Wannabe Posted: "Old farm boy trick was to start an engine in the dark so see if the wiring is winking at ya in little sparks.
Don't remember ever trying it on an airplane. "

Won't work on aircraft spark plug harnesses as they are covered in faraday shields and would obscure any arcs. But it is a good diagnostic tool for any other spark plug leads.

Another wild possibility: didn't the 3SPA have a Venturi AD that caused some vibration? Perhaps some flutter or cavitation effect at higher flow rates?

Haha that's kinda out there. Carbs and induction can be mysterious though in how they manifest.

wannabe wrote:Newvizor

Don't waste your time looking for an AVCON motor mount: At least not from the alleged AVCON Co. Lots of other postings about them. Some almost humorous. May re-write some of it on request .

Best bet (last I checked) is still DELAIR in Porterville Ca. Young fellow name of Chris took over the business after Harry Delicker died. Chris had worked for Harry for years and has done some of the best "show" quality work I have ever seen. They also have larger fuel tank kits. I installed the larger of two options in my 170-B. I also put in their "forward" mounted muffler system.

They (Delair) have a full STC with kits and materials for 0-360 conversions.

Wannabe a different Chris C

I have drawings/paperwork for the avcon conversion, I can get all the parts relatively easily except for the mount, its the golden nugget. The Del-Air/Stoots STC's are nice although I cant see paying what they want for them. If they were even a few K less I could probably justify it, but using either of their STC's I'll be dumping another 30K into this plane, I'd have 20K more into it than it would be worth...... I can justify being upside down on it a little bit but not that much. I think I would probably part out the plane before going underwater on it by that much.

I'll keep my fingers crossed I can come across an Avcon or other 175/conical mount.

Battson wrote:Are those all Champion massive electrode plugs?

Do they all have the same P/N? Looks like maybe some may not have internal resistors, while others do, which could be messing with your ignition. Otherwise, you have some bad plugs there (cracked internal insulation, maybe, could be shorting out at high power settings).

I am just guessing at the cause, this is internet advice. It sounds like either an ignition or an air/fuel ratio problem.

I will look at the P/N's, I am under the impression that as long as the resistance is less than 5Kohms they should be ok.

Zzz wrote:Another wild possibility: didn't the 3SPA have a Venturi AD that caused some vibration? Perhaps some flutter or cavitation effect at higher flow rates?

Haha that's kinda out there. Carbs and induction can be mysterious though in how they manifest.

I have the MA4-5 carb, it did originally have the 2 piece venturi, although it has since been swapped to the 1 piece design.
One part of the carb that I did not dissasemble when I took it apart was the air metering pin/mechanical economizer thingy....Thats kind of my last hope, I think today I'll try and pull that pin/screw whatever it is out and clean/inspect it. I think I need to find someone that really knows their way around these carbs, I keep coming back to it.....

Again thanks for the replies/ideas, I'll keep updating with my findings and hopefully solution.

Newbizor,

You may have the C-175, 7635M. I only got from 300 to 450 SMOH on the GO-300 when a rod bering turned, quit oiling, and beat the engine to death. I landed in the desert, had it rebuilt, and traded it in Lubbock, Texas for a Pawnee.

The gearbox had some play. That big long prop made it rattle a lot in strong, gusty afternoon winds.

contact

My only experience with surging at WOT is from rebuilding carburated big block V8's, so you can take it with a grain of salt. But...

High RPM stumble can be caused by running past lean on fuel flow as mentioned, and can waver like your video. Running rich generally means bogging down, but I have not seen it manifest with surging. After verifying external spark timing, I'd check carb float operation (easy), then evaluate mixture. If small mixture changes from full rich have an effect right away on how bad it runs, then voila...fuel issue. You might check primer line leaks as well. I was pretty surprised how much one of those tiny tubes can affect performance when it is leaking pretty well. I don't think it would really explain the problem you are seeing though. If primer use during WOT affects things wildly either better or worse, it is another clue.

The dwell is often an overlooked but common problem for high RPM operation though. In a car, point gaps that are too large or too small don't allow a decent spark at higher RPM for different reasons, and it can definitely cause surging. I think the same issue could exist for mags. The procedures for planes are straightforward for both Bendix and Slicks, although I am only familiar with Bendix to check the gap and dwell and opening location. If the mags were worked on, it is conceivable that they both could have been set improperly at the same time. The condensers (caps) are easy to replace and cheap, and so are points if they look pitted or the cam bumper is worn.

The good news is that these are all pretty fast to check- an hour or two if you have a friend to lead you along.

Good luck.

