jasondainter
Regular Contributor
Hi Folks.
Ive had an issue now for a couple of years thats really taking the enjoyment out of my boat/engine and wondered if you kind folks could help me out. I feel like I'm getting close with it! Ill try provide as much background as I can and see if someone clever can figure this out!...
Summary:
Johnson 55HP (1979) had an issue with clutch dog so renovated whole lower unit with new one (fixed problem). At the same time thought it would be smart (it was not smart!) to change the fuel pump, and clean out the carbs so took them all apart with a rebuild kit. When reassembling I get a bogging down issue seen in the video at about 7 knots when going into WOT where the engine bogs and wont pick up speed.
What I tried today:
- When bog is happening I took a rag or hand (or in video briefly disconnected the bottom carb linkage arm so I can move only the lower carb choke) and cutting off air in this way fixes the issue fully. It runs perfectly and goes to about 23 knots (full speed). Covering the top carb or both carbs does not improve things only the bottom one. So this leads me to believe the engine is running lean and not getting the fuel it needs at full speed.
- I tried also a separate test to pump the petrol bulb as the bog is happening and this does not do anything at all. Its a bit above my knowledge but my amateur assumption would be that if covering with hand fixes the issues (running too lean, needs more fuel in the mix) but pumping the bulb with fuel does nothing at all, then this would suggest it's an issue with the carb itself feeding out too little petrol (eg a screw adjustment) rather than it being a problem with not getting enough petrol into the carb. I would love if someone could confirm that assumption though!
My next step
I took out the lower carb from the boat (which is on the water now) and am about to open it up to check if anything looks unusual. Any tips on exactly what I should be checking for area appreciated but I'll check the float is correct (I did take a lot of care to ensure that thing was in the right position so I doubt thats wrong), if theres any obvious blockages, and failing that I was planning to try and turn the high speed jet orifice a little to bring in more petrol. if anyone know if counter clockwise or clockwise brings in more petrol that would be appreciated!
Video of issue
Questions
1. From the above description, do you have any input on what you think is the most likely cause?
2. I do not have the special jet screwdriver tool (part 390934) and they cost delivered to sweden like 100 dollars or so which seems a bit outrageous. I assume you can adjust those jets with a normal flathead screwdriver if you get one to fit nicely? Does anyone have any tips there on a cheaper solution and what kind of sized flathead would work well? I dont want to damage this thing.
3. Does turning the high speed jet orifice clockwise or anti clockwise increase the amount of petrol in the mix coming out of the carbs?
Thanks ahead for any help.
Ive had an issue now for a couple of years thats really taking the enjoyment out of my boat/engine and wondered if you kind folks could help me out. I feel like I'm getting close with it! Ill try provide as much background as I can and see if someone clever can figure this out!...
Summary:
Johnson 55HP (1979) had an issue with clutch dog so renovated whole lower unit with new one (fixed problem). At the same time thought it would be smart (it was not smart!) to change the fuel pump, and clean out the carbs so took them all apart with a rebuild kit. When reassembling I get a bogging down issue seen in the video at about 7 knots when going into WOT where the engine bogs and wont pick up speed.
What I tried today:
- When bog is happening I took a rag or hand (or in video briefly disconnected the bottom carb linkage arm so I can move only the lower carb choke) and cutting off air in this way fixes the issue fully. It runs perfectly and goes to about 23 knots (full speed). Covering the top carb or both carbs does not improve things only the bottom one. So this leads me to believe the engine is running lean and not getting the fuel it needs at full speed.
- I tried also a separate test to pump the petrol bulb as the bog is happening and this does not do anything at all. Its a bit above my knowledge but my amateur assumption would be that if covering with hand fixes the issues (running too lean, needs more fuel in the mix) but pumping the bulb with fuel does nothing at all, then this would suggest it's an issue with the carb itself feeding out too little petrol (eg a screw adjustment) rather than it being a problem with not getting enough petrol into the carb. I would love if someone could confirm that assumption though!
My next step
I took out the lower carb from the boat (which is on the water now) and am about to open it up to check if anything looks unusual. Any tips on exactly what I should be checking for area appreciated but I'll check the float is correct (I did take a lot of care to ensure that thing was in the right position so I doubt thats wrong), if theres any obvious blockages, and failing that I was planning to try and turn the high speed jet orifice a little to bring in more petrol. if anyone know if counter clockwise or clockwise brings in more petrol that would be appreciated!
Video of issue
Questions
1. From the above description, do you have any input on what you think is the most likely cause?
2. I do not have the special jet screwdriver tool (part 390934) and they cost delivered to sweden like 100 dollars or so which seems a bit outrageous. I assume you can adjust those jets with a normal flathead screwdriver if you get one to fit nicely? Does anyone have any tips there on a cheaper solution and what kind of sized flathead would work well? I dont want to damage this thing.
3. Does turning the high speed jet orifice clockwise or anti clockwise increase the amount of petrol in the mix coming out of the carbs?
Thanks ahead for any help.
