1979 Johnson V4 85 hp 2 stroke..bogs down

[wlaur]

At the start of summer I picked up a 1971 Larson with a 1979 85 HP V4 motor...it started pretty easily and then took it out on the motor..as I increased rpm ( to about 4000) the motor would bog down..did this repeatedly. Rebuilt the carbs on it..replaced plugs..and it ran smooth in yard (hose and "earmuffs" attached) and seemed ok..took it out on the water and the same thing occurred. The plugs seemed to get fouled right away as I increased throttle..very frustrating. I have a basic understanding of motors but boat motors seem to do their own thing..compression is real good and there is a bright blue spark on this motor. How can I get it to run smooth

 

[oldcatamount]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Check the basics first, is the fuel tank venting right, bad fuel line, loose fuel line clamp, old gas? Check out the Top Secret File on the Home page. You may need to do a Sync and link adjustment.

 

[wlaur]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Thanks..I suspect I will need to try a few different things. Thanks again

 

[jtexas]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Your symptom is typical of dirty carbs, especially since you've ruled out compression and spark.

did you soak the metal parts overnight in carb cleaner? the top secret file includes a "carb cleaning and rebuilding" link that contains instructions for fabricating a jet removal tool, take the jets out & clean 'em by hand if you need to.

misadjusted floats not closing completely will flood the motor & fowl the plugs.

try squeezing the bulb when it bogs down...if RPMs pick back up, fuel pump needs rebuilding.

 

[emdsapmgr]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Try constantly priming the fuel hose bulb. This will force extra fuel into the carbs. If it runs ok at top end, you may have a weak fuel pump.

 

[wlaur]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Thanks jtexas and emdsapmgr...this site seems to have some great resources..i will try the suggestions about priming the bulb when on the water. Jtexas..I cleaned all carb parts and did soak overnight...surprisingly looked pretty well..wish i knew the history of this boat..it has been cared for for a 40 year old boat, but something isnt quite right..2 stroke of this era seem pretty primitive..they just don't seem to like the mixture..i am wondering if the fuel pump is bad but not sure..on these older motors there is a "warm up" lever on the start up panel..when i use this lever it allows fuel to pass through nicely as you warm up the motor then requires to put lever all the way down before putting into gear..This feature works fine..is there a by pass fuel line for the throttle. I guess my question is this...Why does the warm up lever work fine and the motor sounds good but then the bogging down starts after i put it into gear and increase throttle??

 

[Daviet]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

When you use the warmup lever you are not putting a load on the engine, it is freewheeling so to speak. When you have it in gear it is under a load.

 

[wlaur]

Re: 1979 Johnson V4 85 hp 2 stroke..bogs down

Thanks Daviet..makes sense. I guess it is for that same reason that I need to take the boat out and run it in under load rather than use the earmuffs...I am about 30 minutes from water and it would be more convenient to run using the "muffs"