89 Mercruiser 5.7 starting problems

[tyunker]

I have a 1989 Mercruiser 5.7 motor and in the last two weeks I have been having a problem with starting it. Before I started having a problem, I would throttle up 2 times and leave it at 2/3 throttle (in neutral) and it would fire right up. Two weeks ago I tried to start it and couldn't get it to start. Over the last two weeks, I have tried to start it without giving throttle, with giving throttle, with different amounts and it just will not start on its own. If I give a quick spray of starting fluid, it fires right up and runs great. Take it out and run it, go to the sandbar and sit for hours, it will fire right back up to go home. Next day, I have the same no starting problem without a spray of starting fluid. It's seems like it is flooded but I try it without giving throttle and it still doesn't make a difference, it just cranks over but will not start. I really want to figure this out. I did a full tune up this year, new wires, plugs, cap, rotor, checked timing, replaced belts, changed oil and filter and replaced water separating fuel filter.

Does anyone have an opinion on what this might be.

Engine serial number is 0C532585 with Thunderbolt IV ignition.

 

[alldodge]

Howdy
My thought is there is a weak fuel pump, restriction in the antisiphon valve, line or fitting from the tank

Have you noticed if the oil level goes up any between changes?

 

[tyunker]

If there was a restriction or weak fuel pump, I would think that I would have problems when running but it throttles right up with no hesitation.

Haven’t noticed the oil level going up but will check the level again this week. What would I be looking for if it does change?

 

[Rick Stephens]

That motor could have a Mercarb 2 Bbl, a Quadrajet or a Weber. If the Weber, it probably is leaking all its fuel out into the venturis when you shut down. Known issue.

I'd be considering rebuilding whatever carburetor you have.

 

[tyunker]

I have the Quadrajet.

 

[alldodge]

If there was a restriction or weak fuel pump, I would think that I would have problems when running but it throttles right up with no hesitation.

Haven’t noticed the oil level going up but will check the level again this week. What would I be looking for if it does change?

If oil level goes up, then pump is leaking fuel into the oil

Your able to start first time only with starting fluid
Thought is, fuel may not be able to fill bowl, but once started it does fill
Could also be carb is flooding, but normally if flooding is happening then starting fluid will not work

Remove fuel line from carb and see if you get a good stream of fuel cranking when its cold

 

[tyunker]

I'll check the fuel line pressure and look into getting carb rebuilt. Thanks for the help.