Running rough when cold, helping to diagnose the problem with Mercarb

[Kubaat3lover]

Mercruiser 4.3 MerCarb, was TKS but previous owner probably swapped it to the Mercarb. Im not a Carb guy

When engine is cold (1st start of the day) after start the engine running rough. Lots of black smoke and rough until warming up. Weather is Like 60-70s nowdays, When warm runns great.

When I turn the ignition to ON, slowly the 'butterfly' plate is opening, so the choke is fine, correct?
Plugs were changed on April , any ideas?? Thanks

 

[Kubaat3lover]

[No message]

 

[alldodge]

The choke is working, but it may need to be adjusting. With the motor cold loosen the 3 screws on the choke slightly so it can be rotated. Turn it so the choke opens a bit, then rotate it back until its almost closed. Just about an 1/8 inch gap. Then tighten screws

 

[Kubaat3lover]

Already set Like this..;

 

[alldodge]

Those are there for a new carb, when things get old there spring gets weak, don't pay much attention to it. Adjust like mentioned above

 

[Kubaat3lover]

Will do and post the results! Thanks

 

[Kubaat3lover]

I couldnt move the screws... all are stuck

 

[alldodge]

They can get that way, but only way to adjust outside of bending things is to get them loosened. Might take removing carb so can use an impact screw driver

 

[Kubaat3lover]

Will try with liquid wrench + putting some heat by butane torch

 

[alldodge]

No butane torch :nono:

The carb has gas in it

 

[alldodge]

Take the right size flat tip screw driver, place in position then smack it a little with a hammer (not real hard)

Can also place screw driver in slot, find a way to push in good and hard. Then place pliers or wrench on screw driver handle and use it to turn driver

 

[Kubaat3lover]

Ok ill try to manage it because on the boat there is no room for good screw driver.. need to remove the carb, can i reuse the gasket base again ?

 

[alldodge]

Possibly have to see what it looks like when it comes off. In most cases can go to local auto place and pick up another for not much

 

[Kubaat3lover]

Ok, and the question is regarding the RPMs when cold.
After startup when my engine cold is rough what the RPMS should be with the choke ON ?
Its below 1000, is that correct ? should the choke increase rpm or not?

Thanks
Take care

 

[alldodge]

It should be close to regular idle and would be below 1000

Some carbs the choke will increase rpm's but most do not

 

[nola mike]

....But you'll want to keep it higher than that while it warms up. No fast idle setting on a marine carb.

 

[Kubaat3lover]

Only a chance to keep it higher is to keep it on idle or when boating, the problem starts when I have to leave my dock/ marina in an idle fwd gear but on that settings ive got 650-800rpms and engine is running rough and you can smell smoke/fumes until warms up...which is quite not nice to the other boaters in my marina is that okay? Is it a problem with a choke? i still cannot move the screws, ill put some liquid wrench and try another day
when warm its fine.

....But you'll want to keep it higher than that while it warms up. No fast idle setting on a marine carb.

What Do You mean? Ive got screw with a spring also on the CAM , right?

 

[alldodge]

Nola is talking about you can idle up in neutral. I think once you get the choke adjusted it will be much better

 

[Kubaat3lover]

Thanks I really appreciate your help, here in Poland there is a lack of good Carb guys...
Btw. Now the choke flap is close with that setting, do you think leaning, twisting counterclockwise towards the close positin will help anyway? Take care

 

[alldodge]

Depends on how the choke flap is connected. Some will move CCW to open and others will be CW. There is no issue of rotating it farther and then rotating in back

Can also try this, before you start, open the choke by hand and stick a small screw driver down the carb to keep it slightly open. What your doing is adjusting the flap to be open the thickness of the screw driver.

Start it up and if it runs better, then this tells you it works. The screw drive will not hurt or damage anything. Just don't want it to fall down where it keeps the accelerator plate (flap) open also