Help! Johnson 120 bogs really bad.

[mike91695]

I have a 1985 Johnson 120 VRO V4. It is mounted on a 16 foot Skeeter bass boat. I bought this about 3 months ago with a bogging problem when you give it the gas off idle. It also seems to run very rich at idle as well. I tested everything out according to the Seloc manual I have and everything seems to check out except for the voltage regulator and the power pack. I replaced them both with no luck. Compression is at 140PSI on all four cylinders. Carbs have been rebuilt and cleaned. The funny thing is that once you get it up on plane it runs GREAT! I took it to the local boat shop and they checked the timing , which is right on, and said they could not figure it out either. When you idle the boat around in a no wake area and stop and pull the plugs they are wet. If you run it at cruising speed and stop and pull the plugs they are dry and look great. It looks like somebody has torn the motor apart once and used RTV to seal the crankcase. The boat shop told me that was the only thing they could see wrong. But when you spray carb cleaner around it the motor RPM does not change. Any ideas?????????

 

[HighTrim]

Re: Help! Johnson 120 bogs really bad.

Since you say the carbs are clean, first check to see if the timer base (starboard side, under the edge of the flywheel, linked to the throttle lever) moves smoothly without sticking when you advance the throttle.

Take the airbox cover off and check if the throttle plates are parallel.

Also, the timer base should start it's travel before the throttle plates start to open, if not she will bog and die when you give her the throttle.

 

[tashasdaddy]

Re: Help! Johnson 120 bogs really bad.

if you are postive the carbs are clean, as HighTrim suggest, a link n sinc could be inorder.

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

I know that the timer base does not stick. But I will check to see if the base starts to move before the throttle plates start to open. Also one thing I forgot to mention is that when it is running at idle or just above, it will run smooth and then have a very hard miss or hard spot in it that sometimes will stall the engine. Could that still be timing related? Will the starting point of the timer base affect the overall timing? Because the boat shop told me that WOT timing was right on.
Thanks,
Mike

 

[Dhadley]

Re: Help! Johnson 120 bogs really bad.

What spark plugs are you using? And what's the top rpm?

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

Champion QL77jc4 plugs. Top rpm is 6000 with a 14 X 17 prop three blade.

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

Chris I took the air box off and the throttle plates are parallel. The timer base and the throttle start moving at the exact same time. Could this be my problem? I looked in the book and found the idle timing is suppose to be at 3-5 degrees BTDC can I check this with just running the motor with muffs on it? I took it to the boat shop to check the timing because the book said I had to have a test tank to check total spark advance which is set at 22 degrees and I do not have that option. What is link n sinc?

 

[HighTrim]

Re: Help! Johnson 120 bogs really bad.

No need for a test tank, see Joes instructions here in regards to timing in the future.

http://forums.iboats.com/showthread.php?t=228183

I do believe that you need a linc n sync as Tash suggested. Have you been adjusting the idle?? It is pretty detailed and you should have an OEM Service manual to do this. Not overly difficult though. Check www.ebay.com for a manual, or right here on iboats for a factory reprint.

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

I have not adjusted the idle but I don't know if anyone else has. I will check it out.
Thanks.

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

Well guys I checked it out this weekend and my idle timing was at -10 degrees BTDC. So I adjusted that up to 3-5 degrees BTDC as the book says. I also adjusted the timing and throttle linkage system according to the book. It runs much better but still has a very minor bog or almost a miss for the first second or two when you first give it full throttle from idle or just off idle. But one thing is for sure better, it starts right up and does not stall at all while idling and does not run as rich. The only bad thing is that it idles at 1500-1800 rpm when not in gear and about 1000 rpm in gear.. The throttle plates are completely closed and the little roller on the linkage is not touching the arm. But I can not get it to idle down. Any ideas?? Maybe getting back to one of my first questions about using RTV sealer for the crankcase halves. Could I have an air leak somewhere?? When I spray carb cleaner around the sealing joints it does not seem to change the engine rpm. Thanks for all of your help!

 

[CharlieB]

Re: Help! Johnson 120 bogs really bad.

Forget the crankcase leak, the carb cleaner showed that it is sealed.

Idle mixture is critical to instant throttle response. A dirty idle jet or air bleed can cause headaches troubleshooting.

If it runs fine WOT, timing is correct, good compression, good spark, all that's left is the carbs. The are not thoroughly cleaned.

 

[mike91695]

Re: Help! Johnson 120 bogs really bad.

I pulled off all 4 carbs and cleaned them again making sure to thoroughly clean all passage ways and jets. No luck it still runs the same and idles very high at 2000 rpm. The only way I can get the idle to come back down is to retard the timing back to -10 degrees. Any ideas????