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Fuel System, Performance Mods, Engine, Fuel System, Coupe, Convertible, Hatchback, Truck, Sedan, Wagon
#380 of 399 Re: Pinging noise when accelerating ? [crampton1998]
Jun 27, 2009 (9:45 am)
I wanted to add another perspective to your truck's tuning project, before you start turning wrenches on it: At this point, there are 4 factors which are up in the air and need to be juggled; metering rods, springs, timing, and spark plug selection. Since these four things ALL INTERACT WITH AND DEPEND ON EACH OTHER; there is a logical sequence in which they must be addressed. If that sequence is not followed; it can lead to a series of wrong conclusions and inappropriate choices.
The first step is to find the metering rod that runs best with the engine tuned as it now is; and it sounds like you have already done this.
The second step is to find the springs which work best with that particular metering rod; when the motor is in this state of tune. It seems to me that you have gotten a wrong impression that springs and rods must BOTH be changed at the same time. I may be partly responsible for this; in that I once suggested changing rods and springs at the same time. But that particular recommendation was made for a certain specific situation; and was not intended as a general rule. Right now, the thing to do is to stay with the rods you now have; and try different springs until you find the set that runs best with these rods. Since you are now experiencing pinging which increases with engine speed, and are also reporting that the motor is less responsive than it previously was, I suspect that the springs are too strong, and are making the mixture too rich at low and medium speeds, while it becomes better at higher speeds. If this is the case; a weaker set of springs may be better overall. But I might be wrong about which way the springs need to go; so you'll need to check this out yourself.
The difference between the effect of the rods and the effect of the springs is that the rods establish the basic mixture through the full range of engine speeds; while the springs determine how soon or how late in the speed and load range that effect comes in. A stronger spring will make the richness come in at lighter throttle and lower speeds. A weaker spring will delay the richness so that it only comes in at heavier throttle and higher speeds.
The selection of rods and springs should be made strictly by evaluating how well it responds and how strongly it accelerates. If they make it ping more, or make it ping less, that should not be a concern at this point. The pinging will be addressed in the later steps.
The third step is to find the best ignition timing setting. That will require some experimenting. The goal is to find the timing point that gives the best performance at high speeds; along with the least amount of pinging. At first, I would suggest changing the timing in 4 degree steps. When you find the best setting that way; them try moving it 2 degrees in either direction from that point. And when you find that point, then try moving it 1 degree in either direction from there. This will show you the best base timing setting. And always recheck the idle mixture and speed adjustment when you have changed the timing.
But you might find that the timing that gives the best performance at high speeds does not give the best performance at low speeds. If that happens; use the setting that runs best at high speeds, and see if the low speed perfomance improves if you move the vacuum advance back to manifold vacuum, and reset the idle screws for that.
Please let me know how what you ended up changing and much you changed it in these steps. I'll then make some suggestions about the advance curve and spark plugs.
#381 of 399 Re: Pinging noise when accelerating ? [zaken1]
Jun 30, 2009 (6:02 pm)
I finally got a day off from work and set the timing at 8 BTDC and the engine is running good and the pinging has stopped but I still need to fine tune the mixture screws and the rod + spring combinations. I have excellent low and high end power and acceleration but my mid-range acceleration doesn't seem to perform up to the same level. The truck sounds and runs excellent and the gas mileage has increased by 6 mpg. I got 17 mpg when I first got the truck and now I am getting around 23 mpg. I will take your advice on your latest post and see what will work best for my engine setup. Thanks again for your advice.
#382 of 399 Re: Pinging noise when accelerating ? [crampton1998]
Jul 01, 2009 (1:16 am)
At this point, it sounds like you have it adjusted for the best combination of performance and economy. When a carburetor is set that way; the mid range will not be comparatively as powerful as either the low end or the top end. The reason for this is that the mid range mixture is used for cruising and steady speeds; where the engine does not need to produce maximum power. If the mid range mixture was adjusted rich enough to produce maximum power; the fuel economy would suffer greatly. But the top end mixture can be set for maximum power without it hurting the fuel economy; because it is not used in normal driving. Similarly, the low speed mixture is set relatively rich; in order to enable a stable idle, and to facilitate the transition to the very lean mid range mixture. That also does not hurt economy, because as soon as the throttle is opened beyond the low speed range; it leans out to the most economical setting. So a normal mixture curve on a carburetor will be a little rich on the low end; as lean as practical in the mid range, and a little rich on the top end.
