Honda 5hp engine speed slows above 3/4 throttle

[Jo Beachy]

our 5 hp honda just had a new cylinder head installed, since then it has never gone to full power, engine speed increases until 2/3 to 3/4 throttle and then slows. Our max speed has dropped from 5 kt to 3.5 kt. We have returned it to the mechanic many times, compression check good, installed new carburetor, he has adjusted the idle... the sparkplug gets black with each use for one other clue. Anyone out there had the same problem?

 

[papasage]

Re: Honda 5hp engine speed slows above 3/4 throttle

sound like high speed jets . but new carb should be allright . does it have a ajustable high speed or fixed .
see if the butterfly opens all the way when leaver is pushed all the way . linkage could be out of ajustment .
try spraying gass mix into the carb while w o t see if it will help .

 

[deejaycee_2000]

Re: Honda 5hp engine speed slows above 3/4 throttle

I will also geuss high speed jets .....

 

[Jo Beachy]

Re: Honda 5hp engine speed slows above 3/4 throttle

sound like high speed jets . but new carb should be allright . does it have a ajustable high speed or fixed .
see if the butterfly opens all the way when leaver is pushed all the way . linkage could be out of ajustment .
try spraying gass mix into the carb while w o t see if it will help .

 

[Jo Beachy]

Re: Honda 5hp engine speed slows above 3/4 throttle

thanks for the suggestion. I think the high speed jet is fixed but will check. We have since replaced the coil but that did not help either. the choke might have been sticking open a little as the cable needed adjustment but have not yet rechecjked the spark plug to see if still black.

 

[Jo Beachy]

Re: Honda 5hp engine speed slows above 3/4 throttle

thanks for the suggestion. I think the high speed jet is fixed but will check. We have since replaced the coil but that did not help either. the choke might have been sticking open a little as the cable needed adjustment but have not yet rechecjked the spark plug to see if still black.

 

[Jo Beachy]

Re: Honda 5hp engine speed slows above 3/4 throttle

Hello again, I thought the solution might be of interest... after having the motor to the local Honda dealer 6 or 7 times and replacing the carb and coil, compression check and valves adjusted the motor was still running (laboriously) at 2/3 power. On a long trip it finally quit at a remote location in Canada. A trip to the nearest Honda dealership there revealed the tappet had come off! The motor is now back up to power and sounds happy. It is running better than it has in over a year. Hmmmm.

 

[Bolt49]

Re: Honda 5hp engine speed slows above 3/4 throttle

Hi, glad it worked out for you. My BF20 has the exact same problem. Starts fine, idle's fine, runs fine at low rpm's but has not top end and black plugs. Can you tell what exactly the tappet is? Thanks.