bad city milage 2bbl

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so in the city where my milage has dropped the most im really only driving it like a grocery getter not to much throttle just get up to speed. my timing right now is about 3 degrees advanced i dont got a vacuum can on it because when i looked up super six setups i couldnt fine any examples with a vacuum can, i think the previous owner might have got rid of it, and it is the right carb it's a carter bbd 2bbl which is from what ive seen it is the correct carb. does anyone think it might be worth it to get new jets for it?
 
No wonder mileage is down. It needs a vacuum canister badly.
 
And just 3* of idle timing is also retarded.

That slanty, to be any efficient at all will want plenty of timing for city driving, as well as cruising; plenty. Maybe as much as 40 or 50 degrees at 2000 rpm under light throttle conditions. That cannot happen without a well tuned Vcan, integrated with a fast and generous mechanical curve. You will also want to set the valves just right. And the power valve. Possibly even the float level. But if your cylinder pressure is in the basement, it's hard to pick up mileage under stop and go driving. Your combo can use a lot of tuning.
I can get great mileage out of my 2bbl. Not a lot better than the old single bbl that was on originally on it, but that's not why I put it on there..
So forget jets,for now, they have nothing to do with fuel mileage.
To get mileage in a given chassis, you need 3 things; 1) a decent cylinder pressure, and 2) the exact right ignition timing, and 3) the exact right A/F ratio, and 4) the exact right driving style.
-So, start with a very accurate valve adjustment, and a cylinder pressure test. I would also do a leakdown test if pressure is not pretty even. Normally, if pressure is down, there's not much that can be done, but in your case with the poor timings situation..........
-Next, Get the Vcan installed and working properly. The factory made all kinds of cans including a 20 * can. See if you can find one. If not,Find a can that brings in at least 14, as a bare minimum. I went to a local jobber, and he let me thumb through an old catalog. I wrote down several PNs and eventually got an 18*one, which I modded to 22*.
-Next, let's work on the dizzy! Put a T-lite on it and see what she makes, Just rev it up 'til she stops advancing, and grab the number. If you don't have a dial-back lite, you will have to mark your balancer at 10* intervals, all the way to 60*, or just get a stick-on timing tape.I would, of course, prove the TDC mark before beginning. Then If you don't get at least 36* of non-Vcanned advance, make it so. Then check the idle timing. You will want to see at least 8 to 12 degrees of true, proven, idle timing. Irregardless, grab the number.Now, Let's see what you got.
-Finally. And lastly. We will set the carb. But there's almost no advantage talking about that, much less doing something, until the timing is at least close.
-And then there's you. #4. If you can't keep your foot out of it, or circumstances don't allow it, or you live in hill country, or high country, don't expect much for fuel mileage. The slanty is severely W/P (weight to power)handicapped. It can return excellent results under steady-state cruise conditions, but it takes either; a lot of throttle, or a lot of runway, to get her up to speed; and that takes fuel.And if you need to do it 20 times a mile, well, you get the picture....
- So there you go. You got some homework to do. Come on back when the results are in, and the new parts are on.And BTW, if the plugs are old, well, that won't help.
 
AJ/FormS said:
And just 3* of idle timing is also retarded.

