cold start 3.0 carb

midwest mariah · 07-25-2009, 01:15 AM

Not a major problem, but i'm going to ask. When I start it up for the first time, its hard to keep it running for the first minute or two. After that, she runs like a top, no problems at all, only on cold starts? any ideas?

SEMIJim · 07-25-2009, 01:33 AM

The 4.3L V6 Mercruiser, with 4bbl carb, in our boat is the same way. Have to keep the RPMs up for a bit before easing her back to idle. Back in the day, when I used to wrench on engines all the time, 4bbl Rochester QuadraJet carbs, usually, I'd have known what to do. I've unfortunately lost more knowledge of them than I've retained

.

As I recall, back when my cars had this technology, I'd pump the pedal a couple times, turn the key, lightly rev the engine for a moment or two, and she'd idle fine--even in very cold weather.

TBH: I don't recall ever having this problem.

Maybe the idle mixture?

Jim

Z 202 · 07-25-2009, 02:20 PM

Quote:

Originally Posted by SEMIJim

As I recall, back when my cars had this technology, I'd pump the pedal a couple times, turn the key, lightly rev the engine for a moment or two, and she'd idle fine--even in very cold weather.

This is exactly how I fire up my 5.7L if it has been sitting for a while. If I've been out running, I usually only have to turn the key. Ah the joys of carbed engines.

WetWilly · 07-28-2009, 03:23 AM

I would check the choke and then the idel speed and mixture (be sure the ignition is in "base timing mode" when doing these adjustments). Lastly, check the carb mounting nuts, if they're loose, air can enter from below the carb but when the motor heats up, the metal expands and closes the leak (although rare, it happens now and then). If these all check out, try running a can of carb cleaner and some hight test through the motor.

WetWilly

midwest mariah · 07-28-2009, 03:36 AM

Quote:

Originally Posted by WetWilly

I would check the choke and then the idel speed and mixture (be sure the ignition is in "base timing mode" when doing these adjustments). Lastly, check the carb mounting nuts, if they're loose, air can enter from below the carb but when the motor heats up, the metal expands and closes the leak (although rare, it happens now and then). If these all check out, try running a can of carb cleaner and some hight test through the motor.

WetWilly

Good stuff here Willy. Could you expand on the choke, is this like the late model auto chokes, the ones that had the coil on the side of the carb. Or are they electronic chokes?

We had a really rough time this weekend. Initial starting, letting it idle at about 1500 for a bit, try to give it a bit more and would kill it. starts right back up, idles, try to move it for quick idle, or put it in gear, dies, then starts right back up. Only idles and will not let you touch it for a couple minutes at least. first 10 minutes of driving are very touchy. Even after the initial ten minutes, going from cruise to WOT, it will first die off, then accelerate. Once she's good and warm, runs like a top all day long

pimpadelic · 07-29-2009, 07:14 PM

sounds like the carb needs to be cleaned or rebuilt. my 3.0l always idles rough when its cold. and almost feels like an engine bracket is loose when cold starting. it will kinda shake the boat when it first fires up.

SEMIJim · 07-30-2009, 04:41 PM

Quote:

Originally Posted by midwest mariah

We had a really rough time this weekend. Initial starting, letting it idle at about 1500 for a bit, try to give it a bit more and would kill it. starts right back up, idles, try to move it for quick idle, or put it in gear, dies, then starts right back up. Only idles and will not let you touch it for a couple minutes at least. first 10 minutes of driving are very touchy. Even after the initial ten minutes, going from cruise to WOT, it will first die off, then accelerate. Once she's good and warm, runs like a top all day long

Sounds like it may be a bad accelerator pump.

Jim

midwest mariah · 07-31-2009, 02:05 AM

Quote:

Originally Posted by SEMIJim

Sounds like it may be a bad accelerator pump.

Jim

would it be that even though it runs perfect after the first 10 minutes?

WetWilly · 08-01-2009, 12:15 AM

Hi midwest mariah, sorry for taking so long to get back on the choke thing so here goes (you may need some No-doze

)....

Quote:

Originally Posted by midwest mariah

Good stuff here Willy. Could you expand on the choke, is this like the late model auto chokes, the ones that had the coil on the side of the carb. Or are they electronic chokes?

Your carb should have an electric choke with two wires coming off of it (one for ground and the other for power). Check to see if the choke moves freely, if not, then find where it's binding. The choke should be closed when the motor is cold and as the motor runs the choke should fully open. Electric chokes use a small internal heater so they do not rely on engine heat to open and this is where some boaters and car owners as well have had problems.

If you put the ignition key in the run position without starting the motor the choke will eventually open as the electric heating coil in side of it will get warm as long as there is power going to it. The chock should only be wired to the “run” position on the ignition switch. Take a volt meter and check the power lead to the choke, there should not be any voltage when the ignition key is in the “ACC” or “Off” positions, only when the key is in the “RUN” position should there be any voltage present at the choke.

If you shut down long enough for the motor to cool down and for whatever reason the ignition switch is put in a position that lets power to the choke, it will heat bask up and open even though the motor is cold, effectively rendering the choke system useless.

Quote:

Originally Posted by midwest mariah

We had a really rough time this weekend. Initial starting, letting it idle at about 1500 for a bit, try to give it a bit more and would kill it. starts right back up, idles, try to move it for quick idle, or put it in gear, dies, then starts right back up. Only idles and will not let you touch it for a couple minutes at least. first 10 minutes of driving are very touchy. Even after the initial ten minutes, going from cruise to WOT, it will first die off, then accelerate. Once she's good and warm, runs like a top all day long

Hmmmm, now it sounds like there is more going on with your carb than just the choke.

WetWilly

midwest mariah · 08-03-2009, 12:50 AM

Awesome stuff here Willy thanks for jogging my memory. Been a long time since I had worked on an electric choke. Tore into it this morning and sure enough, the butterfly was stuck open. No choke support whatsoever

Worked on it for a while and got her good and free'd up, works like a charm now

took it out today, pumped twice, turn key, fired right up and stayed running without fail!! awesome and thanks everyone for your help