75 evinrude carb adjustment

[jherlyn]

Re: 75 evinrude carb adjustment

Ok, It's a three blade prop. the nunbers that you speak of around the nut I can't/don't see. Could be there and I'm just stupid though.

Looking into the prop though, I do see some, maybe, fishing line? wrapped around the gear that the prop spins on. Can't imagine that's causing my problem, but can't be good either.

The cavitation plate seems to be right where it should be, still that motor seems to sit aaawwwffuuulll low to the water when its in the lake. And its not from the boat being overloaded or soggy floatation foam. I just completely rebuilt the boat including foam and there is not a single fishing pole or other unnecessary piece of equipment in it. All it has are the oar, fire extinguisher, and other paraphenalia required by Montana boating laws and the coast guard. Anyways, I digress. What would be the harm of me raising that motor a couple inches. Blowouts in corners? Rooster Tails? The idea is to have the prop as shallow in the water as possible on plane right? I'll obviously know if its too high.

I'll try to get you a picture tomorrow, but I just can't see a pitch number on the thing.

 

[levi_tsk]

Re: 75 evinrude carb adjustment

how far off the transom is the motor sitting now that you have that cmc set up?

for every foot back from the transom you can go up from the standard setting 1" you can try lifting it up but wait till you post up a pic so we can see what youve got going on

yes it can blow out, over rev, and frag your motor in a FRACTION of a second at WOT best you get a four blade prop if your gonna go jacking it way up high

take the prop off and get that fishing line off there but dont yank it off slowly unroll it off of the shaft
while your there look under the washer and the nut for the prop for the numbers on the prop also look on the side between the blades, around the flare on the back of the prop,inside the flare,basically all over it as different manufacturers put the number in different places youre looking for either a six digit number OR a __X___P number if you find ANY markings on it at all post em here and well be able to find out what you have

theres a marking on it somewhere believe me sometimes its an odd 3 digit one but theres one on it

 

[jherlyn]

Re: 75 evinrude carb adjustment

Sounds Good, I'll let you know what I find tomorrow. Prolly should replace the prop anyways. It looks old and its pretty beat up. Once I get down there I can notice that there is a pretty good lip on all the fins, like its been bounced off of surfaces or something. They are not sharp and straight, but almost like an L if ya know what I mean.

The cmc Jacks the motor 6" off the back. What I'm kind of picking up here is that the motor location is not the problem, because if it's off it's not off by much.

That's the problem with second hand boats, you don't know if whoever owned them last had the right prop on or if they destroyed the right prop and just put the cheapest one they could find back on.

We'll start simple with the prop, but could it still be something like a sticky base timer or a spark issue. hard to believe because it idles just ABSOLUTELY amazingly, but I just had to ask.

 

[jherlyn]

Re: 75 evinrude carb adjustment

Ok, so the size is 13 3/8X17. I assume the 13 and 3/8 is the diameter of the prop, and the pitch is 17. If that is the case than the prop pitch is waaaayyyy too much. Especially if you are suggesting a 12 through 14. If I changed to a 14, according to the sites about prop calculations, that would be a 1200 Rpm theoretical gain.

 

[levi_tsk]

Re: 75 evinrude carb adjustment

yep yep and yep
also- if its THAT beat up that may be the WHOLE problem im thinking with a 75hp you might wanna go for a 15" pitch 13" diameter
your gain would only be 600rpm youre only changing the pitch -3 inches at -200 rpm per inch of pitch -try to find a loaner prop of about the same pitch and see if it helps
is the one you have aluminum or stainless?

 

[jherlyn]

Re: 75 evinrude carb adjustment

Its aluminum. The minute I get the pitch size right, I'll probably go stainless.

I thought you were talking a 14" What changed? I thought going down to a 14 would be ideal. And I thought it was more around 400 RPMs per ich pitch until you start approaching the threshold where you start losing top end while gaining hole-shot.

