power loss

[minocqa]

hi<br />i have a 1976 70 hp johnson<br />i have owned it since it was brand new.<br />what the motor is doing is <br />it starts overtime it just doesn't have power. about 6 MPH<br />sometimes at full throttle you can hear the RPMs (i don't have a tachometer so all i can do is hear the different increase in RPMs) and the boat will run great until i slow back down. then it wont speed up again<br />I changed the fuel line with a new one<br />i checked the fuel screen on the fuel pump and it seems fine<br />The vents on the gas tank are open.<br />And changed the spark plugs...... I'm stumped<br />thanks<br />Don

 

[Solittle]

Re: power loss

Sounds like a prop that needs to be rehubbed. If you have a spare or can borrow one give it a try.

 

[minocqa]

Re: power loss

so little<br />what do you mean the prop may need rehubbed?<br />what is the hub?<br />i'm confused<br />Don

 

[DJ]

Re: power loss

Don, <br /><br />The prop has a rubber hub in between the hub (that is attached to the output shaft) and the actual part that has the blades on it.<br /><br />If that rubber hub degrades, over time, the prop will "slip". Not unlike a worn out clutch on a manual transmission car.

 

[tr918]

Re: power loss

Guys,<br />I have a 1972 65HP Evinrude that is doing the same thing. I checked the compression, replaced the fuel line and spark plugs. I also put a spark tester on it. I got the spark to jump beyond a half inch. <br />Is it possible that it may be the hub? If you remove the Prop can you see the condition of the Hub?

 

[BF]

Re: power loss

hi guys, <br /><br />for both of you with the similar (?) problem... from what you've said, I can't tell if it'd be the hub or not... when the boat slows and/or is hard to get on plane, is the engine rev'ing up high?? Or does it sound loaded up, like it's bogging/struggling and not have enough power to push the boat like it should?<br /><br />If it's a spun hub, like DJ says, it's like a clutch slipping. Should get rev's but no or little "go". If you think that's it. Take the prop off and draw a line with black marker across the hub and onto the outer part of the prop... reinstall and go for a ride (make sure it acts up). Come back and inspect the prop. If the line isn't lined up anymore, the hub slipped.<br /><br />If it's just a lack of power/boggy problem. That can be clogged carbs, maybe bad fuel pump -try pumping primer bulb while it's acting up and see if it picks up, or maybe loosing spark once it gets hot (power pack/coils etc). Wait 'til it acts up, then check for spark on all cylinders.<br /><br />Anyway those are my thoughts... good luck.<br /><br />Brent

 

[minocqa]

Re: power loss

hi Brent<br />what mine is doing is the motor doesnt seem to have have enough power to push the boat.<br />i dont have a tach but you can hear the rpm,s start to increase and then the boat will start running great. as soon as i slow back down and then return to full throttle it wont speed up again. <br />i'm confused<br />Don

 

[tr918]

Re: power loss

Brent,<br />Mine is more of the boggy problem. Cleaned carbs, checked fuel pump. I am pretty sure I am losing spark at WOT. I was inspecting the coils the insulation on all three of them are cracked. <br /><br />Thanks for the help.<br />TR

 

[minocqa]

Re: power loss

hi<br />one thing i did forget to say after reading the posts is the boat would not plane at all at first then i put in a can of seafoam into fresh gas.<br />that is when i would i could hear the rpms increase,and the boat planed out, until i slowed down.then the boat wouldnt speed up again. So i put in a second can of seafoam in my next tank of gas but i didnt see a ny benefit from it. Question<br />do you think omc engine tuner would help. i have never used it before. <br />So if you do how do i put iot in?<br />again thanks for all your help<br />Don<br />DOn

 

[BF]

Re: power loss

Hi again,<br /><br />for power loss, I think the first thing to check is compression. Maybe something bad happened and you're down a cylinder. If that's OK, then it'd be either fuel (along the lines you've gone, but you didn't say you've gone through the carbs) or spark. Don, your problem could be as simple as varnished/partially clogged/dirty carbs. Seafoam would help with varnish, but can't remove crud stuck in the jets. <br /><br />I'd figure it out before using it much. If it's running lean that could cause you to break a ring or burn up a piston and then you've got bigger problems (that's why step 1 is to check compression and make sure the catastrophe hasn't happened already). I doubt running more stuff (engine tuner) through it would help.<br /><br />TR, yes I'd suspect the cracked coils too.<br /><br />good luck guys (again)<br /><br />Brent

 

[gary11756]

Re: power loss

Help I have a 1972 65hp and today it lost power. the same thing it would go about 5 mph with throttle open. it would try to go faster(trying to kick in)but never did.the carbs all had fuel to them. i have good compression.i have replaced the head gasket. water pump. coils,but still have the original power pack, about a year ago.<br />with the boat moving i tried to adjust the needle valve but it did seem to react.Should my first step be to rebuild the carbs?it sounded like it was running on 1 cylinder. can u get fuel to shoot through a jet if the cylinder isnt firing?