Motor runs at higher RPM's with hood off

vranasaurus

Petty Officer 2nd Class
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Apr 18, 2005
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When I run my 1989 90 HP evinrude I can only get 4200 RPM's no matter what the load.<br /><br />If I take the hood off I can get 5000 RPM's and if I trim it up I can get 5200.<br /><br />Some times with the hood on it will get the 5000 RPM's. <br /><br />I am still trying to figure out how to get the WOT RPM's within the proper RPM range.<br /><br />What is going on here?
 

Basscat 1

Chief Petty Officer
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Feb 11, 2005
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444
Re: Motor runs at higher RPM's with hood off

Sounds like you may possibly have an exhaust leak that is flooding your engine with exhaust fumes.<br />How does the engine idle with the cover on vs. off?
 

vranasaurus

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Re: Motor runs at higher RPM's with hood off

idles basically the same.<br /><br />maybe a little smoother without cover.<br /><br />How can one go about checking for an exhaust leak?
 

Basscat 1

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Re: Motor runs at higher RPM's with hood off

It would probably be leaking between the adapter and the powerhead exhaust, or possibly around the exhaust cover on the rear of the engine.<br />Anyhow, mix some dishsoap with water in a spraybottle. Start the engine, and spray the soapy water around any of the exhausts gaskets or seals and look for bubbles.<br />Thats how I would do it, but somebody else may have another method.
 

DHPMARINE

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Re: Motor runs at higher RPM's with hood off

Has any recent repairs been done,and then this problem started ?<br /><br />DHP
 

vranasaurus

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Re: Motor runs at higher RPM's with hood off

just rebuilt.<br /><br />carbs everything, had a shop link and sync.
 

DHPMARINE

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Re: Motor runs at higher RPM's with hood off

Any chance the lower unit was taken apart,like for a reseal ?<br /><br />DHP
 

DHPMARINE

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Re: Motor runs at higher RPM's with hood off

pull the prop,look inside.You are looking at the bearing carrier.<br /><br />there is an anode bolted to it,that should be down,towards the skeg.<br /><br />is it up towards the engine ?<br /><br />DHP
 

vranasaurus

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105
Re: Motor runs at higher RPM's with hood off

I will have to look next time I go out.<br /><br />I don't know what you mean by anode.
 

vranasaurus

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Re: Motor runs at higher RPM's with hood off

Just returned from the lake.<br /><br />Anode is down toward the skeg.<br /><br />I couldn't find any exhaust leaks around the exhaust cover.<br /><br />That however is the only thing that makes any sense.<br /><br />Will I be hurting anything if I run it with the hood off until I can determine the problem?
 

vranasaurus

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Apr 18, 2005
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105
Re: Motor runs at higher RPM's with hood off

I've been researching this topic and found another problem could be the hood latch interferring with the spark.<br /><br />Does anyone know how to check for this?<br /><br />If I grab the hod latch with motor running and this is the case will I be shocked(I'll make sure I have someone holding my sign when I do this)?
 

umblecumbuz

Lieutenant Junior Grade
Joined
Sep 25, 2004
Messages
1,062
Re: Motor runs at higher RPM's with hood off

As an alternative, check this out:<br /><br />Most hoods have sound deadening material glued inside them. They also have an air inet towards the rear - often disguised as a grab handle. If the sound deadening (or any other debris) is partially blocking the air inlet, you're starving the motor.<br /><br />It doesn't take much. At WOT your motor needs a huge volume of air to mix with the gas. Restrict it even a little, and you could get the kinda result you describe.
 
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