That slanty, to be any efficient at all will want plenty of timing for city driving, as well as cruising; plenty. Maybe as much as 40 or 50 degrees at 2000 rpm under light throttle conditions. That cannot happen without a well tuned Vcan, integrated with a fast and generous mechanical curve. You will also want to set the valves just right. And the power valve. Possibly even the float level. But if your cylinder pressure is in the basement, it's hard to pick up mileage under stop and go driving. Your combo can use a lot of tuning.
I can get great mileage out of my 2bbl. Not a lot better than the old single bbl that was on originally on it, but that's not why I put it on there..
So forget jets,for now, they have nothing to do with fuel mileage.
To get mileage in a given chassis, you need 3 things; 1) a decent cylinder pressure, and 2) the exact right ignition timing, and 3) the exact right A/F ratio, and 4) the exact right driving style.
-So, start with a very accurate valve adjustment, and a cylinder pressure test. I would also do a leakdown test if pressure is not pretty even. Normally, if pressure is down, there's not much that can be done, but in your case with the poor timings situation..........
-Next, Get the Vcan installed and working properly. The factory made all kinds of cans including a 20 * can. See if you can find one. If not,Find a can that brings in at least 14, as a bare minimum. I went to a local jobber, and he let me thumb through an old catalog. I wrote down several PNs and eventually got an 18*one, which I modded to 22*.
-Next, let's work on the dizzy! Put a T-lite on it and see what she makes, Just rev it up 'til she stops advancing, and grab the number. If you don't have a dial-back lite, you will have to mark your balancer at 10* intervals, all the way to 60*, or just get a stick-on timing tape.I would, of course, prove the TDC mark before beginning. Then If you don't get at least 36* of non-Vcanned advance, make it so. Then check the idle timing. You will want to see at least 8 to 12 degrees of true, proven, idle timing. Irregardless, grab the number.Now, Let's see what you got.
-Finally. And lastly. We will set the carb. But there's almost no advantage talking about that, much less doing something, until the timing is at least close.
-And then there's you. #4. If you can't keep your foot out of it, or circumstances don't allow it, or you live in hill country, or high country, don't expect much for fuel mileage. The slanty is severely W/P (weight to power)handicapped. It can return excellent results under steady-state cruise conditions, but it takes either; a lot of throttle, or a lot of runway, to get her up to speed; and that takes fuel.And if you need to do it 20 times a mile, well, you get the picture....
- So there you go. You got some homework to do. Come on back when the results are in, and the new parts are on.And BTW, if the plugs are old, well, that won't help.
Click to expand...

ok so i got a vacuum can from my old slant that ill put on, i dont got a cylinder pressure testing tool and i couldn't find anyone that rented it, but my slant hasnt been showing signes of low compression. in the next couple days ill do a valve lash and ill have to borrow a timing light from my friend to check the timing.
 
ok so the model number for the vacuum amp is 3671424 and it has 4 ports on it and im still unsure of what it hook up the vacuum lines to . oh and i forgot to say the spark plugs are obnly maybe a couple months old with less than 1k on them.
 
one of the things that i want to figure out is why it wants to die when i give it throttle. its like if i go around a quarner i have to hold it at around 1000 until it drops to first gear then i can give it gas, but if i dont do this its like it wants to flood.
 
beebeeri000 said:
ok so i got a vacuum can from my old slant that ill put on, i dont got a cylinder pressure testing tool and i couldn't find anyone that rented it, but my slant hasnt been showing signes of low compression.
Click to expand...

You can buy one for $30 - $60....
 
You know the vacuum can goes on/in the distributor, right?
It should have just one port nipple on it.You stick a rubber hose on it , and attach that to the sparkport on the passenger side of the carb. The sparkport is the nipple that has no vacuum at idle, but picks up the vacuum signal almost right after you begin to open the throttle.
If your engine makes over 15 or so inches of idle vacuum,to, the same under cruise conditions, and the carb has the correct sparkport, I can't see a reason to go through the amp. I ditched mine over 20 years ago.
You say your engine has not been showing signs of low compression, but if you rarely floor it in second or third gear, to sense a power loss, then the next place a loss of compression will show up, is driveability and a loss of fuel mileage.

The dying-engine business is usually a lean condition from either the powervalve circuit or the accelerator pump circuit, or an unvented floatbowl. Retarded timing aggravates it. If it's worse when cornering, it may be an incorrect fuel level. BUT.... this assumes; the cylinder pressure is up and even,and,that the valve adjustment is correct, and, that the sparkplugs are not compromised. So that is why we start with those. You can dick with the carb for a hundred years and get little to no results,if one of those three is messed up. Of course if you know one of those is faulty, and how to fix it, there's no reason not to fix it,right away.

