Rage OMC 115 Jet Boat: Eight Questions

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Chris640
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Joined: Wed Jul 13, 2022 5:05 pm

Rage OMC 115 Jet Boat: Eight Questions

Postby Chris640 » Wed Jul 13, 2022 5:09 pm

ENGINE IDLE SPEED

The OMC 115-HP engine on my RAGE [of unspecified year and model designation] idles between 850 and 1,000-RPM. [The engine idle speed] is suppose to be higher [than 850 to 1,000-RPM].

A loud helicopter thud is head in the "lower" [engine idle speed range].

I have adjusted the engine idle speed by rotating the idle screw all the way [in an unspecified direction]. [The engine idle screw] is not resting on the metal plate to increase the idle RPM.

Q1: what [actions need to be performed to increase the engine idle speed to an unspecified higher engine idle speed]?

Q2: should I buy a longer idle screw?

Q3: is there another adjustment [to alter the engine idle speed]?

FUEL HOSE IN-LINE PRIMER BULB

Q4: when the engine is to be started, should the in-line primer bulb in the gasoline fuel line be pumped until the bulb becomes hard?

My belief was the in-line primer bulb did not need to be pumped at all because the engine has a fuel pump.

My observation is the engine will not start unless I pump the primer bulb four to six times.

MISSING CHOKE CONTROL

Q5: is an engine choke control supposed to be at the helm console?

I can not find an engine choke control on the helm console.

WHITE SMOKE and GASOLINE SHEEN ON WATER

White smoke appears in the exhaust and an oil sheen appears on the water near the engine.

Q6: is the appearance of white smoke normal for a RAGE 115-HP engine?

Q7: is the appearance of an oil sheen on the water normal for a RAGE 115-HP engine?

FRESH WATER FLUSH KIT

A fresh water flush kit installed. When I attempt to run the RAGE 115-HP engine "off the hose" the engine stalls.

Q8: how much water pressure should the hose provide?

If help is given I will appreciate the help.

Thanks!

jimh
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Re: Rage OMC 115 Jet Boat: Eight Questions

Postby jimh » Wed Jul 13, 2022 6:06 pm

Hello--asking EIGHT questions in one thread is very awkward. Please use a separate thread for each group of questions.

To learn about starting the engine, read the instructions in the owner's manual. Every engine has its own method of fuel enrichment for starting from a cold engine. If the engine is in good tune and has not been hacked up by some previous owner, it should start easily and reach the proper engine idle speed. It is typical that the engine will run at a fast idle speed after initial start from cold. When the engine detects that it has warmed up to normal temperature, often about 140-degrees-F, the engine will adjust its idle speed to a normal idle.

The OMC 115-HP engine in the RAGE is probably a two-stroke-poewr-cycle engine, and it was designed long before the Environmental Protection Agency decided that its purview include regulation of spark-ignition marine engines which began in the early 2000's. So the engine exhaust gas emission is not particularly as clean as a 2022 engine that meets all EPA requirements in force now. To have some unburned fuel in the exhaust is normal for an old two-stroke-power-cycle engine.

The purpose of a primer bulb is, as you have already discovered, to help the engine start. If you have a really good battery and enjoy listening to the engine crank over and over for a minute or two, it might eventually start without the fuel primer being used to prime the fuel system. HINT: open carburetor fuel induction systems are prone to gasoline evaporating. If the boat sits without the engine running for a month, most of the gasoline in the engine fuel system will have evaporated. That is why there is a primer bulb.

The forum does really attempt to provide instruction in the basics of theory of operation of old two-stroke-power-cycle engines, and I recommend you find a good book--or even just the owner's manual and even better the factory service manual--to learn more about your engine.

Also, the engine was made by OMC. The OMC corporation went bankrupt in c.2002. This might explain why the engine is not as sophisticated as modern c.2022 engines, does not start immediately, produces some smoke, and its exhaust may contain some unburned fuel.

Chris640
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Joined: Wed Jul 13, 2022 5:05 pm

Re: Rage OMC 115 Jet Boat: Eight Questions

Postby Chris640 » Wed Jul 13, 2022 6:16 pm

Thank you. This is the first time I have ever posted in a [discussion forum]. Thanks for the advice.

