Low Fuel Flow - M20F

[MikeOH]

Going off Savvy data, my M20F is a couple of gallons/hr low at full power.  Their data suggest close to 18 gph at takeoff and I'm at 16 gph.

Fuel pressure is good and boost pump is working properly.  Injectors have been cleaned with no difference noted.

Where should I start looking?

 

Thanks!

[Oscar Avalle]

Mike,

I had a similar problem with my M20C. As a side effect my CHT were very high. I tried many things. In my case the solution was to change the carb. But obviously ya can not do it. Another issue that helped was to go over the diameter of the fuel hoses in the engine. We discovered that some were of the wrong diameter. Thus, my fuel pressure was too high and I was not getting enough fuel. After looking into all these issues (including changing the carb) I was able to get from 16 to 17.5 gal/h on take off.  

[Brian E.]

13 minutes ago, Oscar Avalle said:

I was able to get from 16 to 17.5 gal/h on take off.  

@Oscar Avalle Did you see CHT improvement with you increased fuel flow?

[MikeOH]

47 minutes ago, Oscar Avalle said:

Mike,

I had a similar problem with my M20C. As a side effect my CHT were very high. I tried many things. In my case the solution was to change the carb. But obviously ya can not do it. Another issue that helped was to go over the diameter of the fuel hoses in the engine. We discovered that some were of the wrong diameter. Thus, my fuel pressure was too high and I was not getting enough fuel. After looking into all these issues (including changing the carb) I was able to get from 16 to 17.5 gal/h on take off.  

Great suggestion!  I never would have thought of fuel line diameter.

Thank you!!

And, my CHTs need to monitored closely; especially with summer temps.

I've already overhauled the oil cooler, replaced the oil lines, checked the vernatherm and still experience high oil temps and low oil pressure.  Maybe more fuel flow will help with those issues, as well; at least on take-off.

[Ragsf15e]

2 hours ago, MikeOH said:

Going off Savvy data, my M20F is a couple of gallons/hr low at full power.  Their data suggest close to 18 gph at takeoff and I'm at 16 gph.

Fuel pressure is good and boost pump is working properly.  Injectors have been cleaned with no difference noted.

Where should I start looking?

 

Thanks!

Someone smarter than me will definitely be along soon, but isn’t there an adjustment on the fuel servo to increase fuel flow?  Yeah, I just took off at sea level yesterday and saw 18.5gph on takeoff roll.  Chts stay below 360 in the climb.  I do notice a rise in oil temp with chts, but it’s not more than about 10 degrees higher oil temp with chts at 380 vs 330.

[RLCarter]

1 hour ago, MikeOH said:

And, my CHTs need to monitored closely; especially with summer temps.

What happened to that "Dry Heat"?...sorry couldn't resist 

[Guest]

2 hours ago, MikeOH said:

Going off Savvy data, my M20F is a couple of gallons/hr low at full power.  Their data suggest close to 18 gph at takeoff and I'm at 16 gph.

Fuel pressure is good and boost pump is working properly.  Injectors have been cleaned with no difference noted.

Where should I start looking?

 

Thanks!

How accurately is the “K”factor calculated on the JPI?  No sense worrying about low flow if the gauge is wrong.

Clarence

[Yetti]

41 minutes ago, Ragsf15e said:

Someone smarter than me will definitely be along soon, but isn’t there an adjustment on the fuel servo to increase fuel flow?  Yeah, I just took off at sea level yesterday and saw 18.5gph on takeoff roll.  Chts stay below 360 in the climb.  I do notice a rise in oil temp with chts, but it’s not more than about 10 degrees higher oil temp with chts at 380 vs 330.

No,  The adjustments are on the idle circuit.

When was the fuel servo, Fuel divider, injectors OH last?

[MikeOH]

37 minutes ago, M20Doc said:

How accurately is the “K”factor calculated on the JPI?  No sense worrying about low flow if the gauge is wrong.

Clarence

Excellent point!

I'm within a gallon on a 35 gallon top-off.  So, around 3%...might explain 1/2 gph error.

[MikeOH]

32 minutes ago, Yetti said:

No,  The adjustments are on the idle circuit.

When was the fuel servo, Fuel divider, injectors OH last?

What would be a suspiciously excessive amount of hours for each of those items?

What are the recommended OH intervals?

Edited September 2, 2019 by MikeOH

[MikeOH]

1 hour ago, Ragsf15e said:

Someone smarter than me will definitely be along soon, but isn’t there an adjustment on the fuel servo to increase fuel flow?  Yeah, I just took off at sea level yesterday and saw 18.5gph on takeoff roll.  Chts stay below 360 in the climb.  I do notice a rise in oil temp with chts, but it’s not more than about 10 degrees higher oil temp with chts at 380 vs 330.

