81 merc 90 (inline 6) bogs at full throttle

[mbb]

First trip out in a few months. Ran a total of about 100 miles in 2 days chasing specks in the Louisiana delta. Motor ran fine up to 4300 rpm, so I did all my running 4000 - 4300. Max is 4500 no trim, 4800 trimmed out. Above 4400 or so (WOT) motor would begin to bog down after 20 sec or so. If keep throttle open, motor would eventually slow to 3500 rpm or so. The instant I throttled back some it would jump back up to near max rpm. <br /><br />Seems like fuel flow restriction to me? In addition to checking normal stuff(primer bulb, replace racor element, antisiphon valve), etc, does anyone have any other possibilities to suggest?

 

[12Footer]

Re: 81 merc 90 (inline 6) bogs at full throttle

I think you are on the right track. It sure sounds like a fuel starvation problem. I would rule it out first anyway,by cleaning inline filters,rebuilding the fuel pump, and clean out the fuel tanks.<br />You could be dropping a cylinder due to ignition, but from your descriotion, it isn't likely,as it only surfaces at WOT.<br />Venting,anti-syphon valve, air leaking into fuel line, bad tank-to-hose fitting connection,loose carb,fuel pump, bad fuel,low compression,goo in the carb....<br /><br />Yea, I know a lot to look at.but you are on the right track.