50 hp force questions after recent test run

[kalebsheridan]

Hey everyone,
So I finally got my force out on the water for the first time this season. For context, it's a fixer upper. I just rebuilt the fuel pump and this sucker fired up without even the throttle advance after sitting for 8 months. I was excited. Anyway, on the test run I did 14 miles in rough chop. Max speed about 24 mph and burned about 2.5 gallons of gas. Ran between 110 and 135 degrees (temp sender attached to the top cylinder head). Played around with the trim settings a lot, this motor has no power trim. After this run I have some questions:

1. How do you all secure the idle speed screw? Mine walked out on me completely and I lost my idle setting during the test run. After I re tune it should I slap some loctite on it? Maybe I didn't tighten the lock nut enough.
2. I pulled the plugs the next morning to see how rich/lean I was running. Plugs looked pretty clean. The bottom plug looked noticably cleaner, and the bottom piston head looked dry and tannish. The top piston head looked black. I also noticed a little sea water in the cowling. Bad head gasket maybe? Running lean? I pulled the carb which I will clean in an ultrasonic cleaner in case the carb is dirty. Had good throttle response the whole time but the motor idled higher than I remember. Of course my tiny tach broke on the water so I couldn't verify. Also the motor would get a little harder to start with every startup (I stopped a handful of times to change the trim). Late last summer I tested the comp and she had 125 both cylinders on the dot on my cheap comp tester. Thoughts?
3. I found some cowling foam gathered under the carb. Looks like I blended some foam putting the cowling back on with the motor running and she probably ate some foam. I since ripped that out. Any good replacement foams? Or just leave it?
4. I'm new to boating in general, so is my trim setting good if I'm getting Max speed? The boat doesn't nose up much going 24 mph but cavitates pretty bad at the next highest setting. Again, no power trim so whatever I set is what I get. I may throw a hydrofoil on it. The last owner had one on the last motor for this boat so maybe it needs one. The boat is a 15 ft glass tri-hull. I've been told it's a slug.

Im curious what you all think. I'll send some photos of the plugs and a clip of the boat running.

 

[kalebsheridan]

here are the plugs. Left is top, right is bottom. Of course now they look the exact same in the photo, but the piston heads where certainly different colors.

 

[kalebsheridan]

Here's a tiny clip of the boat at max throttle. The butterfly only opens to about 80-90 % and I just adjusted the throttle linkage so I think that's the best I can do. Does the bow look a little low? This is at my fasted trim setting.
View attachment 1000004747.mp4

 

[racerone]

Maybe some foam bits went into the carburetor.----Reed valves do not like stuff stuck in them that holds them open.

 

[kalebsheridan]

Maybe some foam bits went into the carburetor.----Reed valves do not like stuff stuck in them that holds them open.

Any way to inspect/clean the reeds?

 

[Jiggz]

Any way to inspect/clean the reeds?

Yes, when you clean the carbs and dismount them, remove the intake adapter as well and with a flash light you can clearly see the reed valves.

As for the foam, if you don't mind the noise no need to replace the decaying foam insulation. But if you do want to replace it, the late Frank A suggested using Yoga mats for cheaper version. But if you wanted high quality one, you need something that is fuel/oil resistant, medium density rubber foam. Google it.

The spark plug do not look so bad but the service manual recommends using BUHW (92-99) or BUHX (84-91) gapless plugs NGK or UL18V orL76V respectively for Champions.

A clean piston may sound good but it's not for 2 stroke engine. A clean piston indicates a lean running cylinder equating to higher temps, detonation and eventually a failed piston or cylinder. You may need to adjust the air/fuel mixture screw (min 1 turn out from lightly seated). Initial setting should be I 1/2 turn out. Too rich of idle setting can cause carbon build up fouling the plugs. But too lean and it can cause piston failure.

Without a power trim, it's really a shoot of luck for trim setting as this all depends on sea state, wind state, loading, and speed. The sweet spot is when the boat is just slightly " porpoising" (bow bouncing up about 1~2 feet) about every 2~3 seconds in sea state of 0~1. A boat that is not propoising at top speed is basically "plowing" hence increasing water drag. Again, this is all relative and you just have to experiment and make a choice.

Need to tighten the idle screw tight. There's a lot of vibration inside the cowling or engine especially at top speed. If need be you can use a split lock washer (between timing tower and lock nut) or star washer to keep it in place.

 

[kalebsheridan]

Okay sweet I'll take a look at them. May be a while, I keep my boat on my family property halfway across the state. I don't have space where I live so I'll have to look when I go there next. If the motor sucked in foam past the reeds, will it just burn it up run out the exhaust? Or is it going to get stuck somewhere and be a problem?

 

[Jiggz]

If it went past the reeds, it'll just burn up or it can get stuck with the fuel recirc system. However, since the motor seems to running fine, it probably just burned up. Now if the motor is misfiring it could be jammed making the reeds open.

 

[kalebsheridan]

If it went past the reeds, it'll just burn up or it can get stuck with the fuel recirc system. However, since the motor seems to running fine, it probably just burned up. Now if the motor is misfiring it could be jammed making the reeds open.

Okay cool, all be sure to check the reeds for certain too.

 

[kalebsheridan]

Jiggz, I will look into getting some kind of foam perhaps. Thats good info of the plugs too. I was curious if these were wrong. I went to a marine supply and bought what they said my motor needed. Wouldn't be surprised if they were wrong so I'll order the proper plugs. As for the air/fuel mixture, I was running 1 1/4 turn out. Perhaps too lean? I'll clean the carb and readjust. I'll use something on that idle screw. No good if it just undoes itself. How did my motor performance sound? Is that acceptable for MPH and MPG?

