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1974 70hp johnson no full throttle

zip63

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"model # 70 esl 74m,been worki

"model # 70 esl 74m,been working with this for about 2 weeks now.the problem is it idles and runs good at half throttle ,when i put in full throttle it goes about 10 to 20 secs great,then it surges or cuts in and out.had carbs done.changed fuel line from tank to motor,i left the breather plate off and put it in water ran great ,took it back home put the plate on,now it is surgeing again."
 
welcome to marineengine!!

i


welcome to marineengine!!

it ran great without the air silencer??.......did you have the hood off or on?

you may have a bad gasket allowing exhaust fumes to choke your eng.
 
"I assume that this engine ran

"I assume that this engine ran fine in the past and has the original carburetors installed? If so, have the high speed jets been replaced with larger ID jets?"
 
"thanks for the help.yes,the e

"thanks for the help.yes,the engine has ran fine in the past.It has the original carbs same jets as far as I know.ok,took it back out with the breather plate off,now it is doing the same will take off good then go down to about half speed.I put it in neutral for about 10 seconds,full throttle it again for about 30 seconds run great then goes back to half speed.To me it seems like it is running low on gas but thats why i am here thanks for all the help."
 
"how would i go about checking

"how would i go about checking the fuel pump?I pumped the bulb it didn't seem like it help,if it did it was very little couldn't tell a differance."
 
"Thanks Joe,when ichoke at ful

"Thanks Joe,when ichoke at full trottle it don't seem to do nothing ,i choke at half trottle it seems to boug down.If it is not fuel related then would the impellar make it do this,havent changed it a couple of years.I am confused!If a coil was bad would it be doing like this?"
 
Remove drain plugs screws from

Remove drain plugs screws from float chambers to determine if fuel is actually obtaining access to the float chambers.

Check compression.... what are the readings?

S/Plugs removed. Spark should jump a 7/16" gap with a strong blue spark on all cylinders. Does it?
 
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