Finished Overhaul - A few questions

mejim707

Active Member
So I replaced my engine. I found a crack in the PTO jug and since I needed to do a top end I just said go ahead and get the whole engine and do it right. The previous owner didn't prep for winter and put JB weld which started leaking and I only just found it a week ago smh...

I have a few questions;

1. I felt the PTO wheel after running at idle for a while. It gets a bit hot, not enough to burn you, but like a hot cup of coffee. I had the cover off and touched it and this is the first time I've ever checked that. Is it normal for the PTO wheel to get hot to the touch while running for a while? (I do have the oil lines installed and they are full of oil.

2. How fast should the oil pump, pump oil? It seems to move extremely slow at idle, and I only see the oil move if I crank the engine with the plugs disconnected and pushing the throttle forward. Even when I had the pump off and I was bench testing it I had to pull it's "throttle" back pretty far for it to start pumping. At almost fully open it pumps in pulses back and forth at about 1 pulse each side every 1.5 seconds. But is it normal for the oil pump to pump very very slow at idle?

3. Here is how it sounds running. Does this sound normal to you experts?
New Engine Running

4. What are the stock carb settings for the 96 Challenger Rotax 787? I'm seeing all sorts of things like Low Speed to 1 or 1 1/4 or 1 1/2 turns out. I can't find any true and consistent source of the accurate stock settings. I want to set it stock, adjust for smooth idle, and leave it along.

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Out of the half tank of 50:1 (10 gallons 87 octane with about 26OZ XPS E-Tech 2T) I've used about 1/4 tank so far.

The engine seems to run great at 2k - 3k. It sounds as though the two cylinders are synced and have that 'hum'. I've done a max of 3.2k rpm just putting around. But about 3k there's a bit of vibration, nothing of consequence I think, but more of a humming/vibration. The carbs are synced exactly, and the idle is at 1500 on the money. At Idle though the engine runs fine but kinda shakes a bit.

But I don't know how these engines are "supposed" to run/sound at idle or at higher RPMs. The only one I've ever really experienced is my own.

Does anyone have any videos of their properly running Carbureted Rotax 787s? Like how does it sound / run at Idle and at higher RPMs? I would love to compare notes to make sure mine is exactly where it should be.

Below is a link to a video where it's idling on water then I ease the throttle up to about 2300. This is about 1/4 of the way through the initial break in.

VIDEO -> New Engine Idle up to 2300 rpm
 
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They are not smooth like a car.

Also about 3500-4500 cruising rpm they have a strange, almost misfire sound and that is perfectly normal.
 
They are not smooth like a car.

Also about 3500-4500 cruising rpm they have a strange, almost misfire sound and that is perfectly normal.
Very good to know! I’ve always wondered if everything was ok with that stuff. Thank you
 
Sometimes the word typical is a better word than normal. Mine runs great at idle and above maybe 4000 rpm but in the 3000-4000 range it sounds like it's not getting the right mixture from the carbs, I suspect lean in that range, and it has been said that running lean is not good as far as wear and tear goes. Due to that I just avoid running in that range which is pretty much fine anyway since I'm usually either at marina no wake speed or 6000+ RPM. I plan on replacing the carbs next year with new. I've had bad luck with curing mid range lean conditions by carb rebuilds on several engines and don't want to waste my time on that again. That and the PO indicated the carbs have been rebuild.
 
Still putting it through its paces. Man the break in process takes forever! I'm almost finished with the first 10 gallons of 50:1.

Been going out and varying the throttle on this tank. Then coming back and letting it cool. I haven't yet broken 4000 RPM. The max I've gone is 3800 so far. I'm just putting around. I can't get it out of the hole at this slow speed. So burning through the fuel is very slow going.

I'll finish this up tomorrow. Then I'll fill the tank with fresh 87 octane with no additional oil in the fuel. So I will only be on the oil injection.

I'm also going to replace my plugs since they're likely fouled now.

For the next 10 gallons (half tank) I'm going to push it a bit further. I'm thinking about 4500 - 5000 RPM max. Again varying the throttle.

