omc 5.0 bogging at WOT

[lotty1525]

I own a 1987 four winns 190 horizon with omc 5.0l gm motor. I replaced the u-joints, gimbal bearing, motor coupling, coil, spark plugs, fuel filter/water separator, and opened up the carburetor to look at the float and found nothing unusual. I drained the gas tank and just added all new fuel. The issue is when running at WOT for longer than about 1 minute it will slowly start to slow me down then it will bogg the motor. After it boggs down and i give it speed again it feels like I'm getting some vibration, which doesn't last once getting up in rpms. usually it runs great getting to speed, and runs fine at 75% throttle. Any information on where to start looking would be great.

stock rpm gauge not working, have a 14.5 x 19 pitch prop with a max speed of 38 mph with me alone in the boat. carb is a Rochester quadra jet. motor runs at 160 max temp when at high rpm. oil pressure is from 10-40 lbs.

I'm a first time boat owner and have some mechanical knowledge. if this speed and everything seems off please let me know.

Thanks,

 

[SeanMcl]

Re: omc 5.0 bogging at WOT

My guess is you are running lean at WOT. It gets hot, loses power and starts detonanting giving you the vibration that goes away once you back it off and let it cool. It happens pretty fast, so it doesn't register on the water temp gauge.

Most likely cause is gunk in the carb, float needle not opening fully, etc. Rebuild the carb, check fuel presure and vacuum between the carb and the tank.

 

[lotty1525]

Re: omc 5.0 bogging at WOT

you mention checkin vacum from carb to tank. when I looked at the tank under the floor panel it has 3 connections . 1 larger 2'' line coming fom gas fill spot to the tank nearest back of boat. 1 line about 3/4'' which is next to gas fill line and it goes to the water seperator/fuel filter. 1 line which is on other end of tank which I can't see where it leads, maybe back of boat for vent. I have 1 fuel line going from fuel filter/water seperator to the manual pump on motor then to the carb and then a yellow see thru line going from carb to the fuel pump. is that yellow line the vacum?

 

[Bondo]

Re: omc 5.0 bogging at WOT

Ayuh,... On the Tank, the 5/8th" line is the Vent,...
The 3/8th" is to the filter....

The yellow tube is a safety line, if there's liquid in it, the fuelpump has Failed...