IO-360-A3B6 Idle Set Procedure and AC Spark Plug Question

[Peter Rejto]

A couple of issues have been revealed after installation of an EDM-830.

1. My prop gov needs adjusting down 50 RPM as tach is showing 2750 on takeoff.

2. My mixture appears to be too rich. I cannot idle slower than around 850 RPM full rich. If I slowly lean it will rise to 1150 RPM and then quit. Am I correct that the rise should be more in the range of 20-50 RPM (at ~700 RPM)? Currently if I pull the throttle all the way out, full rich, the engine goes to around 300 RPM and then dies. So, I also may have a throttle cable adjustment to do, or perhaps if the mixture is corrected not?

3. My plugs need servicing/replacement. I have a set of 4 fine wires but they are the old AC HSR 83P. I cannot find a cross reference to Champions. If my memory is correct many years ago I ran these in my J but I want to be certain these are not too hot or just the wrong plug.

Thanks!

Peter

[MB65E]

Your Idle mixture can be leaned 3-4 turns for starters. I’ve always taken the measurement at 900rpm with a warm mixture. Your rise assessment is correct. 
I would leave the prop gov. Adjustment alone. Will it overspeed in cruise or just Takeoff? 
Everyone likes finewires I guess. Just make sure the plug lead size is correct when you order new plugs. 
Darn JPI’s causing more work! ;-)

-Matt

[carusoam]

Peter,

You can Verify your tach reading with a phone app… uses acoustics. Then have the gov dialed in to match… the JPI is pretty accurate, old mechanical tachs were not…

Typical idle rpm is around 700… any lower, the engine skips a beat and dies….  Any faster, the airplane won’t land on the numbers and keeps floating a little further….

Selecting the best of two weevils….

1) Weevil1: Don’t buy Champion spark plugs because they made trash for decades and knew it…. At annual, people measure their resistance, then toss out the ones that have changed to a high resistance….

2) Weevil2 Tempest spark plugs haven’t always been perfect… they lost a few center electrodes over the years… they also found the problem, fixed it, and sent a few MSers replacements….

If unsure that the Tempest plugs are the best for you… get four, and install them in the bottom cylinder locations….

 

There is a lot of Tempest Fine wire experience around here…. They are really good for LOP…

PP thoughts only, not a mechanic…

Go MS!

Best regards,

-a-

[KB4]

37 minutes ago, Peter Rejto said:

or just the wrong plug.

Could be. Check manufacturer references to your engine type 

https://tempestplus.com/wp-content/uploads/2019/01/Tempest_App_GuideV7.pdf

[PT20J]

50 rpm isn’t a big deal, but if you want to adjust it just pull the prop control back to 2700 rpm in the air at full power. Land without touching prop control. Adjust screw on governor until it just touches the control arm. 

Here’s the procedure for adjusting idle:

 

[Peter Rejto]

Wow,  Thanks so much for the great replies! All very useful.

Okay, I may have been totally unclear about the plugs(?). I have 4 new AC HSR 83P fine wires going to waste. I know AC went out of business thanks to Champion. My question is are these compatible with my IO-360A3B6. I'm pretty sure many years ago I ran them in my J which at the time was the A3B6D. But, I can no longer find a cross reference.

I intend to order new Tempest fines for at least the bottom plugs, but it's going to take a while for these to arrive in Australia. I was/am hoping the HSR-83Ps might tide me over. Anyone know?

Thanks!

[carusoam]

Peter,

Sounds like a great trivia question for @M20Doc….  (NOS New Old Stock… spark plugs…. AC HSR 83P… are these still usable in an M20J’s IO360?)

Keep in mind… Peter is really far away from where the new spark plugs are stored….   

Best regards,

-a-

[PT20J]

Maybe this will help stinsonclub-org.pdf

Skip

[Peter Rejto]

8 minutes ago, PT20J said:

Maybe this will help stinsonclub-org.pdf

Skip

I'm impressed by your searching skills!  That is useful, I believe, as it seems the HSR 83P is crossed to the RHM38P (p for platinum dual electrode). I'm already using the RHM38E (massive) so I think these would be compatible. Thank you, and for your tip on Prop gov adjustment!

Actually I have a question. If I'm departing a field at 2,000' full power isn't the same as full at sea level. Is the technique accurate in that circumstance?

Thanks!

Edited February 9, 2022 by Peter Rejto

[PT20J]

17 minutes ago, Peter Rejto said:

I'm impressed by your searching skills!  That is useful, I believe, as it seems the HSR 83P is crossed to the RHM38P (p for platinum dual electrode). I'm already using the RHM38E (massive) so I think these would be compatible. Thank you, and for your tip on Prop gov adjustment!

Actually I have a question. If I'm departing a field at 2,000' full power isn't the same as full at sea level. Is the technique accurate in that circumstance?

Thanks!

