I'm having a hard time trying to get my OSsurpass .91 engine to work.. the last time I used it, it was working great, but then, that time Icrashed my plane... now, Igot a new plane, and Inoticed that when Istart the engine everything is ok, but when Iremove the glow plug ignitor, the engine goes down on the rpm. Ialready change the glow plug for a brand newone, and the things went worse, now when Iremove the ignitor, the engine stops! it keeps running if I open the throttle a little, could this be a problem with the low end needle valve? what else can be causing this problem?

Could be so open low end needle a bit. If it crashed it's possible You have gotten some dirt in carb. And could have even been drawn inside cylinder.

but if it were the case, the engine wouldn't start at all don't you think? cause the problem is when I remove the ignitor

Yes, your low end sounds out of adjustment, twist it and see what happens.

I closed the low end about 1/8 of a turn and it improoved a lot, I removed the ignitor and nothing happened, how ever, I noticed a little hesitation when going to full throttle so I opened it like 1/16 back, after that, I couldn't start the engine again... the fuel thank was almost full, I charged the ignitor overnight... I guess it is time to call an expert :P

If it hesitates when you go to WOTyou need to lean instead of making the LSN more rich. If when you throttle up and it quits quickly then it is probably to lean.

You say you closed the low end needle and things improved, but when you throttle up the engine hesitates, but does get to wide open throttle. You need to close it a bit more. If you throttle up and it quits instantly then you would be to lean and you would have to OPEN the low end a bit.

Reason I didn't tell you what way to twist the needle was so you could figureit out yourself. If you closed it {lean} and it made it better then you opened it up [richened it} and it made it worse what would that tell you?? By twisting the needles and seeing what happens to the engine you are teaching yourself how to tune an engine. There are hundreds of pages writen here on how to tune an engine but twisting the needles and seeing what happens is the best teaching aid anyone can get. If you did a search I bet you can find some of these pages. You can also go into Glow engines and OS support and read all about your engine. It takes a bit of work on your part but you will learn a bunch.

oh yeah that was my guess when you only said "twist it" Iknow the problem now is not the needle valve, but maybe some fuel lines instead, I'll search for the problem tomorrow and I'll let you know how it went. Thanks a lot!

G'day. If the engine was running OK before it came to earth, the chances are that the adjustments are still pretty close to right. I would check that the carby is clean by flushing some fuel through it in both directions with the needle valve out (check where it is before removing) and with the throttle wide open. This should flush out any muck that is in there. I would leave the Low Speed Needle alone at this stage.

Then try again but with some fuel which you know is OK. Poor idling is often caused by fuel which is past its best. We had similar problems recently with a Saito 62 and some different fuel make it a different (and much happier) engine.

If this fails, then start trying to adjust things. Fuel is too often the problem when an engine just won't idle properly.

Hope this helps a bit.

Mike in Oz

Mike, I have never had a moisture problem with fuel and I only buy fuel in cans so it doesn't go bad even with long storage so I have never had a fuel problem. But {you like how I got that but in there} I have had a problem after what I will call hard landings, like when I have flown through a tree. Bent needle valves being just one. After a hard landing I have also had to use a different size prop than what I had on before and the engine may not like the new prop well enough to idle like it used to so a bit of a tune may be called for. Just going from an APC to a wood prop of the same size can do it. After a hard landing I have even discovered a bent push rod tube rubbing the push rod and putting it at a strange angle. If leaning out the low end made the engine run a lot better but not quite right then perhaps giving it a bit more twist would make it run correctly. Maybe it would like to have the valves checked and/or adjusted at this point?? Just a lot of little things can effect an engine after a hard landing. I had one OS .70 that gave me fits after I parked it in a tree. OS service wanted the price of a new engine to repair it, they sent me a list of everything they found wrong with the engine. I had them send it back to me. I got a box of parts. I took the parts to a local service and had them inspected, they didn't find any of the problems OS did? That's when I started doing my own service. I put the engine back together and it still wasn't running correctly. I installed a new needel valve assembly like I asked OS to check and the engine ran perfectly for several years. It can be something that simple after a hard landing.

I need to take this thread back to life, I thought everything was ok with my engine but I took it to the field today, turned it on and taxied to the runway and then it died on me, turned it on again, taxied to the runway again and it died on me again...   is there any way to check the low end adjustment? like on the 2S engines that you take the plane at 45° and it is supposed to stay at the same RPM. how can I tell if the low end needle is ok? other than accelerate to full throttle and check if it doesn't hesitate ?

another thing, how wise would it be to take apart the engine and wash it by myself? I'm not an expert at all but I can take a 2S engine apart and put it back together with no problems.

Welll, Chocorrol. It all depends on your experience with working with four stroke engines. By design, they are somewhat more complicated than a two stroke... and of course, it also depends on how far you want to take it down.

What you are experiencing sounds more to me like a tuning problem than anything else. I would focus on getting that part of the process corrected and perfected for that engine and not worry to much about cleaning the engine out as you suggest.

CGr.

