jtexas
Fleet Admiral
- Joined
- Oct 13, 2003
- Messages
- 8,646
Re: '75 Johnson 70hp is running really rough!!
rage, you were having difficulties with your choke solenoid - mine did that last week, just spit the plunger right out the solenoid, kinda funny - but you're right, that spring has to hold the choke plates open, if they flap around you'll get some weird symptoms.
greaser, your fuel pump needed rebuilding anyway - its not at all uncommon to have more than one issue contributing to a symptom. Especially after a few months of inactivity.
Your upper & lower carbs should be the same.......its the one in the middle should have extra parts: the intake nipple for the fuel line from the pump, the throttle cam follower, and the choke linkage (for the spring mentioned above). The throttle linkage is the crucial piece - seems to me the location of the fuel intake shouldn't matter (but I'm no expert). I wouldn't rearrange the linkages until I'd ruled out all the other possibilities.
Agree with mikesea that the bulb won't be hard while the engine's running but squeezing the bulb should have no effect on a running engine - and it should stay firm enough after you shut the engine off that you don't have to pump it up again to restart. Could be fuel pump, but also could be a float adjustment. Float valve not opening completely could make a partial obstruction that you can force fuel through with the bulb.
You can test the operation of the float valves by blowing through the fuel intake (best to take carb off engine and empty bowl first LOL); holding it upside down, no air should pass through, rightside up should have very little resistance.
What exactly are the symptoms at this point?
Primer bulb gets hard, but its soft after running the engine?
Engine starts ok, runs a few minutes then dies? Just for grins.....after that happens, remove the screw plug and drain the bowls (tilt the engine up a bit) - normally the same amount of fuel would drain from all three.
Before you switched the top & bottom carbs - it started & idled ok but bogged on acceleration, and squeezing the primer bulb improved it?
Have you lake-tested the motor since starting your repairs, or is this all on the muffs?
I think you have to get the fuel line to hold pressure before you can rule anything else out. Engine not running, air silencer cover off, tilt the engine up all the way, see if any fuel runs out the carbs. Pump the bulb up and squeeze it hard (but not like you're trying to choke a kitten or anything), look for fuel leaking around carb bowl gaskets, into carb throats, around the fuel pump.
curious - have you compression tested this motor?
rage, you were having difficulties with your choke solenoid - mine did that last week, just spit the plunger right out the solenoid, kinda funny - but you're right, that spring has to hold the choke plates open, if they flap around you'll get some weird symptoms.
greaser, your fuel pump needed rebuilding anyway - its not at all uncommon to have more than one issue contributing to a symptom. Especially after a few months of inactivity.
Your upper & lower carbs should be the same.......its the one in the middle should have extra parts: the intake nipple for the fuel line from the pump, the throttle cam follower, and the choke linkage (for the spring mentioned above). The throttle linkage is the crucial piece - seems to me the location of the fuel intake shouldn't matter (but I'm no expert). I wouldn't rearrange the linkages until I'd ruled out all the other possibilities.
Agree with mikesea that the bulb won't be hard while the engine's running but squeezing the bulb should have no effect on a running engine - and it should stay firm enough after you shut the engine off that you don't have to pump it up again to restart. Could be fuel pump, but also could be a float adjustment. Float valve not opening completely could make a partial obstruction that you can force fuel through with the bulb.
You can test the operation of the float valves by blowing through the fuel intake (best to take carb off engine and empty bowl first LOL); holding it upside down, no air should pass through, rightside up should have very little resistance.
What exactly are the symptoms at this point?
Primer bulb gets hard, but its soft after running the engine?
Engine starts ok, runs a few minutes then dies? Just for grins.....after that happens, remove the screw plug and drain the bowls (tilt the engine up a bit) - normally the same amount of fuel would drain from all three.
Before you switched the top & bottom carbs - it started & idled ok but bogged on acceleration, and squeezing the primer bulb improved it?
Have you lake-tested the motor since starting your repairs, or is this all on the muffs?
I think you have to get the fuel line to hold pressure before you can rule anything else out. Engine not running, air silencer cover off, tilt the engine up all the way, see if any fuel runs out the carbs. Pump the bulb up and squeeze it hard (but not like you're trying to choke a kitten or anything), look for fuel leaking around carb bowl gaskets, into carb throats, around the fuel pump.
curious - have you compression tested this motor?
