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Outboard Motor Info

Old 01-14-2006, 03:34 AM
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Default Outboard Motor Info

Ok here it goes, this is going to be quite long.... lol. Plan on getting into a Top Speed 2 Tunnel in the next month or so, and want some info on some outboards to hang on the back. I know they suggest putting the o.s. .21 but I've been interested in the KB motors. Seems alot of people run them. As far as simplicity to run and maintain which one takes the cake. I've got experience in running nitro stadium trucks, so I can tune an engine. I do realize however this is the marine side of it, and things seem to be a little more complicated. I have a few questions....

1. Are the two basicly the same set up, I've seen posts on an "exhaust throttle" and have NO idea what this is and how it works. Please elaborate on what this is and how it works.
2. Does a bone stock KB have an exhaust throttle, or does it run off of a basic carb?
3. I'm getting into this for the sport, and not the speed. Not yet at least. So what motor out there besides the two can give me a good time, but still can be tuned fairly easy and give me a long life span.

I love the look of the outboard, so I'm really not interested into getting into an inboard. I buy and rebuild older outboards for my small v-bottom fishing boat so, I'll know most of the terminology associated with these minature motors.

Any imput at all is good imput to me good or bad, so have at it, just keep it clean please. Thanks a ton guys!
Old 01-14-2006, 11:30 AM
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Default RE: Outboard Motor Info

Both are good engines but more people are now leaning more towards the O.S.'s.
Being new to boats and outboards but with previous R/C experience helps. If for just one thing, keep in mind that these engines run the reverse of other engines so when starting you have to swap around the starter wires. The K&B drive also has left-hand threads if you opt for that one.
It's a great boat for the price and you might find that it will porpoise at low speeds until there is enough of a cushion of air under the tunnel for it to do its job.
Old 01-15-2006, 02:35 PM
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Default RE: Outboard Motor Info

Thanks Ron, btw I have read that the TP2 does porpoise a bit at low speeds but I don't see that as a major problem or flaw. I'm sure you've seen the life size version of these boats and they too porpoise at least half a lap untill they get some speed. I also have read that the outboards are "backwards" and need to be started in "reverse". As far as parts, are these parts readily available for the KB motors? Also I've been reading about a hopper tank thats needed to run the KB if you plan to use more than half of a tank of fuel. Is this a problem, or a hard fix?
Old 01-15-2006, 11:58 PM
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Default RE: Outboard Motor Info

The TS 2's aren't the only ones that are known for that, the Dumas tunnels will porpoise also at low speeds.
Parts can be found for the K&B's. Things were shaky for a while when MECOA bought out K&B as they had to retool all of the machinery for production but still a lot of parts are around, both from dealers and aftermarket suppliers.
There haven't really been too many changes since they first came out in the late `70's but try to avoid getting an early one as those parts are really hard to find. The biggest thing that you would notice about them is the short skeg on the lower unit.
Using a hopper tank will depend on where the main tank is located. If it sits low in the hull then it helps to have a 1 or 2 ounce tank sitting up near the carb but not too high as the carb can siphon fuel into the carb when not running, flooding the engine.
Old 01-16-2006, 01:59 AM
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Default RE: Outboard Motor Info

KB motors are quite easy to find on places such as eBay and I'd like to pick up a good used one. I know there could be trouble getting into a new motor seeing is you don't know what your gonna get. But I'm a risk taker and the prices they go for look awfully good. Is there any other place I can find used motors? A used O.S. would be nice, but I haven't seen one for sale, let me think, ever. Any good suggestions? I may just get the hull, and get it all put together and ready to accept a motor, then as spring rolls around pick up a motor.
Old 01-16-2006, 09:16 AM
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It should be the other way around as if you get a used engine from eBay you don't know what you're getting either as you could be getting a worn-out piece of junk.
There were some problems with some of the early runs out of the new K&B as owners were finding a lot of machine filings inside the cases so before turning one over, it's best to tear the whole thing down to inspect the inside. Compression on a used engine can be misleading also as they have taper-bored sleeves that can feel good when cold but as the engine heats up, the expansion at the top end will loosen things up and lose compression.
Old 01-17-2006, 04:14 AM
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Default RE: Outboard Motor Info

