Trying to reprop, but how can I tell if my engine gets to WOT?

[jimmwaller]

Hi all,

I have an old pre-alpha (MC-1) drive coupled with a GM 165hp inline 6 motor. A few months back, I replaced my outdrive with a different MC-1 drive, but instead of the 165hp drive, it was the drive for the 120-140hp motor. Asked around here and the consensus was, no big deal, but the ratio is different so maybe I'll have to reprop, which is totally fine.

So, here's the problem. I replaced the drive, which involved resetting the shifter, so I essentially changed two variables at once (dumb, I know). My boat used to.... hard to explain, but it used to "feel" good. I'd hit the throttle and it was responsive, it hit about 4.5k RPMs, all that.

Ever since I changed the drive and had the shifting adjusted (I didn't adjust it, I don't know how to do that, unfortunately.... but might be time for me to learn!), it's felt bad. It feels less responsive (like, I feel like I have to push the throttle pretty far forward in order to get it to respond) and it's only hitting like 3k RPMs. So something is definitely wrong.

But here's the problem I'm having. It's hitting 3k RPMs.... so is this a prop issue? Like, if I'm actually running at WOT and it's hitting 3k RPMs, I need to reprop. But how do I tell if my motor is actually running at WOT? Like I said, the throttle is not as responsive anymore, so when I push it forward, it takes a second for the gear to engage. And then as I press it forward, the RPMs climb and the boat goes faster, but then eventually, my throttle runs out of play and it hits the dashboard. So what I don't know is: When the throttle runs out of play, am I at WOT? Or am I at, like, 50% throttle, and if the throttle lever had more play, I could keep climbing up to the 4.5k range?

Something else to consider: When I'm at the 3kRPM mark, so basically with the throttle as far forward as it can go... my bow seems pretty high. My boat used to be pretty good about staying relatively level and going up on plane felt good, but now, the bow comes up so high that I can't even see in front of me. Is that a prop issue? Or what could be causing this? It started right after I changed the outdrive and had the shifter adjusted, so I'm guessing it's related, but I don't love it. I have to stay under about 2.5k RPMs, otherwise I feel like I can't safely pilot the boat as I can't see the 100 meters or so in front of the boat.

Thanks for any insights!

 

[itsathepete]

with the engine off and the cover removed, push the shifter forward until you see the linkage move and fully engage forward gear. then watch the linkage on the carburetor until you see it start moving. it should start moving very soon after the gear shift linkage is fully engaged. then continue to push the shifter/throttle forward until it stops. with the spark arrestor removed from the carburetor, make sure the throttle blades in the carb are fully open (straight up and down) if not, you are not getting to wide open throttle and your throttle linkage needs to be adjusted

 

[Rick Stephens]

First, is the throttle opening the carburetor all the way?

A: With the motor not running, take the flash arrestor off the carb, open the throttle all the way and look to see if throttle plate is opening all the way. You will have to manually open the choke plate to see.

Did adjusting the shifter change the way the boat responds?

A: No. All the shifter does is put in forward, reverse or neutral gears, which it is doing. And it opens the throttle plate in the carburetor, which you can check with above.

As far as gearing in the outdrive and prop'ing, I am missing something. If you installed an outdrive for a 3.0L motor, the gearing should be shorter, meaning all else, like prop being equal, the motor should over rev, not lug. Your description makes me think the outdrive you got was geared for a much bigger motor.

 

[jimmwaller]

with the engine off and the cover removed, push the shifter forward until you see the linkage move and fully engage forward gear. then watch the linkage on the carburetor until you see it start moving. it should start moving very soon after the gear shift linkage is fully engaged. then continue to push the shifter/throttle forward until it stops. with the spark arrestor removed from the carburetor, make sure the throttle blades in the carb are fully open (straight up and down) if not, you are not getting to wide open throttle and your throttle linkage needs to be adjusted

Thank you. Sorry, when you say "throttle linkage," do you mean something part of the shifter adjustment (that's in the transom), or part of the throttle lever (at the helm) or part of the carb? thanks

 

[ThomW]

Throttle linkage is part of the throttle control. Its the second cable--not the shifty cable. Really, watching that is not essential to answer your question. Like Rick said...with motor NOT running, put it in forward full throttle. take flame arrestor off carb and look down. Are the plates in the carbs open all the way? straight up and down? if so...that's WOT. If they aren't, you are not getting WOT.

