big twin will not throttle up in forward.help

[Hambone187]

i have a 1963 evinrude big twin 40 hp. the motor ran fine a month ago. i had to replace the shifter rod a few weeks ago. so i dropped the mid section from the powerhead, replace the part and put it back together. put it on the water a week later. and it will not throttle up in forward gear. it throttles up fine in neutral. any help would be greatly appreciated. iam not looking to spend a bunch of money on this motor, so iam hoping i can do this my self

 

[Daviet]

Re: big twin will not throttle up in forward.help

Running on both cylinders?
Spark and compression OK on both cylinders?

 

[Hambone187]

Re: big twin will not throttle up in forward.help

i know it has spark in both cylinders, i havent done a compression test. but it seem fine in neutral

 

[Hambone187]

Re: big twin will not throttle up in forward.help

i will get a compression guage here today and get back to you

 

[HighTrim]

Re: big twin will not throttle up in forward.help

Are you saying that it will mechanically/physically not throttle up in gear....

OR that is just sputters and you have no power?

 

[Hambone187]

Re: big twin will not throttle up in forward.help

i had a mechanic look at it and he couldnt figure it out. when its on the water it runs at 1/4 its normal speed. sometimes it kicks in for a second or 2 and then goes back to running slow. any thoughts?

 

[Hambone187]

Re: big twin will not throttle up in forward.help

i did a compression test. both cylinders are at about 120

 

[Bigkat650]

Re: big twin will not throttle up in forward.help

Sounds like a poor spark in 1 cylinder. If you are sure its not the plugs or the wires, it could be a bad coil. Might have a bad coil that is sending a real weak signal to one of the spark plugs. You can check them visually, they are under the fly wheel--if they look old, weathered or cracked, they may need to be replaced.

 

[Hambone187]

Re: big twin will not throttle up in forward.help

thanks that will be my next plan of attack

 

[matth121]

Re: big twin will not throttle up in forward.help

i had a similar issue with a new to me motor- ran great in the barrel, nothing on the water. for me it turned out to be my carb- high speed needle was out of adjustment. Anychance it might have gotten moved while you were servicing it? all i had to do was gently seat it, back it out 3/4 of a turn, then while in gear at WOT slowly adjust back in until revs start to drop, then back out 1/8th turn. Running great now. Might not be your problem but worth a look. i'd mark its position and then turn it in and count- if you get one full turn- it's too far out, if you find it's set correctly, just back it off until you reach your mark, no harm done. Good luck

 

[matth121]

Re: big twin will not throttle up in forward.help

also, just as an FYI- everything thats been suggested to you was also suggested to me in a thread i started- http://forums.iboats.com/showthread.php?t=556633
everything suggested checked out ok so it lead to the carb. Some pics of the carb if it helps, not sure yours is the same but probably is

 

[Hambone187]

Re: big twin will not throttle up in forward.help

i replaced the coils and the condensers and the plug wires and it works much better. not sure if its running at 100% yet but its runni9ng 2 or 3 times faster than it was. thanks so much for all your help.