I have two props for my Evin. 40952R, one is a 10.75 by 11, and the other is an 10 by 12. What differences should I expect to see between these two props, performance wise?
Both of those seem to have a pretty low pitch for a 40hp. Can you describe the boat you've got a bit? If you could tell us the weight of it, that would be pretty helpful.
Boat is a fibreglass 14', open bow tri-hull, short leg motor and transom. Weight is probably about 600 lbs with the motor; I;ll have to weigh it sometime and find out exactly. I haven't hooked up a tach yet to see what my wot speed is yet.
You have a 1969 40 HP. Unfortunately i dont know the gear numbers for that lower unit, but on a newer you should certainly be running a 15" or 17" pitch at least. Was that prop bought for that boat. Have you tried to connect a tach to the motor ? Rmps should not exceed 6000 WOT with you alone in boat.
I have an '88 40 and a boat that's about 600 pounds also. I actually have three props, a 13 pitch, 15 pitch, and 17 pitch, all about 12" diameter. The 15 is the best all-around prop for us (waterskiing, trolling, etc.) Your gear ratio may be different - not sure.
I have a 85 Johnson 40hp bass boat and just purchased a 13 pich prop. would it be better "performance wise" to stick to original 15 pitch prop?? Its not a sped boat but sure like to get to point a-b really quickly. Max boat weight i beleive is around 700lbs with motor. Its a 14 footer.
The only way to find out what is the optimum prop to use is to have a reliable tach. Most of the motors (1980+) should by set up to run 5800 with average load. Setup include adjusting the height of the motor on the transom first and trim angle then as a last resort, changing props. Having multiple props is a good idea. I have 3, 1 speed, 1 good overall and one power prop.
Yup, my "Tiny Tach" is on it's way ($36). Now that we're skiing alot more, I want to make sure we're not over-revving with the 13. Man, that 13 pops skiers out of water (even slalom) like a speedboat. Wakeboard pops up in about a second. If we are over-revving with the 13, I'll probably just ventilate the 15 and keep the motor up pretty high - it'll do fine also. BTW, my manual specifies "4500-5500" as the WOT range.
fishnfiend<br /><br />Most of the manuals say 4500-5500 but the experts recommend 5800. I have a tiny tach too & love it. One of my props is a 4 bladed adjustable compostie prop (propulse)with pitch range from 12"-16". That sure does get up & go for tubing. My all around prop is a 17" aluminum ptich & my speed prop is a 19" SS.<br /><br />BTW It's an 89 J50 on a 15' skiff.
You have a little more motor (50 vs. 40) and maybe a little less boat weight (15' skiff vs. 16' aluminum semi-v with deck, console, livewell, storage, trolling motor, etc.) than me. My boat will eventually go with the 17, but is quite a bit slower to plane. Now, the adjustable prop, that sounds like the best of all worlds. Hope the hurricane missed you down there, and your boating is for fun, not survival!
My boat is probably heavier than yours even though about the same size. About 1200lbs ready to go. I know that the gear ratio will make a big difference between motors of same hp. But for reference, I started with a 13 pitch and was hitting the rev limiter. Switched to a 15 pitch cupped and now it runs right at 5000 wot. Light load top speed is 29/30 mph. My motors gear ratio is 2.416:1 I think yours is more in the line of 1.5:1 which is why you have the shallower pitch props; they turn faster at the same motor rpm than mine does because of the difference in gear ratios.
Who says these little 40's can't get you where you need to go! Mark - which 15 cupped prop are you using? And question 2, how is your holeshot? Sounds like you have the setup dialed in. Did you get your motor going again? I was sad to read about your overheat awhile back. I went VRO-less years ago when I was too cheap to switch over to the 4-wire and needed a fuel pump.
The gear ratio for fishnfiend's outboard is 12:21 (1:1.75) where the more modern 40s are more like 12:29 (1:2.4). So compare props in this light.<br />I would think a 13" prop or so would be appropriate for your engine. Since you're saying you seem to be sluggish with 11" or 12", you may want to have a close look at the health of the engine.
Compression is right around 100 psi for both cylinders. I did adjust the float level, because it appeared the float was touching the top of the float chamber when the needle valve closed, so I lowered it slightly. I don't have a manual, so I am not sure exactly what the float height should be. I suspect I might have a slight upper seal leak beacause slow idle under load is a little erratic, but I don't think this would affect wot much. I examined the idle passages and blew them out, but overall the carb was very clean. Ignition is all new and works fine.
Sounds good, but most people find these engines a little more powerful than they'd expect from an old 40hp. I would expect you'd be using a 13" prop rather than an 11 or 12 (which are more appropriate for very heavy boats or the 25/28/35/33 engines). An 11 or 12 should give you more get-up-and-go when you take off, the problem is that you wouldn't be able to achive top speed since the engine will overrev and suffer breathing problems. Sort of like staying in first gear.<br /><br />But that sure doesn't sound like whats happening to you. Can you pull out the spark plugs and compare their firing ends at all? A minor air leak should not affect top end much though it does cause a really lousy idle, but I'm wondering if your dropping a cylinder?<br /><br />The correct float setting is for the float to be level with the gasket surface of the carb when it's held upside-down. It sounds like you have it adjusted a little rich (high), but I don't think that would cause such a performance loss.<br /><br />If you want to hold off getting a manual for whatever reason, you can often borrow one from the local library. There's a bunch of factory manuals on ebay right now, but the '69s seem kind of pricey. There's better deals on the '70 manuals. Search:<br />(40, 40hp) (evinrude, johnson) manual 1970<br />There were changes in '69 so don't go earlier.
Plugs are both a nice tan / grey color, so I don't think the mixture is too far off, and both cylinders are firing fine at all speeds. I'll have another look at that float setting though. <br /><br />I verified the gear ratio, and it is indeed 1:1.75 that you cited in the previous post. So with that in mind, you think that going to a 13" diameter by 10" pitch might be more appropriate for a lightly loaded boat? I still need to verify wot rpms. I don't have a tach, but I do have a frequency counter, maybe I'll see if it will give me an accurate reading off the points.
13" pitch for a 10" (or whatever the prop designer decides, it's really not important to your) diameter. But that's sure not going to help with sluggishness! (More like taking off in 2nd gear).<br /><br />I've tried reading the rpm with a frequency meter myself, but there's so much interference from the sparks & ringing on the coils I could never get a reliable reading. Might be worth a shot with your meter though. I've got a half-designed filter that should help if you want the schematic...<br /><br />Make sure you've got the link&sync right:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=033290#000006 <br /><br />Points well adjusted to .020"?
Points are dead on at .020, and the throttle sync is set up as outlined in the instructions at the link you provided. Maybe I'm expecting too much from this motor. I think the first step is to get an accurate wot rpm measurement. I'll throw together a low pass filter for the meter, or even better I'll scope' it. I think my scope will run fine off a dc inverter in the boat.
Cool. The filter is nothing complex by any streach. Expect 100v+ spikes though most the pulse is at a much lower voltage.<br /><br />I'm very curious to hear what you get for WOT RPMs, as your engine sounds like it's perfectly healthy.
