Zenith Aircraft Builders and Flyers
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O-200 Won't start, pop, cough, anything...
Very frustrated.
I rebuilt my own O-200. I have significant engine building experience from a prior professional life as a Chrysler tech. I also built my own AeroVee VW conversion for my prior plane, a Sonex. I know, I know, it's not the same. One mag was less than 75 hrs when the core became available. I sent the other mag to our local mag shop for 500 hr servicing. The MA-3SPA carb also had less than 75 hrs on it, so I did not send it out for overhaul. I could put 100LL into the fuel bowl, pump the accelerator, and have fuel come out of the accelerator port (on the bench).
I've been trying to start it. I can crank and crank, and nothing happens anywhere by anything indicating an attempt to start.
I thought I had spark issues. I re-checked; I'm not 180 deg out, and all timing marks line up. I disconnected the P leads, since I didn't know if the GRT tach sense connection was somehow grounding the mags. I've had folks tell me to hold the spark lead next to engine ground and have the impulse coupler pop to produce a spark. Could not see a thing. Had other folks tell me that was a waste cuz you usually cannot see the spark anyway.... I traced all plug leads to make sure they ran to the correct plugs in the correct firing order. Rechecked using the mag synch tool. Spot on together.
I then shot some starting ether in the air filter. That produced some pops and sighs. Didn't spray much, so I wasn't expecting it to start. However, I'm *assuming* that because things were popping that *something* was lighting the fuel/air mixture, ergo, the mags must be firing.
So now I'm thinking fuel issues. Zenith tech support suggesting using a fuel pump to ensure the bowl was filling. Since my wings aren't on, and the tanks are in the wings, I plumbed up a facet pump in rubber fuel line and used a milk jug for a fuel tank. Fuel was getting to the fuel bowl because I had a slight fuel leak at the fuel linlet. Tightened that and tried again, still no sign of life. I checked all the intake manifold rubber joints.
I can understand if it started and ran poorly or only on 2 cylinders, but not having ANY sign of ANYTHING going on, I just don't know what to do.
How 'bout filling the fuel bowl with super whiz-bang carb cleaner, let it soak, then drain the bowl and retry with 100LL? Or would that ruin seals and gaskets in the carb?
I really don't want to replace the carb unless I know for a fact that it *IS* the carb. ~$1000 to "just check" is something I care not to waste.
Thanks for any suggestions. I'm at a loss.
Replies to This Discussion
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Permalink Reply by Clint L Gosch on
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Hi Carl, It does sound fuel related but I can honestly say you can see the spark, but even more so you can FEEL it if not careful! :) You mentioned the accelerator pump worked on the bench, were you able to fill the bowl through the normal inlet? Just wondering if the float is stuck? Or maybe the fuel level in the bowl is not correct, since it's a used carb it's hard to safely assume anything. The float level can be checked by attaching a short piece of clear tubing to the carb drain. Also, while cranking do you have the throttle approximately 1/4" open?
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Permalink Reply by Carl Orton on
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Hi, Clint; good to hear from you.
I guess it's possible the fuel level is off; I drained the fuel bowl from the bottom drain, but didn't catch what came out, so no idea how many ounces came out. I'm aware of using the sight tube to ascertain fuel level. When I bench-tested the accelerator pump, I did fill it thru a hose/fitting to the normal fuel inlet port, so it's not stuck.
The engine came out of a 150 that had a prop strike. Carb was on that engine. Was running just fine up to the point of stoppage.
I've tried pumping the throttle and cranking while it was cracked, 1/2 way, and full throttle. Nothin'....
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Hmm, bummer... now that I think about it, even if the float level is off it should still start and idle. Odd that neither the idle circuit or the main jet seem to be feeding fuel enough to run even at idle. Seems like you were able to confirm spark with the starting fluid, so it sure does seem to be a fuel delivery issue. You might try removing the carb again and blast some sea foam fogging oil down into the main jet while moving the mixture lever. Keep the bowl drain removed and see what kind of (if any) gunk flushes out. If anything flushes out, might as well send the carb out for an overhaul, who knows what else might be in there. Do the same for the tiny holes in the throttle body near the butterfly. Might be good enough to get something to light off. I guess I'm wondering if the previous owner used auto fuel, if they did its possible some of the small passages got gummed up during storage... maybe... I recommend fogging oil opposed to anything with strong solvents. I'm kind of paranoid about the gaskets in these old carbs, but maybe someone with more experience can chime in. Hope this helps!
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Update: well I mentioned that with ether I get pops etc, but nothing consistent. Pop, crank some more, a half hearted pop, sigh, etc so I thought I had spark. Tonight as our son was leaving after the game I decided to see if I could see a spark. With crank set for #1 tdc I pulled the prop until impulse coupler popped. No spark. Was low light so thought I might see something. Kept prop in same position and tried #3. Nothing. Tried #4. Wow, STRONG spark at #4. Firing order is 1-3-2-4, so I’m 90 deg premature in my firing. I THOUGHT the plug wire harness cap would only install in one orientation. The engine was static with cam n crank timing marks aligned when I installed the mags with the Slick timing pin in each mag, so I don’t THINK the mags are installed wrong. But at least I have something to investigate.
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Cool! Always better to have something to investigate instead of scratching a head. I think you are close! Keep me posted!
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Did some checking this AM just to make sure. When I saw the spark on #4 last night, I wasn't sure about where the engine was in its cycle. Turns out if I set everything so that #1 had compression (thumb over plug hole) with timing marks lined up, #2 plugs (both) fired when the impulse coupler popped. To me, that says something is 180 out, since the firing order is 1-3-2-4, so #2 is halfway, or 180 deg, out of the entire 4 cylinder sequence.
Don't know what to do. Yes, I could pull the mags and retime them MAKING SURE the timing pin is in the LEFT hole (L stamped on each data plate), then retime. But, being lazy, I really don't want to do that until I *know* that's probably the problem. I would bet a dinner that I put it in the L hole to start with....
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Solved and fixed. It Runs!
Evidently I installed the mags with the prop flange timing marks 180 degrees out. I KNOW, and KNEW that the timing marks align with the bottom crankcase seam, but enough time transpired between crankcase assy and mag installation, that that's the only logical explanation I have. Both mags were timed together, but things were just firing 80 deg out of normal firing order.
Pulled mags, reinserted timing pin, reinstsalled mags, tweaked with the mag sync tweeter, and it fired right up.
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Permalink Reply by Don Morrisey on
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Hurrah!!!! Always something, now you know. How did it sound?
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Strong, Don. Only ran a few secs as only used the gas in the fuel bowl.
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Great to hear! Good work!
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