RVman

hi
I can't get this engine to idle for more than 10 seconds. I was using 10% nitro and switched to 25% but it made no difference. The idle loads up so much it practically floods it and i have to empty the cylinder and muffler before i can start it again. The engine is still pretty new and it has a good pinch at TDC. If i lean the needle out it wont run at the top end. I can hardly get my plane on the ground with the engine running because it just dies. Any ideas on what i can do?
Tom

Lynn S

You may not have it broken-in yet. If you run it too rich it will not heat up enough to for the piston to wear-in. Then again it may be your fuel.
Make sure you are using 20% castor oil, not synthetic oil.
Do not run it sloppy rich. I would run it wide open where it just breaks into the 2 cycle sound. Run it two min then lean it out some, run for 2 min then back to just above the 2 cycle sound again. Do this 2 min. rich/lean cycle for about 20 minutes, then it should be broken-in enough to fly.
Also, check for air leaks in your fuel line, head tightness, trash in the needle valve. It is also easy to over adjust the needle, it only takes a few clicks to make a big difference.

gws1

My Feedback: (13)

I bought an .074 used and had the same problem.
After really looking at the carb on it, I found that the throttle barrel was 180 degrees off of where it should have been. What I mean is that I was expecting it to function like all my other R/c carbs and have the barrel close as it rotated forward, toward the prop. The Norvel carbs are setup so that they close as the barrel rotates closed to the cylinder side of the motor. The barrel assembly is threaded so that as it closes, the needle is pushed in more thus leaning the mixture for idle. Mine was initially setup so that as it closed it was actually pulling the needle out and making it way too rich to run. I called Norvel before I took it apart myself, and they thought it just needed more run time also. They really need some better instructions on this.

So looking at it from the muffler side (the fuel nipple side of the carb), It should rotate counter-clockwise to close and clockwise to open. If you remove the throttle stop screw, you will see that the barrel has to be un-screwed to be removed. This is really a clever way of changing the mixture without having to add a second low speed needle.

Good Luck,
Greg

combatpigg

My Feedback: (3)

I haven't run across this problem, maybe because there are so many airleaks from the sloppy fit of the carb into the case, there is already a variable airbleed going on?

RVman

The engine is broken in and i have had about 25 8 min flights. i bought the engine at the beginning of this year so it is still fairly new. The throttle barrel rotates the correct way so that cant be the problem. I was running two head shims i will put one back in and see what happens. The head and backplate are all tight and my fuel system has no airleaks and there are no air bubbles while running.
Combatpigg. i dont know what you mean by the carb having a sloppy fit in the case because i cannot even get my carb off it is so tight.
Thanks tom

RVman

I just ran the engine and the idle is not improved at all. i ran 25% nitro, the needle did not seem to effect the idle at all and it was not terribly sensitive. I had the engine apart and cleaned all the parts so there should not be any dirt anywhere in the carb or needle valve. i also added one head shim and a new glow plug which made no noticible difference. It also spits out tons of oil if i put my hand behind the exhaust at the tail i can feel raw oil. At idle fuel will come spitting out of the carb. Please help.
Thanks tom

flyinrog

My Feedback: (1)

the needle wont effect the idle as it is the high speed needle, not sure why you are so concerned about the idle anyway....raw fuel/oil should be coming out of the muffler, this is normal,,if you have 25 flights and it is now acting up, did something else happen to the engine?..some fuel will come out of the carb at idle also but not much and that would be a low idle......Rog

rrragmanliam

My Feedback: (1)

A couple of ideas. Is the needle in good shape? It should have a fine point at the end. It's not broken off into a blunt end is it? Also is the fuel nipple on the side that the needle contacts in good shape? If the needle was screwed in excessivly tight it can open up this oraface so it's too large to be effective. Also you arn't using a bladder (surgical tubing) type fuel tank are you? This type of system is for full throttle aplications only and will not work with a throttle. And finally do not use a one way valve between the exhaust pressure line and the tank. If you do it will overpressurize the tank and the engine will not idle or run well at anything below full throttle.

Darren

Just read Rog's post and he makes a good point. Set the needle at full throttle for max RPM without sagging( a sign of lean out) then give it one to two clicks to the rich side. It should idle. Also what prop are you using? If it's wayyyy too big for the engine it can stall the motor at idle.

combatpigg

My Feedback: (3)

RVMAN< if you are running a fresh glow plug and are doing everything else correctly, then maybe it is time to install your own airbleed. If you can drill 2 intersecting holes, and tap one of them for a screw, you have it made. You can drill a tiny hole to introduce air without the adjustability feature in most cases to improve the idle air/fuel ratio. My .074 needed at least 16 flights @ 2ozs of fuel per, before it came to life. With 25% oil this engine will run with great power at a very lean setting all day.

Japanman

Oh cool, I have been waiting to skite about how to install an airbleed on the newer norvel carbs
- Best yet, you use the stupid throttle stop screw for something!

But I want to reinforce the check everything else first bit- My guess is that if all else is o.k there may be a casting flaw acting as a choke at lower rpms. If this is the case you should be able to see it if you take the carb off, and look at it carfully with the mesh screen removed from the mouth. If there is a 'choke' effect, the barrell will close off the mesh screen side before the engine side of the carb- take a look, does it happen? If so, you can very carfully file it off a bit at a time untill both sides of the barrell close at exactly the same time as you rotate the barrell- then try running it- it should be a lot better but maybe not perfect. more very gradual filing and experimentation will get it to where you want- but remember it is a bit of a one way street!
There is an ulternative to this- you can install an adjustable airbleed hole that will allow you to setup the idle mixture- or you can send the carb back to norvell if you are sure of a flaw.

And one more thing-

How does the screen look? it occured to me that it may be blocked up with something- The first thing I`d try after checking all other things is to take off the mesh screen- If for no other reason than it should give you a better view of what is going on! (you can stick it back on later of course!)


J.M

combatpigg

My Feedback: (3)

That's very sharp advice, JM. I've never considered the choke effect if the barrel closure isn't even [top and bottom]. Taking off the screen is a good idea too, and I wouldn't bother putting it back on.

RVman

hi
i got the problem figured out. I switched to a new tank with all new fuel lines, mounted the engine on a test stand so i wouldn't have to clean my plane and it ran perfect. I am getting rock steady 17000 on MAS 7-3 and 25% nitro. It will stay idleing at about 4000 which is fine for my plane. I think that with the old tank it was developing an airleak at full throttle when the tank has the most pressure which required me to richen up the needle. Then when i go to idle the airleak dissappeares and the mixture is way to rich for the engine to run.
Thanks alot for the help
Tom

rrragmanliam

My Feedback: (1)

Right on Tom! Man it feels good when you get somthing like this figured out. Cant tell you how many times I've traced a poor running engine issue to the fuel system. Glad you got it figured out.

Rrragman

cali_dream

I have to say one of the most challenging things about running a model engine company is dealing with engine running problems that are not the engine's fault. Fuel systems are often the culprit, a tiny leak, crack, etc. can cause hours of frustration. Also, old fuel.

Of course, when an engine is truly bad after all the troubleshooting, then that is frustrating, too. We are glad to hear this case worked out well for you!

Ed Stevens
NORVEL, Ltd.
www.norvel.com

2fast4u

My Feedback: (5)

I must add one point to this. What do you call idle?? My .074's idle real well at around 4000 rpm. Seems fast on paper, but it will allow the little planes sit still on the ground. I run an APC 7x3 and they idle at 4K all day long. You have to have muffler pressure run to the tank, because backplate pressure WILL flood the low end every time. Good luck.