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Engine basics => Engine set up tips => Topic started by: Steven Kientz on March 09, 2012, 12:50:11 PM

Title: K&B sportster.20 r/c
Post by: Steven Kientz on March 09, 2012, 12:50:11 PM: Picked this up on an out of town trip. Looks like its had very little use. Was hoping it was a .28, but measured as a .20 when I got home. Will it pull a lite Skyray size airframe? Or are we talking something smaller? As far as id on the venturi, same size as a .25 to start with?

Thanks
Steve
Title: Re: K&B sportster.20 r/c
Post by: Bill Little on March 09, 2012, 01:24:38 PM: Hi Steve,

From what I remember, it isn't quite as strong as the OS .20FP. But not far off.

Bill
Title: Re: K&B sportster.20 r/c
Post by: Balsa Butcher on March 09, 2012, 02:47:49 PM: Friend had one back in the day. Nice engine, smooth, one speed run. I think it would do fine in a Skyray. 8)
Title: Re: K&B sportster.20 r/c
Post by: Steven Kientz on March 09, 2012, 04:11:58 PM: Thanks, now I have an excuse to build another one.

Steve
Title: Re: K&B sportster.20 r/c
Post by: Clint Ormosen on March 09, 2012, 10:38:34 PM: As a bonus, they're usually one flip starters, too! Even hot restarts are no problem.
Title: Re: K&B sportster.20 r/c
Post by: Steven Kientz on March 10, 2012, 12:45:58 PM: Any comments on id of the venturi? I've been making my own out of some flared tubing(auto parts) and some plastic and brass water line fittings(new pex or plastic). Yeah they aren't real pretty ,but VERY functional.

Steve
Title: Re: K&B sportster.20 r/c
Post by: Bill Little on March 10, 2012, 12:57:01 PM: Quote from: Steven Kientz on March 10, 2012, 12:45:58 PM
Any comments on id of the venturi? I've been making my own out of some flared tubing(auto parts) and some plastic and brass water line fittings(new pex or plastic). Yeah they aren't real pretty ,but VERY functional.

Steve

Hi Steve,

I am just guessing here, but I would expect a venturi the size of the OS .20FP should work fine. (I don't know the measurement, though)

Bill
Title: Re: K&B sportster.20 r/c
Post by: Tim Wescott on March 10, 2012, 02:34:04 PM: Quote from: Bill Little on March 10, 2012, 12:57:01 PM
I am just guessing here, but I would expect a venturi the size of the OS .20FP should work fine. (I don't know the measurement, though)

I'm upstairs, but if someone else hasn't answered by the time I get down to the shop I'll send some dimensions.

Search on venturi size, you should find lots of posts.

Remember that the important thing is the venturi area; for these dinky little engines with spraybar-style venturis the area is heavily affected by the spraybar diameter -- so if you just match someone else's throat diameter without taking their spraybar size into account, you'll get it wrong.

(and to complicate things, if you're building your own and you get the spraybar significantly off-center, you'll end up with a bigger venturi area than you would have with the spraybar centered).
Title: Re: K&B sportster.20 r/c
Post by: dennis lipsett on March 10, 2012, 06:27:12 PM: A venturi for the K&B 20/28 Sportster is easily done by getting a Fox venturi and NVA for their current 25BB engine. It is a direct fit usually needing a thicker O ring to bed well. I have used them with a piece of 1/4 inch brass tubing flared and fit to the venturi for the 20's but it really isn't necessary. This is a painless conversion done this way.
As to it's ability to fly the Skyray I flew my first Primary Force ARF with a 28 and then to prove that the 20 was the equal to the task it went on the 2nd one. These are not light models and they did a very credable job flying them. I am at 500 feet above sea level and flying was on 60 ft .015 with Powermaster 5/25 and 10/5 props. The Sportster series are not high rev engines and can deliver very good power in Fox type rpm ranges. Just don't look fot that 4/2/4 run on them.

Dennis
Title: Re: K&B sportster.20 r/c
Post by: Steven Kientz on March 11, 2012, 08:02:08 AM: Thanks guys

Steve
Title: Re: K&B sportster.20 r/c
Post by: Don Curry AMA 267060 on March 11, 2012, 02:01:55 PM: Scott Riese made a venturi for my .28 Sportster and used the clamp bolt hole to make a sprinkler type spray bar that does not go through the middle of the opening. It worked very well until the engine swallowed some crud off of the black top and ruined the engine.
Don
Title: Re: K&B sportster.20 r/c
Post by: Steven Kientz on March 14, 2012, 02:22:26 PM: thanks Don

Steve
Title: Re: K&B sportster.20 r/c
Post by: Mike Greb on March 14, 2012, 05:02:51 PM: Anybody else broke the rod in their K%B 20 Sportster? Running it on a tipan 7-4 on a monoline trainer may have had something to do with it.
Title: Re: K&B sportster.20 r/c
Post by: RDJeff on March 15, 2012, 09:52:20 AM: In case anyone is interested, I have a couple that I don't need...
Title: Re: K&B sportster.20 r/c
Post by: Paul Wescott on March 15, 2012, 12:56:37 PM: Quote from: RDJeff on March 15, 2012, 09:52:20 AM
In case anyone is interested, I have a couple that I don't need...

RDJeff - A couple of what? Rods, Venturi's, or K&B Sportsters?

Paul
Title: Re: K&B sportster.20 r/c
Post by: L0U CRANE on March 17, 2012, 01:36:24 AM: Mike G, on a 7 - 4 ? ? ?

Yeah, might have had something to do with it...

Interesting to know that the Fox 25BB choke fits. Have a K&B Sportster .20 that was not an easy starter on the OEM carb. So, cut a venturii for it and it is a very easy engine to start. The stock muffler can give you a very quiet run - it can be VERY loud with no muffler, btw.

RJL might have rods or any other parts for the Sportster K&Bs - they are the current producers of K&B engines.