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Throttle Linearity

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Old 08-04-2014, 05:02 PM
  #1
Skinny Bob
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Default Throttle Linearity

I would appreciate any help with obtaining throttle linearity on a DLE 20, I have tried throttle curve without success, will exbo work? I am using a Tactic TTX650 trans.

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Old 08-04-2014, 07:07 PM
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In the first thread there is a post on how to somewhat achieve this mechanically without computer throttle curves.

There are diagrams
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Old 08-05-2014, 03:36 AM
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Welcome to gas! It's not just the 20, they're all this way. Even string trimmers and leaf blowers! Fortunately we've learned how to deal with this.

The diagram he's talking about is here: Newbie to Gas General Information

Drop down to the bottom of post #34. It illustrates how you can achieve a linear throttle using mechanical differential. Many suggest you start using the 50/50 setup you would use on a control surface. Thinking you're here because you've found out how well that works. It doesn't.

Of note is that the position of the servo in that first/top section demonstrates the point well, but if set up like that, it's difficult to adjust your idle speed or set your throttle up so the engine can be shut down by closing the throttle. Instead, start with the servo positioned as it is in the second section of the drawing. Then you should be able to adjust you idle speed, as well as maintain throttle linearity.

You have a throttle curve available? Not familiar with your radio, but that's certainly an option here as well. Many guys start out with the mechanical differential, then trim as desired using their curve. You would want to set it up so the carb is only about 50-60% open at 3/4 stick. Hard to help much more without knowing more specifics about your radio. Just remember there are positive as well as negative values that can be entered. If you're struggling, you may not be using the right direction? -Al

Last edited by ahicks; 08-05-2014 at 05:36 AM.
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Old 08-05-2014, 03:58 AM
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Quote:
Originally Posted by ahicks View Post
Welcome to gas! It's not just the 20, they're all this way. Even string trimmers and leaf blowers! Fortunately we've learned how to deal with this.

The diagram he's talking about is here: Newbie to Gas General Information

Drop down to the bottom of post #34. It illustrates how you can achieve a linear throttle using mechanical differential. Many suggest you start using the 50/50 setup you would use on a control surface. Thinking you're here because you've found out how well that works. It doesn't.

Of note is that the position of the servo in that first/top section demonstrates the point well, but if set up like that, it's difficult to adjust your idle speed or set your throttle up so the engine can be shut down by closing the throttle. Instead, start with the servo positioned as it is in the second section of the drawing. Then you should be able to adjust you idle speed, as well as maintain throttle linearity.

You have a throttle curve available? Not familiar with your radio. That's certainly an option here as well. Many guys start out with the mechanical differential, then trim as desired using their curve. You would want to set it up so the carb is only about 50-60% open at 3/4 stick. Hard to help much more without knowing more specifics about your radio. Just remember there are positive as well as negative values that can be entered. If you're struggling, you may not be using the right direction? -Al
Good advice for the OP on this thread. Note also on the thread referred to above, that a longer throttle arm on the carb is required. My excellent Walbro clone carb came with a control horn about 1/4 inch long so I had to fabricate a longer one myself. The short control horn made setting a throttle setting nearly impossible on my first engine runs.
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Old 08-05-2014, 04:11 AM
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Excellent answers
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Old 08-05-2014, 08:09 AM
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Thanks for the help, I will try the setup in the diagram.

Bob
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Old 08-06-2014, 06:30 PM
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I use throttle curve on all my gassers, works great. Only reason I can see that a curve wouldn't work is not enough points, both radios I use (Airtronics SD-10G and Taranis) have 9 point curves, and it pretty much takes all 9 to get a good, linear throttle response.
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Old 08-13-2014, 03:00 PM
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Quote:
Originally Posted by s3nfo View Post
I use throttle curve on all my gassers, works great. Only reason I can see that a curve wouldn't work is not enough points, both radios I use (Airtronics SD-10G and Taranis) have 9 point curves, and it pretty much takes all 9 to get a good, linear throttle response.
I have achieved very good throttle linearity using throttle curve with my Tactic TTX650 but, I can't get a low 1700 rpm idle. The DLE 20 just won't do it, 1890 is as low as I can get.
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Old 08-13-2014, 06:37 PM
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Retarding the spark timing a couple of degrees may help. Capt,n
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Old 08-14-2014, 03:46 AM
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Is this a new engine Bob?

What prevents a lower idle? Is it running rough, or are you unable to slow it further?
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Old 08-14-2014, 05:24 AM
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Quote:
Originally Posted by ahicks View Post
Is this a new engine Bob?

What prevents a lower idle? Is it running rough, or are you unable to slow it further?
Both, It is running rough and if I try to reduce idle speed less than 1890 it dies. Could the reed valve plates not sealing fully cause this problem? I read somewhere that poor reed valve seal sometimes happens.

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Old 08-14-2014, 05:41 AM
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Quote:
Originally Posted by ahicks View Post
Is this a new engine Bob?

What prevents a lower idle? Is it running rough, or are you unable to slow it further?
Yes, it is a new engine, not yet a gallon of gas through it yet.
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Old 08-31-2014, 11:27 AM
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I held off on getting into this until I got may current gasser working the way I wanted it. I was just starting to get into this back in 2007 when I gave IMAC a rest and now that I am flying again I wanted to go through the setup from A to Z. I realize that this is not going to be for everyone but for those who want as Linear throttle response as possible give it a shot. It is very time consuming and I had to do it over a couple of days.

First is to set up your linkage. Fabricate a throttle arm that is fairly long. On my DA 150 it ended up being 1.5". Obviously for smaller engines it will be shorter. The object is to have a 3/4" arm on your servo and need to almost max out your ATV to get full travel at the carb. As far as servo position goes, this is where lots of guys will dis agree based on Jodi's linkage diagram. Like I said this may not be for everyone. I set up the arms position so that with the servo arm 90 degrees to the servo and stick at half, the carb is not quite 1/2 open. I'm not too worried where they position at high and low just as long as the ATV is as close to being maxed out as you can get it and the butterfly position is correct.mThis really helps with resolution. The high should be set so that the carb really only opens up 7/8 max. Trust me this will not take anything away from the top end as that last 1/8 really does nothing. Now that the linkage is set up its time for a run up. Set the needles to factory setting, start the engine and allow to warm up. Adjust the high to peak without over leaning and then the low just until you get hesitation on transition then open the low just to the point of a clean transition.

Now go fly and optimize your needle settings. At this point most will notice a slight burble at mid throttle and find that the throttle comes on a bit soon. It's time to employ a throttle curve. I use what is called an " S " curve. That is that the curve graph should be shaped like an S by flattening out the low and high. Most times you will want to drag the mid point down too.

Now we are close and to the most difficult part. If you have the needles adjusted correctly and still have a burble at mid or have an rpm drop while inverted you need to go into the carb and adjust the midrange. This is done by adjusting the amount of fuel that gets by the metering needle by adjusting the travel of the pivot fork that is activated by the diaphragm. To lean the midrange you have to adjust the fork inward. This will reduce the amount of fuel getting past the metering needle. Yes you guessed it, it will also affect the high and low needle settings. You will have to set them back to factory settings and begin the carb adjusting sequence again. If the engine won't transition out of idle with factory settings then the fork was adjusted too far in. It's a real pain but make adjustments to the fork in .005" increments. Most likely your first attempt will be too much. For the engines with rear carbs it will be even more work. Again this is not for everyone but if you are as OCD as I am about throttle response then it may be worth a try. In my case it makes getting good scores when throttle response in nice and smooth.
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