Low RPMs?

[GlasstronJim]

Hello, I have a 1975 70hp johnson on a 1975 Glastron fishing boat with a 13.75x15 prop. I wanted to get a 13.25x17 prop but everyone I talk to says I need more rpms. I am running about 5000 now. My question is what tricks do you seasoned boaters know that I can try, if any?

 

[JUSTINTIME]

Re: Low RPMs?

u will be around the same or even lower rpm

 

[mikesea]

Re: Low RPMs?

what are you aiming to do,get more speed?out of hole quicker?get more rpm from the eng.?

 

[emdsapmgr]

Re: Low RPMs?

You will loose speed and rpms by switching. The rpms will decrease by nearly 300, putting you close to the point where you are lugging the engine. You should be looking at a 13 to get the rpms closer to 5500.

 

[Dhadley]

Re: Low RPMs?

Personally we only look at reducing pitch as an absolute last resort to gain rpm. We'd start by verifying that the motor is healthy and running on all cylinders at all times.

Depending on which Glastron it is, you may have the right prop now but need to change the set up and / or get the motor running right.

Let's start with the basics. Take a compression test and then look at sync & link to make sure everything is going to full advance. If the compression and s&l are OK, look at the timing. Make sure it's correct.

Don't spend money on a prop just yet.

 

[GlasstronJim]

Re: Low RPMs?

Thanks,everyone everything ok now got a new 13.75x15 Hustler alluminum prop. the michigan wheel prop that was on it was beat up.Should gain back rpms, maybe a few knots watch out when the ice melts.