1977 70 johnson bogging out

[capymac]

Started runing into a problem with my engine where it would idle perfectly then i could put it in gear and move at a trolling speed but when i would put the throttle down it would bog out and stall. I did some trouble shooting and cleanned the fuel filter and changed the spark plugs same thing still happening. Then while it was running i disconnected the spark plug wires one by one and found that the #2 clinder was not firing. what could be causing this to not fire?

Just found this forum and have got lots of info from it so far.
first post.
Thanks for any help.
Ryan

 

[Chinewalker]

Re: 1977 70 johnson bogging out

Hello Ryan,
When you said it "wasn't firing" do you mean that there was no spark or that the motor simply wasn't running on that cylinder (no change in RPM)? You need to determine if this is a compression, fuel or spark issue. Check compression. Should be even and above 100 psi in all three holes. Check for spark on all three cylinders - should be fat and bright. If you have spark and compression, then move on to the fuel system. How do the plugs look? With the motor running, will the motor pick up RPM if you spray mixed fuel into the carb feeding the "dead" cylinder? You don't want to run the motor too much like this if it is indeed a fuel issue, as the cylinder that isn't getting fed isn't getting lubed, either... My gut feeling is that you'll need to pull the carbs and rebuild them.
- Scott

 

[HighTrim]

Re: 1977 70 johnson bogging out

NO SPARK OR INTERMITTENT ON ONE OR MORE CYLINDERS:

1. Check the timer base resistance from the black/white wire to the white/black wires. Reading should be 10-20 ohms (or 30-40 ohms for CDI Electronics Blue Timer Bases) .
2. Check the DVA output from the timer base. A reading of at least 0.5V or more is needed from the black/white wire to the white/black wires (while connected to the pack) to fire the pack.
3. Check the DVA output on the orange wires from the power pack while connected to the ignition coils. You should have a reading of at least 150V or more. If the reading is low on one cylinder, disconnect the orange wire from the ignition coil for that cylinder and reconnect it to a load resistor. Retest. If the reading is good, the ignition coil is likely bad. A continued low reading indicates a bad power pack.

 

[capymac]

Re: 1977 70 johnson bogging out

Thanks for your help guys. I tested it for spark and the spark was looking good. I wanted to check the compression but the shop i was going to bring it to was closed because of the fires. So if all the compression is good in the cylinders then i have to rebuild my carb, and if the compression is bad in one of the cylinders im guessing it would be my piston and rings..is that right or can it still be something else?/

 

[jtexas]

Re: 1977 70 johnson bogging out

compression gauge, $20-$25, handy gadget to have around.

bogging on acceleration is a classic symptom of clogged carbs - remove, disassemble, soak overnight in carb cleaner, blow compressed air (or aerosol carb cleaner) through orfices, reassemble with new carb kits, put 'em back on, link & sync, good as new.

I use the sierra kits from iboats, you won't need new floats unless the old ones are saturated (unlikely).

meanwhile don't run it like it is...if #2 is starved for fuel it's also not getting any lubrication.

highly recommend the OEM shop manual, available at kencook.com or marineengine.com - will pay for itself 2 or 3 times with your first carb rebuild.