Vintage Oldsmobiles Curved Dash, Limited Touring, Models 40, 53, 66; Series 60, 70, 90

55 Ninety-Eight

Old July 21st, 2018, 09:49 AM
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Bfg
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55 Ninety-Eight

My 55 Ninety-Eight has been hard starting lately. Seems like a long time to fire. Thinking maybe fuel pump needs to be rebuilt. Also bad idle after starting. Runs ok if I increase idle. Could bad fuel pump effect idle. ( vacuum leak? ) maybe two isolated problems? I've owned the car since 95 with no repairs to either.
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Old July 21st, 2018, 11:32 AM
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In theory, bad fuel pump should have no effect on idle. It's job is to fill the float bowl in the carburetor, nothing more.

Now vacuum will definitely have an effect on engine idle. It would be a good plan to check all vacuum hoses and lines.

I am not conversant enough on the subject to opine as to whether vacuum has any effect on engine starting and shall leave that for others to advise.
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Old July 21st, 2018, 12:59 PM
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Thanks, checking vacuum will be my next job
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Old July 21st, 2018, 01:25 PM
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If you have owned the car since 1995 with no repairs you are very fortunate. I would recommend a rebuild of the carb. The plunger in the carb is probably not ethanol proof. At that age the throttle shafts on the carb could be worn and causing a vacuum leak. When the car is idling, spray some carb cleaner around the base of the carb and on the intake manifold and heads and see if the idle changes. If it does you have a vacuum leak. Get you a vacuum gauge (they are cheap) and check your vacuum. You should have at least 15" of vacuum. The other thing to look for is if the needle is steady or fluctuates. A vacuum gauge is very helpful on these old cars.
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Old July 21st, 2018, 04:20 PM
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When you say hard starting is this only on the first start or does it happen after warm up also. If it's all the time check the plugs timing and points, if only on the first start up and good after that you might be experiencing fuel evaporation of the carb. It happnes often now a days with the alcohol ENRICHED gas we get ...... Tedd

Last edited by Tedd Thompson; July 21st, 2018 at 04:22 PM.
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Old July 21st, 2018, 04:32 PM
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Actually if you have never done anything to the car since 1995. I would start with a good tuneup with points, plugs, condenser and a carb overhaul. Be sure and check the cap, rotor and plug wires. It will probably run like a different car. I am going out on a limb here and say an electric fuel pump will cure that hard starting. I don't have that issue with my 54 which has an electric fuel pump. Of course Tedd may not have it with his either and I know he has a mechanical fuel pump.
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Old July 21st, 2018, 04:44 PM
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You can rent a vacuum gauge from the auto parts store. Although it is an essential tool to have for tune ups and setting the carburetor.

If you install an electric fuel pump make sure you install it as close to the tank as possible. Also, you can wire it to 12V ignition through an oil pressure sensor so the fuel pump would shut off in the event of car trouble.

x3 for doing a full tune up with points, plugs, condensor,wires and carb rebuild.
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Old July 21st, 2018, 11:06 PM
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Actually it starts right up after it's been started initially. Makes sense to be the carb leaking down. I have a vacuum gauge to check for leaks for vacuum. I guess I can do a complete tune up. I guess I can rebuild the carb before I rebuild the fuel pump and see what happens. Maybe the idle circuit could be clogged causing rough idle? Car just doesn't get used that much causing problems.
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Old July 22nd, 2018, 07:43 AM
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As a test before you spend a lot of money, look down the carb(after it sets for a couple-three days), pump the throttle and see if you get two good squirts of fuel from the accelerator pump.. If yes there is fuel in the carb bowl, if not the bowl is dry and it is leaking or evaporating. Next step is to find out which one it is, could be one or a combination of factors. Our new gas does evaporate faster than the older stuff did or you are experiencing leak down.

A weak fuel pump will also exasperate this problem by not getting fuel up to the carb in a timely matter because of leak back of the gas in the fuel line from a bad valve in the fuel pump. You may need to have your pump checked if everything else checks out.

When all the parts work so does the whole car.... Let us know what works... Tedd
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