JIMARRINGTON

I have been having trouble with an engine I converted. It is a Poulan 25cc with XYZ electronic ignition. Most of my troubles have come from having the timing advanced too far. Sometime or another during the building process of the airplane, I ended up losing the spot where I was supposed to mount the sensor and ended up putting it way too advanced. But I digress. What I am writing about here is what happened to me yesterday when attempting to fly with this engine. Engine started easily and throttle response was good. Idle was stable but from midrange to WOT, it would tend to surge at times. Not quick surges but extended surges. I made sure it was plenty rich and proceeded to fly. On acceleration, it stalled a little but picked back up and took off. Flew a few circuits and it seemed to smooth out. Tried a few tricks and if attitude is changed abruptly like a tight left turn, the engine would sputter. Tried a loop and it died. Tried this on a couple more flights with an even richer mixture and did the same.

Let me describe the carb. It is a WT-324 Walbro. I replaced the fuel pump diaghram, the regulator needle and the regulator before mounting it. It sticks completly out of the model with the regulator forward and in the slipstream. I am guessing that the problem is with the regulator and that when something happens to change the air pressure on the regulator face like quick changes in speed or attitude where the slipstream changes, the engine starves for fuel. I have a Zenoah g20 mounted in another airplane with the carb sticking out just like this one but with no problems.

Last night, when I got the plane home, I replaced the regulator cover with a cover that has a tube soldered on in the regulator hole and ran a hose into the fuse to get the regulator out of the slip stream. I also finally put a timing wheel on it and rechecked the timing and found that I still had the timing too far advanced. It was somewhere near 40 degrees BTDC. I also moved the timing to around 28 degrees BTDC.

My question is do any of these actions sound like I am correctly diagnosing the problem or does it have another problem altogether.
And if I am diagnosing the problem, is it the timing or the regulator.


Thanks
Jim

Twin Star

Sounds kinda lik carb trouble.
Try this link: http://tech.flygsw.org/carb_shop.htm

JIMARRINGTON

Interesting Twin Star. I did not mention that I had one of those aftermarket velocity stacks on the engine and that the stack is facing forward. From the site you listed, that is wrong and could lead to running problems. The website states the stack will pressurize the atmosphere side and cut off the fuel. Which may explain what I have been seeing. I will turn that thing around before the next time.

If anyone has any comments on this let me know.

Thanks
JIm

adrian222

My Feedback: (1)

I had the same surging problem with my ryobi at high revs, was driving me mad but after changing 2 diaghrams it seemed to fix the problem sometimes diaghrams seem ok but they are not supple enough and don't perform.

Adrian.

JIMARRINGTON

What really confuses me about it is it goes lean when attitude is changed. Just like a glow engine can. I thought gas engines were immune to that.

I went ahead and turned the velocity stack around on it last night. I had set forward so the the propwash was blowing into it. Now it is facing rearward.

My youngest had her tonsils out this morning to no testing until this weekend probably.

Any more ideas would be welcome.


Thanks
Jim

av8tor1977

My Feedback: (6)

Go with what you have done. I think you probably fixed it. Just be sure to properly re-tune the needles before you fly.

AV8TOR

JIMARRINGTON

Went flying last weekend. On first startup it ran fantastic. After about 8 minutes of flying it started to miss. Brought it in for a landing and nothing else I could try would make a difference. Moved the timing back and forth, fiddled with the needles. I did notice that my crankshaft had a little play in it and that the magnet had struck the sensor. So I figure the crankcase or bearings were bad. I had several more engines at home so I just decided to build another engine. When I pulled the engine out, I found that the ignition wire to the sensor had rubbed on my engine mount and was shorting out. So I think I have found my problem. Anyway, Since I had several crankcases, I went ahead and rebuilt the motor using the same head and piston with same carb and muffler. I did find that the crankcase I used this time had wider transfer port openings. After all put back together, this engine seems to have more compression. And no slack in the crankshaft.

I was really excited on my first flight cause the engine was running really well. I rerouted the ignition wire to the sensor and put some conduit around it to protect it. Hope to run it this weekend.

This does explain why the engine sounded so much like it was out of time.


Jim

karolh

Hi Jim, what's the latest update on your engine, is everything back to normal and it's running okay again .... hopefully so.

Karol

JIMARRINGTON

New motor and repaired ignition are doing fine. Has been test run but have not had time to fly yet.

Jim