Question for the older guys here. What's the normal service interval for a carb rebuild on a daily driver?

Posted by Blu_yello_husky@reddit | askcarguys | View on Reddit | 29 comments

I built the carb on my oldsmobile a little over 2 years ago. It was great for maybe 8 months with no issues. Then it started having cold start difficulties. Not a big issue at first, but it slowly started to get worse, eventually getting to the point where I have to pump it upwards of a dozen times to get it to start in the morning. Then, last fall, it started to run a little rough. Again, not super noticeable, but a little stumble here and there and a Intermittent misfire at idle sometimes. It's been marginally ok over winter but just this week it's gotten really bad, where I've actually been afraid it was going to stall on me at red lights and in parking lots. Barely runs, hesitates and bogs.. I took a peek at the carb yesterday and it looks pretty nasty, all covered in grease and varnish and such, but its only been 2 years since it was serviced? Is 2 years a normal amount of time in between cleanings for this to happen? Yes, I use oxygenated fuel, yes, it gets daily driven, even in winter. This isn't a show car or a "sunny day weekend" car. It's my regular commuter car and I drive it almost every day. What was the service interval for carb jobs back when the car was new? (1983)

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29 Comments

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Gunk_Olgidar@reddit

TL/DR: annually Also, the number one reason people convert carbureted cars to fuel injection is, was and always will be world without end, amen: Cold Start Difficulties. In the old days, an annual pre-winter tune-up was normal: Remove plugs, read them for quality of combustion, regap the plugs as needed (or replace if worn), new air cleaner, adjust rocker preload, lube chassis, oil change, clean the carburetor, adjust the jets, verify the choke is working, clean/inspect/adjust throttle linkage, adjust the brakes (drums all 'round back then except on the fancy performance cars like corvettes), swap over to winter tires, oil spray for rust proofing (if you were rich and could afford it unlike most of us).

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Blu_yello_husky@reddit (OP)

>Cold Start Difficulties. The cold start thing, though annoying, isn't really a major concern of mine. Ive owned many cars already in my lifetime, plenty of them in much worse shape than this one, that all had cold start issues. To say I'm used to using ether to start my car in the winter would be an understatement. It's kind of become just a normal part of owning a car. The thing I'm mainly concerned about is stalling when I'm at an intersection or hesitating/bogging when I'm trying to accelerate. These things are what finally convince me to start looking for answers. Ive been dealing with 16 pumps and 2-3 start up attempts every morning for the last year and a half and I've never once decided it would be worth the effort to try and fix it

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Sweaty_Promotion_972@reddit

Have you got a functioning heat riser ? Have a look down the carb throat a few minutes after cold starting.

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Blu_yello_husky@reddit (OP)

It's not a choke issue, it's the spray from the accelerator pump is weak on one side and nothing on the other side until it warms up. Though now I'm starting to think it's just getting to be like that all the time, with the rough running and bigging it's been doing, clearly it's not getting enough gas.

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Sweaty_Promotion_972@reddit

I didn’t mean choke stove, I meant the hose that brings warm air from near your exhaust up to the valve on the bottom of the snorkel on your air filter assembly. This stops ice crystals forming in the carb venturi.

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Blu_yello_husky@reddit (OP)

Thermac? No, it's never worked and it's not hooked up anymore because it did nothing and I wanted to get rid of all vacuum lines that weren't essential. I've been told by many gm guys that those thermac things often didn't even work off the showroom floor, so I didn't see any reason why to try keeping it. I know what they're SUPPOSED to do, but if it doesn't work, no point in having it on there

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rudbri93@reddit

remember to make sure your fueling problems arent actually ignition issues.

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Blu_yello_husky@reddit (OP)

I did a tuneup 3 weeks ago and it didn't help it at all

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gumby_twain@reddit

Did you check your timing?

