Hard starting warm - carburetor problem???

I've read many posts trying to solve my problem and think I've narrowed it down to the carburator. I have a 1978 165HP Mercruiser I/O that starts just fine cold and also starts fine right after shutting off the engine as long as it's restarted within a minute or two at the most. Let it sit for any longer and it just cranks and cranks. Points, cap, rotor, plug wires, coil are all new. Plugs are clean and in good shape. I've cleaned all terminals from the battery to the starter and solenoid. Compression is good, within specs. Carburetor was rebuilt recently. Engine runs great once started.

When I try to restart, I don't pump the throttle, I just move it forward maybe 1/4 of the way down, then turn the key. Out of frustration, i've even brought along starting fluid for the situations when it won't start, but that didn't work either. If I open the engine cover, remove the flame arrestor and let it air out, it eventually starts. So I'm guessing the engine is somehow getting flooded. Is it possible the carburator ports or jets are too far gone for a rebuild to help? Is it possible the carburetor is leaking after the engine is shut off? If so, is there a sure fire way to check for that problem? I'm just a weekend warrior mechanic and just know the basics so any input would be welcomed.

Re: Hard starting warm - carburetor problem???

your proceedure for starting is about how i start mine. many 1/8th throttle when warm though.

have ya checked out the trouble shooting guide in your mercruiser service manual?

for flooding some of the items mentioned are.

needle and seat worn, damaged or dirty
float adj. incorrect
leaky float
carb gaskets leaking
cracked carb body
auto choke defective or out of adj. (flooding on hot starting)
excessive fuel pump pressure
clogged flame arrestor

when ya rebuilt yer carb. did ya soak it in carb cleaner and use compressed air to blow out all the small passages. + did you set the specifications of the carb up to the specs in your mercruiser manual?

Re: Hard starting warm - carburetor problem???

Could be a bad float, or needle in the carb. I've also seen a similar condition caused by a cracked float bowl in the carb. Assuming everything else is good, these are just 2 thoughts that i had.

Re: Hard starting warm - carburetor problem???

The float and all parts (gaskets, needle, etc.) included in the kit were replaced when the carb was rebuilt. The carb was dipped and all passages blown clean with compressed air. I haven't messed with the auto choke because I didn't think that would cause flooding. So back to one of my original questions: If the carb IS leaking after shutdown, is there a way to test for that leakage?

Re: Hard starting warm - carburetor problem???

The only way I know of to test if it's leaking after shut down is to watch it. Mine did that before I rebuilt it and it was fairly obvious. You could actually see it drip and the carb smelled of fuel.

Carbs are pretty fickle, meaning even the smallest particle can get lodged somewhere and cause a lot of problems. Point being, just because it was recently rebuilt, doesn't mean that something didn't get in there afterward. And, the rebuilding procedure demands great attention to detail.

It could also be choke related. Does your choke open as your engine warms, close to within .080" or so when cold, and is it open fully when you are trying to restart it when it's warm?

Re: Hard starting warm - carburetor problem???

I could see my carb dumping fuel, too. After shutdown I could see a stream of gas dripping inside. Mine turned out to be a leaky float that got too heavy.

Re: Hard starting warm - carburetor problem???

The choke operates as it should. Almost closed when cold, opens up as it warms, and is open when I try to restart. If the carb IS leaking and that leaking is due to a bad seat (assuming all other parts are new and good), would another rebuild do any good? Or is it time for a new carb? I don't even want to think about that.....sounds expensive.

Re: Hard starting warm - carburetor problem???

....let's try this:

Run the engine until the choke pulls off (on muffs is fine).
Immediately upon shutdown, remove the flame arrester and ensure that the choke is OPEN. Peer down the carb's throat. If any vapor is present, gently blow it away. Look for the presence of LIQUID fuel. Observe the venturi boosters...see ANY drops of fuel? Very gently and slowly, so as not to activate the accelerator pump, open the butterfly all the way open. Again, if vapors are present, blow them away. See any LIQUID fuel puddled in the manifold?

If you have answered positive to any of the above, sum'thin is wrong in the carb, more than likely a too high float, a heavy float or a needle that is not seating.
FWIW....Ed in 'ol Virginny

Re: Hard starting warm - carburetor problem???

this is a questionable statement. but i've heard of needle and seats sticking after rebuild. some have claimed they remidey this by tapping on the float bowl with a screwdriver handle... ?????


have ya checked your fuel pump pressure?

Re: Hard starting warm - carburetor problem???

I'll check the carb like EddieP recommends, and let you know what I find. As far as fuel pump pressure, I haven't checked that yet. Will that cause flooding?
Now I'm assuming that since it starts out fine cold, or when I restart it immediately after shutting off the engine, that it is not an electrical problem. Is that a proper assumption? I'm getting a lot of good info on the carb from you fellow boaters. And I'll keep troubleshooting with your suggestions. I just hope I'm not missing something electrical that could be contributing to this.

Re: Hard starting warm - carburetor problem???

All of your symptoms are classic flooding symptoms. Before I rebuilt my carb mine was flooding also. If you remove the flame arrestor and look into the carb while it is running, you might see it dripping fuel (mine was). It also continued dripping after shutoff until the bowl had drained enough to stop overflowing.

I'm also going to assume that your fuel pump is mechanical. It is unlikely that a mechanical fuel pump can overpressurize your carb leading to flooding, although it may be possible. Most common flooding issues are carb and choke problems.

Did you do the carb rebuild yourself? If you didn't, double check that the float was replaced, as it is not included with the rebuild kit. Either way, I would bet either the float is set incorrectly or there is debris keeping the needle from seating properly.

If the carb IS leaking and that leaking is due to a bad seat (assuming all other parts are new and good), would another rebuild do any good?

Click to expand...

If you replaced all the parts that came in the kit, then you have a new MATCHED needle and seat. If you did not replace both with the rebuild, then your needle is not seating properly in the seat.

The float adjustment is critical, as is the float mass. Adjusted too high and fuel will overflow. Mass too high and the float won't raise enough to close the needle valve, resulting in fuel overflow. Related to mass is the possibility of cracks/pinholes in the float. This allows fuel to enter the float and become too heavy to close the needle valve properly.

Bottom line is, rebuilding the carb again should not be necessary. Checking the float and needle/seat are the first things I would do.

Hope this helps

Re: Hard starting warm - carburetor problem???

Was the needle and seat gasket replaced with the same thickness one. In the kits there are 2 one thin and one thick.

Another item is the tiny holes on top of the main jets that are in the venturi.
If this tiny hole becomes plugged the jets will siphon fuel from the bowl. You can tell this by presence of fuel vapor in the carb throat after shut down.

It took me a few passed thru a carb to determine this. It is not common but a real situation.