84 100hp Evinrude HELP!!!

[BDP40]

I have 1984 100hp Evinrude. It runs pretty good in the driveway. When i take it out in the water, it idles fine. I throw the throttle down and it takes off and gradually raises rpms, then after 20 seconds it drops down to about 2,000rpms and is barley moving. If i let it go like that for 10 more seconds it jumps up to about 7,000 RPMS again..it repeats..HELP!!! PLEASE.


(&)=7,000 rpms
(_)=2,000 rpms

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[iceman121]

Re: 84 100hp Evinrude HELP!!!

Mine did the same found it to be a bad power pack.

 

[emdsapmgr]

Re: 84 100hp Evinrude HELP!!!

Could by syptoms of a weak fuel pump. The engine may be consuming the fuel faster than the pump can supply it. You will get that rpm variance scenario you describe. Try constantly priming the fuel hose bulb. If it runs full speed while constantly priming the bulb, consider replacing the fuel pump.

 

[BDP40]

Re: 84 100hp Evinrude HELP!!!

I did change the fuel pump and it didnt change anything. When i pump the ball constantly it runs at maybe 4,000 rpm's constanly but only when i turn the red knob on the automatic choke all the way to the left. Its so wierd. Couold it be the reeds???

 

[BDP40]

Re: 84 100hp Evinrude HELP!!!

I also cleaned the carbs and they were as clean as a whitsle. I cleaned them very well with a compressor and small wire through all the jets. I cleaned all the fuel lines and made sure none of them were kinked and i also replaced the fuel line from the gas tank to engine. Yes, my valve is open on my tank and the sending unit is in great shape. I just replaced the fuel pump and did a compression test. The cpmpression is at 119-120 in every cylinder. All the coils are good. Just changed the plugs and wires. I checked them for spark and they are good from what i can see. The only thing i can think of is the automatic choke or the reeds. It is def. a fuel problem, when i pump the ball it runs at a constant rpm, but even then only at 4,000 when it should be at 6500 to 7000. Someone please givvv me an idea. I would be so greatful!!! Thanks

 

[emdsapmgr]

Re: 84 100hp Evinrude HELP!!!

You should be looking to 5500-5600 as the target max rpm on that engine. A couple of things to check when the engine starts to act up by dropping rpm's. I'd shut if off and check all 4 plugs and compare them to each other. Are any dry, or wetter than the others...? Also, when it only runs 2000 rpm, put an inductive timing light on each plugwire and check for spark in the flashes from the gun. An engine will run on 2-3 cyls just fine in the driveway. It's another story when the engine is buried deep in the water and in gear. It may run fine when cold. Weak ignition components tend to fail when the engine reaches normal operating temps.