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Unknown Boat +tuning questions

Old 06-30-2005, 11:47 PM
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TX_Firehawk
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Default Unknown Boat +tuning questions

Hello everyone- im a reg over in the electric airplane area but I just got a 10+ yr old boat from a older gentleman that knew I would give it a good home. Well this is my first boat as well as glow engine. I have been reading a lot about the engines and tuning but I have a few questions. When the boat is not in the water I can tune it to idle down low. Well the first time the prop had a load (water) what happned? You guessed it- motor dies.

Well now I know the boat needs to be tuned while its under a load. Well I am having a problem doing that. Let me back up- what I would like the boat to be able to do is idle down in the water and be able to go really slow if need be- However I asked the original owner about it and he just told me that he would start it and toss it in the water and go! So I am not sure if I am trying to tune it to a spec that it cant do. I can get it to run at 50% to full throttle but its still not 100%. I thought it might be starving for fuel so at one point I opened the needle valve a little more and I think it was too much b/c it was spitting unbuned fuel out the tail pipe ( not a lot ).


I have no info on the boat except for the engine and hull size. Its 2 1/2ft long and has a K/B marine engine and says 3.5 on the side of it. Here are a few pictures of the boat. The yellow paint is splotchy on the inside- it needs to be repainted in there. Anyway- I replaced the fuel tank, all fuel lines, added a fuel filter and also new water lines. It also has a new glow plug that matched the length of the one that came out of it. I purchased 5% fuel also- some have suggested going to 20%. I cleaned the whole motor and drivetrain and applied a lil household oil (not WD-40) to the internal bearings and what not. The action on it is smoooooth.







She is a beautiful boat







Engine all cleaned up. Notice the belt around the drive shaft- that is how I start it.






Backside of everything.


One question I have is the cooling. It is also making it hard to tune. I went and got a lil 8ft circle pool to test it at home. If the boat isnt going really fast in the water- no water goes through the system. There is a 1/2 inch long copper barb under the boat cut off at 45 deg- facing forward. I guess the water is ramed into there so to speak. I've seen it kick water out sometimes when its going fast. Well when I am working on it and its sitting still it heats up quick. The only solution I have found is a handpump but that gets tricky. Is this the way most boats are set up? I am already thinking of rigging a lil electric water pump that would only switch on at a low throttle position. Could slap a spare little LiPo on it for power

Any ideas or suggestions?


Thanks in advance!




Old 07-01-2005, 06:30 AM
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ob nut
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Default RE: Unknown Boat +tuning questions

The fuel tank needs pipe pressure.. Is there a nipple on the pipe? If so, connect a fuel line from that to the open line on the tank. If there is not one there, it'll need it. That might very well be the issue you are having keeping the motor running. Also, the K&B 3.5 LOVES high nitro. Think about getting 45% or higher.. Also, nitro motors are not known for going slow. As the previous owner told you, toss it in and go. Can't help out on the boat mfg, sorry...
Old 07-01-2005, 06:38 AM
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Default RE: Unknown Boat +tuning questions

First, this type of setup is designed to go fast. If you want a boat you can run reliably at idle speed, this is probably the wrong choice. They can do it some, but the way the carb is setup, they are mostly supposed to go in the 50-100% range that you said is working ok. Additionally, as you've found, the cooling system is a "forced cool water". If you don't go fast enough, water will not flow through the head. Over heating this kind of engine will lead to a premature death of the piston and liner. Electrics and gas boats with a clutch and water pump (for cooling) are a better choice for people who want to be able to go at slow speeds.

If you are going to stick with it, here's some tuning tips. With a mono, I can think of 3 significant factors to getting the engine running correctly. These are fuel mixture, pipe length, and prop size/depth.

I'll start with the pipe. The tuned pipe is designed to boost performance at a specific engine RPM range. When the engine is in that range, having the pipe will increase the RPMs. When the RPMs are not in that range, the pipe does little other than act as a muffler. You tune the pipe by changing the length. If the RPMs are slower, you make it longer, and for higher RPMs, make it slower. If you get the length too long, the engine won't "come on the pipe", and if it's too short, the needle becomes extremely sensitive.

