I have learned a great deal from these threads, and it is time to give back.
I have an '86 Mercruiser 140 which I inherited last summer from my father-in-law. The boat has always suffered from an acceleration problem ever since I have known, but runs fine once up on plane. I installed the Pertronix ignition kit which was a fantastic improvement at speed (no more smell of unburnt gas, no more smoke stains on the back of the boat, and significantly improved fuel economy...and yes the points/condenser which were replaced were relatively new and set by a factory mechanic). However this did not fix the acceleration problem
Since the acceleration problem was still there, I replaced the accelerator pump in the carburator. This still did not make any difference.
I replaced all the vacuum fuel lines to remove the possibility of vacuum leaks in the older lines. This did not make a difference.
I cleaned the fuel screen at the inlet to the carburator (which only had a few particles in it). This did not make a difference.
I had our reputable Mercruiser mechanic rebuild the carburator. This did not make a difference, and the acceleration problem became significantly worse after the carburator was rebuilt. He even said that he had to back out the fuel mixture screw 2.5 more turns than nomal to get the engine to run.
The reputable Mercruiser mechanic pulled the carburator apart and replaced the accelerator pump under warrantee since the accelerator pump was defective and a piece of the rubber fell off and blocked the intermediate jet in the carburator. That clue led him to find a bunch of other junk stuck in the intermediate jet along with the piece of accelerator pump.
Apparently the intermediate jet is the only piece of the carburator which is not serviceable (it is cast into the body of the carburator), and it is a very difficult place to see or access in the carburator. The intermediate jet is responsible for delivering fuel while accelerating in the intermediate RPM range...right where I was having my issue ~1500 - 2500 RPM.
So for all of those who also have the never-ending hunt for the mystery acceleration problem and have tried everything possible, check your intermediate jet in the carburator for debris and attempt to remove the debris. My Mercruiser 140 accerates like new now!
I have an '86 Mercruiser 140 which I inherited last summer from my father-in-law. The boat has always suffered from an acceleration problem ever since I have known, but runs fine once up on plane. I installed the Pertronix ignition kit which was a fantastic improvement at speed (no more smell of unburnt gas, no more smoke stains on the back of the boat, and significantly improved fuel economy...and yes the points/condenser which were replaced were relatively new and set by a factory mechanic). However this did not fix the acceleration problem
Since the acceleration problem was still there, I replaced the accelerator pump in the carburator. This still did not make any difference.
I replaced all the vacuum fuel lines to remove the possibility of vacuum leaks in the older lines. This did not make a difference.
I cleaned the fuel screen at the inlet to the carburator (which only had a few particles in it). This did not make a difference.
I had our reputable Mercruiser mechanic rebuild the carburator. This did not make a difference, and the acceleration problem became significantly worse after the carburator was rebuilt. He even said that he had to back out the fuel mixture screw 2.5 more turns than nomal to get the engine to run.
The reputable Mercruiser mechanic pulled the carburator apart and replaced the accelerator pump under warrantee since the accelerator pump was defective and a piece of the rubber fell off and blocked the intermediate jet in the carburator. That clue led him to find a bunch of other junk stuck in the intermediate jet along with the piece of accelerator pump.
Apparently the intermediate jet is the only piece of the carburator which is not serviceable (it is cast into the body of the carburator), and it is a very difficult place to see or access in the carburator. The intermediate jet is responsible for delivering fuel while accelerating in the intermediate RPM range...right where I was having my issue ~1500 - 2500 RPM.
So for all of those who also have the never-ending hunt for the mystery acceleration problem and have tried everything possible, check your intermediate jet in the carburator for debris and attempt to remove the debris. My Mercruiser 140 accerates like new now!
