Hi All,

I have had a case where I think I was trying to run an engine too lean previously. It was running ok, idling fine and throttling up to about 1/3 but then would die. I would try to adjust the HS valve but never by enough to make a solid difference. Finally someone mentioned that I was probably way too lean, so I should try to find the factiory settings or go 1 to 1 and 1/2 turns out richer. The next time I tried it, it seemed as though the setting was better at mid - full throttle but the engine died relatively fast

I says to turn needle CW full in, and then open 2 and 1/2 turns. Does 1 turn mean 360 degree (12 oclock to 12 oclock) or does 1 turn mean 12 to 6 in R/C world ? I ask because on some Nitro truck you tube video's they refer to 1 turn and it is actually 1/2 a turn (?)

I always had the habit (maybe bad habit) of priming the carb manually with a few drops directly in the carb mouth. Also from the truck video's I see where a thumb on the muffler hole (when cold) aids to get the fuel in teh line right up to the carb.

Today I tried to get it going and as usual it starts easily BUT doesn't keep. I almost seems as though it was not getting enough fuel and after it burnt the primer fuel in the carb it stops.

What should be my trouble shooting steps ?

Thanks

If it is just dying and not gurgling then dying, then you definitely are lean. A turn does mean a full 360 degree revolution in RC. The factory settings are typically very rich, so if you are there then you have another problem. I'm assuming you are using a new glow plug and fresh fuel. If not, change those first.

Then check your fuel tank and lines. An air leak anywhere will cause your problem, as will a tank that is too low or a pickup line that has come off or is leaking. Your vent line going to the muffler could be clogged or leaking also. And don't forget the pickup line inside the tank.
If all of that is right, then you may have an air leak in the engine itself. There are 3 normal places for that to happen: The carburetor inlet where it attaches to the engine, the backplate gasket, or through the front bearing. To check it, get a straw that fits your carburator venturi and seal the exhaust outlet. You should be able to blow a fair amount of pressure into the engine without any air leaking out. If you hear leakage anywhere, a little soapy water will help you find it.
If your tank is good and your engine isn't leaking air, your 2 stroke will at least start and run with a wide variety of needle settings.

The other problem you may have is that the low speed needle valve is to lean. Turn it counter clockwise about 1/8 turn. That richens the low end. If it is a new engine, and you have the manual, adjust both needle valves to the manuals spec's. I like to run my engines rich, and never to lean.

Thanks for the inputs.

- I think the plug is good, but I will check the color and condition, as well as the "glow", I have another so if in doubt i'll probably replace it although I don't think that's my issue.
- The fuel could be old, so I will drain it out
- Before I add more fuel, I will remove and disconnect all the vents and fuel lines and check the tank for leaks maybe with soapy water (?), probably will replace all the hoses if tank is good. Either because it was very cold or due to a leak or both, I did notice it priming very slowly. I would assume my issue is an air leak somewhere in there.
- I should add the fuel filter back that I removed some time ago, and I might add the air filter off my OS46 (if it fits) .. i do live in a dusty area.
- Then I'll try my best at checking for leaks in the engine with straw as explained ..
- Then I'll go to 2.5 full turns from closed on the HS valvle and give it a go. I'll leave idle alone for now as it used to idle good, I've read to adjust that only after your HS is set.

Many thanks

You do what you feel is necceary. I question, why did you ask the questionif you wanted advise? I gave you my opinion and only a suggestion.
In my limited experirence, the low end is too lean. Blow bubbles until you find out.

Hi FLAPHappy, yes I did ask for advise. And no offence intended, but no need to send me off blowing bubbles. I'd rather check the basics first and I think it is basic info that the low end should be adjusted only after the high end mixture is ok. If I still have the same issue after I check that that the basics are Ok, then I will see where LS / idle is closing it and counting how many turns. Then I could richen it to see the result.

Definitely sounds like a fuel problem. Tank is too high/low or like the other poster said a problem with the fuel lines. Make sure you don't have your lines switched and that there are no breaks/cracks in them.