I mentioned the prop size and depth because it will control what RPM range the engine runs in, which will effect the required pipe length. If the prop is too big, the RPMs will be lower, and you will need a longer pipe setting. I can't tell from the pics if your boat has a surface or sub-surface drive. This will also be related to prop size.

And finally engine tuning. Adjusting the needle so the engine idles well on the shore will result in a too lean setting, and your boat will do exactly what you described, die soon after launch. You've got to set it rich on the shore and then see how it runs on the water. I don't have a 3.5 inboard, but on my 3.5 outboard, the starting point for the needle is around 3.5 turns out. This results in a very "sloppy rich" idle, but not bad running once I open up the throttle while it's on the water. If you find that it's still rich, you bring it to shore, set it a bit leaner, restart it, and launch again. When I ran my new outboard a couple weeks ago it took about 4 short runs to get the needle to a point where it was still rich enough for break in, but lean enough to start working on trimming the way the boat ran. If you find this process too troublesome, reread my recommendation on electrics or gas boats. I think nitro is great, but of the 3 main power sources, they definitely require more adjustment. Once you get the needle correct, you should not need to change it much. If you keep it a bit rich you will not have to adjust it as often, and your engine will last longer.

One last comment on tuning. From your final paragraph, it sounds like you are looking for a way to make adjustments on shore. Here's a bit of advice, DO NOT TRY to adjust the high speed needle while running the boat on shore. These engines are designed to run under load. If you try revving up the engine on shore it's almost certain you will break the rod.

I've tried to cover the highlights, hope it helps.
Old 07-01-2005, 06:42 AM
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Default RE: Unknown Boat +tuning questions

ORIGINAL: ob nut
Also, the K&B 3.5 LOVES high nitro. Think about getting 45% or higher..
Not disagreeing that they "love high nitro", but my experience is that it's not necessary for casual boating. Mine have always worked quite well with 10-15%. For a non-racing boater, this is a much more economical choice.
Old 07-01-2005, 11:19 AM
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Default RE: Unknown Boat +tuning questions

wow thanks for all the info! Well I have to go in for a few hours today- on the way home I am going to check out some slightly higer % fuel and also a higher torque rudder servo.

As for the boat going slow- if it cant, thats cool, just would have been nice and helped with docking it or whatever. As for the fuel tank not having any pressure- there is no nipple on the muffler or anywhere for a hose to be attached. Do I need to tap the muffler? Also the muffler is 10.5 in and later today I will try and determine what prop I have (its metal- i guess brass?)


Thanks again gents!
Old 07-01-2005, 11:56 AM
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Default RE: Unknown Boat +tuning questions

Here's a link to help decide where to add a pressure fitting: http://www.macspro.com/pressure.asp . You will also need to add a second line in the tank to attach to the muffler. If the stopper seems hard and inflexible, replace it, many shops sell just the stopper kit, or just get a new tank, they're cheap.

Take the prop off and look for any names or numbers. There might be something on the hub where the prop nut contacts it, or perhaps between the blades. These numbers will help people tell you what prop you've got.
Old 07-01-2005, 02:42 PM
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Default RE: Unknown Boat +tuning questions

Talk about being on the ball chuck! I went out and got some fittings to tap the muffler. On the way home from work I was like dang! Now I am not sure where to put it. I will check out that link on where to tap it. I am going to the garage now, I will have some updates in a few hrs.

-Also got some 15% fuel w/ 18% (i think I will have to look) oil in it. Told em it was for a boat and he was like "ya you need more oil"



Old 07-01-2005, 06:44 PM
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Default RE: Unknown Boat +tuning questions

18% oil is what you are looking for. Best place to put the pressure nipple is at the point where the two cones meet, front or back of the weld. Then just hook up the pressure line from that nipple to the tank tube that you have pointing up. Only need the two tubes out of the tank. If the tap doesn't work, get some JB Weld, cut a few notches at the hole and "weld" the nipple on.

