lower carb smoking

[RaScLeS]

The lower carb on my outboard has smoke coming through it with the motor off and the plugs are oily. would anyone want to tell me how to fix that ? its a carb that runs the 2 lower cylinders on a 3cyl merc.

 

[carbineone]

Re: lower carb smoking

Sounds like the carb is getting to much fuel,maybe a stuck or inproperly adjusted float needle or crap in the float needle?

 

[sschefer]

Re: lower carb smoking

Smoke comming from a carb can be a sign of bad rings or a failed piston. There will always be some percentage of leak down simply because rings don't actually seat and are never 100% sealed. There is also some gap at the ring ends that will allow pressure to be released into the crankcase.

Reeds have an allowable tolerance and only new or special custom reeds seal 100% flat and that's when they're under pressure.

So, since combustion only takes place in the cylinder and neither crankcase temperature nor carbs should ever reach a temp high enough to produce smoke, the problem is most lkely in the rings or a failed piston.

A leak down test will help diagnose the problem. Reading the plugs and looking into the cylinders will also help.



A decarb with seafoam might clear the carbon out of the ring lands and correct the problem.

And you thought I was gonna tell you to tear it down... LOL..

Best of luck

 

[RaScLeS]

Re: lower carb smoking

its got decent compression atleast 115psi all across. this lower carb is too rich im guessing ? and it needs tuned from the inside ? which is bs

this thing flew last year till the stator stopped working now its intermitent over 3000rpm under that is smooth enough. but wot it wont pass much over 3300 now. last year 5000 + np

this project is a tough one to get going good

 

[sschefer]

Re: lower carb smoking

its got decent compression atleast 115psi all across. this lower carb is too rich im guessing ? and it needs tuned from the inside ? which is bs

this thing flew last year till the stator stopped working now its intermitent over 3000rpm under that is smooth enough. but wot it wont pass much over 3300 now. last year 5000 + np

this project is a tough one to get going good

If you're calling my diagnostic bs, that's fine I wish you the best of luck.

 

[backyard mechanic]

Re: lower carb smoking

RaScLeS you should pay attention to what is posted. You asked for help and got good advise. Don't ask for additional if you are not willing to use what is offered. If you think it's bs then fine... but don't dis the folks in here trying to help you.

Furthermore... check on how a two stroke works. You will find that the info provided was dead on. Based on what you provided us in your post, there is no other way smoke can come from your lower carb.

 

[RaScLeS]

Re: lower carb smoking

just looking for what as many sources think is the cause thanks

oh and the tuning the mixture from the inside of the carb is whats bs

 

[sschefer]

Re: lower carb smoking

just looking for what as many sources think is the cause thanks

oh and the tuning the mixture from the inside of the carb is whats bs

That theory does have its merits. If the float needles and seats aren't doing their job they can make a carb super rich because they'll puke fuel. An overly rich carb can contribute to smoke that might not occur in a leaner engine with problems in the cylinder.

A higher than normal fuel mixture in the cylinder can lower the combustion rate and would produce less pressure. That lower pressure would be less effective at clearing the unburnt fuel from the cylinder. This lower pressure would most certainly contribute to your inability to make power after 3000 RPM.

The remaining fuel would still be in the cylinder when the engine was shut down and might continue to burn after the engine was stopped but not at an explosive rate thus producing smoke.

With a problem in the cylinder, if the cylinder was postioned such that the exhaust ports were closed the heat and expansion of the still burning fuel coupled with a leaky cylinder could cause the smoke to be forced into the crankcase and the only way out would be the carb.

The reeds would be in a relaxed state and need to be slightly opened for smoke to seap through. .020 is allowable so this is entirely possible without saying the reeds are bad.

 

[RaScLeS]

Re: lower carb smoking

Its hard to even think about having to remove the carbs again, i had the mechanic clean them. and install a new trigger. the boat worked great ! smooth power and a fast wot.

one day i took my bro out for a ride, i eased it the whole ride and hammered it outside my house, lost power. my stator gave out. replaced stator at the shop and they drained the lake. I didnt care i paddled out to the middle and hammered it and thats all I could do. nothing else just idling or wot

now its getting worse to where wot wont pass 3500 and 2 days ago 4200 would go but cut out quickly.

the motor idles MINT i can drop the idle to 500 and it still puts nice.

maybe ill try the seafoam stuff but im sure the lower carb has issues (but if it ran mint before the stator gave out it was tuned fine so...??)

my mechanic and I are pretty much lost with this motor I almost want to spray some nitrous thru the carb at wot and end it but i love my boat when its working good !

& again thanks for the detailed replies on whats going on, the last one sounds right on why it could be smoking. (but if the carb was tuned and working its hard to see it go out of wack) but its old and its a possibility

Ill prob. make a video when im back up there of the motor and how its running for iboats to hear, I really need this beater to work ive been boating my whole life my 25hp johnson would NEVER give a problem

 

[Faztbullet]

Re: lower carb smoking

A little smoke from the carbs are normal after shutdown on a multi carb engine, just most people dont notice it as engine cover and air cover are installed and you are seeing it as your troubleshooting the engine. The engine you have shares #1  carb to feed #2 cylinder and from what you have posted the engine sounds lean instead of rich(fuel starvation) or a bad rectifier overheating stator. Check the float level to see if set to high, inlet needles swollen restricting fuel flow, debris in high speed jets and rectifier and stator. Usually the "smoke" you are seeing is from cold fuel charge setting in warm crankcase, like the "smoke" off the sides of a cold tea glass.

 

[RaScLeS]

Re: lower carb smoking

ill have to get in there and do something im very disapointed with my engine at this point and just going to the cottage and seeing it in the water "not useable" is just frustrating

ill be up again this week, i might run another compression test since im a bit worried about that smoke.

a lean carb would usually leave the plugs hot and white looking no ? mine get gunked up with oil on them.

its sad, but the motor idles great, ive had it as low as 600 rpm and it will hold that all day. around 3000rpm is a steady smooth speed but over throttled to get there.....slammed all the way down it still wont pass 3200 or so at this point.

a few days before i could hold 4200 wot some what kicking in and out with spark it seems but i dont know whats going on.

I drive hondas and im fully ready to "rig" a honda civic engine into a boat and have it for the rest of my life instead of this brick of the century merc engine