TOPIC: Question tuning the 80 HP UPDATE

Ok, so I couldn't take the clipper out to test the 80 Hp so I was tried to tweak it until I can get it on the water again. While I had it running on the hose I tried tweaking the low RPM jets. I started at 1 1/2 turns and the rpm's didn't increase when I made it richer so I turned them in and leaned it out and the rpm's increased. Unfortunately the further in I turned them the more the rpm's increased until they were basically closed then of course it stalled do to no fuel flow. Unless I'm mistaken, the rpm's should have started decreasing as I got too far to closing them. I turned them back out to one full turn, since I didn't want to burn it up. It runs decent this way and actually runs up pretty good from idle this way.

Anyone have any ideas as to why the rpm's kept increasing all the way to fully closed?

Bob

Simply put you can NOT fine tune a motor on a hose !

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It needs to be in the water and in gear.

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Most motors will speed up when doing that because you now have a finer spray of fuel going in.

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Sort of like kindling on a fire, it burns quick and is gone long before the big logs.

professor wrote:

Simply put you can NOT fine tune a motor on a hose !

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It needs to be in the water and in gear.

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Most motors will speed up when doing that because you now have a finer spray of fuel going in.

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Sort of like kindling on a fire, it burns quick and is gone long before the big logs.

Yep! Same reason why a motor will speed up when running it out of fuel before it quits.

Thanks guys, well a rookie questions I guess. I'm hoping I can get her out this weekend before it gets too darn cold!!!!!!!!!

Bob

Bob, gotta agree with the others. I replaced several pistons in my buddys old Ski-doo more than once because he would always lean it out to get more speed. Some of the pistons had nickel sized holes in them.

Yep! Lean and mean will get ya a 'Hole in one!"

Sung to the tune of "Silver Bells"..

"Silver balls, silver balls, silver balls on my spark plug"!

Haven't gotten her back out yet. I'm hoping to get her out there tomorrow. I'm going back to 1 1/2 turns to start and see what we get.

Bob

Well I got her out on the water today and definitely has more power than the Fat Fifty. She jumps on plane right away now. I forgot to take the GPS with me so not sure what her top end is now.

Odd thing is she torque steers to the left really hard at 3/4 throttle and higher. The Fat Fifty torqued to the right. Kind of weird, didn't expect that. She also starts fishtailing at 3/4 throttle but stops at full throttle. I moved the tilt rod out one more hole and it seemed to help a little but not completely. Anyone have any ideas as to what could be causing this? Someone had mentioned to me that maybe it needs a larger prop. I didn't look at the original small hub prop but I have a PJ76 10 1/8 x 11 larger hub prop that I can try in the spring.

Any ideas?

Bob

what was her attitude just prior to fishtailing? slightly bow up, then leveling out once she starts fishtailing? She could be rolling over her center of gravity per thrustline AKA X Dimension. re propping would help with this, or shortening her up. I would suggest trying the larger prop, then go from there.

also tilt n trim would help a lot with this.

Hmm ya know now that you mention it, she is riding much flatter so I was wondering if the transom was coming up too high. Lifting the tilt one more row/hole seemed to help some so maybe switch the prop out then tilt it one more row/hole and see what happens. I don't have a power tilt and trim on her, just the factory tilt holes in the housing.

Bob

Bob,

Nice that you finally got to take the boat out. On any motor that doesn't have electric trim, the tilt angle is going to be a compromise between too far in & too far out. Tilting the motor out or "up" usually will cause the bow rise. Tilting it too far out will cause fish-tailing and instability at full speed. It will also cause the prop to "blow out" upon turning the boat with power applied. An engine tilted too far inward will cause the bow to plow, and will harm the speed of the boat. Fishtailing is normally only a problem when the lower unit is not deep enough in the water, either by incorrect tilt angle or transom height. You must shoot for a "happy medium" between in & out tilt angles on your boat.

As for torque steer - that is almost a given for these old boats and engines. I have seen many people that state their boat doesn't torque steer at all, but personally, I've never owned an old boat that doesn't do it. This is especially a problem at speeds above 25 MPH. It's my opinion and experience that changing props will have little effect. Your best cure is to install an anti-feedback steering box and cable system. The old cable and pulley systems tend to torque-steer the worst, because they are so easy to steer. The less resistance in the steering, the more you are going to get "feedback" from the engine. I HATE having to crank the wheel sideways trying to get the boat to go in a straight line. I finally installed a Teleflex "no feedback II" system in my Reinell because of safety concerns. What a difference. Set the wheel on course & forget about it. The wheel and boat stays on course. My only dislike is the stiffness in the system; it isn't horrible, but it takes some getting used to. (it's a heck lot better than battling the old tiller system torque steer though)

Thanks Bruce. I think I may drop it all the way down and see what it does then work it back out again and see where she's happiest. I do think she's going to plow a lot, all the way in but we'll see.

I knew I was going to get torque steer, what caught me off guard was the fact that it was opposite of what the Fat Fifty was. I hear ya on the Teleflex but I want to keep her period specific and original as possible. I can live with it.

Probably won't happen until Spring now. Just too cold here now.

Bob

A General rule of thumb, a transom height of roughly 15" run a short shaft. A transom height of roughly 20" run a long shaft. I suspect that you are healing over your center of gravity as a result of your line of thrust is too low. but I could be wrong.

Bob, what is does your transom height measure? Also what is the distance from the keel to center of prop hub? Judging from your picture, I'd say your sitting about 10-12+" from keel to center of prop, ideally you want to be between 8-4" here, you will see more top end and mid range with no major impacts on handling. The part No I've listed in my Dorset project in member projects will work for motors to 1968 and can be found on marinengine.com for 125 + shipping.

Yeah sorry should have posted the specs hugh. Same set up as the Fat Fifty, it was a long shaft also. Transom is 20" and 9" from keel to center of prop.

Bob

ok, then it's not the x dimension. So Bruce is right. taking the spacer off, would put you at 4 inches, which is acceptable, but also some of these older hulls rely on the x being deeper to force the bow up out of the water. I'd say put some strakes on the bottom n see if that helps, but that would not be for the faint of heart.

Thanks Shake. I thin k I'm going go with the tilt adjustments for now and see what happens. Well in the Spring that is.

Bob

I know of a party that replaced a V-4, 85 HP (1968 ) with a newer 3 cylinder 70 HP motor.---Same boat.----Said he was amazed by the different handling of the 70 HP motor.

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All you have to do is look at the size and shape of the newer lower unit. Much larger surfaces to help in the control of the boat.

Bob,I use a small piece of plastic pipe when the motor needs a little more trim out and the next hole is too much. It helps mine.

Cool thanks Jim, great idea. I'll try that in the spring. I think I may also try the other prop that I have. There's a 10x9 on it now and I have a 10 1/8x11 I can try out. I didn't hook up the tach/dwell meter when I ran her so I'm not sure what rpm it's running at WOT. I'll hook it up in the Spring and see what it does with the current prop then switch to the bigger one and see what I get.

Bob