K&B .45 Sportster (old engine) - RC Groups
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Mar 30, 2006, 09:50 PM
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Kyle G.'s Avatar

K&B .45 Sportster (old engine)

Hello everyone! I'm generally new the Gas planes and engines. I'm primarily and electric plane kinda guy, but I recieved a Trainer with a K&B .60 motor and it's been a real pain to tune. The engine is probably 7+ years old, rarely run I believe. Not sure if it was broken in, but to be safe I'll say it wasn't. I took apart the motor, cleaned it out, and relubed it. Now I'm not all that new to engines. I used to do gas cars and have the idea on how engines work. I was told by someone at my flying field that K&B motors were a royal pain to tune. Is this true? It idles fine, but bogs down and dies when I throttle up. Too Rich? Any advice would be greatly appreciated. I'm about to take a look at the tuning thread at the top of the forum for some guidence, but was hoping someone with experience with this motor could pop in. Thanks!
Last edited by Kyle G.; Mar 31, 2006 at 11:19 AM.
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Mar 30, 2006, 10:06 PM
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mode1's Avatar
Sounds rich, but there are many other things to check. Tank location. Make sure your fuel is fresh and has enough nitro. Plug needs to burn bright. Prop correct size. Every part tight. Carb, head, backplate not leaking. What condition was the piston and cylinder in when you took it apart. Bright with little or no brown discoloration?

Never a top line engine but should run ok if not wore out or needs broken in some more and everthing else is correct.
Mar 30, 2006, 10:26 PM
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Kyle G.'s Avatar
Fuel is fresh, and has 10% nitro. Brand new plug, and that burns pretty bright I'd say. The prop is a master airscrew 10X6. Too small? I tightened everything on the motor when I reassemebled it, but I guess it couldn't hurt to check again. The piston looked new when I took it out, no discoloration.
Mar 30, 2006, 10:58 PM
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rockom's Avatar
I had a K&B on my first trainer. A royal pain in the arse. One of the older guys in the club said he and his buddies used to fly them all the time. He said the first thing they would do when they got a new K&B was to take off the carb and throw it away. They would replace it with a perry carb. The K&B engine idles so nice....but thats about all it does with a stock carb. I guess one good thig was I got practice with dead stick landings. Most of the time It woudl die on takeoff. Once in a while it would work ok. Next time out to the field I had to start all over again to find that sweet spot. I got tired if screwing around so I purchased a GMS 40. Never had any problems since. And Mecoa ( www.mecoa.com/gms/index.htm) gave me $20 off the GMS for sending in my old K&B. No questions asked....just put your old engine in a box with an order form from the website.

On my second GMS...A GMS47, I had some issues when I forst got it. Comparing it to my 40, a friend noticed the throttle set screw was missing a small gasket. Air was leaking into my carb. I put in a small gasket washer and it has ran perfect ever since. Another great feature of these engines is they are still available with the needle on the carb.

Mar 31, 2006, 02:23 AM
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Kyle G.'s Avatar
Rocko- do you have a link to the Perry carbs? I'm thinking that might be cheaper then getting a new engine. Though, thanks for linking me to that site, I'll be looking for a motor most likely for my Lanier seabird .40 sized float plane. Might be a good canidate. I don't have the money right now though to be getting a new engine.
Mar 31, 2006, 07:33 AM
Registered User
Well these engines dont need nitro and 0%-5% of nitro is enough. Actually they dont like nitro at all.
Mar 31, 2006, 08:34 AM
Figure Nine Champ
madsci_guy's Avatar
I LOVE K&B!!!! Been running them since 1978. Never found one I didn't like. I'm assuming that you have a standard .61, not a gold head ABC? And that it's not a .45 or .65? the fins are all the same diameter on a .61. Here's what one liooks like:


Does it say "60" stamped on the motor mount? Then it's probably a .45 Sportster. Here's what one looks like.


The way to tell is that they have 11 cooling fins not counting the head.

Here's a .65


They have 13 fins.

A 10-6 prop is too small, more like for a K&B .40. Try an 11-7. I really recommend the Perry carbs if you can get them. They like 15%-20% nitro or idle is going to be a problem. If the motor bogs down when advancing to full throttle, then close down the idle screw (on a stock carb) just a little. You need a really fine touch. The Perry carbs don't need adjustment on the idle disc generally.

Adjust the full throttle first, then the idle. You generally only want the thing to barely break into a two cycle at full throttle.

You need to listen carefully to the engine when you throttle up, after an idle. When it bogs down, does it go lean (sags with no four cycling at all) or rich (sputters in a four cycle)? That tells you which way to adjust the idle mixture. Does the problem get worse when you idle for a couple of minutes? Then it's probably too rich. Slowly tweak the idle screw on the throttle arm side until it gets better. You have to have a fine touch, but the results are well worth it

Make sure you get idle bar long glow plugs. These engines need them. Get Fox if you can find them, but K&B work good too.

