke close but then it opens up a third and does not start. I can smell gas and the gas is new, as is the in line filter.
    Interestingly enough, you mention the Smog Pump (or "Air Pump" as Haynes refers to it). It simply has no belt. Is there a chance that if that was reconnected, it could have an effect in starting?
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