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"Different" Behavior on Brison Engine?

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Old 03-27-2006, 03:38 PM
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splais
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Default "Different" Behavior on Brison Engine?

I have a new Brison 5.8 engine that has not even flown yet. I have run it on the ground three or four times. The engine has a stange throttle response to the several other gasoline engines I have had.

Most gas engines seem to develop all their rpm in the first half of throttle movement unless you adjust your throttle curve. This Brison engine has a linkage with no slop, and yet coming off idle I can go to half throttle before I get a serious increase in rpm. All the increase comes in the last half of movement. The only other thing I can add is that the engine has mechanical advance. I'm really not a fan of this delayed throttle response. I'm pretty sure I could adjust it with some positive expo on the throttle; but I'm not sure I want to do that. thanks for any knowledgable comments
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Old 03-27-2006, 04:47 PM
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Default RE: "Different" Behavior on Brison Engine?

Gotta be the way the mechanical geometry is set up..You can change the linkage to get linear throttle...Try different holes in the bell crank or on the carb...
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Old 03-28-2006, 12:56 PM
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Default RE: "Different" Behavior on Brison Engine?

I have a Brison 5.8 that is several years old in my Ziroli Corsair. What you described about your throttle operation is exactly opposite from my experience. I checked my Futaba 8U transmitter and I have -40 expo on the throttle channel. Without the expo, the engine tries to get most of the RPM in the first half of throttle stick travel as you mentioned about your other engines. Otherwise, does your engine run good? My 5.8 has been super good. Here is a photo for comparison purposes.
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Old 04-09-2006, 07:54 PM
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Default RE: "Different" Behavior on Brison Engine?

Big Bird,

yours looks exactly like mine. I have watched the throttle movement. It seems pretty normal through the range. But the rpm just doesn'tr come on until half throttle. I'm going to have look at the linkage and actually watch the throttle baffle to see if the geometry is causing the problem I guess.
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Old 04-09-2006, 08:19 PM
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Default RE: "Different" Behavior on Brison Engine?

Have you tuned the engine?

What size arm are you using on the servo, how much ATV percentage? My experience with gasser linkages suggest we need to move the carb throttle shaft approximately 80 degree's and the servo near 120 degrees to realize decent resolution and throttle response. Obviously the linkage/bellcrank ratio plays a big part of the final output ratio. You should be using near MAX ATV or end-points with the appropriate servo arm length for the best results.
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Old 04-10-2006, 09:32 AM
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Default RE: "Different" Behavior on Brison Engine?

For all.

I'm taking all this into consideration. But isn't the bottom line that rpm depends purely on how far the the throttle plate is open regardless of what your linkage is doing. I've never actually looked at any of my engines before - but maybe the plate has to be at say something like 45 degrees open before the rpms kick in. Is this the case? Because if that is true then how fast your linkage opens the plate in relation to the throttle stick position would be an issue.

Do I basically have it figured out?
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Old 04-10-2006, 09:45 AM
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Default RE: "Different" Behavior on Brison Engine?


ORIGINAL: splais

For all.

I'm taking all this into consideration. But isn't the bottom line that rpm depends purely on how far the the throttle plate is open regardless of what your linkage is doing. I've never actually looked at any of my engines before - but maybe the plate has to be at say something like 45 degrees open before the rpms kick in. Is this the case? Because if that is true then how fast your linkage opens the plate in relation to the throttle stick position would be an issue.

Do I basically have it figured out?
Yes, BUT if the engine is not properly tuned its all realitive...
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