1QwkSport2.5r

The second picture in this post is mine... Must have dug it up from a previous page in the thread? Funny.

Any muffler led that fits will work. The sportster has really low timing and high compression and won't benefit much from a larger muffler. Running mine without a muffler didn't produce that much more power over the stock muffler. The baffled sportster muffler keeps it quieter but it does make more power without the baffle.

dakoris73

I do believe that I found this pic on the web so that I could use it as an example of what my muffler looked like before I blew the backend of it out. Since I have the k&b 61 muffler available, I will try this and see if this works for my motor. Another quick question: from what I've been reading about these motors, using an 11x7 prop may not be the best prop for this motor. I'm using this motor on a kit built Dirty Birdy to fly Intermediate Pattern sequences with, and speed is not as much a concern as torque and power for the long verticals, and it sounds like maybe putting a 12x6 prop on this might be a better choice. Can someone confirm this thinking so that I can get the best usage out of this engine?

1QwkSport2.5r

The sportster .65 is a torque engine. I use a 13x6 on mine, but it will turn a 14x4-5 too. With big props, keep the nitro low! 5% nitro and a 13x6 and you're set. A 12x6 works too but they rev about the same whether it's a 12" or a 13" diameter.

dakoris73

Thats something thats good to know. I'm used to using 15% nitro on all my planes, but I guess I might need to consider carrying two fuels for all my planes....... Why would I need the lower 5% nitro fuel instead of the 15% nitro fuel if I were to change to a bigger prop? Guess I'm not fully understanding how the % of nitro affects the different props used.

aspeed

Just a thought, you could replace the tail piece with a mousse can type muffler and maybe get more power. For bigger motors, I like to use lower nitro mostly because of cost. Higher nitro can normally run a bigger load, or more pitch at least. I could be wrong, maybe the motor might get hotter with the nitro, but a proper setting should take care of that.

aspeed

Just a thought, you could replace the tail piece with a mousse can type muffler and maybe get more power. For bigger motors, I like to use lower nitro mostly because of cost. Higher nitro can normally run a bigger load, or more pitch at least. I could be wrong, maybe the motor might get hotter with the nitro, but a proper setting should take care of that. http://www.spadtothebone.net/SPAD/Mufflers/ sorry for the double post, guess 'edit' is better than 'back'

earlwb

The nitromethane in the fuel acts like it is advancing the ignition point of the fuel. Generally the engine designers reduce the compression ratio as the nitro percentage increases which has the effect or retarding the ignition point in glow engines. Thus when you try to run too much nitromethane with a larger size propeller it can lead to detonation or pre-ignition occurring. That can cause overheating or a hole in the piston if it goes too far. But you can try it to see if it works or not with your engine and propeller combination. Just be aware of what happens so you can stop the engine before anything bad occurs.

1QwkSport2.5r

The sportster engine is timed and compressed in such a way so it can turn big props. They are designed to be the 2-stroke equivalent to a 4-stroke essentially; "the poor mans 4-stroke". I measured the compression ratio at about 11.9:1 on my engines; most sport engines are 8-9:1. High prop load and high nitro on high compression engines is dead stick territory. My engine would get hot and quit using 15% and a 12x6 or 13x6. Drop to an 11x6 or 11x7 on 15% and it behaved better but it still got pretty warm. Dropped to 5% and it throttled much better. The combustion chamber is not shaped well for higher nitro either.

I settled on 5% nitro 25% castor fuel and it runs significantly better.

dennis

My Feedback: (90)

Thought that I would show that the K&Bsportsters particularly the 20 and 28 are excellent engines to convery and use for ControlLine purposes. This is on my Primary Force model. They are particularly useful because of their 4 stroke ability and also the large prop that they can use relative to their size

dakoris73

Hello again.....

I replaced the muffler on my Sportster 65 with a k&b 61 muffler and it appears to be working great. I also changed my prop to a 12x6 MA prop and at full throttle, tacked out to 9800 rpm. I made a test flight with this, and the performance was acceptable, with quite a bit of vertical climbing power, which is what I wanted. However, there didn't seem to be much change when going from half throttle to full throttle, and flying about half throttle, the engine was rough, and "throaty" / hesitant sounding. I was hoping for a better transition on this motor, but currently not getting this. To help with diagnosing this new development, I'm using 15% nitro with about 25% castor fuel, and a new fox miracle long glow plug (made alot of difference from the OS 8 I was using previously), and I' using this in a kit built dirty birdy to fly the intermediate pattern sequence (alot of verticles in the sequence).......