I have also read that alot of KB owners are going to a hopper tank mounted as high as the carb to assist in siphoning fuel to the carb. Does this have to be completed for EVERY KB motor, or just some who's engines are figity? If I do go down the KB route how do I mount this tank? Is there a tank size thats standard? Where do all of those lines go too? Also when mounting an engine to this perticular hull, is there a mount that would help in trimming the motor, if so is the a neccessity? I know this is alot of questions but who wants to have a boat dead in the water? I'd rather do my homework now, rather than learn the hard way. Your help is much appriciated Ron.

One more thing. Is there a reliable way to tell the difference in the older KB motors, and the newer models? Also is there a way to distinquish the models in general? i.e. 3.5cc/SS/SX
Old 01-17-2006, 10:39 AM
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The mounting and need for a hopper tank will depend on the boat itself as to where the manufacturer has the tank mounting area. If the tank is mounted low for improved handling then the hopper tank will help. On some you can only raise it only so high to keep it under the cowling. This doesn't apply to just K&B's but any outboard but can also be used in inboards.
The routing of the lines is to run your pressure line to the main tank as usual then the fuel line runs to the pressure/vent line of the hopper/reserve tank then its pick-up line to the carb.
The earliest K&B's have the short skeg, then the long skeg ones have a smaller crankshaft (12mm) will have the longer skeg and a black carb. The newer ones have a gold carb and a larger 13mm crankshaft. The SS is the easiest one to notice as it has a gold air-cooled head and a cannister muffler. The SX went back to a water-cooled head which I think it black. The cannister muffled exhaust was originally used on the old inboard engines that used an exhaust throttle as you can see where that was as they put plugs in the holes where the butterfly linkage was. www.mecoa.com will show you some of the differences in the engines. Some people have done carb swaps so if you buy a used one that might have been done. There were 4 different carbs that I know of, the black, gold, a red one that was made for the 7.5's that has a larger bore and a rare purple carb.
Motor mounts. There are a lot of them out there. Most prefer the Du-Bro. I've used those a lot but then I discovered the Octura. It's better but will also set the engine out a little farther than Du-Bro's. The one that I didn't like was the Prather, really hard to do adjustments on, especially when having to raise or lower the engine. You can find probably a dozen other ones on the market, some really fancy.
Until you decide on which OB that you're going to hang on your Top Speed 2, hold off on drilling any holes for the motor mount as the OS and K&B used different mounting holes. There should be a pattern for both in with the kit. Make sure that your instructions have been updated for the motor mount holes as there was a mistake made when they were printed.
Old 01-19-2006, 12:28 AM
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Default RE: Outboard Motor Info

Was looking around eBay and found this. Don't know about the tunnel hull, what is it anybody know? The motor looks brand new, KB SS. Claims it was in the water only an hour. What do you think? Good buy?

http://cgi.ebay.com/Tunnel-Hull-R-C-...QQcmdZViewItem
Old 01-19-2006, 12:56 AM
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The hull could be one of several. It possibly has the Dumas 7.5 cowling on it but may have been built from plans as Jerry Dunlap had some plans that used that cowling. It doesn't look too bad and at the current price, the engine alone is worth that and more. An hour's run time would translate into around 10 tankfuls of fuel roughly if it is true.
Old 01-19-2006, 11:33 PM
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Boat appears to be a Dumas 3.5 ABS Hot Shot Sprint. If you do get the buy, sell the boat on ebay and then buy a TS2. You'll be much happy if you do this.

