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45hp not up to speed with weight

I have a classic 50 that seems to run good when just me in the boat (though I am not sure I am getting full throttle throw or not). My boat is a heavier v-bottom fiberglass boat. Anyways, had it out the other day with a few friends (4 people total), motor barely got us up to 10MPH and would not get up to speed. Then, had it out with 1 other person and it took a little once at full throttle for it to rev up and get to speed. Is this normal? Do I need to be adjusting the motor angle/tilt with more weight as maybe its not getting up to plane? Dont quite understand it. I dont have electric tilt, I need to manually move the rod and have it fully adjusted with rod closest to stern so very little tilt to the motor keeping the bow down. Not sure my prop pitch either.

Also, how do I check to make sure I am getting enough throttle throw? It idles great though.
 
Sounds like you could be under powered,heavy boat + four not too light people,50HP could be under pressure.
To check if you are getting full throttle,push control as far as it can go,check that both carb butterflies are full open
 
Throttle is easy, with the engine off push the throttle all the way open and look at the throttle plates to see if they are all of the way open. Try changing the tilt and see what it does and once you get it happy compare your wot rpm with the recommended max revs to see if your prop is reasonable. If the top speed rpm isnt very close to right make sure to check and see what the recommended prop size and pitch is so you dont blame the prop for an engine problem and dont blame the engine for a prop problem. A fairly heavy boat with a lot of weight (you are within the boats weight limits right?) will run slower but it sounds like it's a lot slower.
 
I fully agree it is under powered, I believe the boat is rated for over 100 HP motor. My boat is too old so no data plate for weight. I will check carb butterfly positions. Have not checked compression or spark, but shop changed all 4 plugs last year. So if more weight and boat is flatter on water, will changing the tilt to get bow up higher get better speed?
 
Part of the reason to change the tilt angle is to accommodate different amounts of weight and it in various places around the boat. Is everyone and two big coolers in the back, need to get the bow down. Is it two adults and several kids in the front, different story. I would start with getting everything right with just you, make sure there is no basic problem, you know, engine weak or prop totally wrong and then see what can be done to carry more weight. If the engine can't run at its rated max rpm and and your local prop shop says that the pitch is about right for the boat you have then more investigation needs to be done on the engine. Start with the cheap easy things first and then work up from there. (I love cheap and easy!)
 
It seems to run good with just me in the boat. I have a tach so what do i look up to see about rpms and prop? Didnt see a chert in the factory service manual.
 
Close to the back of the manual there a number of appendicitis that give various specs. You want the one that gives engine specs by year, the wot column is the one that will give you what you need. Flat out with the correct prop the engine should be turning sort of in the middle of that range. If it can't then you have either the wrong prop, a sick engine, too small an engine for the boat or a ton of fouling on the hull
 
Throttle is easy, with the engine off push the throttle all the way open and look at the throttle plates to see if they are all of the way open.

Checked my throttle plates. Top carb plate appeared to be 90 degrees open, fully open. The bottom carb plate was maybe 80 degrees, just slightly from fully open. I did notice on the side of my motor the throttle lever is not stopping due to the full trottle stop screw. I am getting stopped by the maximum spark advance screw.
 
Checked my throttle plates. Top carb plate appeared to be 90 degrees open, fully open. The bottom carb plate was maybe 80 degrees, just slightly from fully open. I did notice on the side of my motor the throttle lever is not stopping due to the full trottle stop screw. I am getting stopped by the maximum spark advance screw.

After looking further, I'm guessing something else is stopping the throttle arm as i think the throttle stop moves separately from the max spark. Should probably adjyst the max throttle stop incase I am stoppying by the butterflys.
 
Got some of the linkage adjusted. Took boat out today with 2 of us on it. Max speed qas 26mph and rpm was 5300. Noticed a slight lad when hitting the rhrottle for it to rev up.
 
I understand that the approved way to adjust the mixture screws on the carbs is in forward gear and about 650 idle speed, and turn the screws in first to where the engine starts slowing down due to being lean then out to where the engine is starting to stumble due to too rich and then set the screw midway between the two extremes. Is known to help acceleration stumble..
edit: the engine needs to be warmed up when this is done.
 
I understand that the approved way to adjust the mixture screws on the carbs is in forward gear and about 650 idle speed, and turn the screws in first to where the engine starts slowing down due to being lean then out to where the engine is starting to stumble due to too rich and then set the screw midway between the two extremes. Is known to help acceleration stumble..
edit: the engine needs to be warmed up when this is done.

edit again: I thought I added that the engine needs to be in the water or in a deep tub but it seems that didn't happen.
 
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