Eratic Engine Running

[t michael jennings]

Gentlemen,

About two weeks ago my engine started sagging about 2/3 the way thru the run.
Engine runs are not steady, like to speed/slow a couple hundred RPM (not much)

It starts normally when cold.
Starts harder when fairly warm.

Adjusting the needle valve has almost no effect on engine RPM. 
It causes about 400 RPM change no matter how much the needle valve is opened/closed.

Tried the following props:  11X3;  11X4;  11X5;  12X4.
Same RPM results adjusting the needle valve (at different RPMs).

Engine Info:
OS Max 46LA,
PA Needle Valve,
Aluminum back plate.

Fuel System:
6 oz Sullivan plastic clunk tank,
Uniflow set up,
No leaks in the PA Needle Valve/connection.

Fuel:
SIG 10% nitro 20% oil  (Castrol/synthetic),
Has had about 2 gallons of fuel run thru the engine.

Weather Conditions:
85-92 degree,
70-80% humidity.



Thanks for your input.

T Michael Jennings       
Knoxville, TN.

[Tim Wescott]

I have no clue from the symptoms, so here are some wild-ass guesses:

Have you tried changing the glow plug?  Granted, I'm not sure that your problem sounds like a glow plug problem but it's an easy thing to try.

Did you notice if it seems to have much compression when it's hot?

Did you check to see if the glow plug is tight?

[C.T. Schaefer]

Checked your fuel flow? ie. clogged filter, spraybar, tank?

[David Fountain]

Hmm could be vapor locking quite possible with the heat, also check your compression does it feel weak when warm check the head bolts too you can also try adjusting the nitro content with the heat and humidity you are experiencing. you could also have an air leak somewhere maybe the back plate? (David)

[RandySmith]

Hi

not enough info to diagnose online, but first thing i would try is a new tank and fuel line

Randy

[Steve Helmick]

I had a similar problem with the Magnum XLS .36/Twister. It was rich at the originals setting, but would not come up to peak rpm as expected. This was at NW CL Regionals, and I was up soon. I replaced the fuel filter (Crap Trap) with a new one, and fuel tubes, but didn't have time for a test run. I got it started for my official, opened the NV as much as I could with the battery still on, then leaned it back out to where it needed to be (by tachometer). Something I did fixed it! I figured it was probably stuff in the spraybar. I was running muffler pressure. Not saying that will fix yours, but it didn't make a lot of sense what it was doing, either! Loose glowplug or leaky glowplug seal might also do it, I suppose.    Steve

[t michael jennings]

Gentlemen,

Thanks for your input.

T Michael Jennings
Knoxville, TN.

[Steve Helmick]

T-Mike...you'll come back and report on your findings, correct?!!!  Steve

[t michael jennings]

Gentlemen,

Still struggling.  Actions completed today;

1.  Replaced fuel tank with another uniflow clunk tank. 
     Checked internal fuel connections to assure correct no lines were misconnected.
     Pressure tested before installing.  No leaks.

2.  Cleaned crap trap.  It was clean, no debris came out.

3.  Removed needle valve from assemble and used very small bottle brush to clean valve seat.

4.  Checked muffler pressure tap to ensure it was not plugged.

5.  Pressure tested (soap water mixture) complete fuel system.  No leaks found.

6.  Checked to insure needle valve hole was perpendicular to air flow.
 
7.  Started engine and it acted no different.  Seemed to over heat. 
     Adjusting needle valve did not change engine run.

8.  Replaced glow plug with Fox glow plug.

9.  Removed fuel line from muffler.  No change in engine run.

10. Replaced engine with another OS Max 46LA. 
      This should tell me if it is an engine issue or fuel system issue.

Will test again tomorrow with changed engine.

The Good thing today, was found a lot things that was not the problem.

Hoping for a more successful day tomorrow.

NOTE:
The attached photo was taken before I received the PA Needle Valve Assembly from Randy Smith.


T Michael Jennings     
Knoxville, TN.

[Phil Krankowski]

Check for trash or carbon buildup in the muffler.  Symptoms of overheating can be from an exhaust restriction.

Take the muffler off and check for varnish or carbon buildup through the exhaust port into the cylinder.  (I doubt this since you are running a blend of castor/synthetic, but the muffler may be easier to inspect off the engine anyways.)

Phil

[bob whitney]

be sure to check the pressure nipple in the Muff for blockage

[Larrys4227]

Bad fuel?

[RandySmith]

change fuels and take it  OFF  of pressure, that can cause  bad runs, and can, and many times  does, magnify  ant little problem you have. it also fill the entire tank with a seething mass of bubbles.
you will need to turn the  needle out quite a bit

Randy

[t michael jennings]

Gentlemen,

Replaced the OS Max 46LA with another OS Max 46LA.  Purchased two together last year.

Did not change the uniflow tank or the Crap Trap.  Did back flush and clean out the fuel tank.  Did back flush the Crap Trap.  Used the SIG fuel purchased in Apr 2015.

Started the engine with in 3 flips.  It flew 5.1 second lap time and engine did not flutter.

On the Problem engine, I removed the needle valve assembly.  Removed the needle.  Was able to look thru the needle valve throat.  It was not clogged (no obstruction).

Put the disassembled needle valve assembly in a container of lacquer thinner and agitated.  A black material appeared in the solution.  It seemed that there was an obstruction in the needle valve body opening to the ventura. 

Reasonable sure that that was the engine run issue.
Reassembled the engine and put some After Run oil in the engine.

Thank each of you for the timely info in running this issue down.


T Michael Jennings     
Knoxville, TN.

[C.T. Schaefer]

BOOM!