Update: Yesterday I noticed cyl #2 had the sooty plugs so I pulled the valvesprings on both the intake/exhaust valves and brought them to a shop and had them checked. The exhaust valvesprings were down to about the service limit, but still at the service limit or better. Both intake springs although were under the service limit for spring pressure, for instance at the first measurement on the big spring it's compressed to 1.55in it was 5-6lbs under the service limit of 40lbs, the second measurement is compressed to 1.16in and the range is 77-83 with a service limit of 74lbs, it was down around 65.

Two cylinders are superior, the rest are original continentals I believe. The superior cylinders have 3 valvesprings while the continentals have 2. Does anyone know if these configurations are interchangeable? Like can I buy the set of two valvesprings for every one of the valves including the superiors or do I need to keep the 3 valvespring setup on those cylinders? I guess I'll call superior tomorrow and ask them, maybe I'll end up buying the 3 spring setup for all of them or just end up replacing the springs on the continental cylinders only. Either way I'm going to put new springs on it and run it again before I try anything else so I can isolate the problem down to one thing for my own knowledge.

contactflying wrote:Newbizor,

You may have the C-175, 7635M. I only got from 300 to 450 SMOH on the GO-300 when a rod bering turned, quit oiling, and beat the engine to death. I landed in the desert, had it rebuilt, and traded it in Lubbock, Texas for a Pawnee.

The gearbox had some play. That big long prop made it rattle a lot in strong, gusty afternoon winds.

contact

I've got 7534M, I'm at 1425ish SNEW, there is a small amount of play in the gearbox but I'd assume that's to be expected, nothing concerning. I understand the wind on the prop running static like this might move the rpm a little bit, maybe even 50is like in my second video, but I can't see it causing the vibration/200+rpm jumps I'm getting at full throttle.

lesuther wrote:High RPM stumble can be caused by running past lean on fuel flow as mentioned, and can waver like your video. Running rich generally means bogging down, but I have not seen it manifest with surging. After verifying external spark timing, I'd check carb float operation (easy), then evaluate mixture. If small mixture changes from full rich have an effect right away on how bad it runs, then voila...fuel issue. You might check primer line leaks as well. I was pretty surprised how much one of those tiny tubes can affect performance when it is leaking pretty well. I don't think it would really explain the problem you are seeing though. If primer use during WOT affects things wildly either better or worse, it is another clue.

The dwell is often an overlooked but common problem for high RPM operation though. In a car, point gaps that are too large or too small don't allow a decent spark at higher RPM for different reasons, and it can definitely cause surging. I think the same issue could exist for mags. The procedures for planes are straightforward for both Bendix and Slicks, although I am only familiar with Bendix to check the gap and dwell and opening location. If the mags were worked on, it is conceivable that they both could have been set improperly at the same time. The condensers (caps) are easy to replace and cheap, and so are points if they look pitted or the cam bumper is worn.

The good news is that these are all pretty fast to check- an hour or two if you have a friend to lead you along.

Good luck.

Thanks for the reply,
I do seem to be getting a change in rpm rather quickly as I pull the mixture back, but maybe it's just me in my hypersensitive state trying to blame something. I'll try and get some more evidence next time I run it. The first video I shot of the rpm jumping was with the primer line capped off. My gascolator is now completely bubble free (had some air in it that I traced back to the drain valve), and I don't think any air is getting in anywhere.

I'm going to change the valvesprings since I already have some out and run it again, if the problem persists I'll dive into the mags as you described.

Thanks again for the help, I'm still trying to figure out exactly what the air metering pin/mechanical economizer do exactly and if they might be affecting the air/fuel mixture at full throttle.

Newbizor wrote: I'm still trying to figure out exactly what the air metering pin/mechanical economizer do exactly and if they might be affecting the air/fuel mixture at full throttle.

If you want the O/H manual, let me know.

Check your fuel flow. Could be in the hose that feeds carb. Might be an internal flap inside the hose. it happened to me took lots dollars to find.

lesuther wrote:

Newbizor wrote: I'm still trying to figure out exactly what the air metering pin/mechanical economizer do exactly and if they might be affecting the air/fuel mixture at full throttle.

If you want the O/H manual, let me know.

I have the old version, if you have the new version I'd be greatful. The old manual shows how to remove/install it, and how to take the adjustment with the flush tool but I don't have the tool and I'm afraid to even remove it in case the needle adjustment moves and I can't get it back to the correct location.

fast eddie wrote:Check your fuel flow. Could be in the hose that feeds carb. Might be an internal flap inside the hose. it happened to me took lots dollars to find.

I tried looking into the ends with a flashlight to see if I could see the flap as you described, I couldn't see anything abnormal. I also ran about 40 gallons through the line when I drained the tanks, the whole fuel system including that line was flowing 35+GPH.

