1990 4.3 merc bogs a little at WOT

[ccustomrides]

Anyway boats runs great and idles fine. My problem is WOT throttle. When I slowly add throttle it will run fine and I can trim it out. If I am running half throttle and punch it all the way it will pick up speed and then choke out at full throttle and drop few RPM. If I back the throttle off just a little it picks up the RPM and runs good. Same thing goes if I pull back on the throttle and then slowly feed it again it will run fine also. So is my problem,prop,engine or carb related. Thanks.

 

[cooter2506]

Re: 1990 4.3 merc bogs a little at WOT

Sounds like yuour loosing fuel. Check up in the adult sticky section to see how to trouble shoot your fuel system. But I did have a similar problem and it was the antisiphon valve.

 

[pawpaw1951]

Re: 1990 4.3 merc bogs a little at WOT

partial plugged fuel filter?

 

[ccustomrides]

Re: 1990 4.3 merc bogs a little at WOT

Hello, You mean the valve on the tank.(valve in between the fuel pickup and pump) Yes it was replaced with new. I had another problem earlier in season with timing being off because cap got moved but it made me replace the valve in process of troubleshooting. Also my timing is set at 8btdc. Can I run 4.3 around 10 or will it help to get few extra horses out.

 

[ccustomrides]

Re: 1990 4.3 merc bogs a little at WOT

Sorry guys. All new fuel filters,spark plugs last year are all done. Maybe a bad pump?

 

[cooter2506]

Re: 1990 4.3 merc bogs a little at WOT

Do the tests in the adult sticky and you will find your problem. its under how to test your boats fuel system

 

[ccustomrides]

Re: 1990 4.3 merc bogs a little at WOT

Well I think it's my carb. I talked to one of my mechanics and he said to run sea foam and try 93 octane. He said if it was fuel or pump related then I would see surges on all my rpm range. He also said there are bushings on the main link that go bad and create vac. leak inside the carb and create same problems I have. It could also be fuel pump but I need to test it under load in the water.