OK, I've got a YS .91FZ that hasn't even been on a plane yet. It's about 1 year old and I've run about 1 gallon of Cool Power 20% through it on the bench all the while trying to get the idle right. Seems like I get it, then next tank it's off again. Anyway, today I was bench running it again and noticed that there were air bubbles in the fuel line that runs from the pump/regulator assembly to the carb. There are no bubbles it the line from the tank to the pump/regulator. I only noticed this today because of the way the sun was shining on the stock (dark) fuel tubing, so I don't know if this is a new problem or one that has been with the engine since day one. I'm assuming (yeah, I know ) that the air bubbles are causing the idle problems. This is my first YS and my first 4 stroke. Can some of you in the know give me suggestions as to what is wrong here and how to remedy it. I've had the engine for over a year now, so I wouldn't expect the dealer ( Central Hobbies ) to make good on any repairs. Thanks to all in advance
I guess that's why it's spelled ASS u ME. Any way, I can get it to idle at
1900 with a 14x10 prop which is just a bit too much prop, but it idles fine, good response when advancing the throttle and drops off to a nice 1900 rpm idle again when the throttle is cut. Then next tank it'll idle at 1900 then slowly ( over maybe 60 seconds) creep up to 2300 - 2400. So I'll fiddle with the idle air screw some, get it to stop creeping, but then the response to high speed is bad - it'll stumble b/4 winding up and may die. So I'll fiddle with the air screw again and It'll be fine for a tank or maybe 1/2 a tank then things get weird again. When I make the adjustments, I only move about
1/8 of a turn at a time, and the extremes of all adjustments are with in 1/2 of a turn.
Ok.....first things first. There are a couple of things you need to check before you start making adjustments to the engine.
The check-valve. Make sure it's working properly (ie only letting pressure through one way) and it's pointing in the right direction. It should only allow pressure to go FROM the engine TO the tank. If it's letting pressure back the other way, replace it.
The tank. Make absolutely sure you've got no pressure leaks in your tank and plumbing, including your fuel filters. These things run about 9 pounds of pressure, so you need a good tank too.....make sure it's not swelling under the pressure. Tettra tanks are ideal.
Regulator. Where is this set? It should be left at wherever it was from the factory, but if you've played around with it, return it to be flush with the regulator body and leave it there.
Plug. Make sure you're using either an OS#F or a YS 4-stroke plug and start with a new one. No point trying to tune an engine with an old plug......one lean run is often enough to fry a plug, so better safe than sorry.
Fuel. Make sure you're not using fuel with castor oil in it. The instructions tell you this I think. I mix my own fuel, using Klotz KL200 oil. Never liked the Coolpower oil.
Throttle linkage. Make sure it's coming back to the same place at idle every time and not vibrating open (obvious I know, but you never know....)
Why are you running a 14x10? Unless you specifically have to use the 14x10, I'd get a 15x8 APC comp before you do anything else. It's the perfect prop for the .91. 9000+ rpm easily, still quite rich.
Once you're sure you've got no leaks and your pressure system is ok, then you can start arsing about with engine settings.
Set the high end first. Start at the factory setting and lean it to the point where it stops losing revs at WOT (ie rich, but not so rich that it loads up and drops revs). No point going leaner than that at this point.....the engine is still new!
Set the idle so it will drop to 2000rpm instantly. No slow creep up or down.......set it so it goes there straight away. Mine will sit there and tick away at that all day (even lower now, but 2000 is a good start on a new one). If it gradually gets slower and stops, it's too rich. Wind the air bleed screw (idle screw) OUT a tiny bit. My adjustments are less than 1/8th of a turn. If it gradually speeds up, it's too lean. Wind the air bleed IN a tiny bit. After ANY idle adjustments, run it to WOT again for a few seconds, THEN drop it to idle and check it again. Don't dick around with idle settings until you've run it up to full power again. You'll just end up chasing your tail.
If you've done all that, and you're sure your tank/plumbing system is perfectly fine, you may have something stuck in the regulator assy. If you're confident that you can follow the parts diagram, pull it out and check to make sure it's clean. As a last resort, you could try winding the regulator in a tiny bit at a time until you get good transition, but don't go more than a turn in from flush with the reg body. You're not using onboard glow (or leaving the glow on after starting) are you? You don't need it with these things, and it *can* make the idle hard to set. I found that out the hard way with both of mine. My YS's were my first ever
4-strokes too, and I'd read lots of posts about ppl having trouble getting
4-strokes to idle inverted, so I put onboard glow on both of mine. Waste of time and money. They idle better without it :-)
What I will add to this is to use a YS blended fuel. Coolpower, from my earlier experience, is low on oil. Oil is your friend! I used Excalibur and Powermaster YS 20/20 blends and they ran great. I have also seen Red Max and Wildcat run well. All of these fuels use 20% nitro and 20% high quality synthetic oil.
A 14X10 isn't too much prop. It is one of the preferred props for the aerobatic group. I prefer to let mine rev a bit more as this seems to be easier on the bearings.
When I run the 14x10 on mine, it really knocks the revs down, compared to the 15x8. I'm the same.....I like to let mine rev a bit more. I also like the extra braking of the 15 on downlines with my pattern ship.
Thanks for the advice, guys. The fuel system is OK, it will still be holding quite a bit of pressure even 10 min after the engine stops, although I don't know how many psi it actually is. I started with the YS 4 stroke plug then switched to a OS #F and couldn't detect any difference at all between them. The fuel will be the next thing I try. I've been running it on Cool Power
20%, but my LHS ordered a case of Wildcat YS 20 today for me to try. ( He said he's had others ask for it, so I didn't need to buy the whole case ) The set-up procedure that you describe is pretty much what I've done. I think I'll wait 'till I get some of the Wildcat brand fuel and then start from the beginning all over again. Thanks again, I'm just glad to learn that the bubbles in the fuel line are normal and that there probably isn't anything wrong with the engine. I'm surprised that isn't mentioned in the instructions.
If you are using a DuBro or other molded tank, be sure to wrap it with strapping tape (reinforced tape). If you don't you risk the tank rupturing and blowing fuel all ove r the inside of the plane.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.