Mercruiser hard to start when hot

[kaliona]

I have a 1978 165 hp Mercruiser I/0 that is very difficult to start when hot. It fires up just fine cold, runs fine hot whether its pulling the kids on skis or trolling for hours at low speeds. But if I shut it off and then try to restart after a few minutes, it just cranks and cranks. I can usually get it started after removing the flame arrestor and cranking it with throttle wide open. But sometimes to a point of almost running the battery down. Coil, distributor, points, condenser are all new. Carburetor was just rebuilt even though fuel is clearly squirting into throttle chamber. Compression ranges from 55 to 65 psi. The only thing I haven't changed is the fuel pump, but I've ruled that out because it runs fine...once it's started. What am I missing? Does anyone have any ideas?
This is really frustrating. I just want this to start reliably.

 

[chiefalen]

Re: Mercruiser hard to start when hot

Almost missed it compression is 55-65?

Should be nothing under 100. If truly under 100 you have valve problems or ring problems.

 

[APPALOOSA2]

Re: Mercruiser hard to start when hot

If your compression is that low I am impressed it runs at all. I would think at least when its hot it would a little bit more compression after everthing has expanded. Sounds like she is just tired and needs a rebuild.

 

[lkbum]

Re: Mercruiser hard to start when hot

Anytime an engine exhibits this type of sympton, consider vapor lock. When you are moving, the engine compartment is getting fresh air and the compartment stays fairly cool. When you stop moving it heats up. Your gas line routes near your engine on the way to the carb. If the gas in this line gets too hot, it vaporizes and will not feed liquid gas to your carb. Repeated cranking flushes and cools the line until the vapor is purged and not regenerated. Try opening the hatch when you stop and see if this improves the condition. Check you gas line routing, you may need to install a shield between it and the engine.

 

[kaliona]

Re: Mercruiser hard to start when hot

Now I'm really worried guys! Yes, my compression results were 55 to 65. I did the compression check on a warm engine, all plugs removed, coil disconnected, screw-in type gauge, cranked engine at least 8 times for each cylinder. The boat is a 17' bowrider and can hit 40mph if not loaded down with ice chests and people. I would have thought these compression readings were normal the way the boat runs. Are you saying the low compression could be my hard starting problems?

lkbum, as far as vapor lock, I can see fuel squirting into the carb when I'm trying to restart it, so wouldn't that rule out vapor lock?

 

[Don S]

Re: Mercruiser hard to start when hot

Are you saying the low compression could be my hard starting problems?

It's a wonder it runs at all with those numbers, as stated it should be 100 minimum. A good engine would be in the 130 to 150 range.

 

[maxumized]

Re: Mercruiser hard to start when hot

I have the exact same issue. My 3.0LX has hot start issues and my workaround is to open the throttle (throttle only) wide open and start. It starts very quickly and I'm able to throttle down to idle again. I knew it was a rich condition on hot start so I figured an open throttle would give it the air it needed. It's not a fix, but I'm using it as a work around until a overhaul this winter.

 

[lkbum]

Re: Mercruiser hard to start when hot

lkbum, as far as vapor lock, I can see fuel squirting into the carb when I'm trying to restart it, so wouldn't that rule out vapor lock?

Yes, sorry about that. I missed that point in your original post.

 

[kaliona]

Re: Mercruiser hard to start when hot

Perhaps my compression gauge is out of whack, because the boat definitely has power and like I said can cruise no problem at 35mph. I'll try to get another gauge and retest compression. Again, if the compression is indeed as low as 55 to 65psi, could that be the cause of the hard starting when the engine is hot?

 

[JustJason]

Re: Mercruiser hard to start when hot

yes

 

[ziggy]

Re: Mercruiser hard to start when hot

throttle plates wide open for the compression test too......

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[drrm123]

Re: Mercruiser hard to start when hot

I'd check to make sure the choke is open fully when engine is hot? other than that you need to check for ignition spark, since your getting fuel and no vapor lock, there is a spark tester you can get at parts store to plug in line with spark plug and wire. i would recommend just taking an extra plug out but some purist would surely complain of that method. If it's not burning oil the compress should not be that low unless valves are out of adjustment. so i'd say the gauge is probably wrong. do you smell fuel after shutting engine off when hot? if so check float level. could be to high and letting fuel leak into engine flooding it. did boat do this before carb being rebuilt? you can try cleaning the flame arrestor also but i dont think that's causing your hot starting ploblem.

 

[chiefalen]

Re: Mercruiser hard to start when hot

Ok say your compression is GOOD.

I would clean the ground, follow the neg cable from your battery and clean that ground real real good.

First disconnect your battery positive cable.

Than make sure all your connections are good when the positive cable is still off.

The starter ones, take them off clean em shiny clean.

The solenoid connections every one of them.

Ok connect up the battery with clean cable ends and take it for a ride.

Now if you have the same condition, don't keep cranking it with the key.

After 2- 3 trys if it don't start stop.

Leave they key to the start position with a screwdriver jump the 2 solenoid large screws, does it start then?

If yes solenoid went, new one 14 bucks any auto store.