Is the "pinch" test also applicable to 4c engines for adjusting the LSN? I have a FS91SII which was well tuned before but after sitting idle for a month or so, the thing would quit as soon as I removed the booster. That happened even after I replaced the plug. It would race with the booster on but drop in rpm suddenly when it was removed. I need to get this engine operational this week to put into a new airplane.

Also, do 4c engines compulsarily need nitro in the fuel. After a lot of problems running 2C engines on a batch of fuel containing 10% nitro, I moved to a batch with 0% nitro and the engines are now happy. I would intend to use the same batch on the 4C engines

Another thing, how do you know whether the tappet valves for a 4C engine need to be re-set?. I am recently getting a lot more misfires at WOT from the FS91SII and have never had any 4C engine before this one. I have the OS valve adjustment kit but no experience in doing the adjustment

Ameyam

the same thing happens to me, when Iremove the glow plug ignitor, the engine goes very low on RPM, I can tell you this is not because of the glow plug 'cause I changed it and still the same as happened to you. Regarding the valves adjustment, I asked the same a little while ago, and Ifound that you don't need to check the valves unless you have a loss of power, but if you still want to make sure it is ok, you already have the kit so just take the rocker cover off and align the crakshaft, there is a mark on the crankcase and another on the drive hub, you need to align those marks then check the clearence on the valves. those marks suppose to be align right after the conpression is felt. Some one correct me if I'm wrong

OK, enough suffering, time for a trick or two. When to adjust valves: I open up the rocker cover maybe twice a year and use a feeler gage on my COLD engine and check the valve lash. If they are out of adjustment it's time to set them again. If your engine was running fine last week or last month but it sags now when you remove the ignitor it is usually telling you the glow plug is getting old. If it still does it with a new plug {not a used plug} then it is telling you the low end is a bit fat. Trick time!! With the new plug installed, engine running, remove the ignitor, if it sags then put the ignitor back on, lean the low end a LITTLE!! Remove the ignitor, if it still sags replace the ignitor and lean it a LITTLE more. Do this until it no longer sags. Now open up the low end just a LITTLE until you get a very slight drop in RPM. OK, low end is set. Now the high end will be a bit out of adjustment. SLOWLY bring it up to full throttle, twist the needle until you hit the max RPM then back off about 500 RPM, you should be good to go. Usually when your engine dies or sputters on take off it is telling you it is too lean on the high end. I found that dropping the engine that 500 RPM is about right for my four strokes. I used to try to get away with 300 but if the weather changed a bit I would have to twist my needle and I'm one of those guys that doesn't twist a needle for months on end. Nitro and a four stroke, nitro is not required but if you are going to use FAI fuel then you have to tune for it. Nitro makes getting one in tune a lot easier. I did a test one day on one of my YS 1.10s starting out with 30% nitro, I usually only run 15% with 18% blended oil. Not much difference with the 30%, a couple hundred more RPMs and a smoother idle. 15% was my normal so again, no big deal, 10% the low end was a bit rougher but it kept idling without any adjustments. 5% the idle was pretty bad and I didn't have the normal high end RPM, it was down a couple hundred. I could have tuned the low end for a smoother idle but I was just testing a bunch of fuel I was given. I ended up just mixing it together and using it up. No, you don't need nitro in a four stroke but you may loose the sweet spot on the low end and loose power. Nitro will give you a wider band to tune, make it easier and more reliable.

thanks a lot for the tip Gray Beard I was doing what you suggested but my glow plug ignitor got discharged... one more question (if you don't mind) should I expect any drop on the RPM when I take the ignitor off?  I mean, once it is set up properly. the reason I ask this is because a guy from my club says with 4 S engines you always get this drop when taking the ignitor off, he says it is a normal behaviour on this kind of engines no matter how well it is tuned or how good the glow plug is.

Most of them do drop a little so yes, it isn't anything strange. That's why I said after you get it to not drop then fatten it up until it does drop a little. I found my engines like to be just a tad on the fat side on the low end. I have one old YS that drops a big bunch when I remove the driver. I'm thinking it's just old age and telling me it would like to be freshened up a bit. Thing is the engine just runs so darn well I don't want to open it up for a rebuild. If the engine is in tune and running well don't over think it, just enjoy it. Don't try to squeeze every RPM or ounce of power out of the engine unless you are a racer. The old addage, the top end has no effect on the low end but the low end effects the high end is true up to a point. Stuff can happen though. I'm also lucky, where I live I haven't any big weather changes or problems with humidity so I almost never touch a needle after I have the engine set. As winter moves in on us I do have to fatten up the high end a little at a time. When it gets down into the 30s and 40s from a norm or 100+ my high end will be about 4 clicks fatter, the low end doesn't seem to be affected.

Hey Mike109, even girls know when you cross the equator fluids flow through a drain in the opposite direction. Therefore, it stands to reason that the needles would have to be twisted in the opposite direction to achieve the same results as explained by the ridiculatum principle.

ok I'll keep trying, at this point it should be good to get back to factory settings to start over again, after all it is only a screw if things gets worse, I only need to screw back to the other side right?

Yeah, reverse (or ist it inverse?)[8D]

Thanks for the tip Gray Beard (now I know here you got your nick-name). I think I have the same problem with a 75ax 2c that I deliberately set rich as I was reopening it after a year

Ameyam