Tech advice needed

[Naut]

Hi all, my first time posting good to meet you.
I have a question about my motor I hope you can give me a little advice.

I have a 2000 50 hp 4 stroke Mercury Bigfoot, it sat for a few years so i took it in to my local marine shop to have the oil changed, water impeller and fuel filter replaced and the carbs rebuilt and tuned.

The mechanic couldn't get it to run right and told me he thinks the head is bad or maybe the block and head are cracked, he said maybe a valve issue.

With that said I'm the original owner and don't agree with his diagnosis so I've reluctantly been doing more tinkering than I'm comfortable with to try and figure if he is right.

I started with compression and it seems ok to me right at 90 lbs with the motor warm, next I tried pulling the plug wires off one at a time to see, #1 plug didn't make a huge difference but I could tell it was a small drop in rpm.
#2 plug made a big change motor almost died.
#3 plug didn't do anything at all no change.
#4 plug same as #2 motor almost died.

So since compression seemed ok I figured has to be a carb problem so I took the carbs off #3 carb was fairly clean but there was a little cleaning.

Now the important part I swapped carb #2 with was working the best with carb #3 which that cylinder seemed dead put it all back together started it up seemed to run just a tiny bit better but not perfect so I went back to the plug wires and started again.
#1 plug same as the first time.
#2 plug also same as before.
#3 plug now drops the Rpms when unplugged and seems to be working fine.
#4 plug no difference in motor sound or rpm.
By switching the #2 and #3 carbs #3 now works but #4 now acts like a dead cylinder.

Any opinion on this would be nice because I'm honestly very confused, also the guy that worked on my motor didn't have the proper computer to tune my carbs I found out after the fact, thanks a ton for reading sorry it seems kind of a long post.

 

[Tnstratofam]

If your not confident in rebuilding your carbs I would find another mechanic. The one who worked on your engine doesn't inspire allot of confidence in my opinion. Not to mention he doesn't have the tools needed to tune your engine. It sounds like rebuilding your carbs and generally cleaning your fuel system would be a good starting point. Lots of bad things happen to your fuel system when it sits for years at a time.

Almost forgot :welcome: to the best place on the web for all things boating.

 

[Naut]

I apologize from reading the reply I realize I was not specific enough in my question.

Do you think the mechanic was right about a bad head and or block, maybe valves,
Or with the testing info I provided is it the carbs.

Once fixed you can be sure I will keep the maintenance up, thanks again.

 

[MTboatguy]

I agree, it sounds like your problem is in the fuel system, the first thing I would do, is find a mechanic that knows what he is talking about because the guy you took it to, didn't know. See if you can find a Mercury certified repair shop, that will give you a better chance at finding someone who actually knows about your motor.

 

[Naut]

Thanks Mtboatguy the main reason I'm asking is I know some of you are a lot more knowledgable than I am about outboards I just spent $550.00 dollars I would like some input from you guys before taking it 100 miles and spending a lot more at the dealer just on my feeling alone.

 

[Naut]

Problem fixed it was the carbs I cleaned the little jets took it back to the shop to get them in sync it runs like new again, thanks for the help, happy boating.