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91 ac idle problem

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Old 03-30-2012, 05:31 PM
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octanehuffer
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Default 91 ac idle problem

Used in the box. Mint condition and had gummy after run oil in it for the last 10 years. I lubed it up and soaked it for a week before use. Fired right up, but has an extended idle problem. I rebuilt the carb and replaced the diaphragm. No changes. It was really clean inside. I can set peak rpm and bring it to idle for about 20 seconds. Then it dies all of a sudden. No rise or sag in rpm before it quits. It will idle all day with the glow driver attatched. Im trying to get a reliable 2000 rpm. On my 3rd type f plug. I do see air coming to the carb once in a while, but when I see it pass through and into the carb, nothing seems to happen. How critical is the low end needle adjustment? I can be 4 turns out or 1 turn out and it seems to act the same. Was also wondering if I should try an Enya 3 plug in hopes that the plug stays lit. Or onboard glow.
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Old 03-31-2012, 05:10 AM
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Default RE: 91 ac idle problem

Those air bubbles going for the regulator to the carb are normal. The YS goes from injecting to drawing fuel at idle (below 2400RPM). I wouldn't use a different plug than an OS F or YS 4 as I learned that one the hard way but I am wondering why you are on your third plug? Are they fouling?

Before we dig into what the issue might be can you give us some info on your set up? Fuel? Prop? Idle RPM before it dies and what the transition is like? WHat did yo clean and soak the engine in?
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Old 03-31-2012, 02:37 PM
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Default RE: 91 ac idle problem

Engine was sitting so long with the after run oil in it, that it turned to gel. The exhaust valve was pretty sticky and I lubed the engine with Zep 45. Works great. I rebuild and tune many, many engines. Not a noob, but definitely don't kow everything. New Mojo 60 profile. New lines. New tank. Glow plugs have been changed as a "why not" method. No fouling issues. I didn't have YS 20/20 on hand at the field last weekend, so a friend put in a tank of his last year old stuff. Its been working just fine in other models and I had a tank of it. Untill last night. I pulled out the last ounce of that and put in Wildcat 20%. Less oil, but great to test with for comparision. I was able to keep an idle for about a minute and half. Probably around 3000 rpm though. I am going out to the garage in a bit to retest outside in daylight where I can get a good tach reading. Prop is a 15 x6 APC. Going to run a 16x6 IF this engine is worthy. Ihave a feeling like I'm chasing the needles, or something really strange is going on. Hence the question of running a hotter plug. I can run the engine at half turn out to 4 turns out on the low end and the only difference is when its richer it smokes more. At 4 turns out, it is slightly higher in idle speed
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Old 03-31-2012, 04:01 PM
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Default RE: 91 ac idle problem

Zep 45 will do bad things to the diaphragm if it got in the regulator. Now lets break this down into parts. Regulator should start at being flush and about 2400 RPM you are running on the regulator which will make the low speed needle just about useless. The low speed needle works reverse of the other settings on the engine as it is an air bleed so the screwing it in RICHENS the mixture. You might want to pull the regulator apart and make sure the diaphragm is not out of shape and that the plungers is opening and closing without hanging.
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Old 03-31-2012, 07:41 PM
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Default RE: 91 ac idle problem

I got it figured out. The low end needed to be between 4-5 turns out. Manual says 1.5. It was a long ways off. The Zep 45 will not harm anything it is a penetrating lubricant with teflon and I have been using it for years, not only in the hobby stuff, but building engines and transmissions as a career. No, I'm not endorsing. lol. I did replace the diaphragm at the time of carb overhaul last week. I can get it to idle at 1800 rpm now for several minutes. Sounds great at 2000. At first there was a noise exactly like detonation when I tried 4 turns out last night, but discoved it was the airframe. I thank you for the help
What is the procedure for adjusting the regulator? I kept it flush, but during some forum research, some mentioned doing it, but didn't say why
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Old 04-01-2012, 05:15 AM
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Default RE: 91 ac idle problem

I like this for getting the YS set up:

http://www.julton.net/Fact%20Sheet%20YS%20Engines.html

I won't debate whether Zep will harm the diaphragm, I have used their products for a long time. Suffice to say there is a reason I only use raw fuel or alcohol to clean my YS engines.
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