1970 80hp, will not rev up

[ozarkjeep]

Ive been working on this engine on and off for almost a year, im sick of it, and in need of some help.<br /><br />it starts and idles great out of the water, timing is set to max at around 21 degrees, linked and synched, throttle butterflies are opening all the way.<br /><br />it starts and idles fine in the water also, but when I give throttle it just barely speeds up, moves at a fast idle speed.<br /><br />I can hear when the carb butterflies begin to open, and I hear a bogging type sound, but it goes no faster.<br /><br />engine has 120 psi in all 4 cylinders, solid strong spark on all 4 cylinders, new plugs, new water pump.<br /><br />carbs were removed, totally cleaned out and reinstalled, I have moved the idle/mixture screws around trying to make it better to no avail.<br /><br />any advice is appreciated, IM ready to trash it and buy something else.

 

[KCLOST]

Re: 1970 80hp, will not rev up

Fuel line and bulb ok, filter?<br /><br />Fuel+compression+fire=combustion<br /><br />Leads me to believe you have a fuel issue based on what you have mentioned above...

 

[ozarkjeep]

Re: 1970 80hp, will not rev up

It could be KC,<br /><br />when I was testing on the water, the bulb was leaking a little.<br /><br />when I got home I replaced with all new hose, and new clamps, and fixed th eleak, but it still wouldnt rev up, not even out of the water.<br /><br />I could hear the butterflies open, but just no increase in speed.<br /><br />the engine has 2 fuel pumps, I took the top apart and cleaned and replaced the diapragm, it was new ( this engine had alot of work done before I got it), so I just popped ht ebottom fuel pump off and looked inside it, same deal looked like new parts, no junk in there, so I just reassembled.<br /><br />How can I test or verify fuel volume? all the plugs are wet with fuel after its been runing and I pull them, does this indicate anything?<br /><br />where is the factory filter? I have been runnign a filter inline with the fuel tank, but the tank is plastic, I dont think I found a factory filter on the engine, maybe I missed it?

 

[Chris1956]

Re: 1970 80hp, will not rev up

ozarkjeep, You may have a prop with too much pitch, or a boat that is too heavy, those motors will simply not rev up under too much load. <br /><br />For example, I had a Merc 1500 with a 23" pitch mercury prop on my 16' speedboat. I could plane quickly and had 50+MPH top speed. When I tried to pull a skiier, however, the motor would not rev past 2000RPM. I replaced the prop with a 21" Pitch prop, and I could pull two skiiers.

 

[Clams Canino]

Re: 1970 80hp, will not rev up

Yep.....<br /><br />-W

 

[dka1ser]

Re: 1970 80hp, will not rev up

I had a similar problem in my old Glastron, until I realized she had about 50 gallons of water trapped under the floor behind a 2nd drainplug in the bilge area. It would rev up fine in idle, but trying to plane would never get up the speed and just bog down, exactly the same symptoms as a over-pitched prop. <br /><br /><br />Does it rev to high RPMS while in neutral? You said it gets to "fast idle" but can you rev it at least with no load up to higher RPMS?

 

[booka]

Re: 1970 80hp, will not rev up

Ozarkjeep Did you pull the carbs right down? I found on my "78 850 I had the mixture screw too lean. It ran great at idle but wouldn't rev past 2000. Now for the fun part unless you have access to a test tank you need to find a dam/lake or still water to fix.Remove the wraparound and air box. Start the engine and bring it up to the point where it starts to playup. Now adjust the mixture screw on one carb until the revs start to pick up then adjust the other screw.I needed to go nearly 2 full turns. You may need to fiddle for a while but it's great when it comes on song! Good luck and cheers from Downunder