Christmas conundrum - RCCanada - Canada Radio Controlled Hobby Forum
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Old 12-22-2004, 09:45 AM   #1
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Christmas conundrum

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I have two engines, both MDS .68's. They both have approximately the same run time on them, probably about two hours or so. The problem is that even using the same prop and fuel, one develops WAY more power than the other. The only difference is that one has MDS stamped on the carb and one doesn't. I understand that this means the difference in having the new replacement MDS carb and the old one, but would it account for such a drastic reduction in power? The one with the unstamped carb is the dog. I don't have a tach to measure actual RPM, but on a Top Flite P-39 and a 12x6 APC, the strong one will pull the plane so fast, I actually worried about flutter. The other engine won't even get it off the ground in longish grass! Both are fantastic runners with instant transition and idle, but I would sure like to fix the one. Any ideas?
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Old 12-22-2004, 09:59 AM   #2
Ed Smith

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I would suggest that you take them apart and measure the setup of each. Timing, head clearance, ports etc. Also measure the carb. throat dia. Look for obvious internal differences, poorly fitting parts, bad bearings.

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Old 12-22-2004, 12:01 PM   #3
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Have you tried the Engines by Swapping the Carbs around :
They should be interchangeable .
Then if the "Dog" puts out a little more power, The solution then -is buy another carb.
Bear in mind, that you may have to give the "Dog" engine a bit longer time in running, because of the "Hopeful" increase in RPM. :
Make sure you borrow a Tachometer to establish what the rpm is first, before the change over carb.
Hope this helps. Merry Xmas. D.B.
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Old 12-24-2004, 12:54 PM   #4
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Hello; I had a similar problem with 2 sSaito 80's, I swapped carbs, exhausts, and props, but was unable to find what was causing one to run a thousand revs lower then the other. I finally just gave up on it and put the weak one in a GB Cub and the livelier one in a Bingo. Changing the carb didn't make any difference. I should have removed teh cam chest and checked the cam timing, but it ran so good at low throttle, I couldn't believe it was cam timing.
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