3.0l OMC bogging at full throttle

[greasemonkey1985]

My brother and I just bought a 1986 thundercraft with a 3.0l OMC. The boat was and older gentlemans which seemed to take very good care of the boat, it just had points, carb kits, and fuel filter replaced at the local marina. When we bought the boat we put it in the water and it ran great, we were doing almost 40mph and steady cruise at 32-35 at 3/4 throttle with no problems. After buying the boat we put it in the lake and went out jumping some waves and having some fun and after about 30minutes on our way back the boat started running rough, it wasnt really bad but it was noticable. At full throttle it seems to be holding back. we thought possibly old gas, before I took it out the second time I went to fill the gas which took a long time(for only 30l). Everytime I went to pump the gas in it kept coming back up the filler tube. It still ran bad, shortly after it warmed up. Is it possible the vent line is plugged?? Old gas?? any other suggestions?? sorry for the long post just wanted to make sure that the problem was explained and circumstances.

 

[Schmoe]

Re: 3.0l OMC bogging at full throttle

Not unusual for fuel to come out of the vent pipe, especially if your fueling it up after riding around. A lot of gas will be sloshing around in the tank. That could also be your problem, you might have stirred up some loose sediment from inside the tank. Check the fuel filter going into the carbuerator.

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

Ok, I know the filter is new but I will check it, the fuel was coming out of the vent while filling. It would back up the filler neck then come out the vent, after waiting 10 seconds I could then keep filling. I will check the filter and reply back, do you think that bad gas could cause that problem, it seems only when it warms up. It has a good pull out of the hole then 2-3 minutes later it starts acting up. (has new plugs too) Possible coil overheating??

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

we checked the fuel filters and they all seem clean, and we blew out the vent and still have the same problem. Is there any other ideas? Coil? Points misadjusted? I have seen on other engines people talk about an overheat sensor that will reduce power, is there one on this engine to check? any ideas will help.
Thanks

 

[Howard Sterndrive]

Re: 3.0l OMC bogging at full throttle

I have seen on other engines people talk about an overheat sensor that will reduce power, is there one on this engine to check?

no

anti-siphon valve at the tank where the fuel line connects might have debris in it.
I'd also be inspecting the carb linkage, choke, and looking at the heat tube and various connections around the intake for vacuum leaks.
I'd also clean the flame arrester.
And yes it could be a 23 year old coil packing it in.
The fuel out the vent thing is just a badly designed tank and fill hose routing. Just pump slower.
I'd also try a cruise with the ESA unplugged.

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

ok, may be a stupid question, what is the esa?? and where would I find it?

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

And my brother had it out last night with a fuel pressure guage on it and said at full throttle the pressure drops 2-3psi(it has an electric inline pump) is that normal or something we should replace??

 

[futz]

Re: 3.0l OMC bogging at full throttle

electric fuel pump on a 86 omc 3.0l? You can d/l the manual at the top of the forum, and see the correct pressure the pump should be giving you.

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

The manual says it wants 3-5psi, I assue that at wot the pressure will be less?? Is that true? it doesnt state difference between idle and wot. The pump currently puts out 5 at idle and 3 at wot. We finally opened up the tank and found the gas to be pretty bad so we sucked it all out. we also noticed that the anti syphon has grass and crap in it. and when we pulled the pick up, the tube going into the tank was not tight, which would allow for air so we are fixing that too. Hopefully get it on the water tonight and will report back with results.
Thanks again for the help

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

Ok, so we took the boat out and it seemed to run worse, so we took the carb apart today and found that the throttle pump(???) spring seat was missing so we put a washer and clip on it and reassembled, and cleaned out the carb, now its out to the water again. fingers crossed

 

[greasemonkey1985]

Re: 3.0l OMC bogging at full throttle

So there is no difference, if anything it has gotten worse. I am thinking that it has something to do with spark, the points were done at the bginning of the season by a local marina, and the boat ran good for the first run and 30 minutes of the second run, I am thinking possibly the coil is overheating and not providing proper spark?? It runs better at low throttle, cruising in the no wake zones, (still slight missfire) but really boggs under load sometimes it will go, and bogg and sometimes it wont even go. How does the spark advance work on this boat?? any other places to look?? I have the manual and will start reading and checking each item one at a time but any hints or ideas will be appreciated.

 

[KazenNYC]

Hey having the same issue here on a 88 OMC 3.0 did you ever figure this out? .

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