Mercury 50 hp (500) mystery !

[Evenrude25]

Hi all

I hope somebody will be able to help me with my mystery.

I have a Mercury 50 hp Thunderbolt, I think it is also called 500. Number 9101164, made in Belgium, I think in the late 80?s.

It has been in the garage for a couple of years and I just bought it. The guy I bought it from said that it ran ok when he put it there - But who wouldn?t say so ?

I tried to start it - electric start - and it ran a couple of seconds (very humpy). Enough to see that there where no water coming ! New impeller and trying again. Lot of water, but only caughthing away.

Cleaned the carburator (twice) and it got a bit better.

I think the ignition is ok - I tried unscrewing the sparkplugs and only having one in - And the engine runs almost better ??? I tried this on every cylinder, and it runs ok ?

But having all 4 sparkplugs in there is no change ? Still running like s... ! It fires up ok, runs for about 1 or 2 seconds at WOT (but not full rew.) and dies ?

Any ideas on whot could be the problem ?

 

[achris]

Re: Mercury 50 hp (500) mystery !

Looks like about 1975.... Does it have a distributor?

Check the firing order....

 

[crem1]

Re: Mercury 50 hp (500) mystery !

Check the compression of the cylinders then do a good job of cleaning the carbs and the fuel pump. Taking carbs off and soaking them in solvent for a day

 

[Evenrude25]

Re: Mercury 50 hp (500) mystery !

Thanks for your replies.

Firing order is right, compression is good, carbs are as clean as I can get then.

I have the engine running It starts well, idle is good and WOT is good.

But.... at middle speed it has it a bit hard and will not accellerate good. Like it only runs on 3 cylinders sometimes ? When opening the throtle to full speed it kind of caughs and thinks about "Do you really mean it ?".

I think a cleaning of the ignition could do the job, but I do not know much about this. This link shows how it looks: http://www.usboatsupply.com/Mercury_Mercruiser_Parts_Catalog3a.php?mc=01&ms=4110&si=449

 

[achris]

Re: Mercury 50 hp (500) mystery !

...When opening the throttle to full speed it kind of coughs and thinks about "Do you really mean it ?"....

Open the mixture screws 1/8 to 1/4 turns.

Chris......

 

[sstRobalo]

Re: Mercury 50 hp (500) mystery !

is exhaust plugged up(mud wasps) and pee hole plugged

 

[mike1245]

Re: Mercury 50 hp (500) mystery !

might want to pull off the pump and look at it i have a 1973 merc 500 and was doing the same thing found out i was getting air bubbles in my fuel line between pump and carbs when i took it off to reseal pump i found it all rusted up inside got new pump and runs great now by the way mine also sat up for 2 years but not in a garage