Any help / ideas would be muchly appreciated as this is my first Sportster engine, and from what I've read, I'm considering another 2 more of these 65 Sportster engines if I can get this one all figured out.....

1QwkSport2.5r

My Sportsters turn an MA K-series 12x6 at 11,000 peak on 5% fuel. Your engine is running a bit rich. I noticed a similar phenomenon with not seeing a big rpm difference between 3/4 and WOT too.

earlwb

Actually most all of the engines tend to exhibit throttles being non-linear from 3/4 to WOT. I think that the only carbs that didn't tend to do that were the slide valve types of carburetors like the Webra Dynamix carbs for example. Some of the Chinese made engines tend to have carbs with too large of a bore and those are even worse for throttles being non-linear. You can even see it with the Walbro carbs on the gasoline engines too. I think it evolved over time as engine companies made the intake venturi bores are the carbs larger to increase performance, but at the same time requiring one to use more muffler pressure with the fuel tank to compensate for the reduced fuel draw of the carburetors. With some of the earlier glow engines they didn't use muffler pressure as the engine had to draw its fuel without help and thus the bores in the carbs was more small and those types didn't have as much non-linearity as such. But it was still there to some extent though. I guess what I wanted to say was with the engines the carbs are about at their maximum intake venturi bore size as the difference from 3/4 to WOT has become very little.

jeffie8696

I think manufacturers get in a numbers war over published HP and tend to make the carbs too large. Too bad really, if they just made carbs that worked correctly it would benefit the user a lot more than a tenth of a horsepower at some ungodly rpm that the engine will never see. But if they didn't they would sell less engines because most newbies just look at the power rating. I am as guilty as anyone of this as that is how I bought my first engine, luckily I have evolved and hopefully been able to pass my experience along on a few occasions.

AmishWarlord

My Feedback: (5)

I put up a Facebook Group for K&B engines if any of you guys are on Facebook.

https://www.facebook.com/groups/1464809237126309/

1QwkSport2.5r

Bringing back this old girl (thread) again.... Added two more Sportsters to my collection. A .20 & a .28. The .28 is brand new and quite tight. The .20 on the other hand.... Looks to have been run horribly lean once or twice by the ocean and put away wet. Everything inside is dry; rusty, and corroded. Not a drop of oil anywhere inside. Soaking parts overnight, will evaluate tomorrow if she's viable or not.

jeffie8696

I just picked up a minty 28 too.

1QwkSport2.5r

My .28 is tighter than a frogs butt! Like squeaky tight... The .65s I have were loose as a goOSe. Can't tell on the .20 yet. She might need a new piston and jug. She's pretty corroded. I didn't take any more pictures of the basketcase .20 other than the two I posted but should have. It's in pretty bad shape for only having been run probably one time.

jeffie8696

Mine is minty but it looks to have been run a lot. A good sign in my opinion.

AmishWarlord

My Feedback: (5)

Nice. I'm on a break from RC but still looking out for Sportsters on ebay. I have added four more.

1QwkSport2.5r

The .20 I got recently is the old non-bronze bushed crank and o-ringed head. The .28 has metal to metal head seal with shims and bronze bushed crank. Hoping with some elbow grease I can get the rust and corrosion life's and not jeopardize the piston seal. When I bought these two engines together, they were both said to be unrun "best as I can tell" as so the PO put it.

jeffie8696

I haven't looked at the 28 close enough to tell if its bushed or not but it is a remote needle valve model.

1QwkSport2.5r

Those are bronze bushed. Mine are non remote NVAs.

1QwkSport2.5r

Stupid dupe post...

carlgrover

I've got a .28 I just put on a Bokkie. That thing is fast as heck. Funny thing about the motor; with the stock muffler it's really quiet! Doesn't really make much more noise than an electric. Starts easy, runs great, and tolerates a very wide needle which is nice.




carl

1QwkSport2.5r

They have very effective mufflers. If you remove the baffle, they are a bit noisier but make more power. My .65s run fine without muffler pressure.