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Discussion Starter · #1 ·
I have a '90 150 Johnson GT on a 19ft Bass boat recently the boat has been getting on plane really slow,most of the time I my passenger has to get on the bow to get on plane but once I get on plane it feels strong as ever....but my top speed has decreased alot also..when I first got the boat it would do over 60 but now 54mph is about all I can get...I have a 4 blade stainless prop....I also tried another prop that was brand new and it was a size smaller but it did not help....The thing is that the motor has always ran about 5500rpm WOT when it use to run 60 it did 5500prm & now when it only goes 50-54 it still runs about 5400-5500rpm......how can I lose that much speed and that much hole shot & still run those rpms??
 

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The speed loss may be due to a drop in the RPM and the hole shot due to engine power loss. Another possible is that the prop may be slipping, if is an insert type and you used the same insert for the new prop. I am not familiar with Johnson's design.

This could possibly be a fuel filter problem if it has not been replaced in a while. If not I believe that it is a fuel system issue.

I have a 60 Merc that had loss of power issue and I chased it to the fuel pump. Another issue I had was the check valve at the gas tank was sticking and starving the engine for fuel but the indication of this was the priming bulb was collapsing during operation.

An air leak could cause some issues. I have a clear tygon tube for a fuel line before the fuel filter (a convenient location to see it but close to the carbs) so you can see if there is air intrusion. My tygon tube gas been in place for 3 years and 3 fuel filter changes without a leak.

A few ideas to think about. It is a pain hunting this stuff down.

Rockonafly
 

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Discussion Starter · #3 ·
thanks Rockonafly...what you are saying makes sence but when I tried the other prop it did the same thing and it was brand new so I dont think its slipping...but the fuel thing is a good place to start looking thanks man
[grin]
 
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