Because of this; and because of the outstanding fuel economy you are now getting, I expect that the spark plug configuration and the springs will not benefit from further changes. I think this is as good as it gets (or can get). So I would leave well enough alone!!!
Dec 31, 2009 (8:24 pm)
I have a 66 cadillac with a holley carb. I am getting fuel into it and the first two ports are squirting fuel into valle body but the car wont stay running unless I am spraying in fuel using a squirt bottle. Any ideas??? Thanks
#384 of 399 Re: Carburetor [swfuturecpt]
Dec 31, 2009 (9:18 pm)
You didn't state whether this car has been in storage for a long time; or how old the fuel in the tank is. If the fuel in the tank is more than about 8 months old; it should be drained and replaced with fresh fuel; before the motor can be capable of being made to run right. If the motor has not been run for a long time, you also should run a compression check on all the cylinders. If the compression is below 120 in any cylinder; or varies more than 30 psi between any two or more cylinders; the rings and valves may be sticking or worn excessively. If the motor has not been run for years, and the compression is now low or uneven; it might improve if you changed the oil and oil filter; added a bottle of Chevron Techron to the fuel tank, filled the tank with premium fuel, and ran the car at highway speed for 50 or 75 miles. But if the compression does not come up to factory specs within that time; the engine will have to be overhauled.
If the engine has good compression and is otherwise mechanically sound; the other thing that may be going on here is that A> The fuel pump is not producing enough fuel pressure, or the fuel filter is clogged. B> The carburetor float valve is clogged or sticking partly shut, or C> There is dirt or corrosion blocking the air bleeds, idle fuel jets or main fuel jets. So I would first check the fuel pump pressure and volume. It should produce at least 4 psi pressure, and be able to pump at least 16 ounces of fuel in 30 seconds or less. If the pump is good, and the engine is good mechanically; I would rebuild the carburetor and also do a complete ignition tune up (replacing plugs, points, condenser, rotor, cap, and plug wires, and adjust the dwell angle.) I would also replace the PCV valve, check the automatic choke operation; the choke vacuum break; and distributor vacuum and centrifugal advance mechanisms for proper functioning; and replace any defective parts in those systems. After this is done, make sure the engine runs at normal operating temperature (or replace the coolant thermostat if it doesn't warm up), I would then set the ignition timing, and adjust the idle mixture and idle speed screws. It should be able to idle and run normally by that point.
It may be a challenge and a hassle to successfully rebuild the old Holley carb. Those old Holleys are particularly troublesome. If you're not stuck on keeping everything original; I'd consider replacing the Holley with a new Edelbrock performer 750 CFM or EPS 800 carb; or an 800 CFM Edelbrock Thunder AVS (for slightly greater adjustability). These carbs will run better than the Holley, and will give better fuel economy.
#385 of 399 Problem with too much air, too lean
Apr 19, 2010 (9:48 am)
I'm scratching my head at this one. It's a ford auotlite carb, pretty simple, 2bl. . As far as I know, the engine is ok (no valve leakage). I have yet to set the timing but believe it's close enough right now (it starts).
Anyway, when the car warms up and the choke begins to open, the engine will not idle. Nor will the idle screw adjustment work. There is simply no effect. If I close the choke, the car will idle (badly).
I've replaced plug wires and gapped the plugs correctly. The car is a 1977 mustang ii. The orginal carb had this same issue, so I put on a different one. Same problem. Both are used carbs and could be bad I suppose. New power valve and new acc. pump. However, no fuel in the power valve bowl (don't know if there should be).
there is a PC valve that could have a problem (right now I have unfiltered air goint into the engine. (I'll purchase a new valve)
The egr is disconnected and plugged.
Any suggestions would be most welcome.
