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.
The Bearcat has two carburetors, so the odds of both having the same issue at the same time is almost nil. Try loosening the linkage between the carbs. Then try to accelerate with only one carb throttle opening. It should accelerate, abiet slowly, but won't bog. If it does, try to accelerate with the other carb. This process allowed me to narrow down a problem on my homelite, where the seat screw inside the float bowl had backed loose and fallen out inside of the float bowl.
Ok ,so I finally got around to working on the Bearcat again.Installed a new Bosch coil.New plugs and opened the gap a little wider.Now I can get the boat to plane,but my rpm,s top out at about 3800 and then the tach starts to jump up and down.
I took the cover off and when I put my palm over the intake on the top carb,the engine stalls.If I cover up the bottom carb,the engine continues to run, and the rpm,s increase a little. Does this shed any light on a possible carb problem?
When I get about 3/4 on the throttle lever,the rpm's don't increase any further.Thoughts?
Not an expert, but maybe you are only running on the top carb. The bottom one is basically acting as a vacuum leak with no fuel being delivered, so when you block it off you get more vacuum through the top carb and increased rpm. As I recall the fuel line goes to the top carb and then there is a T to the bottom carb. Make sure the line to the lower carb is not blocked. As suggested above, maybe the fuel pump isn't pumping enough fuel to keep the lower fuel bowl full. You might try gravity feed from a small gas can to rule out the fuel pump.
Hi Homeiste,do you mean to bypass the pump and feed directly into the top carb?The fuel line between the top and bottom carb is new. I take it i would have to keep the can elevated above the top carburetor.By the way,do you have any Bear Cat parts left.I think I have used every part you sold me.
I would guess that it is more likely you have some issue with the lower carb, but you said you switched to another set with no change, so that led me to fuel supply to the lower carb. So, yes, disconnect the line from the pump to the carbs. Gravity feed from above carb level directly into the carb lines to bypass the pump. [First, disconnect the gas line and run it dry or the pump will pump gas out of the disconnected line from the pump while you are feeding the carbs by gravity.] If this fixes the problem you have a pump issue, but I still don't understand the tach issue, or whether it is related to the 'bogging.'
The tach is triggered from the rectifier. Issues could be in the tach, in the rectifier, or in the stator. You can check the rectifier with a multimeter (directions in the manual; I think you already replaced it though), you can also test the output of the stator with a mulitmeter (I would have to research how to best do that test, but you can google it if it isn't in the manual). Not sure how to test the tach itself but you might be able to google that too. I'm wondering whether your stator is shorting, but not sure why that would only happen at high rpm.
I sold the Bearcat and you got all the extra parts I had. The only thing I have left is a prop I ran across in the garage at the lake.
She found it. Michigan Wheel 90852 11B. Online search says that's 11 inch 11 pitch. In a box with some parts I didn't know my dad had. Looks like some impellers, water pump housing, fuel sediment bowl and assembly, gaskets. I'll figure out what's there in mid July when I get there. she also just sent a pic of another unopened Michigan wheel box PS-74, 11.5 x 10 pitch.