bkdavy

My Feedback: (1)

Help!! I'm at my wits end and am hoping someone can help me figure this one out.

I have a Magnum 91 Four Stroke, ringed, that has about 3 gallons of fuel through it over the past 5 months. Its never given me a day of trouble - until today. Last Sunday it ran without any difficulty.

Today, I arrived at the field, fueled it up, started it, warmed it up, removed the glow igniter, and as I was getting ready to check the high speed needle, the engine sputtered and died.

Raise the throttle a bit, restart the engine, remove the glow igniter, and after a few seconds, again it sputtered and died.

Now this is normally a good indicator that the glow plug is going bad, so I changed the glow plug. Same behavior. Possibly a bad plug out of the pack? Could be, so changed it again - same thing.

Now I'm getting frustrated, and thinking that maybe the needle valve is contaminated. Pulled the carb out, took out the barrel, took apart the needle assembly. All is clear. Reassembled, hoping that maybe something cleared out and I just didn't see it.

Same behavior. The engine will run fine as long as the glow igniter is connected, but as soon as the igniter is removed, it won't run below 3/4 throttle for more than about 10-15 seconds.

Fuel is being delivered no problem. There are no air bubbles in the fuel line while its running.

I checked the valve clearances. Good to go. Valves are moving freely.

I pulled the head to inspect the valves. Other than some minor carbon, the valves look great. The cylinder walls look pristine. Good compression and good suction, so the rings are OK.

At this point the only thing I think it could be is bad fuel. Has anyone ever had this experience from fuel thats been sitting for too long (drop in nitro content or water contaminated)?

Any other suggestions?

Brad

w8ye

My Feedback: (16)

The fuel has gone bad

liquid_TR

99.9% possibility for bad fuel.

broke_n_bummin

Yup. It doesn't take a whole lot of exposure to the elements for the methanol to start evaporating dramaticly raising the oil content.

bkdavy

My Feedback: (1)

Well a new gallon of fuel and she's running like a top again. Guess I'm going to have to be more careful with my fuel when I get down to the bottom of the jug.[&:]

Brad

w8ye

My Feedback: (16)

Keep your fuel jug closed at all times and keep the fuel out of the sunlight

Kenk

I know this is an old post, but for the benefit of others with this problem, I have also seen this behavior when the glow plug does not get hot enough.
If your glow plug ignitor battery is not charged enough you will not get your plug hot enough to maintain ignition after pulling the ignitor off.

Just from my own experience.

Ken.

chashint

Up until this summer I thought bad fuel was a myth, then (as luck would have it on a Magnum 91 four stroke) I experienced the exact same symptoms as the original poster. Fortunately I did not do any engine disassembly. After changing the glow plug, I drained the tank and refilled out of a fresh jug and the engine ran normally.

Gizmo-RCU

My Feedback: (27)

I keep the old fuel for break-in's and other bench type running where it is not critical. If it works well on the bench by all means burn it that way.

Gringo Flyer

My Feedback: (18)

I do the same thing with plugs. I never run a new plug on break. I have broken in several engines on one plug thats not good enough to fly with. I then put a fresh plug in the engine after break in. Every little cut corner helps