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OMC Operation Questions

mlaymance

New member
"Hi all,

I am a recent purc


"Hi all,

I am a recent purchaser of a boat powered with an OMC 305 (Or so I am told)1979 model.

This motor ran actually pretty good (or so I thought) until I was talking to another boater friend, who said some things that actually made sense, so I am asking some questions to verify what he is telling me.

My Idle speed seems high (1000 RPM) Shouldn't it be closer to 650 RPM or so?

My WOT tops out at about 3000 RPM. I would expect from what I was told and what I have read that it should be about 4200 to 4600.

My top speed was about 18MPH (according to GPS). I thought it should be closer to 25 (knowing this type of boat and its weight)

I believe part of my top speed issue was due to trim tabs that weren't working (and since have been fixed), and my assumption (please correct me if I am wrong) is that the trip tab issue shouldn't effect the low WOT. (if it is low).

I really didn't hear the secondaries open up and am wondering if that is where the problem lies.

Since I haven't looked, I don't know if the secondaries are mechanical or vaccum operated but will check tonite.

It doesn't appear to be starving for gas and doesn't stall, so for now I can assume that the fuel system is operating properly (with the exception of the secondaries).

How do I check the secondaries if they are vaccum operated without the boat being in the water. I have an internal hose connection but was told to not run it above idle with this setup.

Any thoughts or Ideas will be appreciated."
 
"WOT rpm should be 4200-4600.

"WOT rpm should be 4200-4600. verify the tachometer's accuracy, and verify speed with GPS. Low wot rpm usually fuel related (fuel pump, filters, plugged tank vent, faulty anti siphon valve at fuel tank) but could also be related to stuck/rusted advance weights in the distributor. Other common causes: waterlogged hull (flotation foam underfloor all full of water), wrong propeller pitch, low engine compression"
 
"OK, I can verify WOT with inf

"OK, I can verify WOT with infrared tach and will do that this weekend. I will change the filters as well this week.
I have a water seperating fuel filter and a filter at the line inlet to the carb. There is also a water seperating bulb at the fuel pump.

How is the best way to verify that the secondaries are operating properly? I was looking at it last night, and it seemed like there was something mechanically not allowing them to operate.

I can also do a tune up, what should the point gap and dwell setting be?

How can you tell if the advance weights are operating properly?

Thanks once again for making this boating experience one worth all the effort. The forums are so invaluable to us that have some mechanical knowledge, allowing us to perform some of our own service.

Michael"
 
"when you are changing points,

"when you are changing points, just look in at the weights and springs and do a visual...see if they are all rusty..common on boats as the bilge is so damp. Best to look for a factory manual on eBay for specs. or you can get a Seloc manual from this site. avoid Clymer manual
Bulb? there shouldn't be any primer bulbs in the fuel lines like an outboard... if that's what you mean get that out of there."
 
My grandfather used to call it

My grandfather used to call it a settling bulb. It is a glass (or see through) type device (seperator?) mine is located just off of the fuel pump.

Should I be able to move the advance mechanism with my fingers? I haven' tried yet but just wanted to know.
 
"ok..that glass in this case i

"ok..that glass in this case is not the same thing, it's there on a boat to catch fuel if your fuel pump diaphragm ruptures...where on a car, the gas would just spill on the ground it would be an explosion hazard on a boat. If you ever see gas in it, the fuel pump needs replaced. I dont know if you can move the advance with your fingers...never tried..you might break it"
 
"I will order a manual today,

"I will order a manual today, however i won't be receiving it for a few days. If anyone knows the point gap, and dwell settings It would be greatly appreciated. also what is a good recommendation for spark plugs? I may as well change them while I am in it up to my elbows as well.

May be doing the tune-up tonight.

Thanks"
 
"For a 1979 V8 Chevy,they do n

"For a 1979 V8 Chevy,they do not identify it by CID but by HP, 185/200/230/260 HP, all the same:
Dwell 30°
Points Gap .018"
Spark Plug RBL8 Champion
Plug Gap .035"
Fuel Pump pressure 7-9psi
Timing Marks Degree 7° except 260HP - 10°
Hope this helps."
 
"Herbert,

Thank you so much


"Herbert,

Thank you so much. My manual should be here soon. In the meantime the information is really appreciated."
 
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