Low RPM and low SPEED on '90 90hp Force

[Beamerman1]

Hi all,<br />I'm new to boating and this board. I read many post here and most advises are awesome. So, here are my issues. Recently bought a used Pontoon, it is a 1990 Grumman Funship with a Force 90hp Engine. It starts up great and idles quiet. <br />1) First time running on the lake, at WOT, it only registered ~4200RPM and its speed at about 15mph.<br />2) When pushing throttle lever forward, engine does not do much untill the lever is about 1" from max WOT. Shouldn't it pick up speed smoothly through its full range from N to F? Can a cable be adjusted?<br />3) Third time on the lake the speedometer stopped showing the speed, but RPM's still remained same.<br /><br />Currently it has a 3 blade prop, but I'm not sure what it's size or pitch is. Someone suggested that I replace it with a smaller one. Would that help me raise the RPM's and gain some more speed?<br /><br />Thanks for all advises in advance.

 

[jim dozier]

Re: Low RPM and low SPEED on '90 90hp Force

You probably need to verify that the engine is running right before you buy a new lower pitch prop, but if the engine is running right you do.<br /><br />Verify that it is running on all cylinders. Verify that the throttle on the engine (not the throttle in the cockpit) is fully opened. Veryify that both the ignition timing is fully advanced at WOT and verify that all the carb throttle plates are fully open (parallel to air flow) when the throttle linkage is WOT. You may find that you need to synchronize the timing advance and the carb linkages.<br /><br />Get a manual.<br /><br />My guess is you need a different prop.

 

[Beamerman1]

Re: Low RPM and low SPEED on '90 90hp Force

Thanks for the suggestions Jim, I will check that next time I head to the lake. Also, any suggestions regarding the speedo?<br /><br />Thanks again.

 

[roscoe]

Re: Low RPM and low SPEED on '90 90hp Force

Speedo? Yeah, buy yourself a $79 gps unit if you are concerned with your speed. Most boat speedos are terribly inacurrate and you have no way of knowing if it is off by 5mph or 15 mph.

 

[force01]

Re: Low RPM and low SPEED on '90 90hp Force

You are pushing a pontoon boat through the water which takes a great amount of horse power. The reason your boat takes off with the last inch of throttle is because of the way the throttle cam is designed you are on an economy range until the last 20% of the cam, which finally opens up your throttle butterflies so that is normal for a pontoon boat. Your speedo is just clogged with debris clean it out with a very small drill bit. You want your top rpm @ 5200 WOT not 4200. Bret<br /><br />If you need further assistance please email me @ forcepower01@yahoo.com. thanks,Bret

 

[Beamerman1]

Re: Low RPM and low SPEED on '90 90hp Force

Thanks Roscoe and Bret.<br />- Bret, is there a way to adjust the throttle cam off the economy mode? Two friends of mine have pontoons as well, (18' Suntracker w/25HP motor(don't remember brand) and 24' Lowe w/75HP Evinrude) both do not have that "economy mode" because their boats accelerate gradually through the full range of the throttle lever. Is that only on Force? Also, I kind of "raced" my friend with the 24' Lowe w/75HP Evinrude and his pontoon left me in the dust (sort of speak). I don't know what kind of prop his motor has.<br /><br />Thanks in advance again.

 

[force01]

Re: Low RPM and low SPEED on '90 90hp Force

Beamerman,<br />You should have someone check the adjustments for your carburation to make sure everything is set up correctly. have you played with your trim while running the boat? More you trim the motor up the faster is should run. bret<br /><br /> If you need further assistance please email me @ forcepower01@yahoo.com. thanks,Bret

 

[Beamerman1]

Re: Low RPM and low SPEED on '90 90hp Force

Force1,<br />I have tried to adjust the trim. As it was moving up the RPMs were fluctuating but only very small amount (~25-50). It just looked like the guage needle was shacking a bit, but never went above 4200. It only went above 4200 when I raised it up too high (above the sea level) since I do not have the trim guage.<br />In the previous post you mentioned that I can clean out the debris with a very small drill bit. I have not picked up the manual yet, can you please let me know where the slot is that I need to clean out.<br /><br />Thanks again for your suggestions...