4.3 lt Mercriser Cranks But will not start on idle and will not idle.

[SearayFranko]

So I have been working on this boat for about a month now becuase it was running really rough. New fuel pump, rebuilt mercarb. good compression, new plugs and wires, new rotor and cap. Was then hard to start but got it running ok on the trailer for a while a couple of weeks ago. Now it will not start at idle. It will start at idle if I pour gas down the carb and run for a few seconds. Oherwise it will not not start at idle. If I place throttle at 1/4 to 1/3 it will start and race but cuts off when I back off to idle. Ive adjusted the idle mixture from 1-1/4 turns out to two turns out. no difference. Lately have heard some popping out the carb as I crank it to start.
Any Ideas?

 

[ste80]

Wich 4.3 you have? Lx?
Carbs normally has more difficult to start just at idle, you need to give gas a bit.
I just rebuilt all my motor and yes it start at idlle but with low low rpm so if i give some gas it is much better.
Normally you shoud pump a couple of time, kepp a litle bit the gas open 1/3-1/4 wait for pump to fully fill carbs and it should start.
If you have issue it could be the registration of the timming or some issue with choke. In hot condition does it get better?

 

[SearayFranko]

Wich 4.3 you have? Lx?
Carbs normally has more difficult to start just at idle, you need to give gas a bit.
I just rebuilt all my motor and yes it start at idlle but with low low rpm so if i give some gas it is much better.
Normally you shoud pump a couple of time, kepp a litle bit the gas open 1/3-1/4 wait for pump to fully fill carbs and it should start.
If you have issue it could be the registration of the timming or some issue with choke. In hot condition does it get better?

Thank you for you responce. Here in Florida now its 80 -90 all day long. Not sure if the choke is doing anything. The choke blades are always full open. I'm starting to think it may be a timing at idle issue. I dont understand how to check timing on these engines. I have the thunderbolt V ignition system.

 

[SearayFranko]

Thank you for you responce. Here in Florida now its 80 -90 all day long. Not sure if the choke is doing anything. The choke blades are always full open. I'm starting to think it may be a timing at idle issue. I dont understand how to check timing on these engines. I have the thunderbolt V ignition system.

 

[alldodge]

Using MR43LTS plugs and TBV should be 1995 or later
Pump the carb and do you see fuel squirt down throat of carb?

Is the fuel filter full of fuel?

 

[beruken]

Are you adjusting the jet or the idle set screw? Also, review the procedure for setting up your throttle cable too.

 

[SearayFranko]

Using MR43LTS plugs and TBV should be 1995 or later
Pump the carb and do you see fuel squirt down throat of carb?

Is the fuel filter full of fuel?

Thank you for your responce.
I have those plugs, Fuel water seperator filter is new and full. I disconected the fuel line from the carb and energized the fuel pump, and it is pumping gas. Its a new fuel pump. When I push the accelerator pump lever I do see gas pump out the jets.

Does anyone have a wiring diagram for this engine to check my wiring.?

 

[SearayFranko]

Are you adjusting the jet or the idle set screw? Also, review the procedure for setting up your throttle cable too.

Thank you for your responce.
I adjusted the Idle Mixture needle to 1-1/4 turns out from bottom initially. then to 1-3/4 and then to 2 turns out. No change in start. I adjusted the idle RPM screw to 2 turns after contact with the cam at full throttle.

 

[alldodge]

Did I read you correctly? It will start with pouring gas down the carb but not when fuel squirts from the jets?

If that's the case you have bad fuel in the tank

 

[SearayFranko]

Did I read you correctly? It will start with pouring gas down the carb but not when fuel squirts from the jets?

If that's the case you have bad fuel in the tank

Clarification;
I have only seen fuel come out the jets when I push the acelerator pump on the carb with my hand.
I have not looked to see if fuel comes out the jets when I am cranking with throttle at idle since I am working by myself.

I guess I should get someone to help and see if I can see fuel in the carb when cranking.
If I pour fuel in the carb , then go and try to start, it will start and run for a few secounds then shut down if i do not accelerate it.

During this troubleshooting period, I am not running from the main tank to eliminate the bad fuel possibility. I am running from a 5 gallon jug with fresh fuel.

 

[Eric 3.7LX Alpha 1]

I agree, it sounds like bad gas. Collect a sample.. a half teaspoon of it (out of the boat) and see if it will light on fire. If you can't light it the engine won't either.

 

[alldodge]

Clarification;
I have only seen fuel come out the jets when I push the acelerator pump on the carb with my hand.

If I pour fuel in the carb , then go and try to start, it will start and run for a few secounds then shut down if i do not accelerate it.

I am running from a 5 gallon jug with fresh fuel.

ok, than your rebuilt carb idle jets are clogged up.

You get fuel when you pump the carb, so you should be able to keep it running if you pump the throttle a little (back and forth) to keep gas going in.

 

[SearayFranko]

ok, than your rebuilt carb idle jets are clogged up.

You get fuel when you pump the carb, so you should be able to keep it running if you pump the throttle a little (back and forth) to keep gas going in.

OK thank a bunch.
Makes sense to me. I will get some help to be able to look and verify if there is some fuel coming out the jets or not as I crank it at low throttle.

 

[nola mike]

You may not need need your choke at those temps, but maybe it would help.

 

[Scott06]

So I have been working on this boat for about a month now becuase it was running really rough. New fuel pump, rebuilt mercarb. good compression, new plugs and wires, new rotor and cap. Was then hard to start but got it running ok on the trailer for a while a couple of weeks ago. Now it will not start at idle. It will start at idle if I pour gas down the carb and run for a few seconds. Oherwise it will not not start at idle. If I place throttle at 1/4 to 1/3 it will start and race but cuts off when I back off to idle. Ive adjusted the idle mixture from 1-1/4 turns out to two turns out. no difference. Lately have heard some popping out the carb as I crank it to start.
Any Ideas?

either fuel is not getting to fuel bowl or idle passages in carb are not clean. Either way when you dump gas down you are providing fuel until it burns off. When you advance the throttle you are coming off the idle to transition and main circuits that must be flowing fuel.

My carb rebuilding improved dramatically when I got an ultrasonic cleaner from Harbor Freight. If you open idle mix screws up and it does nothing, means those passages are plugged

Is the idle speed screw out enough to keep throttle blades from fully closing ?