I need help with my new boat.

[rcboatlover]

Hey I finaly got done with my 36" Dumas Skdaddal and tried it out last night. I was able to run a few laps with it, but the engine keep bogging down and quiting. I had it set pretty rich and slowly leaned it out untill it seemed too lean. No matter what I did the engine speed slowed down till it quit. Do you think it's over heating? There was always a steady stream of water comming from the water outlet. Everything is new and I don't think it's a fuel problem.

The engine is a OS .40 four stroke and I'm running a Octura 452 prop with the toung cut off. The drive is set up as a surface drive.

Any ideas would be appreciated!

Dale P.

 

[ScottVanSlooten]

Not sure about four stroke motors but if these are like dirt bike motors you may be over proped. At frist It sounded lean but when you got to 4 storke you lose me . Try a smaller prop . Scott

 

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1) Check for any leaks in the fuel/pressure lines

2) Make sure the cap on the fuel tank is good and tight. You can check by pinching off one line and blowing into the other. If the tank swells and holds it's good with no leaks.

3) Is the tank set up with a clunk pick up?? Maybe it's facing the wrong way?? I like to bend the fuel pick up down into the lower left hand corner and point it towards the carb when i put the tank in the boat.

4) Check the gasket and back plateseals for leaks as well, could be a good indication that the bearings are bad.

5) Is there a low end adjustment on your carb??? Maybe it's so lean no matter what it kills the engine going into the turns.

6) The 452 prop sounds rather big for an OS .40 engine, do you have an X-447??

7) Is this the engine with the little airplane barrel pipe?? Or do you have a tuned pipe on this motor?? You should maybe be at 9 3/4 to 10 inches.

 

[Preston_Hall]

Dale,

Is this engine a marine four stroke version? If not, then I am curious as to how you are cooling the engine as we normally cool the entire head and you have a valve cover there. Got any pics? It does sound as though you are overheating or drawing water into the carb.

 

[Don Ferrette]

"The engine is a OS .40 four stroke and I'm running a Octura 452 prop with the toung cut off. The drive is set up as a surface drive."

I'd also wonder if the X452 is a bit much for a .40 four stroke. Try propping down to say a X447 until you get it close then size up from there. B)

 

[Preston_Hall]

A four stroke would be much more capable of pulling a larger prop and shouldn't suffer such great ill effects. R/C airplanes may slow because of too much prop, however I haven't seen one overheat because of it. I still would like to see the water cooled head for a four stroke. Even if it encloses the valve cover it isn't directly cooling the head button.

 

[rcboatlover]

Thanks for all the replys! The engine is a marine version that OS made back in 1983. I got two of them NEW in the box off E-Bay for $200.00 . Every thing in boat is new. Fuel tank, lines, etc. I checked every thing twice and it all looks great, so I don't think it's a fuel delivery problem.

You might be on to something about the prop size. I will have to try a smaller one. The owner of the local hobbie shop said I should be able to swing a Prather 270 or X470/3 with that engine! I whish they knew what they were talking about before trying to help poeple out. Well I though it would at least turn a X452. But I will have to try something smaller and see.

As for the muffler... It has a small manifold maby 3/8" in diameter with a muffler and pressure nipple at the end. It is the stock system that is to be used with this engine. I'm pretty sure that a tuned pipe won't work with a four stroke. The valve would be closed when the charge tried to come back into the engine.

Keep the ideas comming!

Thanks for all the help

Dale P.

View attachment 2587

 

[Brian MAhoney]

Was the marine four stroke ever a sucess, the cooling does not look suficient to me.

Also in aircraft don't the four strokes turn bigger props at lower revs than 2 strokes? Could be that a bigger prop with lower revs would better match the engine.

Brian

 

[Preston_Hall]

Was the marine four stroke ever a sucess, the cooling does not look suficient to me.
Also in aircraft don't the four strokes turn bigger props at lower revs than 2 strokes? Could be that a bigger prop with lower revs would better match the engine.

Brian

I agree. The planes can turn anything. The lower revs with more pitch will often provide better performance.

Dale,

Still make sure you aren't sucking up any water. The fact that it goes out and bogs down still sounds like heat or water. If it were fuel or air leak then I don't think you would see a bogging but more of a quit. One other thought would be to remove the back plate and check that the timing marks on the cams are lined up.

By the way, what does the plug element look like after it runs and dies. Is it still shiny, kind of dull, or real dull? Shiny is good and rich. Kind of dull is good. Real dull is too lean. Now that we are talking plugs maybe your problem is a lack of heat on the plug. Maybe somebody could suggest a hotter four stroke plug. Or you could try an on board ignition.

Pic is cool. 1983 is before my RC days.

 

[rcboatlover]

It's been raining here for three days and I haven't had a chance to try it again! Lot's of flooding every where! I'll be able to try it again on Sunday.

To answer your questions...

