1979 chevy caprice efficiency

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Anonymous

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My grandma has a 1979 chevy caprice classic with i believe a 250 and an automatic transmission. I know its a really heavy car, but it only makes about 10 MPG. It has a new carb in it. What do you think could be wrong with it? I took out the spark plugs a few days ago and there was oil on them so i guess the oil rings are going to have to be replaced. Also, what mod's if any could be made to make get a better gas mileage out of it?

Thanks for any help provided.
 
You haven't given us much to work with. The first thing I would check is to make sure that the choke is funcioning properly. I don't know much about that particular model, does it have an electric choke? Then check the float level. Did this car get better fuel mileage before the new carb? Is this city driving or open road? Or maybe oval track racing? We would like to help you out but need to know what sort of animal we;re dealing with.
Lazy JW
 
That would be careful city driving and gas mileage has only gotten worst as time has passed. I believe it has an electric choke.

How do i check if the choke is working fine and the float level?

Thank you for replying.
 
Howdy Tatao,
Remove the air cleaner, (the element is clean, right?) the choke plate is the topmost flapper thing inside the carb. When the engine is cold, the choke should be just closed, but should open with light finger pressure. If it has an electric choke, turning on the ignition key should energize the heating element which will cause the choke to come open. If it is non- electric, then you will need to warm up the engine to see if the choke opens. If the choke is adjusted too tight, you can loosen up the choke spring element and rotate it to where it just closes. This is usually a small round gizmo on the end of the choke shaft. The choke MUST be fully open when the engine is at normal operating temperature. To check the float level requires removing the top of the carb,probably best to remove the entire carb from the engine first. Turn the top part of the carb upside down, and see where the float is setting. This needs to be set to the book specification for your particular carb. Also a leaky float can sink in the float bowl and cause the fuel level to be higher than it should, resulting in high fuel consumption. You said this is a new carb, did the fuel mileage get better, worse, or stay the same compared to the old carb? I probably wouldn't pull the carb just yet, make sure that the ignition timing is correct, and that the vacuum advance is hooked up and working properly. What are the chances that a 1979 Chevy in El Salvador has all of the proper vacuum lines, etc. attached? Try to find a service manual for this car and get everything set up as close to factory specs as possible. Don't worry about doing special mods yet, you need to get the performance up to stock levels first. That will be tough to do with a worn engine that burns oil. If it never gets driven at high speeds, try a hotter spark plug to keep the deposits burned off. I would put in the hottest ones I could find, and then monitor them closely. An oil burner can also plug up an exhaust system pretty badly. Does the car have good power or does it seem pretty sluggish? If you let this car idle a lot it will really plug things up, and remember, you get zero mpg at idle. Having driven old junkers most of my life, I know just what it's like, and sometimes there is no cure but an overhaul. This should be enough to keep you busy for a while, keep us posted on your progress :D
Lazy JW
 
Did a compressions check and all cylinders are at about 160 psi. The mechanic said the oil rings do not need to be changed. The vaccum line from the carb to the distributor was clogged so that was fixed and put back together. The car has a little bit more power now, but im getting 10.3 MPG so apparently i was getting even less before. What else should i check for or do to improve gas mileage?
 
Sorry Tatao, I think I must have overloaded you with my long winded advice :oops: Let's just take it one step at a time now. Did you verify if the choke is opening when the engine is warmed up?
Lazy JW
 
The choke opens up fine when the engine has warmed up. I disconnected the vaccum hose going from the distributor to the carb and sucked on it and the engine did not speed up like someone told me it should. What does this mean? Im also gonna check the muffler tomorrow. What's the difference between a silencer and a turbo muffler as far as air flow, performance or anything else it might influence goes?
 
Good, sounds like the choke is working fine. The vacuum advance may not be working correctly. When you pull the vacuum line off from the carburetor and suck on the hose, it should advance the ignition timing inside the distributor. You can check this by removing the disributor cap and sucking on the hose. it should cause the mechanism inside to rotate a few degrees. If it doesn't move, the vacuum canister may be bad, or it may me binding up mechanically. If you have access to a timing light, you can verify this by sucking on the hose while monitoring the timing marks as the engine is idling. Yes, it should cause the engine to speed up when you do this. Hang in there, you'll figure it out yet :)
Joe
 
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