97 Mercarb running rich on warm up

[Moggy23]

As being a mechanic, this one has got me thinking.
My 23 Caribbean is fitted with a 5.7 ltr 250 hp Mercrusier,1997 fitted with Mercarb.
Starts easy and the choke stays on for about 15 secs and goes off, running at 1000 rpm.
Bring it back to idle and then it starts to to run rich, so I increase the revs so it doesn't stall and as it warms up, it gets worse.
Once it gets to 160 deg. every thing is fine and not a problem for the rest of the day, idles nice and starts easy, this has only started to happen as winter came around, colder the morning, worst the problem.

Rekitted the carby, cleaned and blew it out with compressed air.
Checked float level to 9 mm as to the Mercruiser service bulletin for spring loaded needle and seat.
Cleaned small holes under carby, in manifold for exhaust recurculation.
Timming is 10 deg and idle mixture set in gear when warm which is about 1.5 turns out

Still the same, so I fitted a air bypass in the pvc line to lean it out untill warmed up, just to keep the plugs clean. this is tempory.

The only thing I can think of is too much moisture, condensation around the idle air bleeds when warming up, that causes a rich mixture, maybe.
I,ve shinned a light down the carby when running and there is no flooding, it's as if fuel is building up or puddling on the floor of the manifold.

Has anyone come across this problem in cold climate of about 5 -10 deg C or 40 - 50 deg F

Thanks Moggy

 

[John_S]

Re: 97 Mercarb running rich on warm up

Hmm, choke is open, still running rich until it hits 160, no dribling in carb... Are you seeing any icing in the barrels? I saw it happen in much warmer temps than yours. Trying to think of a safe way to warm the carb prior to a start-up test.

BTW, Thunderbolt V idle speed and mixture are set in neutral. No need to have in gear. I don't think that is causing your issue, but it is easy to try.

 

[Moggy23]

Re: 97 Mercarb running rich on warm up

Thanks for replying
Haven't seen any icing, just lots of moisture around the venturies and air bleeds.

The mixtures were set at idle in neutral, then as a double check on the water,but the tune was the same and was all fine at operating temp.

I'll check again for icing.

I noticed just after a minute of the engine hatch closed, it right itself, warm air entering carby. mmmmm

 

[6meter]

Re: 97 Mercarb running rich on warm up

Are you saying that the choke is FULLY open after 15 seconds of running? Then it runs rich until 160*? The only thing in a carb that is different from cold and warm is the choke position. Boats don't have PCV valves. They have crankcase vent tubes that have no vacuum. Oil full of fuel?

 

[Moggy23]

Re: 97 Mercarb running rich on warm up

6meter

I actually watch the choke come off in 15 secs
Boats do have PVC valves, mine has both vent tube and PCV valve, factory fitted and the hand book states during servicing the PCV valve to be change yearly. Check out later Mercruiser manuals and you will find they are fitted. P.N. 8M2017060

There is no fuel in the oil, if there was, the carby would be flooding and would not run, even to the point of hydraulicing the engine.
This is burning the fuel with black smoke.
So far I believe there is a problem with too much moisture or icing around the idle air correction holes which is causing the rich mixture, untill someone with some real experience with this sort of problem can tell me different.

I can rev it and clear it, then starts to run rich after a moment or two.
On factory cars with carbies, suck air of the exhaust in cold climates, just a thought.

 

[zbnutcase]

Re: 97 Mercarb running rich on warm up

Are you saying that the choke is FULLY open after 15 seconds of running? Then it runs rich until 160*? The only thing in a carb that is different from cold and warm is the choke position. Boats don't have PCV valves. They have crankcase vent tubes that have no vacuum. Oil full of fuel?

Yes, they do have PCV valves now, starting mid-ish 90's or so

 

[BOYSDAYOUT]

Re: 97 Mercarb running rich on warm up

Are you saying that the choke is FULLY open after 15 seconds of running? Then it runs rich until 160*? The only thing in a carb that is different from cold and warm is the choke position. Boats don't have PCV valves. They have crankcase vent tubes that have no vacuum. Oil full of fuel?

well that not quite right mate as I have a pvc vale on my 888 and had just replaced it moggys right p/s moggy I have a spare carby do you wish to use it mate

 

[6meter]

Re: 97 Mercarb running rich on warm up

I guess I stand corrected and educated today. Mine's an '86 and ones that I have worked on don't have one.

 

[John_S]

Re: 97 Mercarb running rich on warm up

well that not quite right mate as I have a pvc vale on my 888 and had just replaced it moggys right p/s moggy I have a spare carby do you wish to use it mate

Thats because those fords had so much blow-by... "Most" GM powered did not see pcv until the 2000's for emmisions.

Moggy, I do remember the car snorkles with the heat pipe to draw air off the exhaust manifolds. There was a vacuum activated valve, but not sure how that was metered. Probably from some temp.

 

[Moggy23]

Re: 97 Mercarb running rich on warm up

Thanks BDO, I'll keep that in mind about the carby.

Imported_John_S, with your input, what I am going to do is, open engine hatch, start the engine, check for leaks and operation, once I,m happy all is well, close hatch so the engine starts drawing warm air, instead of leaving hatch open while warming up.

I don't open bonnet of a carby car while warming up, just drive it !

I found on the net, there are electric carby warmers, never seen one here.

I'll report after next outting, might be a week or 2

Thanks moggy