ORIGINAL: 1QwkSport2.5r
ORIGINAL: NM2K
None of the K&B Sportster .65 engines that I have ran (belonged to other folks) had a problem with a funky transition from idle to wide open throttle, once broken-in. The latter can take far longer than a normal engine. Remember, the piston is chromed, NOT the cylinder. So, we can expect the engines to run a little differently from normal.
In fact, I was surprised that such funky looking carbs could work so well, but work well they did. See if someone else that owns one of those engines will let you swap carbs for a float or two.
Good luck in your exploits and hang in there.
Ed Cregger
Well, the problem is nobody that I know of has any of these engines, much less any experience with them. There is 1 guy at my LHS that has ran several sportster engines so I have gotten some info from him that tested whether there is any needle compensation going on. He gave me a list of different combinations to try with mixture settings to get the transition clean. None of which worked. Now I understand the construction of the engine, and how it needs a long time to break-in. Based on the information I've gotten, it should be throttling pretty well at this point in time. A hiccup or a burp here and there I would expect. A rough, smokey, misfiring, snotty transition - No.
Randy at Mecoa said the military issued sportsters are ''spec'd to run WOT'' and ''they don't throttle well''. He told me I needed to replace the carburetor. What I dont understand is many of the old sportsters use the same style carb - needle on the carb body, and they run like a champ and throttle well. I'm trying to figure out whats different with my military carb compared to an early sportster carb. My engine's vintage is 1991 or so. The idle orifice on the mixture disk is so small I dont think I can measure the I.D. of the hole. The spraybar I would have a better chance at a good measurement. I have a feeling its in the spraybar or mixture disk or both that is the cause of some of the problems I am having with transitioning from about 4000rpm to 3/4-WOT. I wish I could see a normal sportster .65 running and throttling so I know what it ''should'' run/sound like. I'll have to keep messing with it and if it stays as consistent as it has, I'll order a new spraybar and mixture disk/o-rings. If that doesn't work, well... I don't have a plan C yet.
Being a military configured engine, the "problem" could be anything from porting to the carburetor. The civilian versions throttled well, just like any good R/C engine would throttle. I've seen these engines on the auction sites for as little as $30. A new carb is going to cost you that much. See if you can get one with the bushings installed and low run time. Then you can figure out your engine, or sell it and keep the good one.
Ed Cregger