1996 mariner 30 hot start issues -- at my wit's end

[chrisgt]

I've had this 1996 mariner 30 for a while and it's never started right, these are the things i've done to it over the last couple years and it has left me with one remaining problem:
It does not like hot restarts; it will usually cough, stall, and then start on the second try.

• Compression is around 140 on both cylinders.
• Reed valves were bad (hanging open) so I changed them and installed 40hp reed retainers and 40hp carb jetting.
• I replaced the bleed tubes and verified the check valves work. The check valve between the lower bearing and the induction manifold takes a bit more pressure to open than i'd expect, possible issue?
• I changed upper and lower crank seals which made a profound change to how well it ran.
• New spark plugs of the type and gap suggested in the service manual. (none of this iridium garbage).
• Carburetor cleaned and tuned correctly. 900 RPM at idle in forward gear, adjusted the mixture lean until RPMs dropped, adjusted rich until RPMs dropped, set on the rich side of the center and then reset idle to 900 RPM.

This engine runs and idles perfectly smooth, it starts cold on the first try every time, yet this annoying hot restart issue remains. Usually after about 5-15 minutes of sitting, if i give the engine some throttle it will start right up, but i shouldn't have to do that. Could it be the bleed tube check valve that seems to be just a tad sticky? Literally everything else seems to be in good order.

Edit: it's not bad gas, I run 90 ethanol-free and put 5+ gallons a week through the engine.

 

[boscoe99]

What is the engine serial number?

 

[chrisgt]

The serial number is: 0G357906

It's an early 96, before the facelifted ignition system and intake manifold.

 

[BWR1953]

I had a similar problem with my 1985 50HP. It turned out to be a bad CDI box.

I'd started troubleshooting and was taking electrical measurements on it when I noticed that under the wiring was a long, narrow crack down the full length of the box. The crack had black goo oozing out of it. I replaced the box and the problem resolved.

 

[flyingscott]

It's a carbed motor, perfectly normal to have to give it throttle after 5-15 minutes of sitting. If you don't want to give it throttle buy an EFI motor.

 

[boscoe99]

The Mercury Marine parts catalog shows two versions. One with an electric enrichment valve and one without. Does your have one or not?

 

[Jeff J]

My experience with hot start problems on most non-EFI applications is an overly rich mixture. That’s why opening the throttle works. It allows more air into the intake.

It may be the same with EFI but there are other issues if an EFI engine needs more air to start when hot.

 

[roscoe]

Why did you put in 40 hp jets?
Seems that would create a rich condition.

 

[chrisgt]

Sorry I was on a camping trip (using this boat) with no cell service for a week.

I had a similar problem with my 1985 50HP. It turned out to be a bad CDI box.

I'd started troubleshooting and was taking electrical measurements on it when I noticed that under the wiring was a long, narrow crack down the full length of the box. The crack had black goo oozing out of it. I replaced the box and the problem resolved.

Hmm, interesting. It starts and fires for a second and stalls so I was assuming it wasn't an ignition issue, but i can pull all of that apart and take a close look at everything. I could also use the service procedure where you power the ignition module from 12v instead of the stator coil (this is described in the service manual).

It's a carbed motor, perfectly normal to have to give it throttle after 5-15 minutes of sitting. If you don't want to give it throttle buy an EFI motor.

The johnson 35 I rebuilt starts on the first pull at idle no matter if you shut it off 10 seconds ago or 45 minutes ago, no reason a mercury shouldn't be better than an 80's johnson.

The Mercury Marine parts catalog shows two versions. One with an electric enrichment valve and one without. Does your have one or not?

Mine has the enrichment valve and I have checked to make sure that it isn't leaking.

My experience with hot start problems on most non-EFI applications is an overly rich mixture. That’s why opening the throttle works. It allows more air into the intake.

It may be the same with EFI but there are other issues if an EFI engine needs more air to start when hot.

Why did you put in 40 hp jets?
Seems that would create a rich condition.

Maybe it's a rich condition? I can try putting the smaller jet back in i guess.
Why would i not want the 40hp jet? I have 40hp airflow, if i don't use the jet that matches the airflow it'll run lean. The main jet doesn't do anything at idle anyway, the idle circuit has an emulsion tube from the bowl up to the idle circuits under the cover at the top of the carb.
In fact it DID run lean, when you buy reed valves they come with retainers for a 40hp, I put them in without realizing this and it ran really lean. I forget if it had the same problem, sorta doesn't matter that much since it was pinging and the plugs were bright white.
I would have to assume that the 40hp engine with its airflow and jetting works correctly, so i don't see why this would be a problem.