Chewed up prop vs. Rpm

[Keepi time]

I have a 17ft cc with 90 hp v4. Manual says 4800 rpm's. I am getting to 4800 but only running about 22 mph. Seems I should get more speed. I have a 13.25 x 17" aluminum prop. I know it has been chewed up recenty from my shallow outings at the beach. My question is if I go to a ss prop will it help get my speed up. Or could it be a timing issue. Motor sound great at wot. Also could I just get a new aluminum prop and get my speed back. Thanks for the help guys!

 

[craze1cars]

Re: Chewed up prop vs. Rpm

What speed did you used to have in the past? And what event caused it to drop off? If it was immediately after chewing up the prop, most certainly that is your problem....

Chewed up props are inefficient and do not push water well. Clearly it needs to be replaced or repaired whether it is causing your loss of speed or not.

If your timing is off, your horsepower could be down. It might also be your problem. Why not check it to confirm? For that matter ANY mechanical, electrical, fuel delivery, trim, or engine placement problem could also cause your speed to be low....I'm curious what makes you suspect just the timing?

What kind of 90 hp V4 is this? Year/make/model? How long has it been since last comprehensive tune-up and engine checkover? 4,800 sounds like a pretty low RPM target for a 2 stroke outboard...most are rated closer to 5,500 or even higher. But I'm making an assumption that it is a 2 stroke outboard...maybe it's not. But are you absolutely SURE that 4,800 is your target RPM? And are you absolutely sure your tach is accurate?

 

[SparkieBoat]

Re: Chewed up prop vs. Rpm

more info on the engine is needed, like make and model and year. you could expect about 30+MPH out of a good running 90 outboard on a 17 CC. 17 pitch prop sounds right, so you most likely have engine problems.

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Well guys, the reason I suspect timing is that when I first got the boat, i was at 5200 rpm's. Then one day i noticed that the advance mechanism lock nut had come loose from the thumb wheel. So me being an exceptional guesser, I foolishly turned the wheel a couple of turns in which I thought might have put it back close to where it was and tighted the lock nut. Little did I realize i may have messed up. But since the engine sounded pretty good at wot, i thought i was ok on the timing and maybe just off on something else. It is a 90 HP johnson v4 1989 model. I did notice this morning that when I put the throttle all the way down the butterfly's do not oppen all the way, close but not all the way. But I am worried about messing something up with the link and sync if i try to adjust to get them to open any further. Thanks for all your input guys!

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Well, took it to the shop and found out there was a roller that was broken that allows the carbs to open up that was worn or broken. Also letting them check timing and do a overall check up. Should be a nice day of cruising when I get it back. I keep you posted.

 

[oops!]

Re: Chewed up prop vs. Rpm

change that chewed prop while you are at it !.......even the same pitch....but loose it...

i would not go ss because you chew props..... you have to be way more careful with ss

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Thanks oops by the way learned slot from you rebuilding your boat, inspired me to work on mine. I don't have the skill you have, but I'll get there in time, bought a prop yesterday, went with aluminum because of the shallow water here.

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Thanks oops! By the way I learned slot watching you rebuild your boat, you did an awesome job! Inspired me to work on mine. Don't have your skills though but I'll get there in time. Bought a new prop yesterday. Went with aluminum. I'd rather replace 100$ props than 350$ props. Thanks for the advise. Can't wait to get the boat back. Got some fishing to do with these cooler temps.

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Ok finally got it back from the shop. Timing was off quite a bit. Had them link and sync as well. I can tell it has better hoe shot and over all pick up, but still only getting 5000 rpm's. Also has trouble staying running on initial start up. It idles good once I get going just not initially. Also runs a little rough up to3000 rpm's. Sounds like it is stuttering a little throughout the throttle range. Could the idle spark advance be off. Maybe sucking air somewhere? I am willing to tackle this with any good pointers. Got to be something simple. Any ideas are appreciated!

 

[Mi duckdown]

Re: Chewed up prop vs. Rpm

I would think the SHOP, should have figured that out.

 

[SparkieBoat]

Re: Chewed up prop vs. Rpm

a good carb cleaning is always a good idea...check compression then spark then fuel...if link and sync was done properly and the timing is right, i doubt spark advance is the issue...a new set of correct champion plugs.

 

[Keepi time]

Re: Chewed up prop vs. Rpm

@Mi Duckdown, I would have thought that too. It took them 9 days just do do a link and sync. They rushed the job when I came to pick it up. I heard them running it when I came to pick it up. Went the day before to make sure it would be ready and was told no problem. When I get there the next day, it's all torn apart. I told them button it up and I'll get someone else to take care of it. They seem to do ok on the timing because of the way it responded on the water, thinking must be a carb thing, Low speed jet or something. I refuse to take it back unless it is something extreme. THanks for the advise Sparkie, saw the carb cleaning in here and doesn't look that difficult. Just take lots of pic so I can re-route everything back and try and take the carbs off without messing with the linkage. I'll let you know how it goes. Thanks again!

 

[Keepi time]

Re: Chewed up prop vs. Rpm

Also BTW, they set the timng on muffs. I just heard them reving the engine, shut off for a second and restart. It was not checked under load. I am thinking of taking it out to the lake and check it at WOT to see how close they got it. I know when you do something all the time you get an ear for it but, how do know for sure without testing it at WOT.