Carburator problems - Centurion 755 Cab. 1973

[Martin Borch]

hi.

I am a frustrated owner of a fantastic Centurion here in Denmark. I bought the car with a newly restored carb. After a year I got issues that after driving a bit and when the engine got warm, the carb did not get enough gas (gas was boiling they said) and e.g. holding for red light the engine went out. My mechanic told me that the carb was sitting too close to the engine block and he put a 1/2 inch thick gasket between the carb and the engine block.

Last year that seem to help and it was driving nicely all summer. When I got the car out for the first drive this year, now it does exactly the same again. HOW CAN THAT BE :-(((((

Can anybody give me a hint what to do.

rgds Martin

Edited April 24, 2020 by Martin Borch
more explanation (see edit history)

[carbking]

There are MANY issues which can cause the same symptom.

 

I know it is frustrating to go back to the mechanic to fix the same symptom, but the cause is probably different.

 

I would look at the choke pull-off first; but I am probably 10,000 miles from you

 

I would suggest going back to the mechanic.

 

Jon.

[joe_padavano]

3 hours ago, carbking said:

I would suggest going back to the mechanic.

 

Jon.

 

I would suggest going to a DIFFERENT mechanic. Just sayin'  😉

[Martin Borch]

Thanks for the input. Actually, the old mechanic did not come up with the solution to add the 1/2 inch gasket himself, so I am now looking for one which a better knowledge about the carburator. Actually he said at that time that many take the short cut and install electronic injection, but I love my original car and engine with the a vacuum tubes etc, so I will not compromise and there must be a solution why gas evaporates or not enough gets into the carb when engine is warm. Thanks again for your input.

Martin

[Studeous]

You mentioned it acted up from one season, or time of year, from another. Might I suggest it could be a fuel problem? In our climate in Texas, the gasoline formula changes seasonally. Sometimes in the carb days of yore engines would vapor lock in spring because the fuel blended for the cooler weather (more violitile- lower vapor pressure point) would boil off in the lines and or the carb bowl because of the higher temperatures at that time of year.  Good luck with your problem. 

[joe_padavano]

These cars ran fine when they left the factory. The easiest and least expensive repair is to rebuild the carb properly and adjust it back to factory specs. The problem is that it's been 30 years since the last US car with a carburetor was built, and mechanics today have no idea how to fix something if they can't plug in a computer and have the computer tell them what to do. Yes, today's gasoline with ethanol poses problems, but they are not insurmountable. I have many cars of similar vintage with original carburetors and none of them require spacers, fuel injection, or any other non-stock modifications to run properly.

 

The Quadrajet carb used on your car is complex and few people have the skills or patience to rebuild them properly. The plastic float deteriorates due to exposure to ethanol and should be replaced with a metal one when the carb is rebuilt. The vacuum lines used on your car deteriorate and crack over time causing leaks that make it difficult to adjust the carb properly. These should be replaced if they have not been. None of them have any effect on fuel delivery to the carb, however. Also keep in mind that the fuel pump uses rubber internal parts that also deteriorate over time, especially when exposed to ethanol. If the fuel pump has not been replaced recently, it should be. Finally, the entire fuel system needs to be inspected. Debris in the tank can clog the inlet filter at the pickup inside the tank. The rubber hoses that connect the tank to the tank to the metal lines on the frame deteriorate, and once they do, they allow air to be sucked into the fuel line, causing fuel starvation. Your real problem is that your car is half a century old and requires careful inspection of all the fuel system components. It sounds like your mechanic doesn't want to do this and is suggesting expensive band aid fixes that usually introduce more problems than they solve. Start by getting a factory service manual for your car. Then find someone who has the skill and patience to follow the instructions contained in it. Good luck.

 

[Martin Borch]

Thanks Joe for your thoughts. Really appreciated. When I purchased the car in Charlotte, NC  a few years ago, I had a number of repairs done before shipping it to Denmark. One repair was a complete carb. rebuild. The Chairman for the Long Island Buick Club helped me find the best company to do that, so I kind of trust that this was done properly. I am working to find a mechanic here in Denmark who has skills in this area or at least want to spend the time helping me - and not just doing short cuts.