As for ET's, I love em.. However, I would not suggest an ET for someone gettting into boats. I've used the Prather brass slider and Gardner XXL ET's for my OB's. Once the needle was set, motors screamed. I have someone currently building a copy of the Gardner XXL for my 11cc OB's. Can't wait to get my grubby hands on it..
Old 01-23-2006, 11:52 PM
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Well I didn't get the bid. I liked the motor, but I didn't wanna get into a ABS boat. It went to 180 so I quit. Still on the lookout. If you guys have any boats for sale, or know anyone who is willing to part with one, give me a holler... I just might be willing to take it off there hands. Thanks for the help guys, its much appriciated.
Old 01-24-2006, 10:07 AM
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There is a modded K&B 3.5 on eBay with a Cooper pipe but someone put the header and pipe on backwards. They have it shown sitting on a hull and I can see why they want to go back to electrics as they don't know how to set up the engine height, way too deep.
Old 01-25-2006, 03:38 AM
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Question about the KB engines again. If the engines are a little older, their site says you must replace the lower unit for one of the newer ones. How old is old? What year did they start putting in the newer style lower units? It says the prop shaft is clamped in. Another good one, how can I tell if the motor is so old it needs a new lower unit if any serivce is needed? Just a few questions I've got a bid in for an older Lap Cat with a KB 3.5, just wondering if I ran into any trouble with it what I was up against. I'm not afraid to dig in and make it work, just the tinkerer in me coming out. If you can identify it take a look, the boat is dog ugly but who's judging?
http://cgi.ebay.com/Dumas-tunnel-hul...QQcmdZViewItem
Old 01-25-2006, 06:46 AM
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Default RE: Outboard Motor Info

The lower unit style changed sometime in the mid-80s. The two main differences are a longer skeg and the prop shaft assembly screws in. From the angle it's a little hard to tell, but it looks like the skeg is long enough to indicate that the engine has the newer style lower unit.
Old 01-25-2006, 11:06 AM
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That's the short skeg version.
Old 01-31-2006, 02:22 AM
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Well, I picked one up. A Dumas Hot Shot Sprint tunnel w/ a KB 3.5. It has the older lower unit though, I do plan on getting a new one. I went with this on the account that.... if I got into a new boat and totaled it, I'd be out a good chunk of change. I picked this tunnel hull up for about 100 bucks w/ the motor and decided to tinker rather than go big and burn alot of money. I do realize that if I'm going to get into this hobby, as well as my others, this will cost a considerable amount. I figured if I was to get a good deal on one why not take it and work my way up as I'm just starting. Any input on the Hot Shot? Again good or bad, just keep it clean, I prefer m y ego to be as high as possible! j/k.....
ONEEEEEEEE more thing... lol.... if I have to replace the lower unit, do I just need to purchase the halves and put them together, or an ENTIRE lower unit assembly (lower unit halves, and all the inner hardware). The flex shafts are the same but as far as prop shafts and couplers are the different or do I need to change them. The older motors also used a 12mm crank correct? Parts available for these? Precision Boats has an entire lower foot from KB will the inner parts fit right into this new style foot? Sorry for all the noob questions, just excited to get into something new. Last thing, is it worth working so hard on this older motor? If I have to give it up I'm not going to be that dissapointed... lol....
Old 01-31-2006, 05:48 AM
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Default RE: Outboard Motor Info

The new style lower should be a bolt-on. You should be able to get it complete. Yes, there are still plenty of parts available for the 12mm crank versions.
Old 01-31-2006, 06:05 AM
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ORIGINAL: Thompy
ONEEEEEEEE more thing... lol.... if I have to replace the lower unit, do I just need to purchase the halves and put them together, or an ENTIRE lower unit assembly (lower unit halves, and all the inner hardware). The flex shafts are the same but as far as prop shafts and couplers are the different or do I need to change them. The older motors also used a 12mm crank correct? Parts available for these? Precision Boats has an entire lower foot from KB will the inner parts fit right into this new style foot? Sorry for all the noob questions, just excited to get into something new. Last thing, is it worth working so hard on this older motor? If I have to give it up I'm not going to be that dissapointed... lol....
From memory, the flex shafts are the same length. However, the prop shaft is entirely different. The old style clamped in when you screwed the two halves together. On the "new" style, the prop shaft screws in and out without having to pull the two halves apart. I think the water pickup was the same also.

