E-Rude '83 70hp: Engine loses power above 4900rpm?

I have an Evinrude 1983 70hp on my 14' McKee that I restored. The motor runs pretty well for the most part. I installed a Tach and found my RPM's to be too low. The motor gets up to about 4900prm (30-31mph) and when the throttle is pushed beyond that it hesitates/bogs/chokes...not really sure how to describe it but it loses power. Is this normal for a motor to bog if the throttle is pushed too far? It begins to lose power yet there is still more room for the throttle to go forward. I was hoping to get to the bottom of this as I need a new prop, but cannot begin to choose a prop before I determine my RPM @ WOT.

Thanks in advance!
Matt
Greensboro, NC

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

If your engine has choke flaps in the carbs make sure they are adjusted equal, sticking straight out not pointing up or down. That can throw things off and may cause your problem. Sounds like the flaps are over centering at open throttle. This will cause the engine to bog at open or near open throttle I beleive.

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

Is the tach correct ???

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

linc n sinc, fuel restriction, weak fuel pump.

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

The tach should be correct. The pulse setting is correct, but I was hoping to check it against the true rpm and calibrate. The rpm:mph seem about right. If it were making WOT rpm's I would expect it to be making closer to 36-38mph per other's experience with this hull/engine/prop combo. Definitely a concern on the tach though.

The engine has been gone over pretty well. The link n sync was done, fuel pump rebuilt and all fuel lines replaced. Carbs rebuilt and cleaned. I had the L/U dropped and water pump rebuilt and seals replaced. My mechanic stated that the L/U would need replacing soon as it was in pretty bad shape. I don't know if this could be the culprit but I am on the lookout for a decent l/u to replace it with.

It's not a gradual thing. When the throttle gets past a certain point it's as if it hit's a wall and the power drops a good bit, once you back of the throttle just a bit it pulls hard again?

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

is the engine reving higher, and speed not picking up. or does it seem like the motor revs are slowing. the throttle butterflys, may be going past horizonal, and starting to close the other way, thus sort of flooding the motor. remove air silencer, and work the controls, what the butterfly.

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

tashasdaddy said:

is the engine reving higher, and speed not picking up. or does it seem like the motor revs are slowing. the throttle butterflys, may be going past horizonal, and starting to close the other way, thus sort of flooding the motor. remove air silencer, and work the controls, what the butterfly.

Click to expand...

The revs drop and it feels like it's flooding. You and Maxum are on the same page here. I'll get in the shop this evening and have a look at it. Thanks for all the help guys.

Re: E-Rude '83 70hp: Engine loses power above 4900rpm?

you should have 2 sets of butterflys. from the front the 1st one is the choke butterfly, normal position completely horizonal, it closes to choke the motor for starting. the second is the throttle butterfly, it should only go to horizonal, if it is going past, it is cutting the air flow, effectively flooding the motor.