Half power under load!?!?!?!?!

[dennyjd]

My 1974 Johnson 9.9HP will run GREAT in nuetral. Even at mid to idle throttle, in gear, she run's like a champ! The engine is in EXCELLENT shape (re-work, new components, etc...). I have it on a 17' all alluminum semi-v Fisher. At full throttle, it seems to be "bogged" down. Power is extremely weak. Only running at about half the rpm's. I would think that the engine would rev up to its max, even under a load.?.? Could this be a prop. issue? Are there adjustments in the carb for this? Maybe just too much for it? Any suggestons would be extremely helpful. <br /><br />Thanks for the time!<br /><br />MOD#10R74S<br />Serial#E3955289

 

[The Marine Doctor]

Re: Half power under load!?!?!?!?!

You might try a lower pitch prop...even large engines will not get up to max RPM's if the load is too large.<br /><br />TMD

 

[Solittle]

Re: Half power under load!?!?!?!?!

TMD has it nailed. I have a 75 9.9 on a 13'. It will lug until it gets over the step on plane and then you can hear it max out. Your 17' may be a bit much for a 9.9 even with a lower pitched prop - depends on the load and the distribution of the load.

 

[dennyjd]

Re: Half power under load!?!?!?!?!

I think I may have figured it out. I pulled both spark plugs and only the top one looked like it was firing. I checked for spark and the bottom one was not getting any. Pulled the coil off and it seems to have had a bad ground! Did a little filing to make better contact, and there was spark!!! Haven't had a chance to run it yet, I may tonight. Thanks for the reply's, I will let you know what happens. <br />Thanks again!!

 

[dennyjd]

Re: Half power under load!?!?!?!?!

Well I ran it last night and there was not much change. I am really thinking that the boat may be just too much for it. The prop is in pretty bad shape, am I wasting my time with buying a new one? Am I going to see a significant change worth spending the money for? Also, I ran it up the river wide open for about 1 mile. Shut it down did a little fishin, then tried to fire it back up. Never could get it started again. Any suggestions? <br />Thanks

 

[boso]

Re: Half power under load!?!?!?!?!

DennyJD, look at the coils again. If the isolatio is cracked, you have to change them.