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Sep 26, 2017, 04:27 PM
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Question

OS max 15 nitro motor issues (complete nitro noob)


Hi, I recently went to a fly in at a semi local club and while I was there I saw a guy selling some parts. He had a few nitro motors so I decided to buy the smallest (OS max 15) one since it was only 10$! On my way home I stoped my a local hobby shop and got some things to run nitro. I do mostly fpv but my grandpa has recently gotten into electronic rc planes so I have messed with foamboard electric planes a bit. I got the nitro motor since it was cheap and I like to have smallish projects to work on in my free time. It had a few issues at first, it wouldn't turn over by hand but I just used some pliers to turn the shaft and it turn right over. Then I realized the rotarry barrel was stuck open and I used a trick with some washer so and a screw to get it out. I cleaned inside the carb so the barrel turns smooth now. Now my issue is I can't get the motor to start. Every few turns I can get a pop and a few times I have gotten it to run for about 1 or 2 seconds but then it dies off. As far as I know it is a one needle carb but I'm not sure. I will put pictures below for reference. Also any ideas of a balsa plane kit to put the motor on would be appreciated.
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Sep 26, 2017, 04:35 PM
A man with a plan
Balsaworkbench's Avatar
How did you set up the fuel system on your test stand? Did you pull the needle out of the needle valve and clean the valve out?
Sep 26, 2017, 04:45 PM
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Thread OP
I put the fuel tank on top of a small box like this. Also I have cleaned out the needle valve.
Sep 26, 2017, 05:07 PM
A man with a plan
Balsaworkbench's Avatar
If you get a little burst and then it dies, you may not have the needle open far enough.
Sep 26, 2017, 05:43 PM
Registered User
Be sure the throttle is open, and the needle valve open about 4 turns from a gentle closed position. If you are fast, when it runs off the prime, you can put your finger on the muffler exit hole momentarily to force fuel through the tank and into the carb. A finger over the carb to choke some fuel in while turning the motor over a few times will get the fuel up to the carb. Into it too, for a prime so don't flood it. It takes a bit to figure out for a while before it is second nature,
Sep 26, 2017, 06:07 PM
Registered User
They really weren't the best on piston and liner fits in the world and would benefit from a castor based fuel rather than synthetic based , and around the 25% mark . The barrel in the carb is also a very critical area for them as they become a not so airtight seal in the body with age ,and suck air around the barrel which will affect idle and transition . I check this by simply putting the barrel into the carb with a bit of Vaselene on it and if it runs ok until the grease washes off then you know where you stand . An 8/4 is a good prop to bench run it and about 10% nitro to give it a kick if the compression is a bit low . One can also improve the comp a fraction more by not using the glo plug washer , but check the clearance on the piston by winding over by hand before trying to start it , assuming you are using a starter .
Sep 26, 2017, 09:03 PM
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For a suitable plane, try one of the smaller ones here that recommend a .15. http://www.spadtothebone.org/plans.html There are other kits around. I have a Sig Wonder that I like. It should be built light on the tail. Maybe someone in the club could help you out too, usually guys are pretty good that way. Here is good too. Some electric ARFs can be converted. The ones that use a 2200mah battery are pretty close as a vague rule. I have a couple of those motors, and they are good runners, not too much slower than the newer ones. Geoff is right, they like more oil. You can get it going on the stand first just to see though.
Sep 26, 2017, 09:13 PM
Registered User
You fuel tank is mounted too low, and the fuel line is too long. That's why it won't stay running. Raise the tank so the middle is about even or slightly below the position of the needle valve. It's probably just having a hard time pulling the fuel to the carb. Choke the engine first to draw fuel to the carb, then two more choked turns. Should be about right.

I love those engines. Quite a deal for 10 bucks. I cringed when you said you used pliers on it. If you ever do this again, put a prop on it, and turn the heat gun on it until gentle pressure rotates the prop. Then apply oil. Same with the carb...heat, then gentle pressure to get it to move, then oil. WD40 is sometimes helpful to loosen things up, but follow with oil unless you are going to run it soon.