 

[Jiggz]

Jiggz, I will look into getting some kind of foam perhaps. Thats good info of the plugs too. I was curious if these were wrong. I went to a marine supply and bought what they said my motor needed. Wouldn't be surprised if they were wrong so I'll order the proper plugs. As for the air/fuel mixture, I was running 1 1/4 turn out. Perhaps too lean? I'll clean the carb and readjust. I'll use something on that idle screw. No good if it just undoes itself. How did my motor performance sound? Is that acceptable for MPH and MPG?

24 MPH at WOT is not bad at all especially for a tri-hull boat. A tri-hull provides more stability on the water but at the cost of more drag. So I say 24 MPH is decent. As for the air/fuel mixture screw, 1 1/4 is not bad. Do an assessment again after switching the plugs. If the bottom cylinder continues to be whistle clean, you might want to check for air leaks. Air leaks into the cylinder causes lean combustion. Jerry has a method to detect air leaks.

As for the idle screw, pull it out and check the threads. It's easily replaceable, i.e. 1/4-20 pan head screw and might as well replace the lock nut, if you think the threads are worn out. Replace with Grade 5 or 8 screws and nuts or stainless one.

 

[kalebsheridan]

Okay well that's good to know. I had no idea this was a symptom of tri-hulls. I'll have to do more research on them so I know what to expect. It is very stable. It not a big boat but two people can stand on one side of the boat and it won't tip much at all. How about fuel economy? By my math I was getting between 5 and 6 mpg. I will order those plugs and try again like you said. What's my chances of burning up a piston running on the lean end while I troubleshoot? I know this is a possibility but how likely? Will I see it on my temp gauge?

 

[jerryjerry05]

The foam probably won't get past the reeds. It would just lump up and cause poor running.

 

[Jiggz]

Okay well that's good to know. I had no idea this was a symptom of tri-hulls. I'll have to do more research on them so I know what to expect. It is very stable. It not a big boat but two people can stand on one side of the boat and it won't tip much at all. How about fuel economy? By my math I was getting between 5 and 6 mpg. I will order those plugs and try again like you said. What's my chances of burning up a piston running on the lean end while I troubleshoot? I know this is a possibility but how likely? Will I see it on my temp gauge?

With new plugs, you need to ran the motor (hose and muffs) on the driveway idling and a little short burst not to exceed 2000 RPM. Ran it for about 3 minutes. If you have starting fluid try spraying it into the carb adapter (do not let it in to the mouth of the carb), transfer port covers, etc. And see if there's changes in RPM. A change in rpm indicates there's a leak that is sucking the starter fluid resulting in more rpm. If no change in rpm that means no air leaks. Stop the engine and check the plugs again. There should be a little wetting from oil/gas and a little browning from carbon. This is normal. Fuel consumption on 2 stroke engine is not the best. Especially if you are always running on WOT.

 

[kalebsheridan]

With new plugs, you need to ran the motor (hose and muffs) on the driveway idling and a little short burst not to exceed 2000 RPM. Ran it for about 3 minutes. If you have starting fluid try spraying it into the carb adapter (do not let it in to the mouth of the carb), transfer port covers, etc. And see if there's changes in RPM. A change in rpm indicates there's a leak that is sucking the starter fluid resulting in more rpm. If no change in rpm that means no air leaks. Stop the engine and check the plugs again. There should be a little wetting from oil/gas and a little browning from carbon. This is normal. Fuel consumption on 2 stroke engine is not the best. Especially if you are always running on WOT.

Awesome I will do that once I fire up the motor next. How long would you think it would take for that color to appear on the plugs? Pretty quick or do I need to run the motor a couple hours? Glad to hear my fuel consumption is typical.

 

[Jiggz]

The wetting should happen pretty quick. The discoloration may take awhile until you do the long runs. But with wetting, rest assured there's enough lubrication in the cylinder.

 

[kalebsheridan]

In addition to the performance topic, would there be a any point in trying a hydrofoil? I only ask because I have one from the last motor the previous owner had on this boat (a 70s Evinrude 55hp). I've been told this boat is kind of a slug and maybe the original owner thought it needed it? Just something I've been thinking about. The stern could be pretty heavy for this boat, I keep about 15 gallons of fuel, a battery, and a kicker back there. I still want to troubleshoot further before drilling any holes in my LU but I thought I'd post the question.

 

[Jiggz]

Hydrofoils do help in preventing the bow rising too high by pushing down on the water to keep the stern up. However, there's no such thing as free lunch, for the payback is in lost of speed. Not a whole lot but you will lose some top speed.

 

[kalebsheridan]

Just tried the new plugs like you recommended and cleaned the carb again using an ultrasonic cleaner. Both plugs are now damp with fuel which makes me happy about not running lean. I wanted to tune the motor properly but my induction tach broke. I'm sure she's running a tad rich but I feel better about that than a tad lean. Air mix is set to 1.5 turns at the moment but I have no idea what the idle is at. Sorry for the wait, I live on one end of my state and my boat stays with my family on the other side of the state. I only work on it when I'm over there of course. I ordered a new tach and will tune and test run next time I'm over there.

 

[cyclops222]

I think you are getting RAMMY about the boat and engine. It is FINE.
Buy a decent used boat & use it to absorb all your creative rammy energy.