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Hard Start Hot

J

johnmsch

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I replaced my 1994 Mercruiser 7.4L engine with a custom built 496 stroker with a Holley 850 CFM double pumper 3 years ago. For the past couple years it has gotten increasingly hard to start when the engine is hot. I can see from looking at the 4 bowl windows that the fuel level is always around the same as when the engine is cold.
Any ideas where to start looking for the problem?
Thanks
 
There's probably not an issue with the engine....I would focus on how the boat is operated....maybe if you provide a description of what your typical outing events are, we can go from there...
 
Thanks for the reply @makomark.
Typical outing events are taking the grand kids out for some tubing, then chilling in a cove for a couple hours. Some times a couple friends for some mild cruising, followed by cove chilling. Then there are times when its just me cruising the lake for a few hours.
This boat is garage kept, washing it every time I get home. Still get many compliments on her most every time I go out. No one can believe it is 30 years old!
When the engine is cold, I'll put it in neutral, pump the throttle 2 times and she fires up almost instantly. This issue is driving me nuts!
 
so you take it out and run it for a while...things are warm and in a steady state...when you decide to chill in the cove, what happens once you slow down, at the cove...specially with respect to the boat/engine??
 
Nothing out of the ordinary. I let the boat idle for a couple minutes while I drop the anchor and get it set. Never shut your engine off until that is done! It idles perfectly normal.
 
Better to do a fast idle (1200-1500 RPM) than down on the stop....you ant to get rid of as much heat as you can...

You can also try running the blower .... If they are set up correctly, they pull air from the lowest section of the bilge...but the air coming in helps to circulate what is in the engine compartment...

If the engine compartment is tight, you may want to try opening the hatch...on some boats, the excess heat isn't enjoyable.

When you go to start the engine, try advancing the throttle between 1/3 and 1/2...as soon as the engine starts, pull the throttle back.

IF things persist, get an IR temp gun and check the temps inside the engine compartment after making a run for at least 10 minutes...most engine makers spec less than 150 deg F which is very tough to satisfy....driven by the characteristic of the fuel they sell as today's gasoline...
 
If you can see the same level of fuel and if your accelerator pump is squirting fuel, then it's not a fuel problem. To verify, dribble a little gas down the carb. If it doesn't start when you know you have fuel, then it's ignition. Some coils, when too hot, short out internally, but work when cooler. In the old days we used a bag of ice around the coil. Take tools so you can remove a spark plug and check for spark.
Also when a gas engines warms up and moisture is available it can rise up the distributor shaft and collect on the cap. The cap will be cooler than the engine after sitting and droplets will form on the cap underside causing the spark to jump around between cylinder contacts. When checking spark, you'll have very weak spark. A crack in the cap causes the same problem. There are sprays to make the moisture evaporate. WD40 might work. WD stands for water displacement.
And a weak condenser can also react to temperature and show weak spark.
Many, many years ago I had a commercial fishing boat with gas engines. I had the problem of moisture forming on the underside of the cap. It could persist overnight. So I just carried spare caps and changed them in a couple minutes.
 
Thanks so much for this info!
makomark said:
Better to do a fast idle (1200-1500 RPM) than down on the stop....you ant to get rid of as much heat as you can...
Click to expand...
Never thought of doing that. Trying to understand how that would lower the heat?
makomark said:
You can also try running the blower .... If they are set up correctly, they pull air from the lowest section of the bilge...but the air coming in helps to circulate what is in the engine compartment...
Click to expand...
I replace the blower and bilge pump about every 5 years and put the current one in after the engine rebuild 3 years ago. It draws air in from near the bottom of the bilge then exhausts through the exhaust opening on the port side of the transom. I actually have been thinking about adding a second blower on the starboard side of the transom where the opening is to naturally draw air in. Then blow that air directly towards the engine.
Attached is a picture of the engine after the bench seat was removed. Had to do that to put in a new starter.
makomark said:
If the engine compartment is tight, you may want to try opening the hatch...on some boats, the excess heat isn't enjoyable.
Click to expand...
Relatively speaking, there is plenty of room on both sides of the engine. I have tried multiple times opening the hatch/sun deck 10-15 times before trying to re-crank and it has never helped the issue
makomark said:
When you go to start the engine, try advancing the throttle between 1/3 and 1/2...as soon as the engine starts, pull the throttle back.
Click to expand...
Never thought to try that for fear of flooding. Most I've done is to use the cold-starting technique of pumping the throttle twice, then leaving it in neutral.
makomark said:
IF things persist, get an IR temp gun and check the temps inside the engine compartment after making a run for at least 10 minutes...most engine makers spec less than 150 deg F which is very tough to satisfy....driven by the characteristic of the fuel they sell as today's gasoline...
Click to expand...
Yeah, the engine builder said I should burn 93 octane.
I have an IR temp gun, but do mean just the ambient temp under the hatch? Engine block? Exhaust manifolds?

Really do appreciate all this info. Tomorrow will be the first time I've had her back on the lake in almost a month. Mother nature has been b*tch with all the rain the past few weeks.

Thanks again!!!
 
Keep getting this error when attaching the pic. :(
1722568566446.png
 
Lepke said:
If you can see the same level of fuel and if your accelerator pump is squirting fuel, then it's not a fuel problem. To verify, dribble a little gas down the carb. If it doesn't start when you know you have fuel, then it's ignition. Some coils, when too hot, short out internally, but work when cooler. In the old days we used a bag of ice around the coil.
Click to expand...
Wow, that must have been a PITA!
Lepke said:
Take tools so you can remove a spark plug and check for spark.
Click to expand...
Will try that tomorrow. Fortunately I setup a remote starter years ago.
Lepke said:
Also when a gas engines warms up and moisture is available it can rise up the distributor shaft and collect on the cap. The cap will be cooler than the engine after sitting and droplets will form on the cap underside causing the spark to jump around between cylinder contacts. When checking spark, you'll have very weak spark. A crack in the cap causes the same problem. There are sprays to make the moisture evaporate. WD40 might work. WD stands for water displacement.
Click to expand...
Another use for WD-40!
Lepke said:
And a weak condenser can also react to temperature and show weak spark.
Click to expand...
Check
Lepke said:
Many, many years ago I had a commercial fishing boat with gas engines. I had the problem of moisture forming on the underside of the cap. It could persist overnight. So I just carried spare caps and changed them in a couple minutes.
Click to expand...
I'll add that to the list.

Thank you!
 
Fast idle will take heat out of the engine faster than normal.....

"tight' referred to the 'air transfer' of the engine room, not necessarily the clearances available.

Most every marine engine maker has published an installation manual...most are available with some search effort...their operations manuals have nuggets in them as well...

I prefer a clip on timing light to check for spark...just because it is faster/easier...
 
johnmsch said:
Wow, that must have been a PITA!

Will try that tomorrow. Fortunately I setup a remote starter years ago.

Another use for WD-40!

Check

I'll add that to the list.

Thank you!
Click to expand...
if you dont have one get an inexpensive spark gap tester. should jump at least 3/8" and have nice blue spark.

Would also think either you have fuel dribble into engine or are loosing spark due to heat.

I do get some of the fuel dribble hot restart issues on my 5.0 with a edelbrock carb, what I have found is that advancing the throttle clears the rich condition and is starts easier. You may see some black smoke when it does restart? if so this indicative of flooded engine
 
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