Once I'm done with the next 10 gallons, and I'm on the "second tank" of gas, I think I should be able to get it up to about 6200 RPM (90% throttle)?

This break in process is extremely time consuming and tedious. It's really trying my patience but I want to be sure I'm doing it right.
 
Sometimes the word typical is a better word than normal. Mine runs great at idle and above maybe 4000 rpm but in the 3000-4000 range it sounds like it's not getting the right mixture from the carbs, I suspect lean in that range, and it has been said that running lean is not good as far as wear and tear goes. Due to that I just avoid running in that range which is pretty much fine anyway since I'm usually either at marina no wake speed or 6000+ RPM. I plan on replacing the carbs next year with new. I've had bad luck with curing mid range lean conditions by carb rebuilds on several engines and don't want to waste my time on that again. That and the PO indicated the carbs have been rebuild.
Yeah, this part bothers me because for the first 10 gallons of fuel during the break in apparently you're supposed to remain in that 2000 - 4000 RPM range while varying the throttle. It's really nerve racking.
 
Been doing this over 30 years and break in still makes me nervous and I still hate it but do it anyway.

The way I break it down is first half of the first premix tank is 1/4 to 1/3 throttle. Next half is 1/2 throttle. You don’t want a big load on the engine plowing water so if you have to give it a little more throttle to get it up and out that’s ok, just back it off. Second full tank the first half up to 3/4 throttle and the last half up to wide open throttle but never hold it there. Both tanks varying the rpm and plenty of cool downs. Then you are done.
 
Been doing this over 30 years and break in still makes me nervous and I still hate it but do it anyway.

The way I break it down is first half of the first premix tank is 1/4 to 1/3 throttle. Next half is 1/2 throttle. You don’t want a big load on the engine plowing water so if you have to give it a little more throttle to get it up and out that’s ok, just back it off. Second full tank the first half up to 3/4 throttle and the last half up to wide open throttle but never hold it there. Both tanks varying the rpm and plenty of cool downs. Then you are done.

So can I break the RPMs down like this?

Up to these RPMs, not over all while varying the throttle and taking regular breaks to cool:
1/4 tank - 50:1 Premix: 1700 - 2300 RPM
1/4 tank - 50:1 Premix: 3500 RPM
1/2 tank - Fresh fuel: 5200 RPM
1/2 tank - Fresh fuel: Up to full but for a short amount of time.

Go back to the dock after 30 - 60 minutes of being out on the water and let it cool for 15 - 30 minutes.

The one thing I did not do was push the throttle to get it out of the hole. I didn't know that was allowed lol I'd have to get it to at least 5k I think to get out of the hole. But if that's ok I'll do it.

I have only been plowing water, but off and on, nothing really pushing the engine, just slow going up to 3500 and backing off to 2000, down to Idle and so on..
 
Half tank of 50:1 mix is completely consumed! Finally! I swear I was close to being outta gas lol

Now getting new plugs, going to gap them, then filling with fresh 87 octane. Then I’m going back out!

I believe the Gap is supposed to be 0.022. I’ll recheck the correct spec when I get back.
 
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Took it out with a fresh tank and new plugs.

I got it on plane, feathering the throttle to keep it on plane. But, as I eased it past 4600 up to 5 that thing just opened up and hit 6200 RPM without any trouble. I did not mean to do that! And I definitely did not hold it there.

But I did get it out of the hole on plane a number of times without trouble, feathering the throttle back and forth between 4500 and 5200 RPM to keep it on top of the water for about 20 seconds at a time, then backing off easing it back to idle to settle.

After an hour of doing this I took it home. I'll be back at it in the morning doing the same until the half tank is consumed.

So far, based on everyones feedback, I think everything I've been doing to break this in is on point. I'll keep going until it's finished.
 
Another 1/8 tank to go and then the entire first tank is consumed. This part is hard. You don’t want to plow the water I guess, so you have to get on plane. I have to hit 5800-6000 to get on plane. Then with the lake as absolutely gnarly as it is I’m like getting thrown all over the place. Can’t do anything about that. What a total pain in the butt this is.

1/8th tank left then I’m going to ride it like normal not holding it over 6500 RPM.
 
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