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Blu_yello_husky@reddit (OP)

No, for a couple of reasons. 1, it's only been 2 years since I had the new distributor put in and the shop did all the timing stuff then, and I haven't touched the distributor since. 2, the way they have this car set up, it's ridiculously difficult to check the timing. They have the timing mark on the balancer in a way so it's only going to line up if you check the timing while the car is idling at approx. 650 rpm in gear while not moving. The original spec is just as confusing, it's supposed to be 4° BTDC, but set while the vehicle is in gear. The shop I took it to had to figure out what it translated to for running in park, and set it to that. The reason it's so goofy is because the car originally had a computer controlled carb and ignition system, which it no longer has, so those specs aren't relevant anymore. Long story short, I can't check it because I don't know what it's supposed to be at in park at 800rpm, and there's no timing mark on the balancer to use as a good reference point

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gumby_twain@reddit

If you’d rather rebuild a carb than learn how to check timing, god bless and good luck!

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Blu_yello_husky@reddit (OP)

You act like building a carb is hard. It should take less than an hour if you know what you're doing

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gumby_twain@reddit

Checking timing takes a couple minutes and if it’s good doesn’t require any tools beyond the timing light. Unless you don’t know how. Im not going to waste my time to tell you everything I’ve worked on, but I had a card 350 in a thirdgen a long time ago that ran mid 13s, which was quick for the time, and got 26mpg on the highway with functioning CCCS. Had to dust off the old dwell meter to set the MCS, don’t forget to use the 6cyl scale. But go ahead and tell me again about how hard it is to put in a distributor and check timing.

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Blu_yello_husky@reddit (OP)

Because it's not easy, there are no timing marks and the spec printed on the fan shroud no longer applies to the car the way i have it. It would just be a guessing game of where it's at and what it's supposed to be at, and I don't play that game. Plus, bad timing doesn't go away when the engine warms up. Carb problems sometimes do

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gumby_twain@reddit

You keep coming back so i'll try to help. First, what vehicle are we talking about? I'm guessing like a 307 olds in a 1984 cutlass or something? Let's start with, of course the specs on the fan shroud don't apply if you've replaced the CCCS stuff with a vacuum advance distributor. But i assure you, making that 8:1 compression pig run ain't rocket surgery. I'd set it about 10-16' initial at idle no vacuum advance and be happy. if it actually managed to ping, i'd check my tune or drop it a few degrees. There is a timing mark, you just have to crawl under the car and put some chalk/crayon/nail polish on it. I don;t know if this link will work, but i did a search for 307 olds balancer and found this pic on the first link i clicked where you can clearly see the timing notch on the lower right of the picture, i understand that yours is probably full of dirt and grime so maybe you've never seen it (not meant as a dig, its a fact on a daily driven car) https://i.ebayimg.com/images/g/-XAAAOSw2rNffc4C/s-l1600.webp Retarded timing could make that low compression engine not want to fire. Might kinda run ok once it gets going and warms up. Will run better if you get it right. Please don't act like checking and setting timing is difficult. Some of us have done it in staging while hot lapping at the drag strip. Yes, the first time will be a little pita when you have to clean the mark. After that it's gravy, assuming you have a crow's foot or a proper dizzy wrench. Of course you might have some total oddball car in which case why are you wasting time posting here if you could have been done hours ago?

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Autoscope_SOS@reddit

Not a mechanic, but it sounds like your carb might be gummed up again, especially if you’re using oxygenated fuel. Those fuels can leave behind more deposits over time, and daily driving in all conditions can accelerate that. Two years might seem short, but depending on the fuel quality and how the car is stored, it’s not unheard of. You might want to check the choke operation and make sure it’s adjusted properly cold start issues and rough idle could point to that. If the carb looks nasty, a cleaning or rebuild might be in order. Any chance you’ve checked the fuel filter too?