Hope this helps
Last edited by madsci_guy; Jun 30, 2014 at 05:17 PM.
Mar 31, 2006, 08:46 AM
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rockom's Avatar
Google is your friend

Perry carbs are not cheap. I have never used on but hear they are worth every penny. Keep us posted.


Originally Posted by Kyle G.
Rocko- do you have a link to the Perry carbs? I'm thinking that might be cheaper then getting a new engine. Though, thanks for linking me to that site, I'll be looking for a motor most likely for my Lanier seabird .40 sized float plane. Might be a good canidate. I don't have the money right now though to be getting a new engine.
Mar 31, 2006, 11:15 AM
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Kyle G.'s Avatar
Val! Very informative post. It actually turns out I've got the .45 sporter I guess my uncle was wrong (the person who I got the plane/motor from). Either way, is the 10X6 prop still the right size? I just got some run of the mill glow plugs from my LHS. where do I get idle bar long glow plugs? Am I right that the Sportster only has an idle and high speed needle? Thats all we could find at the field when I had some people helping me. Thanks for the tuning tips, I'll have to run it this afternoon to see what I can get it to do. This gives me some hope

Rocko: If all else fails, the perry carbs don't look too expensive. I'll keep you informed on how things go.
Mar 31, 2006, 12:53 PM
Figure Nine Champ
madsci_guy's Avatar
Yeah, that's a real common thing. I can't tell you how many times somebody's confused the .45 Sportster for a .60 on EBay.

I think the manual says a 10-6 is normal. I have heard about, but not tried, an 11-4. One old timer said that the .45 generated more thrust that way and was perfect for slower trainers. Tower has them, but I would go with the 10-6 until that idle problem was fixed. The .45 apparently liked lower RPM, and wouldn't spin as fast as most .40's. It's kinda sorta the same as an OS LA45 in performance.

I think there is only one needle on the .45 carb. I would try the same procedure and see what that does. I think that carb was a little kooky, with the idle screw turning a disk? Does your engine have a remote needle? Then all that's on the carb is a disc with a screw in it. The screw only does a 1/4 turn either way for idle adjustment

Here's the manuals:

http://www.mecoa.com/kb/59/5900.htm (has tuning instructions)

For Fox idle bar glow plugs you can try these. They're called "RC Long":

From Tower

I don't know this brand, but Tower has some idle bar plugs. Some people complained that the welded bar would break off in flight, so they preferred Fox.


Or try your LHS and see if they have some Fox plugs

Good luck!
Last edited by madsci_guy; Jun 30, 2014 at 05:17 PM.
Mar 31, 2006, 10:40 PM
Registered User
Kyle G.'s Avatar
Ok, I took it out today. Tuned it best I could. I got it idling well (not really saying much). But I got it to transition from idle to WOT and back to idle without much hesitation. Now whether it'll do that tomorrow when I go to the field and try flying it, I don't know. I'll see what I can do about finding some of those fox plugs at the LHS.
Mar 31, 2006, 10:44 PM
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Timco's Avatar
Kyle, I have a .45 Sportster. It is a low cost engine but is said to swing a bigger than normal prop at modest rpm's well. There is no replaceable liner, the bore is plated and if damaged, its time for a new cylinder. Since it is a baffle piston design, as mentioned an idle bar plug is called for. It is a high compression engine, so 5% nitro max. I was testing mine on a test stand after I bought it used. I was using 15% nitro and it backfired and blew the prop off and the carb apart. There is an idle adjustment. Just above the needle valve, you will see a slotted screw head protruding through a notch in a brass wheel. Turn it clockwise to lean, and counter-clockwise to richen the idle. This effects the mixture to about 75-80% throttle so you have to adjust it for good transition. I took a picture, but don't know how to load a picture here from my computer.
Last edited by Timco; Mar 31, 2006 at 10:55 PM.
Mar 31, 2006, 11:06 PM
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Timco's Avatar
Kyle, I forgot to mention, the K&B carb that came with the engine worked fine for me. Try a 11x6 prop and don't expect it to scream. It is a good engine for a trainer.
Apr 01, 2006, 03:34 PM
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Timco's Avatar
Kyle, one last thing: This is not a ball bearing engine. A bushed engine needs castor oil in the mix. PowerMaster synthetic/castor blend is 1/3 castor, so this at 5% nitro would probably be the best for your Sportster.
Apr 01, 2006, 10:53 PM
Flyin' Ryan
I had a .45 Sportster in a Flightcraft Arrow (flying brick). It was fine for the first 30 flights or so, then it would take off and lean itself out to the point it died, all in less than three minutes. It would run fine on the ground at any or all thottle settings, but as soon as it got in the air it would lean out. I even took off at the richest setting that would develop enough speed to get it off the ground, then it would last maybe another minute. I never did get that thing to run right. I sure did get good at deadsticks though. I was in highschool at the time, and didn't have a new engine in the budget. It took all I had to get the plane. Most of my stuff back then was .049-.15, and most of it was used. Now I fly all electric, no more needle valves ect.
Good luck, and hopefully your problem is able to be solved.

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