 

[itsathepete]

when you move the shifter/throttle lever at the helm it moves two cables that connect to a linkage on the engine. 1 cable goes the the shift linkage that puts the drive in forward neutral or reverse. the other goes to the carburetor and opens and closes the throttle. when you push the shifter/throttle lever forward you can see the shifter linkage on the engine move. when it stops moving, the drive should be in gear but the throttle linkage on the carburetor should not have moved yet. continue to push the shifter/throttle lever forward until you see the throttle linkage on the carburetor start to move. this is opening the carb throttle. when the shifter/throttle lever is pushed all the way forward, confirm whether or not the carburetor is actually at full throttle. it sounds to me like the throttle cable is improperly adjusted and is moving too late in the throw of the shifter/throttle lever to achieve full throttle. the adjustment is on the cable on the carburetor. you have to remove the cable from the carb linkage, turn the adjusment collar until you are at full throttle on the carb when the throttle lever is all the way forward, then reattach. then verify you still get full throttle on the carb when the lever is fully forward, then verify the throttle on the carb is not opening until after the shifter linkage has fully engage the gear

 

[Scott Danforth]

Hi all,

I have an old pre-alpha (MC-1) drive coupled with a GM 165hp inline 6 motor. A few months back, I replaced my outdrive with a different MC-1 drive, but instead of the 165hp drive, it was the drive for the 120-140hp motor. Asked around here and the consensus was, no big deal, but the ratio is different so maybe I'll have to reprop, which is totally fine.

So, here's the problem. I replaced the drive, which involved resetting the shifter, so I essentially changed two variables at once (dumb, I know). My boat used to.... hard to explain, but it used to "feel" good. I'd hit the throttle and it was responsive, it hit about 4.5k RPMs, all that.

Ever since I changed the drive and had the shifting adjusted (I didn't adjust it, I don't know how to do that, unfortunately.... but might be time for me to learn!), it's felt bad. It feels less responsive (like, I feel like I have to push the throttle pretty far forward in order to get it to respond) and it's only hitting like 3k RPMs. So something is definitely wrong.

But here's the problem I'm having. It's hitting 3k RPMs.... so is this a prop issue? Like, if I'm actually running at WOT and it's hitting 3k RPMs, I need to reprop. But how do I tell if my motor is actually running at WOT? Like I said, the throttle is not as responsive anymore, so when I push it forward, it takes a second for the gear to engage. And then as I press it forward, the RPMs climb and the boat goes faster, but then eventually, my throttle runs out of play and it hits the dashboard. So what I don't know is: When the throttle runs out of play, am I at WOT? Or am I at, like, 50% throttle, and if the throttle lever had more play, I could keep climbing up to the 4.5k range?

Something else to consider: When I'm at the 3kRPM mark, so basically with the throttle as far forward as it can go... my bow seems pretty high. My boat used to be pretty good about staying relatively level and going up on plane felt good, but now, the bow comes up so high that I can't even see in front of me. Is that a prop issue? Or what could be causing this? It started right after I changed the outdrive and had the shifter adjusted, so I'm guessing it's related, but I don't love it. I have to stay under about 2.5k RPMs, otherwise I feel like I can't safely pilot the boat as I can't see the 100 meters or so in front of the boat.

Thanks for any insights!

if you went from a 1.62:1 drive behind your 250 cubic inch motor to a 2:1 drive, and you were turning 4500 RPM before, you would be turning about 5200 RPM which is grenade the engine territory

either you messed up the throttle
or you have a different drive ratio than you thought

 

[jimmwaller]

if you went from a 1.62:1 drive behind your 250 cubic inch motor to a 2:1 drive, and you were turning 4500 RPM before, you would be turning about 5200 RPM which is grenade the engine territory

either you messed up the throttle
or you have a different drive ratio than you thought

Hm.... probably more likely that I messed up the throttle. The outdrive very clearly says "120-140 HP" on it, so I feel pretty confident about the ratio. I'm guessing my throttle is just messed up. I'll confirm tomorrow whether or not I'm hitting even close to WOT. thanks

 

[jimmbo]

Just out of Curiosity, why did you have to replace the drive? And how long was the boat out of commission, Weeks, Months, Years?

 

[jimmwaller]

Just out of Curiosity, why did you have to replace the drive? And how long was the boat out of commission, Weeks, Months, Years?

Old drive was pretty messed up. Bellows attachments points were corroded away to nothing, threads were stripped, etc. It just seemed easier to replace the whole drive with something in better condition. This took the boat out of the water for months (not weeks and not years). thanks

 

[nola mike]

Old drive was pretty messed up. Bellows attachments points were corroded away to nothing, threads were stripped, etc. It just seemed easier to replace the whole drive with something in better condition. This took the boat out of the water for months (not weeks and not years). thanks

Also, swapping the drive shouldn't have affected your throttle at all.

 

[jimmwaller]

Thank you all for the replies so far. It turns out that my throttle is only opening part way. I adjusted the cable today and got it working much better. I can still adjust it quite a bit, and it still needs a bit of work, but it was clear to me that adjusting the throttle will do quite a bit to put me back on track. Once I have it to where it's opening all the way, I can start to play with the prop, so thanks for the guidance there.

Strange thing though—the bow of the boat wasn't riding nearly as high today. Then I had a thought... is it possible that my outdrive just wasn't all the way down the other day? Would having an outdrive that is only partially down cause my bow to ride really, really high? I remember thinking, when I was raising the outdrive, that it felt like it was back to the raised position quicker than normal... so that plus the fact that my bow wasn't riding high today... wonder if the outdrive was just only part way down. thanks!

 

[itsathepete]

Drive trimmed up definitely will cause bow to rise. Do you have a trim gauge or trim senders? Calibrate them if you do