1978 Evin 70HP starts and runs great but after 10min or so bogs

BMinder

Cadet
Joined
Aug 23, 2024
Messages
7
(I just searched thru the forums and didn't find answers) Just got this boat, put fresh fuel in, took it out, started pretty easily, sounded good, ran good at WOT but after about 10 minutes it bogs down and won't go past idle. Changed plugs, put new tank and fuel line and same result. The ball is firm while its bogging, choking doesn't help. Pulled the plugs, no water in the holes.
I took the air box off and removed the bowl drain bolts, all 3 carbs had gas. Sprayed carb cleaner in. With the drain bolts off I pumped the ball and plenty of gas came out all three carbs. (I did them one at a time)
Anything else to check?
Things I've read are possibilities:
- Exhaust leak filling up the hood and starving it from O2, haven't ran it with the hood off.
- A coil going bad when it gets warmed up
- The engine is worn out so runs good when cold but as it warms up tolerances get too much and is losing compression
Ideas?
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,111
Post the actual compression values that you have now.-----Did you install a new impeller ?---Have you tested the overheat horn ?
 

BMinder

Cadet
Joined
Aug 23, 2024
Messages
7
I’ll do a compression test.
I don’t know if it has a horn or where it is.
Water is shooting out the pee hole very strong
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,111
Find the tan wire near top of cylinder head.-----Slide rubber boot away to expose metal connecter.----Turn key to ---" on "----Touch connecter to a head bolt.-----Horn should sound.
 

BMinder

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Joined
Aug 23, 2024
Messages
7
Find the tan wire near top of cylinder head.-----Slide rubber boot away to expose metal connecter.----Turn key to ---" on "----Touch connecter to a head bolt.-----Horn should sound.
Yup did it and horn sounded at control box
 

BMinder

Cadet
Joined
Aug 23, 2024
Messages
7
Just did a compression test, cold motor. 125, 90, 125
Will that 90 cause the symptoms of losing power after it warms up?
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,111
Motor has a blown head gasket if you are lucky.-----Likely a scored cylinder and time for teardown and rebuilding.
 
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