Oh yea, there's nothing wrong with going slow for a bit. As you commented, coming in from a run is perfectly fine. What you don't want to do is just idle around running a tank out.
Old 07-01-2005, 07:17 PM
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Default RE: Unknown Boat +tuning questions

ORIGINAL: ob nut
Then just hook up the pressure line from that nipple to the tank tube that you have pointing up. Only need the two tubes out of the tank.
Yup, you're right. I forgot to look back at the pic of the tank when I posted about the pressure fitting.
Old 07-02-2005, 03:01 AM
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Default RE: Unknown Boat +tuning questions

OK I got the muffler tapped- I decided on the spot that web site suggested for boats. Wasnt too hard at all. Went out to the pond and wouldnt ya know it both my glow starters are dead. Just part of the hobby but frustrating. I also added a fuel filling valve. I am happy thus far with the progress.. I am going to take it out tomorrow and see what happens. Ough, I also polished the muffler with 220 and then 400 grit sand paper. I think it gave the aluminum a nice clean finnish.


















Old 07-02-2005, 06:14 AM
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Default RE: Unknown Boat +tuning questions

Looks good, althought the filler valve was not really necessary. When you get a chance, see if you can identify the prop. Most props have marks either where the hub contacts the prop nut or somewhere on the hub between the blades. Also confirm that it is sharpened and balanced, this can make a big performance difference. Based on one of the pics you just provided, I'm going to guess that your boat was made by Dumas. If not the boat then at least the hardware, the rudder definitely looks like it came from Dumas.
Old 07-02-2005, 12:06 PM
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Default RE: Unknown Boat +tuning questions

I wanted to be coool with my fuel filler valve =/. Heh. Ya I will check on the prop later today.

Old 07-02-2005, 03:07 PM
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Default RE: Unknown Boat +tuning questions

OK the prop is an Octura X440.. How do I tell if its sharp? lol. It doesnt have any dings or chips in it, so I guess it is still good.
Old 07-02-2005, 03:38 PM
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Default RE: Unknown Boat +tuning questions

You can tell if the prop is sharp if it cuts paper or your finger when ran over it. Really though, see if it appears to have been filed / sanded. Back side should have a slight angle on the leading edge of the prop. The 440 should work fine for your boat.

In the past, I used those filler valves with so so luck. After about 15 times of using it, the fuel no longer went where it was supposed to. After that, I gave up on them. You might have better luck. Thinking back, don't know if the electric pump had anything to do with that. Might work better with a manual pump.
Old 07-02-2005, 03:40 PM
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Default RE: Unknown Boat +tuning questions

Do you have a prop balancer? If you do, put the prop on it to see if it's balanced. If not, there are plenty of different makes of balancers to be purchased.
Old 07-02-2005, 04:26 PM
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Default RE: Unknown Boat +tuning questions

I need to get a good prob balancer- the cheapo I use for my planes doesnt hold onto it well. And no the prop isnt sharp at all actually. Looks like it has never been messed with. I can go ahead and sharpen it like you suggested. I had no idea it was suppose to be that sharp! And I thought it was dangerous enuogh with a dull prop

Ough and the fuel brand I purchased (for $18) is PowerMaster w/ PWRPAK additive.


I am going to take it out later and see what happens.




Old 07-02-2005, 05:37 PM
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Default RE: Unknown Boat +tuning questions

ORIGINAL: TX_Firehawk

I need to get a good prob balancer- the cheapo I use for my planes doesnt hold onto it well. And no the prop isnt sharp at all actually. Looks like it has never been messed with. I can go ahead and sharpen it like you suggested. I had no idea it was suppose to be that sharp! And I thought it was dangerous enuogh with a dull prop
There's a thread with sharpening information that Ron was nice enough to pin to the top of the forum. The links have a bunch of pics that will help you know the difference between a sharpened and unsharpened prop. And yes, you need a boat prop balancer. Plane prop ones don't cut it.

I've got a filler valve on one plane. It's been fine for about a year now.
Old 07-04-2005, 07:38 PM
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Default RE: Unknown Boat +tuning questions

Well I was able to run about 2 tanks (17oz approx a piece) through it last night. Ran good. Went home happy. It was not really fast (it has a K/B 3.5 inboard) but I think that may be to my not having it that tuned yet. I have a 6mb 1.30sec avi of it but not sure where to host it.

