Mercruiser 5.7 Comp Ski won't start when warm

[Karl.]

Hi,

I am currently experiencing some problems with my boat.

The engine is a Mercruiser 5.7 Comp Ski from around 1986/87. It has a quadrajet from i5-automotive fitted last summer, mallory distributor with points.

Base timing is set to 10btc at around 800rpm.


I have noticed on my coil that it says that it should be used with an external ballast/resistor.

When my key is on I have 12.3v at the positive side of the coil so I have ordered a ballast to fit. The coil does have some heat in it after running for 15 minutes but its no warmer than the engine. I can hold my hand on it comfortably. (not alot of heat at all)

Once it stops it won't start again, only after sitting for a while.

Once I pump the gas I do see a squirt of fuel into the carb. After its pumped in a mist of steam comes out of the carb, Its really hard to describe. It just looks like automized fuel.

Have you got any ideas?

Thanks

 

[Scott06]

Couple of thoughts

heat soak on carb evaporating gas in bowl phenolic soacer to keep heat from manifold to carb may help.

Q jets are known for primary well plugs leaking gas out if carb to manifold . When it won't restart look down throttle plates see if gas gas leaked down into manifold. If so wells can be plugged with epoxy. Google it as it's a common issue with q jets.

 

[Karl.]

Ok, I will look down the carb this evening to see if any fuel is leaking in.

The jet on the right hand side when using the accelerator pump hasn't got any fuel coming out, is it just a matter of taking off the top of the carb and cleaning it out? The left hand jet is very strong so I think the accelerator pump is still in good condition.

I will get a infared thermometer and see what temperature things are running at and hopefully that will let me know if its heat soak.

 

[Scott Danforth]

Also, check for spark

if you have no spark, look at the condenser.

 

[Karl.]

I have checked for spark and I do have spark when it won't start.

 

[Karl.]

Ok,

I wrapped the fuel lines in some foil this evening incase it was vapour lock causing my problems. I am able to start the engine on my drive no problem but once I reverse the boat down the slipway it refuses to start.

Has anyone got any ideas?

The right side jet of fuel from the accelerator pump isnt working. I think this is causing the engine to bog when I give it the gas.

​​​​​​Any any any ideas how to clear this out? The seal on the pump is in perfect condition.

 

[Scott Danforth]

Ok,

I wrapped the fuel lines in some foil this evening incase it was vapour lock causing my problems. I am able to start the engine on my drive no problem but once I reverse the boat down the slipway it refuses to start.

Has anyone got any ideas?

The right side jet of fuel from the accelerator pump isnt working. I think this is causing the engine to bog when I give it the gas.

​​​​​​Any any any ideas how to clear this out? The seal on the pump is in perfect condition.

Its not vapor lock

Your post indicates dirty carb

Start with pulling the carb and going thru it

 

[Karl.]

I have ordered a rebuild kit so hopefully it's here for the weekend.

 

[Scott06]

Definetly sounds like carb rebuild and cleaning can vapor lock, let us know how it works out . Whenpropely cleaned and set up a q jet is one of the best carbs.

 

[Karl.]

I took the top off the carb this evening.

You can see the casting around the primarys is dented.

I also noticed that the float needle is different to all the ones I have seen online.

First of all there is no hook to hook onto the float and the bottom of the needle is flat. It doesn't have a point on it to block off the incoming fuel like my old carb.

Any ideas?

 

[Scott Danforth]

yes, you have parts missing

time to throw the carb in a bath of cleaner, clean out all passages and put a rebuild kit in it.

 

[Karl.]

What about the dent in the casting? The person I bought it off said that this is to hold the power valve into the housing.

This was causing the primarys to stick, it took a bit of force to push the piston down. From what I understand the primarys pull down under vacuum.

I think this would cause a flooding problem if the vacuum couldn't pull down the primary piston.

I have cleaned out the carb and put it back together. I will try it after work