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here it is ! my mini..but need help

S

sd1042

Active member
Well i pretty much finished my mini and took it for a test drive... everything ran well, reduction drive worked good and it started first pull....Know here's were i need help..the damn thing only went about 7mph..after about half throttle it wouldn't pick up anymore speed ...the engine would spin great and wasn't bogged down at all. it sounded like it was att full rpms, at least it sound like it but no more push , i don't have a tack on it. ..Ill admit the boat it a bit heavy but i would think it should still push that 10 footer faster than that... the reduction drive is 2.6:1 turning a 60x34... when it hit about 3/4 throttle it started vibrating a bunch but no more speed.... Could it be that i need a prop with more pitch? or is it possible the angle of the prop could be pushing the nose down causing it to run that slow.?...Man i really don't think that the weaight can cause it to be that slow.. i have no scale but i estimate that with me in it , the total weight is about 630# It really didn't pick up much more speed after about 1/4 throttle but deffinetly no more speed after 1/2 throttle....any help would be great guys....like i said everything seem to be good and fun great just no push...
Shawn, know lets see if i can get these pictures to the thread....also cna i post more than 4 a day some how..thanks
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How does the boat sit with you in it in the water.?How deep was the water? You need to find some water about 2" deep that's when there fun? How is you engine mount is it level. I think most like the engine a little higher in the back. Did it seem like it was plowing the water?
 
it does seem to plow the water....but it also seems to have no more push after half throttle but the engine seems to keep moving up in rpms...what you think?
 
hahahah I just put them in his original post and was about to tell him to hit the edit button and look at the syntax for each image and he can see how to do it from that :)

Scotty
 
Is your engine mount level? how does the boat sit with you in it when stoped. You may need to move your seat back some
 
Is the prop on right? In some pics it looks backwards but in others it looks right. Guess it just the way the some of the pics look.
 
I was thinking the same thing but I think it just the pics. When I talked to arrowprops they told me a 60x34 so the prop should be the right one.I'm with flyin blind on this I think the belt are slipping also.
 
looks to me as if the engine base as if it could flexing due to no support. the load is applied,engine is moving up,belt gets loose which could cause the vibration increase in rpm but no increase at prop. stiffen the base mount and it might fix ur problem.jmo
 
well I have a couple comments just form what is posted

1) it looks like you did away with the rubber mounts and just hard mounted personally don't like that and will shorten the life of the engine

2) maybe the belts are sip don't know form here but what is the spec out RPMs for that engine 5500 or 8500? are you sure that is the correct ratio for that engine to spin the prop at the speed you want/need

3)yes the prop is on correctly , is it the biggest prop you cage can handle?

4) vibration other then the earlier mentioned hard mount , is there enough support behind the bearing and prop shaft this is where all the thrust is being placed now on those TWO bolts holding the pillow block bearing as far as i can see in the pictures
 
I am trying to find some rubber groumets to put on the engine bolts, i just didn't find some and got a little itchy and wanted to test drive it. Gonna try tightning the belts just in case they were slipping but they didn't seem to be.
Goldhunter, all the thrust is put directly on those 4 bolts holding the pillow block bearings down..while testing it they didn't fex or anything .buuuut then again i wasn't getting alot out of the prop anyway... you think thats bad with them 4 bolts...any suggestions?
I appreciate all and any input..There isn't anyone close to me that knows about airboats...i rely completly on this site for info etc..
thanks fellas, shawn
 
took it out for another test drive and i only gained 2 miles an hour....i tightend the belts because they were slipping a little. I put rubber groumets on my motor and i changed the angle of the engine/prop different ways to see if i get better results and i didn't. it either pushed water or just wouldn't get on plain....OK I think i need a prop with more pitch..its a 60x34 and after 1/3 throttle there is no more push..so my maximum thrust is coming at 1/3 throttle and then from there i can spin it faster all day long and i get nothing more also it doesn't seem to be stressing the motor at all...
Its a yamaha 340 0ff an enticer snowmobile......need some oppinions to why i can't get anymore thrust .......Also the damn boat is pretty heavy...could that be the problem.and if it is, why does the engine act like it has no stress.
Sorry for all the questions, thanks, Shawn
 
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