1978 Johnson 70HP Power Loss when accelerating and die

[caio]

I have a 1978 Johnson 70hp which looses power when throttling forward. <br />The engine dies when put in gear forward or reverse and it doesn't have power to leave <br />The carbs have been rebuilt, the compression are 105, 102 and 103 <br />When I get to leave the boat reaches 35 miles, the problem only happens in low rotation <br /> <br />Any advice would be appreciated, thanks.<br />Caio.

 

[OBJ]

Re: 1978 Johnson 70HP Power Loss when accelerating and die

Goodmorning Caio.<br />Let's start with some basic stuff. Did you rebuild the carbs or did mech do the work? Have you checked the fuel lines for air leaks? The fuel hoses on these older girls tend to get very stiff from the fuel will leak very easily. Primer bulb in good shape? When you pump the bulb up, does it pump up firm? Gas tank vented? Fuel line from tank to motor in good shape? Was the low end sync and link checked out? If you don't have a OEM service manual, this may be something a regular mech might need to do. Since the engine does start, I will assume the ignition system is working OK. Does it idle smoothly? Have the carb low speed needles been adjusted correctly? (I believe the 78's still had needles. If not, just disregard this part) Keep us posted on latest happenings. Good Luck.

 

[caio]

Re: 1978 Johnson 70HP Power Loss when accelerating and die

Jim, thanks for your help and I'm sorry for my english. I checked all your instructions. <br />I my self rebuilt the carbs. I haven't found air leaks. The bulb is in good shape and it pumps up firm. The gas tank is vented, and the fuel line from tank to engine and the low end sync and link are ok. <br />I don't have a manual yet. Can you recommend a tune-up manual for me to buy? <br />This engine does not have needles. I found only one fixed needles (I don't know the correct name in english, in Brazil we say "gicle", it's like a screw with a hole in it) on top of the carbs, but I don't know if is the low or high speed. I think there is another "Fixed Needles", but I don't know where it is. <br />Is there a chance this problem be in the "energy system" that in low rotation does not produce enough energy for the spark plugs ?

 

[JB]

Re: 1978 Johnson 70HP Power Loss when accelerating and die

Hello, Caio.<br /><br />When you reinstalled your carbs did you set the idle speed with the engine under load or on the hose?<br /><br />Idle speed must be set under load or. . . . you will get exactly the symptoms you describe.<br /><br />Good luck.