Don SSDD
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Re: Rage OMC 115 Jet Boat: Eight Questions

Postby Don SSDD » Thu Jul 14, 2022 4:55 am

The engine choke control was often engaged by pushing the ignition key in while the starter is engaged. If your ignition key switch can be pushed inward and springs back out, that is the "choke."
1986 Outrage 18 with 2001 Honda 130 HP
Former Owner 1991 Guardian 19 with 1994 Evinrude V4 140HP
Former owner 1987 Montauk with 1998 Mercury 90HP
Nova Scotia

jimh
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Re: Rage OMC 115 Jet Boat: Eight Questions

Postby jimh » Thu Jul 14, 2022 8:26 am

DON--very good advice re the push mechanism on the ignition key swtich.

The "choke" on an older OMC two-stroke-power-cycle carburetor engine was typically an electrically controlled fuel-enrichment mechanism that permitted a higher concentration of fuel to air in the fuel-air mixture (often called a "richer" or more properly an enriched mixture) during engine cranking. In the OMC it was rather brute force; a solenoid opened a valve that let raw fuel into the airstream into the combustion chambers.

The usual choke is a throttle plate that closes to reduces the air flow, which also tends to enrich the fuel-air ratio. Outboard engine carburetors usually do not have a choke mechanism on the throttle plate.

On the other hand, a marine engine, particularly on a boat that is a small sport boat like a RAGE, is normally only being started in rather warm air temperatures, probably at least 70-degrees-F or warmer. At that temperature an enriched fuel-air mixture may not be necessary for starting. For the several years I had a six-cylinder carburetor Evinrude two-stroke-power-cycle engine, and I cannot recall ever once using the fuel-enrichment switch to get it started. In boating, starting a "cold" engine is not quite like trying to get an engine to start on a cold February morning in northern Minnesota.

Don SSDD
Posts: 313
Joined: Fri Oct 23, 2015 6:58 am
Location: Nova Scotia

Re: Rage OMC 115 Jet Boat: Eight Questions

Postby Don SSDD » Fri Jul 15, 2022 5:10 am

My old Evinrude 140-HP two-stroke-power-cycle [carburetor] needed lots of choke on first startup after sitting a few hours, no matter what the air temperature.
1986 Outrage 18 with 2001 Honda 130 HP
Former Owner 1991 Guardian 19 with 1994 Evinrude V4 140HP
Former owner 1987 Montauk with 1998 Mercury 90HP
Nova Scotia

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Rage OMC 115 Jet Boat: Eight Questions

Postby jimh » Fri Jul 15, 2022 8:02 am

Re engine starting with carburetor two-stroke-power-cycle engines: in many engines the carburetors will spill fuel when the engine was tilted up to a horizontal position. Of course, with an inboard engine in a RAGE, the engine power head never moves, so spilling fuel from carburetors due to tilting up just won't occur.

In my experience, as long as all the carburetors had fuel in their carburetor bowls and the fuel line was properly primed, the engine was amazing good about starting. Again, that experience is from very moderate air temperatures, never lower than maybe 60-degrees on a cool morning.

Spark plugs that are at the proper spark gap and are not fouled also help with rapid starting. Older engines use spark plugs whose electrodes will erode with use, and they often used rather high spark voltages. Erosion of the spark plug gap was noticeable after perhaps just 50-hours or engine run time.

Modern engines today use spark plugs with exotic metals at the tip of their electrode, and those spark plugs can easily last for 300-hours of operation without erosion of the spark gap.

Taming on old OMC carburetor engine requires the fuel, air, and spark are all just right.

Another important part of starting procedure: in some OMC engines the throttle position for starting should be at the NEUTRAL detent. If the engine throttle is advance from the idle detent before starting, the engine's normal starting settings are abandoned. Many people think every two-stroke engine needs to have the throttle advanced during starting, but on my 1990 V6 engine, that was a no-no. If you fiddled with the throttle setting the engine became awkward to start and run. If you left the throttle in the neutral detent--which is exactly what the operating guide instructed to be done--the engine would start beautifully. This is why I recommend that the operating guide actually be read--be read carefully and thoroughly--so the operator will follow the exact starting procedure recommended.