my 75 le sabre has a very slight hesitation accelerating from a stop pump rod is in the inner hole now. would moving it to the outer hole help? carb#is:7045240
ok. wonder if ignition timing would cause that slight hesitation,everything else checks ok.carb may need kit in it,has nefer been off,still has the limiter caps on the mixture screws
ok. wonder if ignition timing would cause that slight hesitation,everything else checks ok.carb may need kit in it,has never been off,still has the limiter caps on the mixture screws
Could be alot of things Jeff, check everything. Timing could certainly do it. Make sure your vacuum advance works. Is it directly connected to the carb, or does it go through a thermovacuum switch? Carb has never been off the car? It needs a rebuild by now. Accelerator pump rubber plunger may be worn. Could be those high resistance plug wires too :laugh:
advance goes thru a vacuum switch that sticks out the front of the intake. is there a way to check it on the car?? i agree the carb may need help,it sat a year before i bought it(gee hope my carb guy can put those caps back on,originality ya know)
To check the cannister itself, find a manifold vacuum source, then hook it directly to the cannister. If it is working, you should note an increase in engine speed as the timing advances. I'm not sure how your thermovacuum switch works. That's why you need a 75 Chassis manual. Were you able to find one on Ebay? If you want to keep the car stock, you have to have one.
i'm working on that and,i do smell a gas odor,after shutting it off. spark plugs were normal color.put new ac R45TSX plugs in(old ones were autolites). but despite the hesitation,i can still do a week's worth of driving on just 4 gallons of gas
just for kicks i pulled the hose off the vacuum advance,while it was running,was no vacuum present at the switch.any other sources that i could use if the switch is faulty? engine was warmed up to operating temp
Jeff, Get yourself a piece of vacuum hose. Then find a source for manifold vacuum. Look around on the carb or intake manifold. Then hook the advance cannister to the manifold vacuum. The idle speed should increase. If it doesn't, the diaphram is shot. I don't know how your thermovacuum switch works. It may provide only ported vacuum to the advance cannister. So you would have to open the throttle, and feel for vacuum at the hose.
The purpose of the thermal vacuum switch is to limit advance until the engine temp reaches 100 deg F. It is intended to control emissions by limiting the advance off idle. It operates through normal thermal expansion; as the engine temp increases, the plunger in the switch rises, finally opening the internal connection, establishing a connection between the source vacuum and the timing advance diaphragm. Normal vacuum advance was connected to off idle vacuum in 1970, in an effort to lessen HC emissions. It is called ported vacuum, as opposed to manifold vacuum. It also permits a slightly leaner idle mixture. Again, emission control in the making. In an effort to make the engine run better, check the operation of the vacuum advance, and bypass the switch. Operate the vacuum advance at all temps, which will improve the off idle performance cold, and likely increase the fuel economy. It may also alow a slightly slower cold idle. Ray
ok ray,carb is exhibiting a gas odor,and slight hesitation off idle too when i pulled the hose off the advance, was no vacuum present from the switch. car was fully warmed up. should i check timing?
weel,i think it is definately gonna get a rebuild. what would be causing a gas odor after shutoff? is real strong sometimes. no external leakage.does not use excessive amounts of gas. original gas cap in place.
It is my understanding that the thermo vacuum switch gave ported vacuum (0 at idle, vacuum if the throttle is open) until the engine got HOT, then applied manifold vacuum to speed up the idle and cool the engine. If I am correct you will have no vacuum at idle even if everything is working properly. As suggested, find a manifold vacuum source (vacuum even at idle) and hook it to the vacuum canister on the distributor to accurately check the condition of the vacuum advance. Or you should even be able to move the distributor vacuum advance with mouth vacuum (yucky, but it works...)
am more concerned with the gas odor i smell after shutting off the engine. there are no external leaks. am now thinking the slight hesitation could be a weak fuel pump
A 1975 car probably has a cannister to absorb the fuel venting from the bowl. There may be a solenoid that controls that. That's why you need the 75 Chassis manual. You can get all the answers from that. Get it on CD if you can't get the paper copy. A weak fuel pump will give you more than a slight hesitation. Your carb needs a rebuild at the very least. We still don't know if your vacuum advance is working, never mind if it gets vacuum or not. The cannister hass to work.
just advertised in parts wanted for a CHEAP set of 75 manuals. canister filter was changed a month ago. there is no soleniod for it. i'll check for blocked hoses,and will test the advance also
With respect to the vapor cannister, and its purging, there are no controls except the mechanical ones. The cannister was used to contan vapor from the bowl, and worked well, but not prefectly. There was still a good possibility that a fuel smell was present. These systems were designed for fuels formulated in the mid seventies. Fuel has changed DRASTICALLY, especially with the advent of fuel injection, which has no openings to the atmosphere. It is more likely that fuel will vaporize to the atmosphere now. Expect it. With respect to the controls, there are essentially two. Both are controlled through ported, or off-idle vacuum. There is no vacuum at idle. The other is the use of a temperature control, essentially a unit having several vacuum ports on it. It is typically mounted on the water passage on the intake, providing temperature info. It is purely a mechanical unit, and though reliable in its day, it may be defective now. It will affect fuel metering when warm as the carb was calibrated to account for the vapor in the cannister, but it was not a really essential control. If it fails, it will not affect fuel delivery enough to make any real difference in driveability. The last control was essentially the sizing of the vacuum lines, which controlled the amount of vacuum and flow. Checking the temp switch is simple. When cold, there should be no vacuum on the control port. When warm, there should be vacuum at the port, at a speed above about 1000 rpm. There should be vacuum from the carb port at all times above 1000 rpm, or thereabouts. Do not confuse the manifold port with the ported vacuum port. Typically, the ported vacuum port is about halfway up the float bowl section of the carb. Manifold ports are typically close to the throttle plate. Questions? Let men know... Ray
