CARS30

just bought an o.s. .75 2 stroke from a club member he purchased new has only one flight that caused a dead stick landing after stalling.i have it installed in a great planes revolver.everyone at the field has offerd help she just wont take the acceleration without stalling you have to feather the throttle slowly or else.we adjusted as nessessery changed the glow plug tryed different size props.checked gas tank for leaks.any help would be appreciated thanks

hugger-4641

My Feedback: (6)

Sounds like the low speed needle and possibly the high speed isnot adjusted properly or it is leaking air into the system some where. How was the low speed needle set ? Do you see any bubbles in the fuel linewhen you throttle up? What prop are you using? What fuel ? What glow plug?

CARS30

no bubbles checked everything a few of the guys who fly and understand o.s. tryed adjusting can get a strong top end and a good idle .give it gas and two out of three times she cuts out.the started out with a 15-6 prop today tryed a 14-4 thought we had it then on takeoff another dead stick

hugger-4641

My Feedback: (6)

Ok, I know you've probably been thru this with the guys helping you at the field, but for our benefit, give us a few details:

What fuel are you using?
What glow plug?
What is your max lean rpm?
What rpm after you adjust back rich from max?
Does the pinch test cause rpm to go back up briefly?
Whatidle rpm?

If you pullthe glow plug out and attach yourglowstarter, does the coil glow all the way to the very outer curve, or is the first few mm of the coil dark and only the portioninside the plug glowing?

At idle, if you perform the pinch test quickly, does the rpm pick up briefly and then return to normal?

I know its a lot of questions, but with out having it in hand, we need to know to be able to help you.

CARS30

will try to get as much info as i can as far as rpms go i myself did not do the test. the fuel is 15 percent glow plug is new factory specs.

hugger-4641

My Feedback: (6)

I have to sign off for a while, but I'll check back later tonight. Some one else may chime in to help while I'm out.

While I'm gone, here's a couple other tips. I have had this problem with other engines that have more sensitive carbs, but only a few times with O.S. engines. Glow plugs can be bad brand new from the package, they can also beruined imediately if run in an engine too lean and gets hot. I would start with a brand new O.S. A3 until you get this undercontrol, then look at changing to a #8. The #8 is a colder plug and will last longer, but itis a little more sensitive to being too rich. So for time being, I would invest in a couple A3's.

Second, I would dissassemble the needle valve, clean everthing with some glow fuel or alchohol, then coat everthing with a thin evenlayer of lithium grease, or petroleum jelly if that's all you have. If there are any leaks in the needle valve and o-ring, it makes adjustment erratic and nearly impossible. Before dissasembling the needle valves, turn both Hs and Ls needle all the way in (clockwise) until they stop, (make a note of how many turns this was for each).Dissassemble, clean, and grease them. Then reassemble, close them all the way again,then open them both back up (CCW) between 2 1/2 and 3 complete revolutions. This will be a good starting point that should at least let the engine run good enough to start re-tuning.

Pylonracr

Good advice Hugger-4641.
It sounds like glow plug or lean idle mixtureto me. If the high speed will adjust to stable peak RPM back off a bit andit should be pretty close. Idle for 3-4 seconds and punch it, if it dies the idle is lean, if it stumbles and picks up it is too rich. A small hesitation is ok.If it still dies after extended idle, put a fresh plug in again (after it is tuned), that should fix it. If it still dies - Hotter plug maybe??

15% should be fine unless you are at sea level on a hot day. If that is the case, maybe you are getting excessive combustion heat from high nitro. Try some 5% or try early in the morning when it is cool, it may make a difference. I live at 4500', and I raise the compression in my engines and run15%. I have not heard of anyone having problems with 15% at sea level but it is possible.

jaka

Hi!
15x6 is too big prop!
Use a 13x4, 13x5, 13x6 or 14x4W APC prop!
Use 5-15% nitro, OS 8´or Enya 3 glow plug.
And set the idle mixture!

carrellh

I think you have too much prop. One of our club members runs a 13x6 on his 75 with good success.

scooterinvegas

My Feedback: (1)

Fine someone with a MityVac and do a vac test and a presue test. If it test good with pressure and vacuum. Check the needle on the carb. Take it out and blow it out with brake clean. If you can, test with a known carb that is good. Put a 13X6 on it. I have a MityVac, ($50) they are GREAT for trouble shooting engines, fuel systems and carbs leaks.

hugger-4641

My Feedback: (6)

I tend to agree, but I wanted to hear what rpm he was getting with the 14x4 before I recommended that he change props. If he's got a good idle and still pulling 13000 rpm with that prop, then he should be able to get a good mid range response as well, but I suspect he's *****g out around 11k or less.

jester_s1

If it's never run right from the factory I'll give 3 to1 odds it's sucking air from somewhere. The carb o ring would be the first place I'd look, followed by the backplate. needle valves, and then the front bearing.

Luchnia

My Feedback: (21)

In a couple cases we had some engines do this and we found a small piece of trash in the carb. One time is was lodged in the needle valve assemble. It is easy enough to pull the carb and double-check that fuel is free to flow through all orifices.