WOW!  CHTs under 360!  I fight to keep mine under 400 climbing in hot weather.  Once in cruise they drop to 330.

[MIm20c]

6 minutes ago, MikeOH said:

What would be a suspiciously excessive amount of hours for each of those items?

What are the recommended OH intervals?

I would think time since overhaul would be important as well. What’s your fuel pressure on takeoff?

[Yetti]

10 years 2000 hours would probably make the most sense.   There are a bunch of rubber parts in the servo and the fuel divider.     Did servo in the spring.   The OHer called with a concern kind of like "Wow there are a couple of SBs on this" And pretty much left the impression that he was quite impressed that it was still working.   He replaced 2 Injectors and flow balanced everything.   It seems like it runs smoother, but maybe that is because I don't have to carry all that cash around.

You might want to check the finger screen in the servo.   Supposed to be done on annual inspection.   But not sure it is always looked at.  

[MikeOH]

7 minutes ago, MIm20c said:

I would think time since overhaul would be important as well. What’s your fuel pressure on takeoff?

24-26 psi on take-off with boost pump on.

[MikeOH]

1 minute ago, Yetti said:

10 years 2000 hours would probably make the most sense.   There are a bunch of rubber parts in the servo and the fuel divider.     Did servo in the spring.   The OHer called with a concern kind of like "Wow there are a couple of SBs on this" And pretty much left the impression that he was quite impressed that it was still working.   He replaced 2 Injectors and flow balanced everything.   It seems like it runs smoother, but maybe that is because I don't have to carry all that cash around.

You might want to check the finger screen in the servo.   Supposed to be done on annual inspection.   But not sure it is always looked at.  

Thanks.  Especially to check the servo screen...now to find out where that is and how hard it is to remove/check!

[MIm20c]

There should be a supply and injector tap at the fuel servo. You could have a mechanic put a gauge on both sides and see if the proper pressures are showing during run up. 

[MikeOH]

3 minutes ago, MIm20c said:

There should be a supply and injector tap at the fuel servo. You could have a mechanic put a gauge on both sides and see if the proper pressures are showing during run up. 

Good suggestion.

Thank you!

 

[Guest]

1 hour ago, MikeOH said:

Thanks.  Especially to check the servo screen...now to find out where that is and how hard it is to remove/check!

This might help.

Clarence

[Yetti]

Some people have said to get to the screen from the non fuel hose side.   The manual says that is a no no.

 

[Ragsf15e]

2 hours ago, Yetti said:

10 years 2000 hours would probably make the most sense.   There are a bunch of rubber parts in the servo and the fuel divider.     Did servo in the spring.   The OHer called with a concern kind of like "Wow there are a couple of SBs on this" And pretty much left the impression that he was quite impressed that it was still working.   He replaced 2 Injectors and flow balanced everything.   It seems like it runs smoother, but maybe that is because I don't have to carry all that cash around.

You might want to check the finger screen in the servo.   Supposed to be done on annual inspection.   But not sure it is always looked at.  

Where’d you send the servo, divider , etc?  Recommend them?  I’ve been searching my logs and can’t find the last overhaul.  At least 1998 and 1000hrs.  Maybe more.  I need to overhaul this annual.

[Yetti]

Texas Carburator and Injector .  in Justin Texas.   Took about a month and a call dropping into my Texas drawl to get it out of prison.   Seems to work first time off the UPS truck.

[Ragsf15e]

28 minutes ago, Yetti said:

Texas Carburator and Injector .  in Justin Texas.   Took about a month and a call dropping into my Texas drawl to get it out of prison.   Seems to work first time off the UPS truck.

Thanks.

[Oscar Avalle]

7 hours ago, Brian E. said:

@Oscar Avalle Did you see CHT improvement with you increased fuel flow?

Actually I did see a huge improvement with the increased fuel flow. CHT's went down by 20 to 30 degrees. That allowed me to install a Electroair ignition without seeing an increase in CHTs. 

[Guest]

7 hours ago, Ragsf15e said:

Thanks.

As you’re in Washington, you are very close to Precision Airmotive, the manufacturer of the system.  We used D & G Supply in Michigan with good results.

http://www.precisionairmotive.com/

https://www.dgsupply.com/

Clarence

[MIm20c]

4 hours ago, M20Doc said:

As you’re in Washington, you are very close to Precision Airmotive, the manufacturer of the system.  We used D & G Supply in Michigan with good results.

http://www.precisionairmotive.com/

https://www.dgsupply.com/

Clarence

I’ll have to stop in some time. This is where I buy my fuel if flying local.