Smoke from carb on 4,3lx?

[SeaRayViking]

Have recently done some fixing on my merc 4,3 lx. There were heavy problems; stuck valves and a broken push rod. We remanned heads and applied new gasket sets and push rod, adjustet valves, set the timing and reassembled things etc, and it just started beautifully and now runs on all cylinders. Phew...!

It has never ran or sounded better - and with the smoothest idle. It's maybe not like a new engine (its 18 yrs) - but definitely like a significantly better one.

but...

It now pops light-grey smoke/vapor from the carb/arrestor. It has never done that before. It's not a whole lot but it shouldn't be like that.
any ideas? Our own suspicions points towards the mixture or something else carb-related.

Thx

 

[fixb52s]

Re: Smoke from carb on 4,3lx?

It could be something as simple as gas or water in the oil burning off, making some steam. I am assuming this is coming from the oil breather to the arrestor? If so, when you had the valve problems, it could have passed some fuel into the crankcase. The water vapor could be something as simple as condensation.

Change that oil if you have not done it already. Then run it for awhile at operating temps to get all of the rest burned out.

Also ensure the timing and dwell (if standard ignition) are correct.​

 

[SeaRayViking]

Re: Smoke from carb on 4,3lx?

Went down and worked on in last night.

It's not steam - it is definitely exhaust comming from the two hoses which connect the arrestor to the valvecovers.
The exhaust STOPS entirely when we push RPMs up and give it some throttle. But in idle it smokes.

Timing should be right - done by the book with timing light etc. And eninge runs beautifully!!

There is obviously good compression on all cyls - so i guess it can't be an exhaust valve problem, or what???? ???

Quite confused...

 

[rodbolt]

Re: Smoke from carb on 4,3lx?

that smoke from the valvecover vents is blowby, usually caused by poor sealing piston rings allowing combustion gas to blow past the piston, from there it has to go someplace, so its vented to the flame arrester.
also in normal running the crankcase is constanly under positive and negative pressures from the reciprocating assy moving.
a certain amount is normal, excessive amounts are cause for a leakdown test.

 

[jerryjerry05]

Re: Smoke from carb on 4,3lx?

A test for blow-by is to pull the hose off the rocker arm cover.It will come out there.
Marvel Mystery Oil,in the cylinders.Get about a 1/2 in in each cylinder keep an eye on it and add as needed.Let it set for a week and then try again.
I have had very good luck with MMO. Jerry

 

[dolemite_1]

Re: Smoke from carb on 4,3lx?

Hey there I'm new to boating but not cars and was working on my boat engine last night and saw those parts that you working on. To me they look like they perform a similar function to PCV Valves ( positive crankcase ventilation) in cars. Inside these valves are most times little balls that open and close due to pressure -- releasing "blow by". Could just be crud in that valve or line preventing proper function

Now for the guess by a rookie--

Can you pull off both plug portions that plugs into the valves cover and clean it out or replace?

Hopefully one of these experts can help you further

 

[SeaRayViking]

Re: Smoke from carb on 4,3lx?

that smoke from the valvecover vents is blowby, usually caused by poor sealing piston rings allowing combustion gas to blow past the piston, from there it has to go someplace, so its vented to the flame arrester.
also in normal running the crankcase is constanly under positive and negative pressures from the reciprocating assy moving.
a certain amount is normal, excessive amounts are cause for a leakdown test.

I'm not sure whether the amount is excessive or not. It isactually not a whole lot - but it's there and it smells awful.
But howcome it doesn't leak when in gear and higher RPM? the smoke seems to dissapear when I push the throttle...

Well - how to perform a "leakdown" test?

SRv