Hard to start after it warms

[iownaboat]

I have a 88 Mercruiser 5.0 with thunderbolt ignition.
Over the winter I replaced the cap rotor electronic module and when its first start its right away first lick it fires up.
After the motor warms up, it get hard to start. any one have an idea what might be causing this?

 

[ohio river rat in KY]

Re: Hard to start after it warms

timing maybe

 

[PowerAddict]

Re: Hard to start after it warms

Agree, check timing.


Also, Have you checked the plugs for moisture when it is hard to start. Cracked manifolds could get water into the cylinders fouling plugs.

Could be a long shot, is the fuel line the stock routing? not getting too close to the manifolds? Is cooling system good, engine temp okay - intake manifold not getting too hot. Just to be sure its not a fuel boiling/vapor lock issue.

 

[littlebookworm]

Re: Hard to start after it warms

Check the choke. '88 engine had a heat box, if I remember correctly. The boxes do rust; the springs do lose their tension or break, and the housings do get filled with crud. On a cold start, the choke needs to close. On a warm start, the choke should be open. If it's still closed, even partway, you'll have a hard-start problem. Hy

 

[PowerAddict]

Re: Hard to start after it warms

Check the choke. '88 engine had a heat box, if I remember correctly. The boxes do rust; the springs do lose their tension or break, and the housings do get filled with crud. On a cold start, the choke needs to close. On a warm start, the choke should be open. If it's still closed, even partway, you'll have a hard-start problem. Hy

^interesting.

Good suggestion!

 

[ktbarrentine]

Re: Hard to start after it warms

I had similar issues when I bought a '90 5.0L. My issue ended up being a bad fuel pump diaphram that allowed excess fuel into the carb airhorn via the sight flow tube, causing a flooded condition between starts. A new fuel pump solved that problem (a boat 20+ years old...Ethanol fuel is not good on the rubber diaphram). Its something easy to check while the engine is running.

 

[Bondo]

Re: Hard to start after it warms

I have a 88 Mercruiser 5.0 with thunderbolt ignition.
Over the winter I replaced the cap rotor electronic module and when its first start its right away first lick it fires up.
After the motor warms up, it get hard to start. any one have an idea what might be causing this?

Ayuh,... Welcome Aboard,... Are ya givin' it any Throttle,..??

Carbed motors need abit of throttle,...

 

[denhajm]

Re: Hard to start after it warms

ktbarrentine, can you elaborate on what you saw that caused you to know the fuel pump diaphragm was shot? I have the same issue where my 4.3L on a '90 sea ray starts and runs great, but takes some cranking to start after it is up to temp. I want to check this fuel hose you mentioned but would appreciate some specifics. thanks!

 

[Puddy905]

Re: Hard to start after it warms

I'm having the same problem and I am assuming it's vapor lock as I have changed the ventilation to my motor by changing the interior of the boat. I posted about it earlier today.

 

[ktbarrentine]

Re: Hard to start after it warms

ktbarrentine, can you elaborate on what you saw that caused you to know the fuel pump diaphragm was shot? I have the same issue where my 4.3L on a '90 sea ray starts and runs great, but takes some cranking to start after it is up to temp. I want to check this fuel hose you mentioned but would appreciate some specifics. thanks!

The sight-flow tube is a clear tube that runs from the fuel pump (above the diaphram) to the air horn of the carbeurator (mine comes in at the aft side of the airhorn). When the engine is running, you can either look at the airhorn with the flame arrestor off, or look at the sight-flow tube that runs along the intake manifold to the airhorn (my SF tube was actually very discolored/yellowed by 20+ years of age, so couldnt see much through it, but did see the gas coming from the SF tube port into the airhorn... After I replaced the fuel pump, I also replaced this SF tube. A bit pricey, but it is a "special" material... Do not use tygon or vinyl tube!!!). I did a post mortem on my old fuel pump and found that the diaphram was shot! I have been told this is due to leaving the boat in storage with ethanol fuel in the pump.

 

[denhajm]

Re: Hard to start after it warms

Thanks for the further info on the fuel pump and clear hose. I'll look into mine. I appreciate the info and photo.