88 johnson 150 lean shudder at idle

[71Windsor]

I have replaced the plugs and wires. Cleaned and went through each carb. Replaced the reg. rect.

Its a random act only at idle once in gear its fine runs great all day long. If I pump the primer ball this some times seems to get better the fuel pump was changed also no difference from the old to the new fuel pump. here is a video of another boat I found on you tube that mimics what mine is doing

Motor Sputter - YouTube

 

[Bosunsmate]

Re: 88 johnson 150 lean shudder at idle

Did you clean all the passages in the carbs?
Pull out every jet?

 

[emdsapmgr]

Re: 88 johnson 150 lean shudder at idle

Likely it's idling lean. Over time, carbed engines can accumulate dried fuel gelatin in the small idle passages of the carbs. (Could be due to lack of annual winterization, or it just sitting for long periods of time and not being started/run.) This restricts fuel flow at idle. This lean condition will mimic an occasional miss-called a "lean sneeze". This is a carb issue-not related to spark. Pull the carbs down and flush the internal passages with a solvent which will dissolve dried fuel, such as the aerosol product called Gumout. Usually these engine have large mid and high speed jets, which will permit that same engine to run fairly well at higher rpm's.

 

[71Windsor]

Re: 88 johnson 150 lean shudder at idle

Crabs are clean. I soaked the carb at work in the parts wash and went through every passage. But I trust your advice (that's why I ask lol) so ill go ahead and go through then once more. I'm not perfect I certainly could have missed something.

 

[emdsapmgr]

Re: 88 johnson 150 lean shudder at idle

Once the carbs are apart, I spray Gumout down one passage, noting the spray volume coming out the other side of the carb. Then pick up carb #2 and do the same thing on the same passage. Watch to see the spray outflow-both passages should spray the same volume out of the same passage. If they don't one is still restricted and you'll need to clean till they both spray the same volume. Then go back to carb one and spray the next passage, then to Carb #2, etc, etc till both carbs are clean. See what you find with this procedure.