Bogging issue.

[royclaypool]

Hi guys. Quick rundown.

Bought used 1984 Renken with a Mercruiser 120 2.5l. Original issue was I could only get a good speed for about 5 minutes. Then engine would bog and gas would be boiling in the carb. Engine wouldn't start for a couple hours once this happens. Replaced coil, fuel pump, rebuilt carb, thermostat, throttle cable, water pump/impellar, and battery. While I don't have the same problem, I suspect the problem I have now is related. I can now cruise at WOT for about 30 minutes. Then, engine starts acting funny and temp climbs to about 150-160. After turning engine off, gas vapor was coming out the black tube that connects the carb/air filter and the rocker cover top. The engine ran great for a half hour. My third time at WOT and I'm hooked.

So, what should my next step be? A local boat shop took a peek and said the carb needed to be re-built. Only it already has. Twice. By the previous owner and a friend of mine. Should I just order a brand new carb? Could this issue be related to the little bar that the throttle cable connects to that requires you to loosen the nut on to adjust? Also, temp after turning the engine off reached 170-180. Cause for concern? Any idea's would be amazing.

 

[alldodge]

Its not the best for any motor to run for prolong periods at WOT, should be reduced around 80% or so. The fumes coming out of the hose coming from the valve cover is oil and combustion by products, not gas. When the rings start getting weak, some of the combustion gases slip past the rings and enter the cylinder block. These hot gases mix with the oil vapors and exit thru the valve cover hose.

So if the motor runs well enough for other speeds I don't see any reason to mess with the carb again. The temp going to 180 after the motor has been turned off is also not an issue, that is so long as temp drops when the motor is restarted. That said, you should let the motor idle a bit after a hard run for a little while, at least a minute or two

 

[royclaypool]

Ok. Thanks for the advise. Just tried starting it, and it won't start now. Are there additional fuel filters(factory) I should be hunting down? I don't see any on the line from the gas cap to the tank, however, I can't see the entire run of tubing. Didn't see any gas going in the carb this time when trying to start either....argghh!

 

[alldodge]

Your motor has the filter as part of the fuel pump. It uses filter part number 35-8M0046752. I would suggest check the antisiphon valve which is on top the fuel tank. Its a barbed fitting which the rubber fuel line is attached to. Inside the fitting is a ball and spring and this item can get corroded and stick, which then restricts fuel.

Here is your fuel pump, carb and other items
http://www.mercruiserparts.com/bam/subassembly/30885/963/120

Here is a link to your motor
http://www.mercruiserparts.com/120-gm-153-i-l4-1983-1986-6229718-thru