Your problem is not likely to be simple. There's an excellent chance we can help you figure it out, BUT you will need tools. If one of us was there, we might be able to solve it in a jiffy. However, from hundreds of miles away,a guy would have to be awfully good at diagnostics, or darn lucky.So we rely on measured data.Sometimes a guy will say something like "the timing is good". Well, that don't mean squat on this side of the screen. His interpretation of good is ambiguous, at best, and misleading at worst. So hard numbers, correctly obtained, and duplicable , are the best data. To that end; beg, borrow, steal, or buy some tools.
The tools you are going to for sure need are: a screw-in compression tester,a timing lite,a stick-on timing tape, feeler gauge set,float level gauge,
The tools it would be good to have, but not mandatory,are; a leakdown tester,a vacuum gauge, a piston stop, 5ft of vacuum line and a Tee to fit the sparkport,
If you get access to a dial-back timing lite, you won't need the timing tape.However, if you are buying,the cost difference between a regular lite and a DB lite far exceeds the cost of a stick-on tape.Or even several of them.
 
it sounds to me like the carb is in dire need of a rebuild. those things can flood and still run . I had one that was dumping gas but would still start and drive but I had to keep it running with one foot on the gas and one on the brake. im betting its blowing black smoke out of the tail pipe very time you start it and give it gas. that's where I would start. especially if its dying when you come to stop.
 
AJ/FormS said:
You know the vacuum can goes on/in the distributor, right?
It should have just one port nipple on it.You stick a rubber hose on it , and attach that to the sparkport on the passenger side of the carb. The sparkport is the nipple that has no vacuum at idle, but picks up the vacuum signal almost right after you begin to open the throttle.
If your engine makes over 15 or so inches of idle vacuum,to the same under cruise conditions, and the carb has the correct sparkport, I can't see a reason to go through the amp. I ditched mine over 20 years ago.
You say your engine has not been showing signs of low compression, but if you rarely floor it in second or third gear, to sense a power loss, then the next place a loss of compression will show up, is driveability and a loss of fuel mileage.

The dying-engine business is usually a lean condition from either the powervalve circuit or the accelerator pump circuit, or an unvented floatbowl. Retarded timing aggravates it. If it's worse when cornering, it may be an incorrect fuel level. BUT.... this assumes; the cylinder pressure is up and even,and,that the valve adjustment is correct, and, that the sparkplugs are not compromised. So that is why we start with those. You can dick with the carb for a hundred years and get little to no results,if one of those three is messed up. Of course if you know one of those is faulty, and how to fix it, there's no reason not to fix it,right away.

Your problem is not likely to be simple. There's an excellent chance we can help you figure it out, BUT you will need tools. If one of us was there, we might be able to solve it in a jiffy. However, from hundreds of miles away,a guy would have to be awfully good at diagnostics, or darn lucky.So we rely on measured data.Sometimes a guy will say something like "the timing is good". Well, that don't mean squat on this side of the screen. His interpretation of good is ambiguous, at best, and misleading at worst. So hard numbers, correctly obtained, and duplicable , are the best data. To that end; beg, borrow, steal, or buy some tools.
The tools you are going to for sure need are: a screw-in compression tester,a timing lite,a stick-on timing tape, feeler gauge set,float level gauge,
The tools it would be good to have, but not mandatory,are; a leakdown tester,a vacuum gauge, a piston stop, 5ft of vacuum line and a Tee to fit the sparkport,
If you get access to a dial-back timing lite, you won't need the timing tape.However, if you are buying,the cost difference between a regular lite and a DB lite far exceeds the cost of a stick-on tape.Or even several of them.
Click to expand...

ok so oreilys by me loans out compression testers so ill get that romorrow and check that when i did a power run in 1st it seemed like it wasn't lacking in power, i got a set of feeler gauges and ill lash it tomorrow, my friend has a timing light that he'll probably let me borrow so ill pick that up this weekend if im out there. i got my distributer hooked up to the port on my carb already. should i have a vacuum amp on my engine? or would it be worth it just to ditch it?
 