If we, for a short moment, assume that all the inside of the Carb was rebuild properly just a few years ago and back to factory specs, then we are back to the exterior being the cause of the issue. So I will focus on that. The issue happens exactly after 20 mins of driving - before that it drives like a dream - so my thought is that it must be heat which causes the problem and not e.g. a broken hose - in that case I would have assumed the issues would be present from the very beginning of the drive.

Do you agree with that ?

Rgds

Martin

[Martin Borch]

22 hours ago, Studeous said:

You mentioned it acted up from one season, or time of year, from another. Might I suggest it could be a fuel problem? In our climate in Texas, the gasoline formula changes seasonally. Sometimes in the carb days of yore engines would vapor lock in spring because the fuel blended for the cooler weather (more violitile- lower vapor pressure point) would boil off in the lines and or the carb bowl because of the higher temperatures at that time of year.  Good luck with your problem. 

Hi Studeous. Thanks for your comments. No, the car had same issue a year ago and the symptoms disappeared when the 1/2 inch thick gasket was inserted between the engine block and the carb. Unfortunately, a year later now it starts again. So it is not happening at different times of the year/seasons. rgds Martin

[joe_padavano]

6 hours ago, Martin Borch said:

Thanks Joe for your thoughts. Really appreciated. When I purchased the car in Charlotte, NC  a few years ago, I had a number of repairs done before shipping it to Denmark. One repair was a complete carb. rebuild. The Chairman for the Long Island Buick Club helped me find the best company to do that, so I kind of trust that this was done properly. I am working to find a mechanic here in Denmark who has skills in this area or at least want to spend the time helping me - and not just doing short cuts.

If we, for a short moment, assume that all the inside of the Carb was rebuild properly just a few years ago and back to factory specs, then we are back to the exterior being the cause of the issue. So I will focus on that. The issue happens exactly after 20 mins of driving - before that it drives like a dream - so my thought is that it must be heat which causes the problem and not e.g. a broken hose - in that case I would have assumed the issues would be present from the very beginning of the drive.

Do you agree with that ?

Rgds

Martin

 

Martin,

 

Obviously I don't know who did the work, nor do I know what's going on with the car at the moment. Long distance diagnosis has it's limits. 😉

 

The most definitive way to diagnose the problem is to temporarily install a fuel pressure gauge where the fuel line enters the carb. Watch what the gauge does when the car starts running poorly. I'll bet that the fuel pressure starts to drop off, which could be due to debris in the tank being sucked up against the inlet sock or it could be due to a deteriorated fuel pump or it could be due to problems with the rubber fuel lines.

[carbking]

Martin - your first post makes me think you may be beating the wrong horse.

 

Quote "holding for red light the engine went out."

 

This implies there is sufficient fuel for the engine to run at cruise, so why is there insufficient fuel to run at idle?

 

Like Joe, my long-distance diagnostic skills may not be the best; but it sounds like you may have too much fuel, which is why in my initial post I suggested the choke pull off. If the choke pull off is bad, the engine would run, albeit not perfectly at cruise, but would probably stall at idle; and testing the choke pull off is quite easy.

 

I like Joe's suggestion of the fuel pressure gauge. Testing is always preferable to guessing.

 

Jon.

[Martin Borch]

Hi Jon, thanks for your input. Really appreciated. I am in contact with a good mechanic and I hope he will accept to take my car in for service and of course I will convey to him all your thoughts. As you can probably hear from my writing, I am not technically skilled, just love my Buick. What is baffling me so much is that the car runs so smooth the first 20 mins, both cruising and holding for red (idling).  But as you say, the problem can be reverse, i.e. that it is just because the engine is cold and gets additional gas and then once the engine gets warm, and when the choke should get off, if that does not happen, the engine would get too much gas. Not sure if you would be able to smell that, but I will try to take a trip and let the engine get warm and see if I can smell any gas under the hood.

Rgds

Martin