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Blu_yello_husky@reddit (OP)

It's not a choke problem. The choke sets when cold and comes off after warmed up, as it should. The issue is that when I pump the gas before starting, instead of 2 steady streams of fuel on both sides, it's one very weak stream on one side and nothing on the other side. So it takes several pumps before it even has enough gas to start, regardless of choke setting. The problem seems to go away once the engine is warm, but as it cools back down, it comes back. I haven't checked the filter for a while, but I have replaced the inline filter I installed and that wasn't really dirty either

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CHLarkin@reddit

From reading through this, I would check the jets for debris and clean as necessary. I didn't catch any mention of it being done, but changing the fuel filter would also be a smart move.

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NightKnown405@reddit

They usually need adjustments one or two times a year and can need a major repair every two to three years.

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TX-Pete@reddit

Actually rebuilding a carb? That’s past service and means either it wasn’t rebuilt/cleaned correctly, or your ignition system is toast. A properly tuned carb does not require servicing when run consistently.

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Blu_yello_husky@reddit (OP)

That has been my understanding as well, turns out not cleaning it for 2 years will mess some stuff up

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TX-Pete@reddit

Nope. Something else is going on. I’ve regularly had carbs go 7-10 years without being touched. It either wasn’t properly rebuilt, has a failing accelerator pump or there’s an outside issue.

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Blu_yello_husky@reddit (OP)

Someone else on here said I probably have a clogged jet, which would make sense seeing as when you pump the gas and watch down the carb, the stream is weak on one side and non existent on the other, when cold

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TX-Pete@reddit

That can also be accelerator pump if your carb is equipped with that. Along with any vacuum tubes that may be connected.

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albertpenello@reddit

If you're using fuel with any amount of Ethanol, make sure your carb rebuild parts are all ethanol free. If you're rebuilding an older carb, you may find that you'll want to use Marine fuel / Ethanol Free as it will wreak havoc on the aluminum or cast carbs and the seals in the auto-parts kits are most likely not ethanol resistant. Cold start with carbs should be absolutely no problem with a properly adjusted carb. Hot starts are actually a more common problem with modern fuels. Even daily driving, the ethanol is going to eat away at parts.

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Blu_yello_husky@reddit (OP)

Non oxygenated gas is very expensive, so I only use it on my 74 mercury I want to keep nice. I've always been told that ethanol gas is fine as long as you run it through right away, not let the car sit for long periods of time. The kits I've bought at napa have always said ethanol resistant, can't speak on the carb castings. The use of ethanol fuel isn't going to change, I just can't afford it. With that in mind, how often should I service?

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tomcat91709@reddit

Ok, so. Carb overhaul was done usually as a last resort. It was not considered a maintenance item. Ignition tune-ups and carb adjustment were every 90 days, along with oil & filter change and chassis lubrication. Back then, fuel quality was much higher than it is today. Some fuel additives like techron by Chevron will help with the varnish buildup and float chamber gumming. But it does sound by your description that you got a jet that is getting plugged up by something. I've seen this when the rebuild kit is a really cheap one, or a very old one.

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Blu_yello_husky@reddit (OP)

>But it does sound by your description that you got a jet that is getting plugged up by something. I've seen this when the rebuild kit is a really cheap one, or a very old one Right, looks like I'll have to figure out what kit I need and get into it then. I was, perhaps idiotically, hoping I wouldn't ever have to touch this again after I built it. I didn't even write down what kit I used when I put it together, which is coming back to burn me right now. You see, I Frankensteined this carb out of 3 or 4 different models from different decades so I could get exactly what I wanted and nothing I didn't want. This makes a simple carb rebuild into a whole guessing game ordeal of what parts from what kits I need to make it work. Why did I do this to myself?

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Automatic-Highway-38@reddit

Well said. Carburetor is a French word, meaning leave it alone. before playing with the carb, ensure the ignition system is spot on. Plugs, points, if you have them, condenser, coil and plug wires. anyone of these failing will give you the same symptoms and fiddling with the carbs will kind of compensate for it somewhat but first, ensure your ignition system is in tip top condition, good luck.