If your idle setting is way off, you may have problems starting. You should be good with factory settings at least to get started.

Steve

One other thing is you say you weren't running a fuel filter. A small piece of dirt can block your fuel flow, so before you do anything else pull out the HSN and make sure the needle and passages are completely clean.

You are too lean on idle screw Adjust or just be stubborn. True it should not have to be done until you have reasonable tuning but when this problem appears that's what must be done.

Some updates :

- glow plug is good, changed it anyway for good measure.
- adjusted (again) HS valve back to factory settings, about 2 1/4 - 2 1/2 turns out.
- found LS valve adjustment info (quite confusing). may or may not be at factory settings. It said open up the carb, close then open 2 - 2 1/2 turns. think i got it
- disconnect hose from muffler and blow to prime .. almost positive no leak.
- disconnect hose off carb, blow and smooth flow.. seems ok.
- connect back to the carb, disconnect from HS valve .. blow to get fuel into carb but it seems very difficult to flow into carb. Maybe some dirt, old gukked up fuel or something inside. I tried getting some WD40 in there.

I'm pretty sure it's either the carb LS jet or some dirt / crap in the carb. Next step I guess remove carb and clean.

damn .....

At idle throttle your low needle should be turned open enough to hear a little air pass through. Otherwise it is too lean - try opening a quarter turn or more to see if it then passes air into the carb. You can always turn it back if no change in air flow.

It should be fairly hard to blow air in, especially at idle. WD40 will eat your o rings. Just use fuel to clean with.

Be carefull of getting hung up on HS/LS needle adjustments. Keep in mind that adjusting them is a balancing act. If you adjust one you may have to adjust the other. There are several tests for each needle I like to set both needles to factory settings then use the pinch test on the low side first. Pinch the line feeding the carb and listen for the engine to rev after 2-3 secs. If it revs in 2-3 secs its good if it takes longer its rich if it dies its lean. After that I start playing the high side needle. Ilean to max RPMthen richen a bit. After all that I then run the throttle up a seond time and have someone pick the A/C up tip the nose up and down and ensure it doesn't lean out at severe pitch changes. Ihad an engine that had a leak in the carb and it was hard to T/S it as I was learning how to tune at the same time. It takes time and tinkering to get an engine set right but once its set don't over tinker it.

Well after cleaning thoroughly the carb, and changing to new fuel (just in case) my problem is solved. Now it seems to run well on the HS needle adjustment so I need to tune it a bit tomorrow. It misses slightly, doesn't transition well yet which is my next task. It appears that factory setting are quite rich indeed.

Many thanks for all your suggestions and input.

Glad you fixed it. Yes, factory settings are always rich, because rich won't hurt your engine. If you will work your LSN just a tiny bump at a time, you will probably notice that at the beginning, the idle only lasts for a few seconds before lowering and then dying. Lean it out a tiny bump at a time until it idles at a steady RPM. Then adjust the HSN, check the idle again, and check the transition last.

Well the engine runs great at top end, a slight bit richer than max rpm,very smooth and throwing a thin puff of white smoke. HS valve opened 1.5 turns. Looks as though i'm quite close with the LS settings as well, but not quite there. Engine is a Magnum XL 32, ABC type engine which is on a 25 size trainer with ailerons, maybe slight over-powered but what the hell ..

I was off getting LS back to factory since I was using a downloaded manual for the 40-46. Just found the XLS25-36 manual and go figure, procedure to get back to fact settings are different on the 32 and 36 size. Complete opposite process ... no wonder my LS valve assembly got all F'd up [>:]

Will try the pinch method to see way to go from here.


Edit: After some back and forth, transition is "almost" perfect, so I basically won't mess anymore with settings for now. I went through about 4 fuel tanks while keeping an eye on the engine temperature. It still not that stable at low idle. We'll see after a few more fuel tanks .. the goal is for this bird to get it's madden flight during mid - end of Feb.