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joeing701(at)simnet.is
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 Posted: Wed Dec 01, 2010 1:35 am Post subject: Problem solved. Rough running cured with carb heater |
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Hello Roger.
What my friend did was to drill out the needle jet to richen the mixture in the mid range.
That tells us that the jet was wrong, i.e. did not work on his engine because of the colder air entering the carbs. Is this not the correct assumtion? Is there another solution to the lean condition? As I mentioned in my last post, my engine in the Zenith 701, does not have this problem because the air entering my carbs is hotter, no airbox. Is this correct? I know you are the expert, and would like to hear your thoughts about this problem. If you tell us that this is not the correct way to solve the rough running at the mid range, what other method can we use?
With thanks,
Johann G.
----- Upprunalegt skeyti -----
Frá: "Roger Lee" <ssadiver1(at)yahoo.com>
Til: rotaxengines-list(at)matronics.com
Sent: Miðvikudagur, 1. desember, 2010 00:09:43 GMT +00:00 Monrovia
Efni: Re: Problem solved. Rough running cured with carb heater
Hi Johann,
Something is wrong some where. I have seen the Rotax 912 run in -20F weather and never miss a beat. It seems like it has to be the wrong needle, wrong jets, wrong needle clip position, some thing else in the carbs? You may have put a band-aide on the problem, but might have not fully solved it?
--------
Roger Lee
Tucson, Az.
Light Sport Repairman - Maintenance Rated
Rotax Repair Center
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=321856#321856
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cscsail(at)gmavt.net
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| Posted: Wed Dec 01, 2010 4:22 am Post subject: Problem solved. Rough running cured with carb heater |
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I tend to agree with Roger. My 701 with a 921uls and airbox runs perfectly
in the summer with temps in the 90s F as well as winter flying (on skis)
here in Vermont where it's often well below 0 F.
Gordon
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Wed Dec 01, 2010 6:54 am Post subject: Re: Problem solved. Rough running cured with carb heater |
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Hi Johann,
My question would be, Unless someone has overhauled those carbs at one time and put the wrong kit in or moved the clip on the needle you should not have had any issues from the Rotax stock carb setup with in the OAT you posted at 40F? If you are having a problem and those carbs have never been touched then I would have pulled those carbs and done a fuel system flow check, a fuel pressure check and dis-assembled the carbs for a good cleaning. Even the the smallest piece of dirt in a carb can cause the issue you describe. I would like to know if the clip on the needle was in the third slot from the top? If it was strictly a mid range problem you could have moved the clip down to the forth slot, but this should not have been necessary. You still have the same problem with what you did, but are masking or bypassing it by allowing more fuel in by drilling the jet. You should also buy the proper jets and not drill them.
I would quit considering the air temp of 40F a major factor and start looking for a fuel flow issue.
My slant on this is you still have the original problem, just covered up now. It could show up later and not in a way you want it to.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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dashwood
Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada
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| Posted: Wed Dec 01, 2010 8:17 am Post subject: Re: Problem solved. Rough running cured with carb heater |
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my 2 cents. i run a 912 with 450 hr on it. the operational range is 40deg C to -20C . the starting procedures change and the oil grade, preheat.changes but nothing else is done to the carbs. in below 0C the oil rad is taped off and the water had has a 60 % blocking out plate. the carbs were disassembled by a rotax tec at 400hr and no wear or problems found.i do not have carb heat. with 2 cone K&N filters. i believe the airflow inside the cowl is in along the bottom through the oil and water rads. then back and up and down past the muffler. some warmed air is going up to the carbs just above muffler then forward along the top of engine and out the hole around prop . i believe there is a low pressure area just aft of the spinner and hub. I had a bad oil leak at the rad connection and this is the oil trail pattern that manifested.
point is when set properly this engine runs great in many varied conditions.
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Ross Alexander: CH701 driver 912ul 788tt
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