It will still work fine. At 2000’ and cruise speed the engine will turn much faster than 2700 rpm were it not for the governor. You don’t really need full power.

Skip

[Guest]

You need and older version of this S/I from Lycoming which should list the AC brand spark plug. A call or email to their tech support should help

https://www.lycoming.com/sites/default/files/SI1042AH Approved Spark Plugs.pdf

Idle mixture and speed adjustments and propeller governor adjustment are easy once the cowls are removed.

Clarence

[A64Pilot]

I’d leave the prop governor alone, it’s only 50 RPM, it will help a little in TO performance and after you get cleaned up in climb just reduce to 2700.

 

[Will.iam]

A photo tachometer works great to verify your rpm’s. Most model airplane hobby stores sell them as well as Amazon. Here is a link to the one i bought and can confirm it works in the cockpit through the windshield so i can verify anytime even in cruise. 
Hangar 9 Micro Digital Tachometer, HAN156 https://www.amazon.com/dp/B0006N72U2/ref=cm_sw_r_cp_api_glt_i_N75XR12Z58G65MGBMRM5

[Peter Rejto]

20 minutes ago, Will.iam said:

A photo tachometer works great to verify your rpm’s. Most model airplane hobby stores sell them as well as Amazon. Here is a link to the one i bought and can confirm it works in the cockpit through the windshield so i can verify anytime even in cruise. 
Hangar 9 Micro Digital Tachometer, HAN156 https://www.amazon.com/dp/B0006N72U2/ref=cm_sw_r_cp_api_glt_i_N75XR12Z58G65MGBMRM5

My EDM-830 has a digital tach. Is it not accurate enough? In fact it's the recent EDM installation that has led to this observation (a "caution" warning from Savvy)

[jaylw314]

FWIW, I used Tempest Fine Wire plugs UREM38S in my IO-360A3B6.  I don't know if it matters, but mine is a rebuilt engine, not a modified A3B6D.

Holy cow, they're $120 each now??  Think about just using massive plugs, I didn't notice a major difference using the fine-wires.

[PT20J]

1 hour ago, jaylw314 said:

FWIW, I used Tempest Fine Wire plugs UREM38S in my IO-360A3B6.  I don't know if it matters, but mine is a rebuilt engine, not a modified A3B6D.

Holy cow, they're $120 each now??  Think about just using massive plugs, I didn't notice a major difference using the fine-wires.

Bet you'd get all the benefits (except longevity) with BYs.

[jaylw314]

11 minutes ago, PT20J said:

Bet you'd get all the benefits (except longevity) with BYs.

Probably!  When I go them a few years ago, they were $75 and the massives were $25.  Now the fine wires are $120 and the massives $30, so that's less good in the cost-longevity equation...

[Will.iam]

2 hours ago, Peter Rejto said:

My EDM-830 has a digital tach. Is it not accurate enough? In fact it's the recent EDM installation that has led to this observation (a "caution" warning from Savvy)

Yes it is once you verify it is accurate. 

[WaynePierce]

I can't run full rich in my J. If I tried to taxi with full rich I'd have at least one fouled plug by the  time I got to run up. My mixture is never close to the firewall tan 3/4 to an inch, even at take off.

[carusoam]

Digital tachs are simple counters of electronic blips…

Pretty reliable, once you know it is catching all of the blips….

There have been some cases where not all blips got to their final destination….

Hence the low cost recommendations to make sure what yours is reading matches the reality of the situation…

 

It is most likely accurate… 

Best regards,

-a-

[Peter Rejto]

Thanks all for the replies!

After an "eventful" day in Sydney with a mechanic it appears that I will need to remove the fuel servo for inspection, possible OH, and seal replacement. Unfortunately it wasn't possible to just leave the plane so I'm back home to a rather remote area where mechanics are far and few. I've got a few things to sort out (none easy) to get this issue rectified that's for sure!

Peter

[Peter Rejto]

A small update. The fuel control unit was pulled out and shipped off to Brisbane. The shop called and said they found at least seven small things that together would explain my problems with overly rich idle and impossible hot starts. Hopefully I will have it back by the end of next week. 

Peter 

[Peter Rejto]

I received the fuel control unit back a few days ago and it's finally installed. The shop said there were probably 7 minor things wrong with it that would have a big combined influence on low rpm operations. The bill was "lovely" as they always are....However, after a few very minor adjustments to idle mixture and low idle rpm, all seems good. The weather is poor so I am unsure just when I can properly test all in flight. 

Peter

[carusoam]

Great follow-up Peter!

Good luck with getting the weather worked out.

-a-

[A64Pilot]

On 2/9/2022 at 5:12 PM, WaynePierce said:

I can't run full rich in my J. If I tried to taxi with full rich I'd have at least one fouled plug by the  time I got to run up. My mixture is never close to the firewall tan 3/4 to an inch, even at take off.

Unless you live at very high altitude, you need to get that looked at, it’s not normal. Something is wrong.