Gear Ratio, Is this my problem

wbrannies · Apr 18, 2003

hey, i have a 120 with a # 1 drive and i am having the same problem. It fills like it takes off in fourth gear and does not pass 25. but i think i have figured it out.. When i bought my boat it did not have the lower uniy on it. Now you know how hard it it is too find one...Well i did, But it was off a inline 6. I think it was a 165. Now someone just told me that the gear ratio is differant for being on that 6 cly. So the guy says that its to much for my 120. He said its like trying to take off in fourh gear....What do you think, could that be the problem, and if it is, can i change the pitch of the prop and fif the problem...... Thaqnks William Needx4xSpeed@msn.com

Bondo · Apr 18, 2003

Re: Gear Ratio, Is this my problem

A 15 pitch prop Might Help.... What rpms at WOT do you get now ??? What is the Pitch of the prop you're using Now ????

MrBill · Apr 22, 2003

Re: Gear Ratio, Is this my problem

Alpha lower units all have the same gear ratios. It is the upper units of the O/D that contain different gear ratios. I'd check into the prop as already suggested...did you use one that was attached to that "new" lower unit?

Bondo · Apr 23, 2003

Re: Gear Ratio, Is this my problem

MrBill, I think he's calling the "Outdrive", the "lowerunit"... Wrong term, Right Unit.... Anyway, MrBill is right.... Gear changes are done at the Top gears in the Outdrive.... Lowerunit gears, Stay the Same....

drgaul · Apr 24, 2003

Re: Gear Ratio, Is this my problem

need4speed all the above is right as far as i can find out. you can go to props above and this may give you some idea if you have a speed prop or one designed for takkkkking off quick, but also check this. your carb may have a bad acelerator pump in it or your mech-advance could be stuck and not working properly. these thing's are easy and cheep to check and cause the same problem.drg

wbrannies · May 15, 2003

Re: Gear Ratio, Is this my problem

Upper unit is stock, Lower unit is what i changed. And it has a 21 pitch prop!!! Is this the problem, Oh and the points were at 11 thousands, I think it should be set at 16

wbrannies · May 15, 2003

Re: Gear Ratio, Is this my problem

Also this is 18 foot deep V Fiberform, its not very light! It's like a 57 chevy, Well built..

akriverrat · May 16, 2003

Re: Gear Ratio, Is this my problem

and flotation foam under floor probably waterlogged.

wbrannies · May 16, 2003

Re: Gear Ratio, Is this my problem

Nope, It's all new

akriverrat · May 16, 2003

Re: Gear Ratio, Is this my problem

well, all repiies to both posts assume that engine is up to snuff. is it? good compression, good cap, rotor, plugs, wires? idles ok? no bogging when you give it throttle? and what is the wot you are gettig with your current prop. another thing is... in 1966 a fast boat only did about 35. tops.

MrBill · May 20, 2003

Re: Gear Ratio, Is this my problem

William, follow-up to your original question, etc after all the responses and replies...the rough prop/pitch calculator that I have says you should be using a 17" pitch prop. If you can borrow one to try I'd suggest that. With the 120 and a rather heavy boat the 17 should be right with WOT about 4400RPM. If the engine is able to go more than 4400 at WOT go to the 19, but think it's unlikely you'll need to. OH...and regap the points to correct spec...

Gear Ratio, Is this my problem

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