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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11080
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Tan, I just had a vapor separator replaced on a 50hp Mercury

Customer Question

Hi Tan,
I just had a vapor separator replaced on a 50hp Mercury outboard.
The engine starts fine, but when you put the gear and accelerate, it does not go to full throttle, it stays in low rpm, like bogged down by not enough fuel.
What do i need to look for?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello George.

We need to check for spark and compression. The spark must jump a 7/16 gap on a spark gap tester and compression must be 90+ psi with no more than 15% difference.

Customer: replied 1 year ago.
Hi Tan,
I will check that, but the motor was running great before we had the vapor separator changed
Customer: replied 1 year ago.
The vapor separator was changed because it was leaking.
The engine starts right away and revs up very quickly under no load. It does not die when in gear and revved up.I was thinking that it could be the fuel pressure or the air pressure in the unit. What do you think?
Expert:  Tan replied 1 year ago.

Then the only thing it can be is clogged injectors. Debris gets knocked loose in the fuel system when replacing any fuel components. This debris can cause the injectors to not fire. We can check for injector fire buy removing the spark plug wire from each cylinder when engine is running. You should hear arcking verifying spark and the engine rpms should drop. Do this check and post back with findings.

Customer: replied 1 year ago.
Thanks for the phone call invite.
It will be great if we can speak on the phone, but I am not in front of the engine right now. I needed to know what to check for and get all the tools needed before I head there. It is an hour away from me.
Expert:  Tan replied 1 year ago.

Ok George let me know.

Customer: replied 1 year ago.
I had already checked that. The firing is good on each cylinder. The engine drops rpm when I removed each wire
Expert:  Tan replied 1 year ago.

Ok then we need to check spark under acceleration with a timing light. This could be an ignition failure only under a load. Connect the timing light to the top cylinder run the engine till it acts up then watch the flash of the timing light. If no misfire then move to the next cylinder do the same test. If you find a misfire then move that ignition coil to another cylinder. Test again doe the misfire move or stay. If it moves that coil is bad. If it stays we have another issue.

Customer: replied 1 year ago.
Ok I will try that.
Is there anything to check on the vapor separator?
Expert:  Tan replied 1 year ago.

Not if they just replaced it.

Customer: replied 1 year ago.
I am not sure of how much they were knowledgeable. They told me later that they were only an inboard engine repair shop...
Expert:  Tan replied 1 year ago.

Was this just the tank they replaced or did they work on your tank and replace it after they repaired your old tank?

Customer: replied 1 year ago.
They replaced the complete unit.
Expert:  Tan replied 1 year ago.

Then no that is a straight forward job. The tank would have been set up from the factory.

Customer: replied 1 year ago.
What should be the air pressure of the tank? and the fuel pressure?
Expert:  Tan replied 1 year ago.

This will not have air pressure it will have fuel pressure. I need the engine serial number to get you the specification. Usually around 35 psi.

Customer: replied 1 year ago.
Great, thank you.
I will get the serial number when I get there.
Could we have a call this Friday early afternoon? I will be in front of the engine and would have tried everything you suggested.
I was planning to change the spark plugs too if needed.
Expert:  Tan replied 1 year ago.

Yes we can. Just let me know when your are ready and we can proceed.

Customer: replied 1 year ago.
I just got charged for the $5 deposit and then $21 again from your company. I did not understand that when I signed up. I thought the $21 will be charged when I get the problem solved.
What happens to the phone call then?
Expert:  Tan replied 1 year ago.

The deposit is to get you started then when I reply you are charged 21 for the amount total of 26. Then if you want a phone call is is another charge.

Look at it this way if you take it to a shop they are going to charge you 100 and hour whether you get it fixed or not.

As you know they haven't fixed your engine as of yet and they still charged you correct. So I am allot cheaper than they are and you are more likely to get it fixed with me. We know they can't.

I have to make money some how as I only get half of what you are charged. To me time is money.

We can stop now if you think this is not right.

Customer: replied 1 year ago.
It is fair, time is money for all of us. What happens when I send you information after I check it and continue the troubleshooting online?
I understand that the call is $26 extra.
Expert:  Tan replied 1 year ago.

You are only charged the one time for the Q&A and then the phone call. We don't have to do the phone call. There are no extra charges in the Q&A on this subject till we get you fixed.

Customer: replied 1 year ago.
Thank you Tan,
I will get back to you with more information.
Expert:  Tan replied 1 year ago.

Ok I'll be here.