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Old 02-17-2020, 10:50 PM
Azjulian Azjulian is offline
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 206

I disagree with John and I only repost because I don’t want you to chase your tail trying to resolve the issue and fiddling with floats etc. the floats will impact the idle circuit, sinking floats will give you a rough idle etc but the rotax carbs at WOT will be utilizing 95% of the main circuit - fuel through the main jet even if that fuel bowl is overflowing with fuel it’s going to keep sucking. If the piston doesn’t open fully (its sticking) that’s going to limit the fuel flow and the air available and it will be out of sync with the other carb and you will get a very rough engine.

EGT is really an indicator of how much energy is being produced in the cylinders, leaner mixtures will cause it to decrease after a peak as less energy is being produced. Rich mixtures also will cause it to decrease but it can also show that no energy or very little is being produced too and that is what I have seen happen in this type of scenario.

Last edited by Azjulian : 02-18-2020 at 04:25 PM.
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Old 04-08-2020, 03:07 PM
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Felix1973 Felix1973 is offline
Join Date: Feb 2020
Location: Miami
Posts: 15
Default Engine data


thank you so far for all your thoughts about the root cause for this engine malfunction. We have not been able to resolve the problem, yet.

So far, this is what we have done:
* we cleaned the carburetor and did find heavy floats and changed them.
* changed the electric fuel pump.
* we analyzed the engine data and determined that the right carburetor must be faulty and replaced it with a new one.

The issue persists. Any thoughts?

See below for the engine data (rpm and EGT):

Last edited by Felix1973 : 04-09-2020 at 08:47 AM.
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Old 04-09-2020, 08:53 AM
John-G John-G is offline
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 759


Sorry to hear you still don't have your issue solved yet.

In your first post you mentioned you are using 93 auto fuel. Of course, this time of the year it will be a winter blend ... and you are in Miami, a warm part of the country, so I'm wondering if you are not falling prey to vapor lock?

Here in Ohio, I have had issues running winter blend 93 auto fuel in the spring when the temps here warm up prior to the change over to the summer blended fuel on June 1. Having the warmer temps in Miami as you do, I would imagine there is very little margin when running winter blend auto fuel.

If you have not tried this yet, suggest you consider draining the fuel tank and replace the 93 auto fuel with 100LL and see if you still have the issue. If the issue goes away, consider doing what I do ... run a blend of at least 30% 100LL during those times when the temps are getting warm but the summer blend fuel is not yet available. I truly hate to mix in 100LL with my unleaded auto fuel ... but feel that is better than a loss of power in the air after takeoff.

A couple of other things come to mind:
Have you verified your return fuel flow back to the fuel tank by looking at it with a camera? Also, have you checked the fine filter in the Gascolator?

Good luck on solving your issue.

RV-12 Wings, Empennage, Fuselage, Finishing, Avionics and Powerplant kits all completed
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Donation paid until September 2022
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Old 04-09-2020, 11:09 AM
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BobbyLucas BobbyLucas is offline
Join Date: Oct 2019
Location: Belleville, MI
Posts: 347
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Originally Posted by suds View Post
Congrats and well done on getting it safely back on the ground. Here?s a link to a webinar of Brian Schiff talking about ?The Possible Turn? on the NAFI website. At some point after takeoff, it becomes possible to make it back to the airfield. He describes how to figure out that point and how to practice. He also describes when not to turn back. Cheers.
That was a great presentation, I will be forwarding to my CFI. Thank you.
Bobby Steinmetz
Van Buren TWP, MI
Student Pilot, Mechanical Engineer, Donating Member
RV-12iS #121228
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