Help! OMC 5.0 no acceleration

[Darcy]

Looking for a little help. Currently on a boating vacation, and the boat wont go...

86 OMC 5.0. Just resurfaced heads, fresh cam, new points, plugs, rotor, oil.
Timing at about 6` BTDC. Dwell at 33`, and doesn't drift. Advance weights advance and return normally.

Boat starts fine, idles at 500 perfectly, and will turn up in neutral no problem. Sounds perfect. Once in the water, I try to get going and the engine starts to chug and backfire through the carb at about 2200 turns. Once I get off the throttle it will keep going along at 2000 indefenitly.
It is a little rough to start after this condition occures, but cranking with throttle WOT will get it going. Seems to be flooding out.

Checked the accelerator pump, and it squirts. I checked the carb filter, and it looks fine. Gas was pumped this afternoon, so it is fresh.

No mechanics open today!


What do I need to fix?
Thanks!

 

[MikDee]

Re: Help! OMC 5.0 no acceleration

Try this and MAYBE save yourself a lot of grief on vacation, beg, borrow, steal, or buy a portable gas tank, and run off that! At least you will know if it's a fuel delivery problem? or not, besides if it works you can relax and use that till you get home to tackle the problem. By the way, one item to check, is your fuel tank vent, make sure it's clear.

 

[Darcy]

Re: Help! OMC 5.0 no acceleration

UPDATE:

Took it out again, with just 2 people. I was able to get it up on plane, and once I was there it ran fine. I was able to make 4200 RPM, which I realize is a tad low, but better than nothing...

while on plane, throttle was responsive, and I was able to slow down and speed up as long as I stayed on plane.

I'm leaning toward a carb problem... Thoughts?

 

[Limited-Time]

Re: Help! OMC 5.0 no acceleration

You have Carb/fuel delivery issues..................There is a post here by Don S for trouble shooting the entire fuel delivery system. I'm sure someone will post a link for you.

 

[MikDee]

Re: Help! OMC 5.0 no acceleration

If the engine runs smooth throughout most of it's range, and will continually run along at 4200rpm, It doesn't sound like a carb problem to me? Is it a 2bbl or 4bbl? it still sounds like a fuel delivery problem to me. If it's a 4bbl, and when you open the secondaries it balks (hence 2200rpm like you said) possibly it's not getting enough fuel then. Did you try a seperate gas tank, like I said? It might eliminate a lot of Wild Eyed Guessing at this time. If you want to get deeper into it, Ok, now, assuming your fuel line is clean, & clear, and not crimped somewhere? All Boats have an antisiphon valve, and filter, at the fuel tank, that sometimes need to be taken off, & cleaned, or replaced, they can create issues like you're having. Use that as your starting point.

 

[Darcy]

Re: Help! OMC 5.0 no acceleration

I just wanted to update this thread.

I found the problem. I had adjusted the valve lash too tight during reassembly. I adjusted the valve lash with the engine running this time, and it cleared the problem right up.


Thanks for the suggestions.

Darcy

 

[MikDee]

Re: Help! OMC 5.0 no acceleration

I just wanted to update this thread.

I found the problem. I had adjusted the valve lash too tight during reassembly. I adjusted the valve lash with the engine running this time, and it cleared the problem right up.


Thanks for the suggestions.

Darcy

Thats the way I do a final adjustment on the valves. Thanks for the reply, Just curious, what's your maximum RPM now?

 

[Darcy]

Re: Help! OMC 5.0 no acceleration

I am able to get up to 4400, with an indicated speed of ~45MPH(18ft searay bowrider).


I am still going to take it to a pro to get that final tune now that I'm back from vacation. I still feel like I'm missing a good chunk of power.

 

[MikDee]

Re: Help! OMC 5.0 no acceleration

Ok, What size boat is it? and what is the rated horsepower of that motor?