Working on the outboards is no harder or easier than any other engine. Take good care of it and the only maintenance should be greasing the flex shaft, do this at the end of EVERY day you run it, and flushing out the fuel and adding after-run oil. Since it's second hand, it would be good to remove the engine from the lower unit and confirm that the bearings are ok. Note that in general I do not disassemble an engine unless I think there's a problem.
Old 02-02-2006, 02:21 AM
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Thompy,

If you are planning on just getting your feet wet instead of jumping in head first, I'd suggest you run the boat with the motor as is. Once you get used to it and want to upgrade, do yourself a favor and buy a new(er) motor. The lowers come as a package, not as a left or right side.

As for the boat, what version do you have? Is it ABS or wood? I've run both and prefer the wood over ABS. Many people have gotten the ABS version to run, but I could not. I do believe a mod'd ABS held the NAMBA SAW record for years. It can be done. My .02, the Hot Shot Sprint is a good starting tunnel boat..

My current wood HS Sprint:

Old 02-06-2006, 08:44 PM
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I've got the wood version, btw OB Nut. I'm waiting on it in the mail as we speak, I'm actually at school so when I get home hopefully my boat will be there too. I'm already wanting to dig in. If by chance this has the longer skeg, does that mean it is a 13mm crank? I'm looking to get a new motor in the future as well as still sticking to my plan on getting a Top Speed 2. I just want to get into a boat and get used water insted of land.
Old 02-06-2006, 09:44 PM
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ORIGINAL: Thompy
If by chance this has the longer skeg, does that mean it is a 13mm crank?
No, it can still be a 12mm. K&B didn't change to a 13mm until mid to late 80's I believe. I've been told that a few rank'd national racers would take the 12mm over a 13mm. Why, I don't know.. Easiest way to figure out what you have is take off the PTO plate. The 12mm will have a "L" stamped on the back side of the crank while the 13mm will have "13" stamped on it.
Old 02-07-2006, 03:43 AM
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Well, I got it in the mail today! Looks good, boat is in good condition no cracks, or anything out of the ordinary. Everything electronicly works great as well. Looking at the motor, it is the long skeg version, with the Black carb w/ the K&B stamped on it. Looks dirty, so I see a carb cleaning in my future. Has the Prather motor mount, and after looking at it, looks like a pain to adjust the motor, suggestions about a new one anyone? Disessembled the leg and the tube and the flex shaft look great, everything was oiled and stored correctly, looks well taken care of. Prop is an old Octura yellow plastic one I believe it says 1240. I know this is a piece of crap so where would be a good start for a couple of props? Took the head off, and the piston and sleeve almost look brand new, no scoring or deep grooves.... big time compression. The tank had some fuel in it, so I just threw it out, the Sulivan tank also had rotten seals so obviously it was rendered useless years ago, going to pick up another one or two to make a siphon tank. Any idea where I can go to get all of your guys suggestive parts? Like to shop at the same place, to make it easier for shipping and all that jazz. Thanks a ton for your guys' help, hopefully by the time it starts to warm up here I'll be ready to get on the water. And as always any other suggestions would be very much appriciated at this end!
Old 02-07-2006, 04:44 AM
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Get ahold of Bob (KRPNOVA on this site) at [link=http://www.philshobbyshop.com/]Phil's Hobby Shop[/link] for your boating needs.
Old 02-07-2006, 07:35 AM
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One more suggestion. Have you looked into joining a club yet? While ANY running of the boat is fun, getting together with others to run boats is even better. It's also a great way to get help. Go to the IMPBA web site: http://www.impba.net and click on the districts and clubs link. There are some great boaters up your way.

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