hard to start when warm

[CaptainZ55]

I have a Mercruiser 350 Magnum with a Rochester 4bbl carb - 1988 vintage. Last season the following started: after running the boat for a while (hot engine) we would turn off the boat and anchor/swim. When we tried to start the engine it would not except after many cranks with throttle in full position. When if finally started is was a sputtering stumbling process. Thought it was bad fuel as ethanol was added to fuel around this time. Drained fuel tank, replaced distributor sensor (Thunderbolt IV) very rusty, and cap and rotor, plugs, wires, and reset timing. Rebuilt carburetor two times with everything looking good. Engine runs great otherwise and will start right up when cold. Believe float setting is correct. Only way to start if warm is advance throttle (in neutral) to full position and the engine will eventually start albeit a stumbling start then have to pull back throttle quickly to prevent over rev. Engine has only 265 hours on it. Prior to this problem engine was rock solid with easy turnkey starts when warm, cold starts needed a couple of throttle pushes to inject some gas.

Any thoughts would help.

CaptainZ55

 

[rs2k]

Re: hard to start when warm

It sounds like your idle mixture is way too rich.

Do you have a choke? It could be malfunctioning somehow.

 

[CaptainZ55]

Re: hard to start when warm

manual choke - it appears to be working but dont fully understand linkage between choke and vacuum circuit on side of carb. in reading posts I was going to check to see if fuel is leaking into engine, any way to check vacuum and choke interaction?

thanks for reply

 

[bayliner1996blue]

Re: hard to start when warm

I am having the same problem. When I figure it out I will let you know. I thought it was my carb, but now I am lean toward the chock.

 

[CaptainZ55]

Re: hard to start when warm

Worked on it this weekend. The boat has what is referred to as an automatic choke with metal thermostat coil connected to linkage sitting on manifold which I took off and cleaned and checked and reinstalled. The part I do not understand is that even with the engine warmed up the choke only opens up about 1/4 inch and is not close to straight up and down. If I disconnect the choke and position the chock valve full open the engine fires up immediately. Otherwise (when connected) I have to advance the throttle to almost full to get it to fire up which is does every time. The vacuum interrupter appears to be working. Did not see fuel dripping down on shut down but did not remove carb to check the bottom plates. Again the confusing thing is the clean starts with warm engine with choke plate in full position (after manually disconnecting linkage).

Comments appreciated.

 

[rs2k]

Re: hard to start when warm

You can adjust the choke, but I've found that chokes are unnecessary on boats. There is no fast idle cam on a boat carb and small block V8s shouldn't be hard to start with just a pump or two of the throttle unless it's REALLY REALLY cold out and unless you've got an ice breaker, who the heck's going to go boating when it's below freezing out any way?

I would recommend just removing the choke coil and wiring the choke valve open. You can always put it back to the way it should be if you want. You probably won't want to though.

 

[bigskiohio]

Re: hard to start when warm

i agree with no choke needed but if you can adjust it i would do that. get the manual or someone will tell you how to fix it here if you wait long enough. a picture will help. I not sure if you just bend the rod to adjust or something else so i cant tell you.

 

[PitchFork]

Re: hard to start when warm

I was having the same problem on warm starts this season. The difference was I changed carbs over the winter. After searching for many hours on the problem I lowered my float level from 15/64" to 22/64" and also wire tied warm water lines away from the metal fuel line that runs from the fuel pump to the carb. I also run the bilge blower a lot more often now. I also read it is good to idle for a minute or two while running the bilge blower after cruising for awhile to lower the heat under the engine cover.

I never checked but read that the fuel may be boiling in the carb and flooding the engine if it sat for a minute or more. Or it could be vapor lock anyways I made those few changes and now it starts within a second or two now.

 

[rs2k]

Re: hard to start when warm

It's a very good idea to let the engine idle a bit after running. The engine is heat soaked and all that heat tends to vaporize the fuel in the float boat. That can lead to very annoying and possibly dangerous situations. Letting the engine idle gets rid of some of the heat. I tend to get off plane and run at an easy displacement speed for about a minute before letting the engines on my twin idle for a few minutes after planing. That gives the engines a little bit longer to cool off.

