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  #31  
Old 08-11-2022, 11:37 AM
lr172 lr172 is offline
 
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Originally Posted by Taltruda View Post
If it’s not there, then I would make a half turn richer, readjust the idle speed and try again. But I would be more concerned with a proper break in first.
He is already richened it so much that the engine died. Why are you telling him to go even richer. You guys keep getting hung up on this EGT rise and we have already posted several rational reasons why he might not be seeing it.

Larry
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  #32  
Old 08-11-2022, 12:00 PM
PilotjohnS PilotjohnS is offline
 
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Originally Posted by Taltruda View Post
It’s been my experience that you pull the mixture quickly, like less than half a second from full rich to ICO. After the fuel turns off, the mixture goes from too rich, slight rise, then too lean to support combustion, and dies. The whole thing happens AFTER the lever is at ICO. I just don’t see how an engine that is too rich can go to “OFF” without the air/fuel ratio sweeping though stochiometric on its way to “OFF”.
Because the engine is not a continuous burning thing. It is firing only once every half a second or so. So one cylinder going thru stoic will not produce a noticeable rise. Especially with fuel injection and uneven idle.

I would pull a plug.
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  #33  
Old 08-11-2022, 12:04 PM
Taltruda Taltruda is offline
 
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Quote:
Originally Posted by lr172 View Post
He is already richened it so much that the engine died. Why are you telling him to go even richer. You guys keep getting hung up on this EGT rise and we have already posted several rational reasons why he might not be seeing it.

Larry
First off all, I’m referencing a RPM rise at ICO, not an EGT rise. Second of all, his engine didn’t “die”, he said his idle rpm went down when he enriched his idle mixture screw. That’s normal. When you make a change to the idle mixture, you have to readjust the idle speed. Since he said when he moves his mixture control to ICO and gets no rise in RPM, that typically means he’s probably at stochiometric or lean of it at idle. He’s either too lean and not getting the rise, or he’s not detecting it with his ears. Perhaps Don at Airflow performance shed some light on this..
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Last edited by Taltruda : 08-11-2022 at 12:07 PM.
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  #34  
Old 08-11-2022, 12:07 PM
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Draker Draker is offline
 
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Quote:
Originally Posted by PilotjohnS View Post
I think if you pull a plug now, you might see if the previous running was too rich or lean. JMHO
So just the standard white = lean, black = rich? I've only run the engine for about 1 cumulative hour since new, not sure if that's even enough time to have a visible effect on the plugs.
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  #35  
Old 08-11-2022, 01:57 PM
lr172 lr172 is offline
 
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Originally Posted by Taltruda View Post
First off all, I’m referencing a RPM rise at ICO, not an EGT rise. Second of all, his engine didn’t “die”, he said his idle rpm went down when he enriched his idle mixture screw. That’s normal. When you make a change to the idle mixture, you have to readjust the idle speed. Since he said when he moves his mixture control to ICO and gets no rise in RPM, that typically means he’s probably at stochiometric or lean of it at idle. He’s either too lean and not getting the rise, or he’s not detecting it with his ears. Perhaps Don at Airflow performance shed some light on this..
the following assumes no change to idle speed - Idle RPM will be highest and the MAP the lowest at the optimal mixture, which is about 13.5:1 for this type of engine. If he was already richer than this, further richening will drop RPM. If he was lean of 13.5, then yes he would have seen a rise. This implies that he was doing it while the engine was running and he stated that he didn't do that. If he shuts off, adjusts then restarts, none of this applies.

As mentioned two days ago, it is best to just get in there with the engine running and shoot for lowest MAP. That will be definitive.
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  #36  
Old 08-11-2022, 02:02 PM
lr172 lr172 is offline
 
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It is firing only once every half a second or so.

I would pull a plug.
At an idle of 800 RPM, a cylinder is firing 26 times per second. Or stated differently, a cyl is firing every 38 milliseconds or .038 seconds. 800 RPM is also ~13 RPS and two cylinders fire on every revolution of a 4 cyl engine.

Larry
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Last edited by lr172 : 08-11-2022 at 02:11 PM.
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  #37  
Old 08-11-2022, 02:09 PM
lr172 lr172 is offline
 
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Originally Posted by Draker View Post
So just the standard white = lean, black = rich? I've only run the engine for about 1 cumulative hour since new, not sure if that's even enough time to have a visible effect on the plugs.
I don't think a plug will get real black after only a minute or two of run time. This assumes that the bulk of that 1 hour was before you started richening the mixture from the factory setting.
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  #38  
Old 08-11-2022, 07:22 PM
Taltruda Taltruda is offline
 
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Draker, I found this manual online..on Step 5, they have you move your mixture control really slow to note the RPM rise, then before the engine quits, you can go back to rich and keep it running. I know you don’t seem excited about making changes to a running engine, (and I don’t blame you!) but there are mechanics that do this every day and perhaps one of them can help you get it set very quickly.

https://precisionairmotive.com/wp-co.../SIL-RS-67.pdf
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Last edited by Taltruda : 08-11-2022 at 07:24 PM.
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  #39  
Old 08-13-2022, 03:44 PM
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Draker Draker is offline
 
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Default Success

Had a day to tinker some more and met with success! Before I reveal the verdict, I want to give a big thank-you to everyone who chimed in to help. This has been a really informative thread and I feel I learned a lot here.

Verdict: So, even after my earlier attempts to enrich the mixture, the mixture was still too lean. When I initially adjusted it, I was afraid I was enriching it too much without results so I stopped and posted to VAF. But it turns out I should have just continued because I only needed about 1/8 of a turn more to get it right. As for why the engine had trouble after enriching last time, that remains a mystery—it was fine the whole time today.

As for detecting the RPM rise, what ended up working for me was very slowly reducing the mixture (twisting the vernier knob in the lean direction until I could see the rise on the glass display). Doing it this way it was very clear and easy to measure the RPM rise.

Started at zero RPM rise, gave it 1/8 of a turn and observed about 50-60 RPM rise on lean-out. Gave it another 1/8 of a turn and observed 100 RPM rise (too rich). So backed off 1/8 a turn, saw 50 RPM rise, and I think I'm done. After all this I had to re-set the idle speed. I could get it to idle smoothly at 700 RPM, pretty rough at 650 RPM, and 600 RPM was so rough it stumbled and would quit. So I'm going to keep it at 700 RPM at least for Phase 1.

Big thanks again, everyone. This is truly the plane that VAF built!
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Last edited by Draker : 08-13-2022 at 04:28 PM.
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