Anyway, back to my questions a few posts ago. Could it still have something to do with the base timer or spark? Or are you pretty sure its in the prop size? I mean, once you get the boat out of the water, she gets up and flies. Just a little worried that if you're right about the only 200 RPM gain per inch pitch that it might be something else. Although, If its JUST enough to get me to plane, then maybe the boat will climb to the desired rpms.....I dunno

 

[levi_tsk]

Re: 75 evinrude carb adjustment

well im running a 60 hp with a 14 i think you can get away with a little more pitch HOWEVER youre better under pitching it then over so if youve found a 14p go with it. the max rpm in the book is 5500 but youre better off running in the 5800 rpm range unloaded with just you and a tank of fuel in the boat. the engine will last longer and run cooler since it wont be "loaded down" by the prop and when you load down with gear and passengers youll still be running 5400-5500 which is the engines sweet spot

if your prop is as banged up as you discribed, it will seriously affect your rpms and performance

 

[jherlyn]

Re: 75 evinrude carb adjustment

So, I'll probably go with a 15 because they don't make a 14 in my motor size. Now, my motor had the potential to have either a 13.25 " diameter or a 12.25" diameter depending on the motor gear casing size. Mine's the bigger but I think there is a potential to drop. Any thoughts on doing this? I mean it wouldn't be much, maybe a half inch at the most.

second, I have taken a level and gone from the transom of the boat to the cavitation plate to see exactly where my motor sits. Now the back of the cavitation plate is dead level with the bottom of the transom, but if I keep going towards the prop, by the time I get to the prop I'm almost 2" below the transom with the anti-cavitation plate and even more by the time I hit the end of the anti-cavitation plate. I'll probably bump the motor up an inch or two, because from what I understand it is too low.

 

[levi_tsk]

Re: 75 evinrude carb adjustment

if you drop an inch in diameter youll gain and extra 200 rpm BUT if you switch from aluminum to stainless youll loose 200 so maybe a 12.5"???? that way when you make the swap to stainless you should be right in the 5800 RPM range again - youll probably be a little high with the aluminum one though so be careful

 

[jherlyn]

Re: 75 evinrude carb adjustment

So, I talked to my boat parts guy today. He's very knowledgable. he looked up the specs for my motor, and low and behold, after checking twice with calipers, I have the wrong size prop for my gear. I have the small gear, and the prop that is on it is for the larger gear. He says that the small gear maxes out with a 17" pitch, 12.25" diameter prop. So, with a 17 pitch 13.25 inch prop I was over max

Hopefully my engine doesn't fail me from this negligence from the previous owner. We will see when the prop arrives. I'm just not trusting of a simple fix until it works due to the fact that there hasn't been a simple fix on this motor yet.

 

[levi_tsk]

Re: 75 evinrude carb adjustment

should be fine since you only ran it once like that.....

so what did you end up going with??

 

[jherlyn]

Re: 75 evinrude carb adjustment

15" aluminum three blade with a 12.25" diameter. I figured with the 2" pitch drop along with getting the right size diameter for the gear setup in the motor should fix most of my problems. I am going to adjust the motor up one hole and then check with a level to the anticavitation plate to see if I can get that halfway lined up with the bottom of the boat too. It won't be exactly level due to the jack plate on the cmc trim, but I think going up an inch might help on that matter too.

I will make these two adjustments and then try her again, hopefully with surprise and happiness. Just because there is NO reason WHATSOEVER that this motor shouldn't be able to just flat haul......

 

[levi_tsk]

Re: 75 evinrude carb adjustment

yeah for sure

this may be common sense to you but set the motor height by raising or lowering the bow of the boat until the bottom of the hull is parallel to the ground then trim you motor until its perpendicular (90 degree angle to the bottom of the boat)to the ground THEN set your motor height your measurements will be much more acurate this way because your cavitation plate will be parallel to the bottom of the boat

 

[JETMORE]

Re: 75 evinrude carb adjustment

Sounds like you have a 15 inch shaft stinger motor, which is geared higher, and has a gear case that is 3/4 inch narrower than the standard stinger. Is it a 15 inch you have, do you know?