#386 of 399 Re: Problem with too much air, too lean [smreiter]
Apr 19, 2010 (12:55 pm)
In my experience; it is highly unlikely that two carbs in a row will have the same problem. The leanness you are encountering can be caused by several different issues. The most basic prerequisite for a motor to run properly is good cylinder compression. You stated that there is no valve leakage; but I don't know how you determined that. There can be compression leakage from many other areas besides the valves; it can leak from worn piston rings, cylinder bores, and a warped or cracked head, or a bad head gasket. This is why a compression test on all the cylinders is the only reliable way to determine the engine's mechanical soundness. When evaluating the results of a compression test; it is necessary that all the cylinder pressures are higher than the manufacturer's minimum allowable limit; and also that there is not more than 15% difference between the pressure in any two cylinders. If both of these conditions are not met; it will not be possible to adjust the engine to run properly. An engine which fails a compression test will have to be rebuilt or replaced.
But, on the brighter side; if your motor passes a compression test, I would expect the lean condition comes from a restricted fuel supply. There should be fuel visible in the accelerator pump well. So it seems to me that the fuel pump may have failed, or the fuel filter has become plugged. Try disconnecting the fuel line at the carb, and running it into a container which holds a quart or more. Crank the motor, and measure the fuel volume from the line in 15 seconds of cranking. There should be at least 8 ounces of fuel pumped in 15 seconds (a quart a minute). If you have a fuel pressure gauge; connect it to the end of the line, and crank the motor until the pressure stops rising. There should be at least 3psi (and very likely 4 or 5 psi). If the pump fails either one of these tests, and you can blow air through the fuel filter without feeling any significant restriction; then the fuel pump should be replaced.
The fuel level in the carb float bowl will also be low if the float level is set too low. Sometimes people adjust the float level by pulling the float upward until it stops; without considering that, on those float valves which are spring loaded, the fuel flow will shut off long before the float stops moving. So if your carb has a spring loaded float valve (which Autolite carbs often do) try turning the carb upside down and measuring the float height when the float is only pressed closed by its own weight. That is the proper point at which it should be measured.
There are separate fuel metering jets for the idle fuel and for the main fuel flow. If the tiny fuel passage in the idle jet is plugged; it will cause the leanness you experienced. A plugged main jet will also cause this condition; but the main jet orifice is considerably larger than the idle jet, so it is much less likely. And clogged internal fuel passages can also cause leanness. You could also completely unscrew the idle mixture screw, and spray carb cleaner into the orifice. Then put the screw back in place, turn it in until it is LIGHTLY seated, and back it out 1 1/2 to 2 1/2 turns. That should be a good starting point for the idle mixture screw setting.
If there are any vacuum leaks at the choke pull off, power brake booster, distributor vacuum advance, or EGR controls; this will also excessively lean out the idle. And if the EGR vacuum hose has been plugged, but the EGR valve is still in place; that valve sometimes gets stuck partly open. And that will cause the condition you reported.
#387 of 399 Re: Problem with too much air, too lean [smreiter]
Apr 22, 2010 (6:44 am)
A bad PCV valve can cause the rough idle problem. Will the engine die if you cover the air horn completely with your hand? If not-look for a vacum leak.
Do put a timing light on that engine.
As for carb I agree with another reply that 2 carbs acting the same would be unlikely-but not impossible.
Along with float setting-if your carb is the Ford type that the top is removed-the fuel level should also be checked with a pocket scale ruler -with the top off and engine running.There are specs on fuel levels in some manuals.
But before anything check the compression and see if it is reasonable and fairly even. Or do a leakdown test if possible.
FIRST OLD SCHOOL TUNE UP STEP IS TO REMOVE PLUGS AND CHECK THE COMPRESSION.
#389 of 399 Re: Carb still bogging [poonamt93]
by MrShift@Edmunds HOST
Jan 18, 2011 (9:44 am)
Carburetors are pretty dumb. They are at best compromises that try to meet every situation----so if anything at all is amiss, the effects are immediate. They have to be mounted just right and adjusted just right or they don't work well at all. They are fussy, and sensitive to tinkering, to climate, and to air filtration.