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k.b .21 tuning/ need HELP!

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k.b .21 tuning/ need HELP!

Old 07-31-2007, 07:04 PM
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fast9
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Default k.b .21 tuning/ need HELP!

Bought a used k.b .21 inboard and I'm trying to get it tuned in. Motor is used and compression is ok, runs fine with no load. Started out rich, wouldn't get on pipe. When I got it lean enough to get on pipe it really took off nice but then just sputtered and died. I tried going leaner and it really jumped up quick on the pipe, but then died again. Went back to the richer setting and really had to work the boat back and forth to get it on the pipe. As soon as it did it died again. Open to any and all suggestions as this is really frustrating!
Old 07-31-2007, 07:22 PM
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mr hydro 1
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Default RE: k.b .21 tuning/ need HELP!

What size prop are tou running on it and what type of boat is the motor in
Old 07-31-2007, 07:48 PM
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Default RE: k.b .21 tuning/ need HELP!

does the carb have a low speed needle? My k&b 67 would get on the pipe at 1/2-3/4 throttle but would quickly sputter and try to die anymore throttle. low speed needle was way out of adjustment.


Old 07-31-2007, 08:18 PM
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Default RE: k.b .21 tuning/ need HELP!

your tuned pipe might need to be....."tuned".....[:-], run thru the "search" function for more than enuff explanations/formulas on how to find the "sweet spot", the results of too long a pipe vs too short of a pipe will really mess with your needle tuning,(and your sanity),......[:@]
Old 08-01-2007, 08:32 AM
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fast9
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Default RE: k.b .21 tuning/ need HELP!

Ok, I'll check out the tuned pipe info as this is something I know little about. I got pipe with the motor and it looks to be a mac. The boat is a small cat running a prather 220. Prop is currently set pretty high, almost surface drive depth. The carb is red, does not appear to have a low speed adjustment. It does have a small hole in the side of it that appears to be an idle air inlet hole?
Old 08-01-2007, 09:23 AM
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Default RE: k.b .21 tuning/ need HELP!

No air inlet hole on a carb, put some pics up if you can.
Old 08-01-2007, 09:59 AM
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mr hydro 1
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Default RE: k.b .21 tuning/ need HELP!

I run a prather 215 prop on my sport 20, and stays on pipe nice with good throttle responce from 1/4 to wide open,with a 220 prop, I'm on and off with the pipe in the corners, If you had to lean motor down to get it on pipe,but ran good for 100 ft or more, then sputtered and died after that , You may want to check the bearings,if the bearings are bad they heat up the bearing housing and cause the housing to swell a few thousands of and inch,and draw air in and lean down the motor,

My k&B 20 likes to run rich and my brothers K&B 20 also, we fond out that in our sport 20's, they ran hot and by the 4th mill time lap and leand out and died. so I made a water cooled header, and haven't had any problems,in fact we moved up to a modifed prather 225 prop (just turned the 225 diamiter down to the same diamiter as a 215, this prop I race with.
Good luck,P.S. This is just my own expereance with them.
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Old 08-04-2007, 01:29 PM
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fast9
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Default RE: k.b .21 tuning/ need HELP!

Thanks for everyone's help. First of all, the main problem was the clunk had somehow looped itself around up to the right front corner of the tank. I couldn't even get it to do it again with the tank out of the boat. Once that was fixed it ran, but seemed to barely pull the prather 220. Hard to keep it on the pipe. Maybe the motor is a little tired. Might be just a little to much prop. I've ordered a new sleeve and piston and a different prop to try.

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