Johnson 175 bogs at high speed

[vortec_cruiser]

I recently purchased a 1986 Cajun Espirit 18.5' bass boat with a 1985 Johnson 175 engine. Both boat and engine appear to have been taken very good care of, and had been always garaged. The problem I'm experiencing is the engine bogging down (fuel starvation?) at higher boat speeds. The engine starts and idles just fine, and even at low to moderate boat speed it does fine. But as soon as I try to give it more throttle, it bogs down. It reminds me of a car with a partially plugged fuel filter, running fine a lower speeds, but not passing enough fuel at higher speeds.

I cleaned the fuel filter, which had some dirt in it, but not enough to cause this problem. Prior to my purchasing the boat it had been started infrequently in the previous year or two, and I'm pretty sure no fuel stabilizer had been used. I had filled the tank with about twelve gallons of stabilized fuel prior to running the engine. As stated above, it starts and runs at lower RPMs just fine. I'm thinking the main jets are plugged. There is also the possibility of a partially blocked fuel tank (built-in) outlet. The previous owner said he had rebuilt the carbs about six months ago, and has a receipt from a dealer who adjusted the linkages.

Any help or suggestions would be appreciated.

 

[emdsapmgr]

Re: Johnson 175 bogs at high speed

If it won't run top end, you could have fuel starvation. I'd do a simple test first: when you want to run full throttle, prime/pump the fuel hose bulb- repeatedly. That will force extra fuel into the carbs. If the engine takes off and runs fine, then you may have a problem with the fuel delivery system: fuel pump, bad hose, too small a hose size, defective anti-siphon valve at the tank, bad fuel pickup in the tank. If the extra fuel priming does not help, you could still have a fuel restriction in the carbs. If an engine has been stored without winterizing, it is not unusual for the fuel to dry up and clog the internal carb passages. I'm not sure what your prior owner did, but cleaning the carbs is a detailed process that involves cleaning the various carb passages with an aerosol carb cleaner and complete disassembly, including all jets. It's not difficult to remove the carb bowl drains and pull out a couple of the high speed jets and inspect them. (you'll need a special jet remover tool-317002.) If they don't look clean/pristine, I'd pull the carbs apart for sure.

 

[vortec_cruiser]

Re: Johnson 175 bogs at high speed

Thanks - I'll check those things.