I agree that castor oil is good in the fuel, but I think part castor is good enough. Mine all have great compression. I agree with the 8x4 prop and 10% nitro or thereabouts, but use the copper washer with the glow plug for Pete's sake! If you use an OS plug the depth will come out correct with the washer, plus tightening down on the copper won't mar the top of the engine.

Jim
Sep 26, 2017, 09:19 PM
Registered User
Once you get it running, adjust the air bleed for the idle. Start with whatever it's already set for, because it's probably about right. Then try a pinch test with the engine at low speed. Should speed up briefly and then stop. If it stops instantly it's a little lean. Close down the air bleed a bit so the idle will be richer. If it run and speeds up, try leaning it a bit by opening the hole a little more.

There used to be tons of balsa kits for this size engine, but nearly all have disappeared. What sort of plane are you looking for? Plans are widely available and short kits too.
Sep 26, 2017, 09:31 PM
Registered User
I think if it won't draw fuel from where the tank is he has other problems. In regard to fuel draw and tank position , have a think about your aeroplane in a vertical position , where is the tank then ???? If one has very little comp ,and that is a problem when these engines get older ,then part castor won't be good enough I'm afraid, and lack of a washer for a test is certainly not going to hurt a lot at this stage .
Sep 26, 2017, 09:53 PM
GloBroz PowerLab
1QwkSport2.5r's Avatar
All of the OS engines I've had and currently own needed a long reach plug to be flush with the top of the combustion chamber (which is how it's supposed to be). An OS plug was 2-3 threads short of being flush with the washer installed. FWIW. My list includes a 10FP, 21SE-M, 25LA, 25FSR, 46FX, 60FSR, 60FP, and even the aged Max .15-III steel fin.

I wouldn't use a plug without a washer. It will probably leak. Just use a long reach plug with washer and go from there.

YMMV.
Sep 26, 2017, 10:09 PM
Registered User
I cannot let this go.
First, if you get it running on that stand setup, you will be in danger. Little wood screws into end grain softwood aren't up to the job.
You very likely have clogged orifices in that carb.
You need fuel with a lot of castor oil as has been mentioned. Along with a tank too low and too much fuel line.
The best thing you could do is get with someone who is experienced with running a glow engine. Which is what you have. A glow engine. On a dangerous test stand.
Sep 27, 2017, 06:09 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Quote:
Originally Posted by dan berry View Post
I cannot let this go.
First, if you get it running on that stand setup, you will be in danger. Little wood screws into end grain softwood aren't up to the job.
You very likely have clogged orifices in that carb.
You need fuel with a lot of castor oil as has been mentioned. Along with a tank too low and too much fuel line.
The best thing you could do is get with someone who is experienced with running a glow engine. Which is what you have. A glow engine. On a dangerous test stand.
+1! And to add - the spraybar is screwed in way too far too.
Sep 27, 2017, 07:53 AM
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Quote:
Originally Posted by Balsaworkbench View Post
If you get a little burst and then it dies, you may not have the needle open far enough.
I opened the needle about 2 to 2 1/2 turns. I thought that was the issue too, but when I open the needle more I can barely even get it to pop once.
Sep 27, 2017, 08:08 AM
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Thread OP
Quote:
Originally Posted by aspeed View Post
Be sure the throttle is open, and the needle valve open about 4 turns from a gentle closed position. If you are fast, when it runs off the prime, you can put your finger on the muffler exit hole momentarily to force fuel through the tank and into the carb. A finger over the carb to choke some fuel in while turning the motor over a few times will get the fuel up to the carb. Into it too, for a prime so don't flood it. It takes a bit to figure out for a while before it is second nature,
Throttle is wide open. Then needle is about 2 to 2 1/2 turns open but it seems like if I open it more I can barely get it to pop. When I prime it I can see the fuel in the carb. It looks to be drawing fuel fine, since even after trying to start it there is no air in the fuel line.


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