Maybe a quick way to determine if it's running too lean at high rpm would be to pull the carb hear and see what it does. This is also a good way to check if you've leaned too much while in the air.

Bdiazair wrote:Maybe a quick way to determine if it's running too lean at high rpm would be to pull the carb hear and see what it does. This is also a good way to check if you've leaned too much while in the air.

I did try that and I get a 200ish rpm drop at full power.

D-Romeo

Understand about shielded harnesses. Curious if they could still be a problem at high power settings..

This comes from an experience where the plane I was flying decided it did not want to climb above 800 msl.
An OLD AP/AI had done the annual on my old 1939 J-5. Another pilot friend and I decide to fly about 10-15 minutes to the south for fuel. I shut down by the pump and get fuel. We crank it up again and start a straight out take off back north - full throttle - best climb - when all of a sudden the engine lost partial power. (Do not remember if it shook - might have) I nose it over to initiate a turn back . Almost as soon as I nose it over the engine wants to run better. Try to climb again - no go - It was as if the engine had the mental attitude of a mule. Nose over again - 3/4 throttle and hold my breath as we crawled north to home base. Get it on the ground - it runs fine. Swing around and take off on the rest of the runway. Now at about 400 feet the same thing starts. Nose over - throttle back a bit - make slow careful 180 turn back down wind. No gliders in the other pattern - land - tie the tail down - start it up - run it up - same s@#$. Now it does shake! So - what was the last thing we did? Buy fuel, but did not seem likely, but an annual had just been done.

Rest of the story: Pulled all the plugs and found what I thought was TOO MUCH anti seize. Cleaned the plugs of excess anti seize. Trimmed inside lip of plug threads with deburring tool.. Blow out with lots of air.
Replaced the plugs. Tied the tail to a fence post this time to run wide open again. I ask Doug, "Wanna try it again?" He shrugs. So we go again - back to the other airport and do a touch and go. This time very little miss and buck. The anti seize had turned into a "GLOW PLUG" after heat saturation and the full power take off and hard climb.

Well - that was more than I started out to write. Chris C

PS: I use those dashes sometimes when vision starts to blur - sorry

PAMR MX wrote:I would bet ya a beer both magneto condensers are bad.

Yup, my money's on condensers and / or points

The harnesses do go bad in spite of a solid conductor. I suspect mine are due for replacement (1200+ hrs)

DeltaRomeo wrote:The harnesses do go bad in spite of a solid conductor. I suspect mine are due for replacement (1200+ hrs)

The harnesses were replaced with new within the last 20 hours, if I can find a bomb tester I'll check them out anyway.

onefitty wrote:

PAMR MX wrote:I would bet ya a beer both magneto condensers are bad.

Yup, my money's on condensers and / or points

how fast can something like that fail? They were changed with the magneto overhaul last January, and only 15 or so hours have been put on it since. I won't rule it out though.

Wannabe,
That's a good tip about using too much anti-seize, I am shocked by how much I find goobered into plugs sometimes! I like to dab a dollop on, then clean it back off with a rag using a motion to go around the threads, it takes most of it back off but leaves a tiny bit on, which I believe is still enough.

I just got off the phone with a Bryan from Poplar Grove airmotive, he seems to think its either valve or ignition related too, so after I change these valve springs (hopefully I can get them today or tomorrow), if that doesnt solve it, I'll probably shotgun a new set of plugs at it, and if that doesn't do it I'll pull the mags back apart. I really hesitate to do that because they were just done.....

Newbizor wrote: I really hesitate to do that because they were just done.....

When something goes wrong, check the last thing you changed.

I was going to guess valve float, but don't know much about these power plants and their symptoms to smartly recommend anything. Seems like that spring being low might back up my completely unscientific opinion, so I'm excited to see how it looks when you get those fixed.

Either way, I hope you nail down the problem soon and that it doesn't cost an arm and a leg!

Sent from my LG-D850 using Tapatalk

NimpoCub wrote:

Newbizor wrote:When something goes wrong, check the last thing you changed.

I hear you there! I want to say it wasn't doing this when I flew it home after I bought it last fall though which was after the mags were done. Either way it will be the next thing I go after if these valve springs don't fix it.

Are your mags slicks? There is a service bulletin on the points. Due to poor quality control, the points contact can become loose and misfire can occur. Happened on my 0-470 with new slicks a couple of years ago.

Newbizor wrote:

Bdiazair wrote:Maybe a quick way to determine if it's running too lean at high rpm would be to pull the carb hear and see what it does. This is also a good way to check if you've leaned too much while in the air.

I did try that and I get a 200ish rpm drop at full power.

That's a big drop for carb heat.

Cary