1979 55 hp motor problem

[Jaydd0531]

I bought a very clean 79 55 hp from a friend that wouldn't crank. I replaced the coil packs and spark plugs and new starter. Cleaned the carbs and a new water pump and got it running. Runs good pees real strong. Took it out a couple times and ran good but last two times I took it out I ran it longer and once I got it warmed up at half to full throttle the rpms go up and down then it cuts off. Runs fine till it gets warmed up every time and it will run at low rpms fine. Not sure if it has a overheating alarm. I don't know what to do. Not sure if it's electical or it's overheating. The motor is hot but I can hold my hand on it and it doesnt burn me. Maybe thermostat is bad.

[Joe Reeves]

Does the fuel primer bulb have a tendency to go flat? If so, that indicates a fuel restriction between the primer bulb and the fuel supply.

If the primer bulb is okay, have someone constantly pump it while underway (acting as a manual fuel pump). If this corrects the problem, the fuel pump is most likely faulty.

Let us know what you find.

[Jaydd0531]

Ok I will try that. Would the fuel pump stop working from the motor being hot because it works fine the first 5 minutes running then rpms go crazy and it shuts off if you stay in the trottle but it will stay running if you let off.

[Joe Reeves]

You didn't answer my question?

Does the fuel primer bulb have a tendency to go flat?
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You can check the overheat warning system as follow:

Have the key in the ON position (engine NOT running). Find the TAN wire protruding from the cylinder head and ground it to the powerhead. This should cause the warning horn to sound off constantly... Does it?
*******************

It's possible that you have a fuel restriction. Check as follows:

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

[Jaydd0531]

I don't know if the bulb goes flat. I'll check today. The gas tank is a use plastic12 gallon. I cleaned it out as best I could. I didn't check the hose going into the tank. I'll let you know. Thanks for helping

[Jaydd0531]

Bulb doesn't go flat while I'm running the motor I took the wire off of the thermostat tried to ground it I get no noise even tried to do it while it was running and it didn't do anything to the motor. Can't get it to act up while running it on the water hose in the yard only does it when I drive an hour away and take it out in the water

[Joe Reeves]

Originally posted by Jaydd0531 View Post

Bulb doesn't go flat while I'm running the motor I took the wire off of the thermostat tried to ground it I get no noise even tried to do it while it was running and it didn't do anything to the motor. Can't get it to act up while running it on the water hose in the yard only does it when I drive an hour away and take it out in the water

I was thinking you had a built in tank. A used 12 gallon plastic tank would probably have no effect on the fuel primer bulb... BUT... keep in mind that air must be able to get into the tank in order for fuel to get out. A closed vent would result in a fuel restriction after running for a time, especially at a high rpm.

[Jaydd0531]

I have the valve open on the cap to let air in. Can the thermostat shut the motor off if it's to hot or does it just sound an alarm to tell you?

[Jaydd0531]

It only does it it the water when it's hot and it keeps doing it till I wait a bit then it does it again after a few minutes. That's the only constant. Runs fine first 5 minutes. I feel like it has to do with the heat.

[Joe Reeves]

Originally posted by Jaydd0531 View Post

I have the valve open on the cap to let air in. Can the thermostat shut the motor off if it's to hot or does it just sound an alarm to tell you?

The thermostat cannot shut the engine down.

Have the key in the ON position (engine NOT running). Find the TAN wire protruding from the cylinder head and ground it to the powerhead. This should cause the warning horn to sound off constantly.

If the horn does not sound off, find out why as that is the only warning you will receive before the engine overheats to a point whereas it seizes up and comes to a screeching halt!

The horn should be inside of the OMC control box... OR... under the console if you're using a console type remote control a$$embly. The wiring would be a PURPLE wire from the "A" terminal of the ignition switch to one of the slide on terminals of the horn... and a TAN wire from the other horn slide on terminal to the heat sensor you'll see at the top portion of the cylinder head.

[Jaydd0531]

Just checked the gas tank again and the air valve wasn't opened enough so that's most likly the problem. I'm still working on the thermostat alarm

[Jaydd0531]

I got the alarm working it just needed to be cleaned. I looked at the gas tank and the air valve wasn't opened enough so I think that's the problem. Thanks for the help. I'll let you know when I run it in the water next weekend.

[Joe Reeves]

Originally posted by hoahoihong1985

Website: Hoa Hồng 24k, Hoa Hồng Mạ V�*ng 24k, Hoa Hồng Sáp - CALL 0966 85 0966 (zalo , viber...)

Buzz the Hell off fellow or I'l tell everybody what you were doing on your knees with that homo out behind the hen house!

[sunrisehimlam]

Đất Mặt tiền HTP nh�* bè 5*40 thổ cư 154m2 giá 3,9 tỉ tluong chút tiếp khách thiện ch�* MTG -QC, Lhe Mr Tâm 0936386879

[sunrisehimlam]

Đất Mặt tiền HTP nh�* bè 5*40 thổ cư 154m2 giá 3,9 tỉ tluong chút tiếp khách thiện ch�* MTG -QC, Lhe Mr Tâm 0936386879