I have a1970 Bearcat 55 that I have been working on for a year now. Yesterday I put the boat on the water for the first time.Starts very easy,idles smooth,but when I throttle up the motor just bogs down.I have replaced the following: Plugs,plug wires,rotor,distributor cap,condensor,had the carbs rebuilt.After repeated attempts to throttle up i replaced the coil,no change.Fuel ball remains hard,pumping it while attempting to throttle up results in no change.I am suspecting electrical issues but don't know where to look next.My tach was fluctuating up and down while I was advancing the throttle.Any suggestions what to look for next.
Most of my experience with bogging down goes right to a fuel delivery problem. How old is the gas, has it been sitting over the season? Ethanol fuel will break down older rubber fuel hoses causing them to collapse on the inside. Something you won't see just by looking at the hose, How about the fuel filter/screen by the motor, if it has black specs it's a rubber breakdown. I also had a problem with the fuel pickup tube in the gas tanks itself, Portable tanks have a drop tube with a fine screen on the end, it it's partially clogged it will let enough fuel in to idle but cannot keep up while throttling up. Anyway you can have a friend ride with you while you adjust the needles underway?
The fuel line is brand new and rated for ethanol.Fuel is non ethanol 90 octane just from the station.The fuel filter is an after market,brand new,the glass bowl filter has been removed.I tried pumping the bulb as my wife accelerated with no change at all.Good compression on all cylinders.You barely have to turn the key and it starts right up.The fuel tank is brand new.I feel like it something electrical,but can't figure out what.Could the accelerator plungers have something to do with it?
I don't know anything about these engines, but in general with a problem transitioning from low speed to high speed it often indicates a lean condition on the low speed. Does the carb have a low speed mixture adjustment? If so,try richening it up.
I donât know your motor, nor am I an expert. I had something similar happen on a different brand and vintage. Idled great but would not accelerate. Mechanic found a bad stator and replace it. Then all ran like new. Just throwing my experience out there and hope you find your issues and get it running like it should. Sure hope other mechanics can give you better direction. 63 Sabre nailed the ethanol issue I had on a different Outboard. Sounds like you have worked past that one.
I ordered 2 new accelerator plungers kits and am going to try that next..At this point I may have to just keep throwing parts at it until it runs well.I wonder if something could be wrong with the distributor spark advance but don't know how to troubleshoot that.
It's a little difficult for me to wrap my head around the problem 'cuz I keep forgettin'' that it's a 4 cycle motor. What about timing advance? Is there any adjustment for that?
It's springtime now and motor issues will begin to pop up. Right now I'm in the process of pulling apart the fuel pump and carb on my Gale 2 cycle. Fuel pump diaphragm had a hole in it where the rubber just fell apart so decided to pull the carb and clean it up also. At least your motor runs
Keep us posted
It does sound like fuel to me. I am just getting started on Bearcats however. As we open the throttle plate, we are allowing more air through the carb. It has to start picking up fuel mist through the high speed jet to keep the mix at the proper ratio. I know you said the carbs were rebuilt, but it would have me chasing the air fuel mixture. If the fuel bowl is full as indicated, it would put me into that high speed jet circuit. Gasket on backward or port plugged, I have created such issues for myself. That motor should accelerate (slowly) even if the advance wasn't working properly. It may not get to full speed. I guess the other question is how fast are you trying to accelerate, can you slowly bring it up or does it bog immediately no matter what. I will look at the timing under harsh acceleration.
It will not increase even if I try to advance it slowly.I don't think there is an adjustable high speed jet.The manual i have tells how to adjust the idle speed jet,that's all.Most of the information I have read on here that the best way to adjust timing is to run at near wide open throttle and turn the distributor slowly until the rpms increase.
Don't dismiss Dr. Go's thoughts. Your statement that the tach fluctuates rings a bell. My tach was triggered with an output wire from the rectifier. The tach quit working and I had to replace the rectifier, which is energized by the stator. As I recall my engine still ran fine during this problem (but I don't remember for sure). There are a couple output wires from the rectifier, to the starter solenoid, and voltage regulator (if you have one). I would study a wiring diagram, check the stator, rectifier and voltage regulator outputs.
My experience is the carburettors are very sensitive to improper adjustment. Often this was for me the reason for stalling when trying to get the boat in motion. Check especially your idle screw adjustment. Probably you should turn them more clockwise. When it idles too fast as a result compensate this with the normal idle screws. Good luck!
The carbs are Tillotson MD 120s and are fixed high speed jet. The accelerator pumps only are a factor momentarily, and while the throttle is being advanced. The original fuel pumps are not available and the Echlin NAPA ones work, but don't have the volume needed for RPMs above about 3500
The ignition timing is static set per manual only. The distributor has mechanical advance inside the disto base. I do not recommend adjusting the timing to any other setting than recommended by Homelite, or Fisher Pierce
I finally got back to work on the Bearcat.Replaced the rectifier,no change.Swapped out the carburetors with another recently rebuilt set and no change.Runs exactly the same.After it is warmed up,you barely have to turn the key and it is running.I am going to get a fuel pressure gauge and see what the pressure is when I throttle up.Could it be fuel pump? Distributor? Now my tach has stopped working all together,so I don't know what the rpm,s are now but it was bogging down around 3000, with the needle moving up and down.The prop i am running is an 11 pitch.