2007 4.3L TKS Mercruiser starts and runs then dies after about 30 minutes.

[Rcantu2]

Ok so today i checked the timing and it was off 12 BTDC and I set it back to 10 BTDC. Ran good for about 30 minutes then began to bog down, surge and cough through the Carb. I am at a loss.. Any other Ideas would be helpful.

 

[alldodge]

You have a new or rebuilt TKS carb, fuel pressure is good, and after about 30 minutes you have the same problem. I for one have no clue, hope someone else does

 

[Rcantu2]

I rebuilt the Carb myself following manual 41. Thanks for the help anyway.

 

[tank1949]

That was going to be my next venture after a new fuel pump being that it is 11 years old.

Automotive or marine electric fuel pump? If marine, pump out 5 gals. into jury can and wait until it stops. If it doesn't then something else is bad. If automotive, trash it. Check for mud-dobers in vent line and anti-siphon valve. Good luck!

 

[AShipShow]

Might also check the tks diode.. might be failing open circuit when hot and cutting the motor off.

 

[alldodge]

I rebuilt the Carb myself following manual 41. Thanks for the help anyway.

Since you rebuilt it yourself, then you need to try again.
As in post 10, the module supply's more fuel until it warms up and shuts off. When it shuts the extra fuel off the motor dies. The issue is the small idle circuits are small. Need to take a thin wire and chase thru them.

If the diode was opens this causes the module to stay open longer because no power will go to it until the temp switch closes

 

[Rcantu2]

Tank 1949 ... it’s a marine fuel pump and the vent line is clear. I also pulled the anti-siphon valve and it looks good and clean.

 

[AShipShow]

Ah, good diagram AllDodge ... I wasn't particularly familiar with the TKS setup, just knew there was a diode that controlled fuel related stuff, so since we were grasping for straws, I thought I'd suggest it lol

 

[Rcantu2]

Ok AllDodge I will take it off this afternoon and clean it up. I don’t need another rebuild kit do I?

 

[alldodge]

You shouldn't unless something gets torn

 

[alldodge]

Try this, disconnect the plug going to the TKS module on the carb. The plunger needs to be retracted, so motor needs to be cold or at least the module does.

If it runs for longer then its the carb, if it doesn't then need to rethink

 

[Rcantu2]

Ok I’ll try that before taking off the carb.

 

[Rcantu2]

Ok so I cleaned the carb again ran good this time for about 40 minutes then began surging rpm’s were all over the place. From 650 down to 400 and back up to around 750 and so on.. any ideas???

 

[alldodge]

How did it go with disconnecting the TKS module?

 

[Rcantu2]

It ran less time and headed the whole time. So I took the carb off and cleaned it again.

 

[alldodge]

It ran less time and headed the whole time.

Headed the whole time ??

 

[Rcantu2]

I meant it hissed the whole time... sorry

 

[alldodge]

The hissing would be normal if the module was open, but with it running less time then when it was connected as normal, then don't think your carb is the issue, its either fuel supply, or ignition. You said fuel pressure is good, so that leaves only ignition.

What fuel pressure are you getting and does it stay that way until it dies?

 

[KJM]

i might be way off here but i once had similar problems that turned out to be a small crack in my exhaust manifold that was allowing some water to enter the cylinders. it would start out ok and progressively get worse until it stalled after about a half hour. i guess water was slowly flooding the cylinders but would evaporate if off for a while. might be worth looking at.

 

[Rcantu2]

Do you mean the entake manifold?