The plug was pretty black, but the needle was set at three full turns to start and it would start to flood out when the throttle was pulled. I had to turn it down alittle to get it to stay running at WOT. Any richer and it wouldn't start. Around 2 1/2 turns out seemed to be the right place for the engine to run well yet still remain on the rich side.

As for sucking up water the boat only went 25 to 30 mph and hardly made a splash. As you can see in the picture the carb is turned down making it even harder for water to get in.

I'll definatly check the timing before Sunday. You don't go through the back plate though. There is a little round cover on the front that covers a tiny cam shaft. I'll have to check the valve clearance on the lifters too. Might be that one is not closing all the way.

Thanks for all the help! I'll let you know how it worked after the weekend. I will post some picts of the boat as soon as I can.

Dale P.

P.S. As for the Marine version ever being a sucess? I don't know? But they only made them for a few years. <_< Could be because they diden't run well, or the fact that they are slower than #@$%! I only expect to get 30 to 35 out of it, but it still should be fun. Not to mention that it will be the quietest nitro boat on the pond.

 

[Don Ferrette]

"The plug was pretty black, but the needle was set at three full turns to start and it would start to flood out when the throttle was pulled."

Put a smaller prop on it.

 

[rcboatlover]

Thanks, I'll check the boat and engine over to make sure everything elce is fine. But the smaller prop will be the first change I'll make.

Thanks again, Dale P.

 

[Propjockey]

I got two of them NEW in the box off E-Bay

Were there manuals in the box? If so, go through it and read about adjusting the valves. I flew with a guy that ran four strokers, and he said the valves always seemed too loose when the engine was cold, but after it heated up the valves/rockers/pushrods would tighten up.

 

[rcboatlover]

Thanks Propjocky,

Yes they did come with instructions. I checked them out and they were fine. I bought a x447 prop and have the boat ready for the water, but it's raining AGAIN! What the @#$%! As if 10" of rain last month wasn't enough! The ponds are nice and full, it can stop raining any time now. Hopefully I will stop sometime today and I will get a chance to get it back out.

* Yes I know I could run it in the rain. It's a boat and it is made to get wet, but I'm not. I work out side all day in this crap and it would take the fun out of boating if I had to go out in it again.

Thanks again for the tips!

Dale P.

 

[Preston_Hall]

As for sucking up water the boat only went 25 to 30 mph and hardly made a splash. As you can see in the picture the carb is turned down making it even harder for water to get in.

Actually I thought it would be easier for water to get in the motor. If there is any water in the boat then the vibrations will certainly have a chance of helping water to the carb. It's just a thought.

 

[rcboatlover]

Thankyou, Thankyou, Thankyou!

I diden't have time to check any thing out on the boat. I put on the smaller prop that you guys said to try and gave it a shot. It ran beautifully! This engine isn't the fastest thing, but it just keeps on going. I could bring the boat to a very, very, very, slow crawl past the dock and it kept plugging away. There were several die hard boaters at the pond and every one said that they never saw a nitro boat run that smooth and flawless. The only time it quit on me was when I ran it out of fuel! It took 20 min to run through 5 oz of gas.

I was worried about the water cooling, but it seemed to work just fine. The engine was alittle hot to the touch when brought in, but it wouldn't boil water when you put a few drops on it.

Thanks again for the the help! I had a cool little boat to show off tonight. It even ran with three other boats in the water and handled the chop well.

Dale P.

 

[Don Ferrette]

" I put on the smaller prop that you guys said to try and gave it a shot. It ran beautifully!"

Glad to see things are working for you. I learned a long time ago don't try to spin a big prop when you're first gettin' a boat wet, dial it in a small blade you know it can handle. In this case it's what it needed to make it all come together. Now you can experiment with small increases in blade size to see if it can pull a little more. Happy boating!

 

[rcboatlover]

Hey thanks again. I don't have a very large prop box. Infact I only have eight at this time! So the X452 was the only thing I had on hand when I tried the boat the first time. I thought the engine would turn it, but I guess it can't . I'm thinking of trying a three blade in it in the future. The LHS has a X447/3 instock. Just might pick that up this week.

Well thanks again, Dale P.

 

[dannyual767]

rcboatlover, I'm very happy to hear that you got your 4 stroke propped right. I've got a 36" SK as well. I haven't finished it yet and my progress is real slow so I don't think that it'll be in the water until later in the summer. I've got some questions.

1. How much does your boat weigh (bare hull or with engine and full radio gear and hardware)? I've been trying to keep my hull as light as possible. I'm already at 2lbs 10 oz for my bare, unsealed hull.

2. How does your boat handle? I'm sure you installed a skeg under the bottom center of the hull as the instructions say.

3. Did you get "propwalk" with that surface drive setup? Maybe that 4 stroke doesn't turn enough rpm to cause much trouble. Not too long ago, others recommended that I not use a surface drive system for this boat because the bottom is too flat and that I'd get too much propwalk with my high rpm OPS 67 or K&B 67.

Thanks.

 

[rcboatlover]

oops