Well I took it out today and I couldnt get it to start. Noticed some friction when i turned the prop at one point (like at TDC). Took it home frowning and took the motor/ drivetrain all apart. Turns out the idle bar on the glow plug had come off and was floating around in the cylinder! Meh. Glad I was paying attention and caught it. Anyway- I did that and also upgraded my steering servo to a Hitec Metal gear digital one a few days ago. Has like 140+ oz on it. Took it out again today with a new glowplug and It would start, but as soon as it hit the water would die. I couldnt not get to the bottom of it. I tried upping the idle screw (even though I was not trying to start it at idle) and also the main needle. Its like it just has no power. It has me stummped for sure. I checked to make sure it was getting fuel and all that, the muffler is creating the backpressure- just not sure why it is acting like this after it ran for a good 20-30 min last night.

Ough and my fuel filer vlave broke So it lasted me a week? lolol. The seal inside it will not break loose so fuel can flow. Ough well, its comming off.

So back to the boat- last night i was able to start it right up with 2 turns on the main needle and I ran it at about 80% throttle most the time. At about mid way through the 2nd tank I noticed the engine started to spin up a little more- like it was just getting broke in again or something. So I know it can run.


Any Ideas? Running 15%/ 18% caster still.
Old 07-04-2005, 08:29 PM
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Default RE: Unknown Boat +tuning questions

Fuel it up by pulling the line off the carb, it's the easiest and best way to do it.
For warm or hot weather running you might want to water cool the head first, then the exhaust.
We don't use idle bar glow plugs, they can hit (and probably did) hit the piston. If you have some that you still want to use, cut the idle bar off.
Old 07-04-2005, 08:43 PM
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Default RE: Unknown Boat +tuning questions

OK I will change the tubes around to cool the head first.. Still not sure why it dies when it hits the water.
Old 07-04-2005, 09:24 PM
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Default RE: Unknown Boat +tuning questions

Oops, I forgot to add something. If you want to post a vid, use www.putfiles.com , it's in a sticky at the top of the forums. The higher-ups here at RCU found this one and are letting us use it because it's hassle free, no joining up or any other problems.
Old 07-04-2005, 09:39 PM
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Default RE: Unknown Boat +tuning questions

OK cool, thank you. I did not see that sticky. Here is a link to a short video from the other evening. It is shot with my Sony Cybershot 5.1 megapixel camera in movie mode. The boat was running at about 80% throttle and seemed to be runing pretty good.

http://www.putfile.com/media.php?n=boat74


Copy and paste if you have to.
Old 07-06-2005, 08:33 AM
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Default RE: Unknown Boat +tuning questions

ORIGINAL: Ron Olson

Fuel it up by pulling the line off the carb, it's the easiest and best way to do it.
Ron, sorry, I disagree with that statement. Fuel up on the tank side of the filter. If done on the carb/needle side, the filter is useless since any garbage will be captured on the needle side of the filter. When this is done, then the garbage will go straight into the motor, if it makes it past the needle that is. Remember our Fun Run in 03? I did just that and the line popped off and had fuel go straight into my eyes. Reason why? The needle was inbetween and it could not handle the pressure of the fuel trying to make it past that. His needle is inbetween the carb and tank as mine is.

TX, what plug are you using? Looks like that K&B you have should be using the short plugs. If you are using long plugs, that could add to the mess you are having. If you only have long plugs, use two washers instead of one. It'll help put the plug where it needs to be.
Old 07-06-2005, 08:40 AM
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Default RE: Unknown Boat +tuning questions


ORIGINAL: TX_Firehawk

run about 2 tanks (17oz approx a piece)
What size of tank are you using? I know you are not racing and don't know if a large tank could be any issue. However, a 3.5 motor would normally only need about 6 - 8 oz of fuel for decent running times.. Wondering if an overly large tank could be another small issue involved with the over all issue of not wanting to run. While on the subject of tank, how are the lines within the tank setup? Pickup line should be bent down to be placed in lower left corner while the vent tube bent to the bubble on top.
Old 07-06-2005, 09:04 AM
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Default RE: Unknown Boat +tuning questions

Yup, you caught me Mark! As I was typing I kept scrolling up and down to keep looking at his pix. I had done some editing of my posting before I submitted it and completely missed that.

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