 

[Bilgamesh]

Re: hard to start when warm

I had the same problem. When you shut off the motor, look down the throat of the carb and see if there is fuel dripping. If there is, it is flooding your engine. Putting the throttle in full forward position evidently introduces enough air to get it going.

Edit: Oops, Just noticed you already checked for this; sorry!

 

[rbh]

Re: hard to start when warm

when you rebuilt the carb how was the main needle and seat?

 

[Bilgamesh]

Re: hard to start when warm

After shutdown, will it start without throttle if you do so right away instead of waiting a few seconds/minutes?

 

[CaptainZ55]

Re: hard to start when warm

Never got this working last season and now we are getting close to a new one. Anyone change out the manual spring driven choke with an electric one and would that solve the choke problem? Also, as I said in earlier post this problem started suddenly and the engine only has 265 hours on it so there should not be any wear issues.

Any thoughts - thanks

 

[Alpheus]

Re: hard to start when warm

It honestly sounds like your well plugs are leaking and causing a rich (flooded) start. Its hard to look down the carb and see them leak as the fuel just seeps out. This is a VERY common problem with Rochester carbs. As for the choke. Is this engine raw water cooled and or ran in salt water? I have seen the intake water passage get very corroded and not allow good heat transfer to the chokes thermal coil spring and not allow choke to open the whole way. take the coil spring off and clean the plate the where the spring attaches to the manifold. When you put it back together use a little thermal paste between the plate and the intake to aid in heat transfer to the spring.

 

[oldsub86]

Re: hard to start when warm

I think the vacuum thing hooked to the choke is intended to open the choke plate a bit right after the engine starts. The spring should totally close the choke plate when cold but the vacuum pot should pull it open a bit as soon as the engine fires up. If the motor starts but then chugs that might be a problem. Should be easy enough to watch and see what it does.

If heat soak is an issue, you can get a thicker insulating gasket to put between the carb and the intake manifold.

Randy

 

[littlebookworm]

Re: hard to start when warm

Your automatic choke is connected to a "stove," basically a coil of metal which changes shape as it heats up. The coils are known to corrode and rust together, therefore preventing the choke from opening. It's easy enough, and cheap, to simply replace the stove with a new one. The only difficulty is the little screw holding the stove cover and the stove in place. It sometimes rusts so much that it breaks when you try to unscrew it. You then have to drill it out and tap for a new screw. Try this before you go tearing your carb apart. You've said yourself that you see the choke only partially open - that's your probable porblem, not your float or needle seat.

 

[skongolf]

Re: hard to start when warm

Did you ever get the problem resolved? I have a 97 maxum with a 5.7 but just a 2 barrel carb and have the exact same issue. Had it rebuilt at a shop and still had issues. Took to a second shop and they said it needed to be rebuilt again because there was gas leaking into the manifold after shut down and flooding the motor. Just curious if you had figured it out yet.

 

[CaptainZ55]

Re: hard to start when warm

Have not had a chance to work on this - no resolution yet. I am thinking about ordering a new choke spring. When I had the carburetor off I looked at the soldered plugs on the bottoom and they looked good. The boat is a 1988 with 265 hours, fresh water cooled, used almost exclusively in fresh water. Last season I took the exhaust riser off to check for corrosion and there was almost none, just thin layer of rust. I have always flushed engine after use when possible. Also, has anyone converted to electric choke? Is there anyway to check if carb is leaking on shut down?

Thanks for your feedback!

 

[bigskiohio]

Re: hard to start when warm

just adjust open or wire it open to check you dont really need it.

 

[HT32BSX115]

Re: hard to start when warm

Howdy,


This is similar to another thread on here.......

If I disconnect the choke and position the chock valve full open the engine fires up immediately.

I also have an electric automatic choke on my 454........ since I don't boat in cold weather, I adjusted it to FULL-open and disconnected the wire.

If you do that, be careful what you do with the wire. It's "hot" and will short out if you don't insulate it.


If you decide to do the above, you'll have to "pump" the throttle a few times and it may quit after initially starting. ........however, you'll foul your plugs a little less, and when the engine is warm, it will probably start easier....

Regards,


Rick