 

[kaliona]

Re: Mercruiser hard to start when hot

drrm123:
When I checked the compression, the throttle plates were wide open and choke was fully open too. Coil, points and condenser are new, plug wires only a couple years old, but I'll do the spark plug test just to make sure. I also tested the plugs by pulling off each plug wire at the spark plug, one by one, and in each instance the engine ran noticably rougher. Isn't that an indication the plugs are good? I don't smell fuel after shutting down and yes, the boat was doing this even before the carburator rebuild. I was VERY careful about setting the float drop and float level when I rebuilt the carb. Also used a new float needle and seat. Flame arrestor is clean.

chiefalen:
I'll try cleaning all electrical connections from battery to starter and test it again. I wouldn't think a bad solenoid could cause dificult starting on a hot engine, but I'm willing to try anything at this point.

 

[kaliona]

Re: Mercruiser hard to start when hot

I bought a new compression gauge and rechecked. I guess my first gauge was bad because my compression shows more normal numbers, 130 to 145 psi. I also bought one of those inline spark plug testers and it indicated all the plugs firing normal. So I have compression, spark, and fuel visibly squirting into carburetor. I haven't done the electrical connection cleaning between battery and starter and solenoid yet, but will try that since it doesn't cost anything. If that doesn't help the hard starting while hot, I'm stumped.
The only other component I can think of is the fuel pump, but like I already mentioned, fuel can be seen squirting into throttle chamber, so can I rule out the fuel pump? Oh, and the batteries are fully charged and crank strong.
I plan on carrying a can of starter fluid in the boat just in case I can't start it when I'm out on the water. Is that a bad idea?????

 

[JustJason]

Re: Mercruiser hard to start when hot

here's a question.....
When you cold start with any carb you have a procedure....
are you repeating that procedure when you hot start the motor?

 

[chiefalen]

Re: Mercruiser hard to start when hot

The solenoid might not be giving enough juice to the coil while cranking.

Thats why i said to jump it at the solenoid with the key on and in neutral i/3 way down.

Or you can try running a jumper wire. With a switch. Just for testing purposes.

Run a wire from the battery + to the coil + with a switch at the helm.

Pump it twice in neutral flip the temp switch and start the boat.

This is very very important, you must flip the switch off. If you leave juice flowing to the coil when the boat is not running or when your not cranking the motor you can boil the coil and burn out the dizzy.

WHAT YOU WANT IS TO FLIP THE SWITCH AND CRANK THE MOTOR TILL IT STARTS, WHEN IT STARTS FLIP THE SWITCH OFF.

Take it on the water when the problem presents itself, Flip the temp switch and try starting the boat.

If the temp fix works than you for sure have a bad solenoid.

Replace the solenoid and remove the jumper wire.

 

[meesh]

Re: Mercruiser hard to start when hot

I Had This Same Problem With My Mercruiser. Fuel Was Getting Hot And Pushing Past Needle And Seat, Dripping At Nozzles While Not Running. Carb Was Rebuilt And Everything Was Correct. I Think Todays Fuels Namely Gasahol Boil Much Easier. I Solved The Problem By Installing A Fuel Pressure Regulator The Closer To The Carb The Better. When Fuel Gets Hot It Cant Push Past Whatever You Have The Regulator Set At. It Solved My Problem.

 

[kaliona]

Re: Mercruiser hard to start when hot

Capt J,
When I start cold, I pump the throttle twice then leave it down about half way, then turn the key. If it doesn't fire up right away, usually one more pump of the throttle gets it to start. When I start hot, I usually just push the throttle about 1/3 down and try to start, and try, and try. Then I go into my routine of removing the flame arrestor, checking for fuel (which there always is), leaving the throttle wide open for a few minutes, then try again to restart.

chiefalen:
If I use a remote starter switch across the solenoid, would that be doing what you're suggesting as far as "jumping" the solenoid? This will be my next troubleshooting step.

meesh:
I thought about the possibility of fuel leaking from carb after stopping, but I don't really smell a lot of fuel when it happens. I'll pay more attention when I try it again. How do you know at what pressure to set your regulator? I'm about willing to try anything at this point.

thanks guys

 

[kaliona]

Re: Mercruiser hard to start when hot

Finally figured out what was causing the difficult starting. I took chifalen's suggestion of cleaning all terminals, from the battery to ground, all connections at the solenoid and at starter. Cleaned everything til they were dirt free and shiny. But before I did all that, I checked the voltage drops from the negative battery post to the engine ground, and from the positive battery post to the starter. Before cleaning, the readings were (-).58 volts and (+).25 volts. After cleaning, the readings were (-).25 volts and (+).19 volts. Fired up the boat with the flush kit on, let it run for about 10 minutes, shut it off, tried the dreaded restart...and she fired up instantly. Took it out trolling for a continuous 2 hours before stopping the engine. Let it sit for a couple minutes like I normally do, tried to restart....she fired up instantly again. What a nice feeling to have it restart on the first crank of the engine. I was so happy it was fixed, I found myself turning off the engine every chance I had just to hear it restart on the first turn of the key. Thanks for all your suggestions. Hopefully this info will save someone else the hot start headaches I've been dealing with for the past few years.