Recently I began to encounter a problem with the 1968 GTO in that it was becoming harder to start and also it would occasionally shut off while idling at a stop light. I tried to convince myself it was due to not being ran on a regular enough basis. During some periods while restoring other cars the GTO is not driven for two or three weeks while I take my most recently completed project to car shows. The GTO has been one tough and extremely reliable powerhouse. As this problem seemed to be slowly and progressively getting worse I finally decided to attempt to determine what was going on.
One of the things that made the diagnosis difficult was the fact that when the car was being driven it appeared not to have lost power or to be misfiring. The only issue was when driving at a slow speed in a higher gear I noticed more of a lobe to the engine. This was nothing new and I attributed it to the performance cam running at too low in the RPM band, but it was becoming more noticeable. With no loss in compression or any evidence of a failure in a head gasket I began to look at the intake and ignition systems. As to the intake it is running an Edelbrock 600 cfm sitting on an Edelborck Pontiac Performance manifold and as to ignition it is running a stock distributor with a Pertronix Flame-Thrower electronic ignition and Flame-Thrower II 45,000 volt coil. After looking at both systems I felt the problem was in the distributor and that it had likely a bearing failure that was causing the shaft to become unsteady and in-turn having an effect on the timing. To make a story short: I was wrong.
The problem turned out to be within the carburetor which was 8 + years old and it appears the ethanol in the fuel had been slowly destroying the gaskets / seal in the carb. This was not something that happened overnight, but rather a slow process of degeneration that I really did not notice until the carb began to actually fail. As a quality rebuild costs almost as much as a new carburetor, I decided to not only purchase a new carb, but also upgrade to a larger 750 cfm due to the addition of other performance items on the engine (cam, headers, electronic ignition etc ). What a difference the new carb made to the engine! Between the old carb slowly losing efficiency and the increased cfms of the 750, I honestly feel the engine gained about 25 HP. I purchased another Edelbrock carburetor, because for the dollar, I feel they are the best carb on the market. They basically run right out of the box. I have owned just about every major brand of carb sold and have had the least amount of problems with the Edelbrock brand. I now use a Lucas Fuel Additive which counteracts the damage caused by ethanol.
One of the things that made the diagnosis difficult was the fact that when the car was being driven it appeared not to have lost power or to be misfiring. The only issue was when driving at a slow speed in a higher gear I noticed more of a lobe to the engine. This was nothing new and I attributed it to the performance cam running at too low in the RPM band, but it was becoming more noticeable. With no loss in compression or any evidence of a failure in a head gasket I began to look at the intake and ignition systems. As to the intake it is running an Edelbrock 600 cfm sitting on an Edelborck Pontiac Performance manifold and as to ignition it is running a stock distributor with a Pertronix Flame-Thrower electronic ignition and Flame-Thrower II 45,000 volt coil. After looking at both systems I felt the problem was in the distributor and that it had likely a bearing failure that was causing the shaft to become unsteady and in-turn having an effect on the timing. To make a story short: I was wrong.
The problem turned out to be within the carburetor which was 8 + years old and it appears the ethanol in the fuel had been slowly destroying the gaskets / seal in the carb. This was not something that happened overnight, but rather a slow process of degeneration that I really did not notice until the carb began to actually fail. As a quality rebuild costs almost as much as a new carburetor, I decided to not only purchase a new carb, but also upgrade to a larger 750 cfm due to the addition of other performance items on the engine (cam, headers, electronic ignition etc ). What a difference the new carb made to the engine! Between the old carb slowly losing efficiency and the increased cfms of the 750, I honestly feel the engine gained about 25 HP. I purchased another Edelbrock carburetor, because for the dollar, I feel they are the best carb on the market. They basically run right out of the box. I have owned just about every major brand of carb sold and have had the least amount of problems with the Edelbrock brand. I now use a Lucas Fuel Additive which counteracts the damage caused by ethanol.
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