73AbodEE said:
it sounds to me like the carb is in dire need of a rebuild. those things can flood and still run . I had one that was dumping gas but would still start and drive but I had to keep it running with one foot on the gas and one on the brake. im betting its blowing black smoke out of the tail pipe very time you start it and give it gas. that's where I would start. especially if its dying when you come to stop.
Click to expand...

its a fresh rebuild and it doesnt smoke at all. if it started poofing black id be a lot more worried about the condition of the engine.
 
beebeeri000 said:
its a fresh rebuild and it doesnt smoke at all. if it started poofing black id be a lot more worried about the condition of the engine.
Click to expand...

ok , pull a couple of plugs and read them. they will tell you a lot about whats going on with the engine. and just because its been rebuilt does not necessarily mean the float is set right or that its not dumping fuel. what you describe is exactly what a flooding carb does. im just trying to help you. ive been at this for 35 years and ive had this problem a time or two. :D
 
As I recall, the vacuum amplifier was a later addition for smog purposes that simply allowed the vacuum signal to the vacuum advance to be controlled in finer fashion than the original ported vacuum straight off of the carb. It did not actually amplify, or increase, the vacuum signal. I don't see where it is needed at all for your purposes of better fuel mileage, but if it is there, you may need to bypass a few other bits. What year is this engine? Is the vacuum amplifier there?
 
the last two could be low because my battery was dead by the end so i might charge it and retry those two cylinders
 
nm9stheham said:
As I recall, the vacuum amplifier was a later addition for smog purposes that simply allowed the vacuum signal to the vacuum advance to be controlled in finer fashion than the original ported vacuum straight off of the carb. It did not actually amplify, or increase, the vacuum signal. I don't see where it is needed at all for your purposes of better fuel mileage, but if it is there, you may need to bypass a few other bits. What year is this engine? Is the vacuum amplifier there?
Click to expand...

i thought that it might help the carb run a bit betterr but it makes sense cause it was hooked up to the egr valve intake and carb. the engine is out of a '78 but the 2amp is from my old '73/6
 
Well now we don't know how 5 and 6 compare to 1 thru 4 since they were done under different circumstances.
I would redo the test, with a fully charged battery and in reverse order.

If you block the throttle WOT, the pressure will come up a little faster, and thus save your battery.
 
AJ/FormS said:
If you block the throttle WOT, the pressure will come up a little faster, and thus save your battery.
Click to expand...

Yeah, and remove ALL spark plugs while cranking. It will spin easier without compression in the 5 other cylinders.
 
Sounds like compression is fine.
 
Sounds to me like he might be talking about the dashpot on the carb, and not the vacuum advance canister. There are so many things wrong here, it is important to fix one thing at a time, and not get confused about cause and effect.
1. Timing.
2. Set the valves.
3. Basic tuneup. Plugs, wires and points, or put in an electronic ignition.
4. Carb rebuild.
5. Do a thorough check of all wiring to make sure you are not losing voltage between the battery and the ballast resistor. I cannot emphasize that enough. It is easy to fix, and reasonably cheap, and makes everything work better. .
These are in order of difficulty, but not necessarily importance. Wire check is easy, but there is a bunch of it. Each fix may or may not make it work better until you get them all right.

For what it is worth, most slant guys set the valves wider than spec. The factory spec is (I think) 10 and 15 intake and exhaust. I have mine set at 18 and 25. This has the effect of increasing the dynamic compression ratio, which improves torque, and yields a margin of error for when the engine gets really warm. Even adjustment is critical. If you want to know more, I can give you a quick explanation on how to adjust them, while running hot.

Once more thing, is the battery and charging system working correctly? It should provide at least 13 volts at idle, and hold that when a load is put on it, or it sits a week. Nothing works well if this is not good.

Sam
 
k ill see about checking pressure again tomorrow, i when i was doing a valve lash i saw that specs were .010 for intake and .020 for exhaust and i lashed it to .012 intake and .022 for exhaust. my battery is kinda crap and likes to stit at around 11-12 volts at idle but my altenator tested good. whats a good place to shoot for on my timing?
 
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