Bigger jets

BH1166 · May 14, 2023

Would increasing fuel flow by drilling/ changing jets for larger orifice have any negative impact on my ability to lean to same fuel flow before drilling/ changing.

MA4SPA 10-5217 carburetor on FP O320 D1A 6A

Seems my GRT EIS measurements at takeoff show low flow compared to others with same engine / RV . As things are, CHT and EGT #1 #2 get a bit high 400+ / 1500+. Pulling back on throttle very little has an immediate reaction … lowering both.

wawrzynskivp · May 14, 2023

No

Your main jet has the role of metering fuel by creating back pressure against the induced flow from venturi vacuum. Bigger jet means more flow for the same venturi vacuum. Providing extra back pressure through the mixture valve assuming it can move to the fully closed position won't be affected by the new jet.

Don't know how your carb is set up but do double check float height before swapping a jet.

If you have adjustable emulsion air on the main metering system then a reduction if air may get you where you need to be.

Drilling may be a little unpredictable. The tooling needed for those kind of fine adjustments are probably better left to the manufacturer. Buy one of their calibrated jets, they shouldn't be expensive.

Do some specific fuel flow calculations based on your set-up. I tend to trust Savvy's conclusions so that should drive a double check before any changes are made. BUT, this is EXPERIMENTAL aviation after all. You have a lot of room on the rich side of stochiometric so going to the next larger jet probably won't foul you up, just be ready to swap it back if you can't see any change in CHT.

lr172 · May 14, 2023

Jet will not impact ability to lean. However, PLEASE do not drill out your jet based upon a simple average provided by Saavy. If you think your TO fuel flow is less than desired, please post some detail here and get opinions. Lycoming has a chart for minimum fuel flow required at all different MAP/RPM combinations. Way better off to start with that. High CHTs are NOT a universal sign of too little fuel flow.

BH1166 · May 14, 2023

Thanks

These readings are/have been consistent for the past 5 yrs / 700 hrs. The Savvy report agrees when looking at individual flights over 5 yrs via EIS. I changed out carburetor 10 months (exact same model) ago due to sticking float, and no evidence in my good logs showing it being touched since installed, soon to be 31 years ago.

Here are some individual flights , winter, summer, over 511/3 years stored on Savvy servers.

lr172 · May 14, 2023

BH1166 said:
These readings are/have been consistent for the past 5 yrs / 700 hrs. The Savvy report agrees when looking at individual flights over 5 yrs via EIS. I changed out carburetor 10 months (exact same model) ago due to sticking float, and no evidence in my good logs showing it being touched since installed, soon to be 31 years ago.

Here are some individual flights , winter, summer, over 511/3 years stored on Savvy servers.

Required fuel flow is based upon RPM and MAP not CHT and EGT. Please post data with FF, RPM and MAP. Please avoid temption to compare to other RVs. FP vs CS prop makes a big difference in TO fuel flow.

caryr · May 15, 2023

One of the better things I did to my -7 years ago was to enlarge the main jet.

I consistently ran too hot for my comfort.

A bit larger on the jet fixed that.

JMHO

BH1166 · May 15, 2023

Fixed pitch prop, I don’t capture manifold pressure.

Thanks Larry

lr172 · May 15, 2023

BH1166 said:
Fixed pitch prop, I don’t capture manifold pressure.

Thanks Larry

So, I'll assume WOT and somewhere near sea level for TO. You go to WOT and RPM spools up to 2400 or so and assumed 29" of MAP. A 320 with 8.5:1 pistons (160 HP) should be flowing around 13 GPH here. You are showing something around 11 or less, which is too low. HOWEVER, it would appear after TO, you go to 2700 and then LOP and report abnormal FF. Have no idea where the throttle is or airspeed is. That said, at lower altitudes, most 320's won't run at 2700 / 7 GPH which is what your FF is showing. Please provide throttle position, airspeed, FF and RPM for that level off of cruise speed.

My first suspicion is that your FF may not be correctly calibrated or is failing and would be best to start there and then determine TO FF to see if it is low.

Are you pulling the mixture at any time during this? I notice that on the initial TO, that as soon as the RPM peaks, FF starts to fall yet RPM is stable or still rising. If this is not coming from the red knob, you likely have some issue going on with the carb, linkage or FF instrument, as that is abnormal behavior and not the jet. The jet meters based upon three things: fuel height level in bowl, volume of air flowing through the carb (directly tied to MAP/RPM) and the ambient air pressure. The most common problem area is fuel height and can be caused by problems with the fuel pump or needle/seat or float. When the fuel level in the bowl drops, the carb goes lean and it is progressive. The lower the height, the leaner it gets. It is the job of the Fuel pump, needle/seat and float to keep the fuel at the right height.
Larry

DanH · May 15, 2023

You mention the plots below were records over a five year period, with a recent carb change. Were the two plots on the right taken with the new carb?
.

BH1166 · May 15, 2023

Dan, I cut off date in screen prints, but believe old carb.

SOP is WOT, rotate, if alarms go off from EIS, I pull back on throttle till alarms cease, below 410 CHT 1550 EGT.I never start any leaning until above 3500’ ( then very little), at cruise I aggressively lean to 7.0-7.8 gph. My cruise is generally 4500-8500’ depending on winds/direction of flight. I have a Whirlwind ground adjustable prop, set to a little on the climb vs cruise pitch. I can turn 2760 rpms as it is today. 2.5 yrs on this prop. Prior was wood ACS WARNEKE, LANDOLL RING.

Yes nearly all flights start below 500’ . I run 2600-2700 generally in cruise always, I lean till all EGTs drop from their high of 1470-1550. #1 & #2 always ladt to drop, #2 always highest it seems. Fuel flow by my GRT setup shows 6.9-7.6 fuel flow on average. When refueling, yes, this flow is pretty close to 100% accurate….. 12gal burned shows on EFIS, 12 back to topping off.

After your HOWEVER LR, what do you mean by abnormal FF? Is it you thinking how could I make the RPMs at low FF? I have checked my Tach and it is correct. I run Slicks, 99% of my 140 hrs oer year is on 93% unleaded past 3 years. Before and after exhaust valves pics, 2 yrs between first set of 4 pics, and second.

lr172 · May 15, 2023

BH1166 said:
Dan, I cut off date in screen prints, but believe old carb.

SOP is WOT, rotate, if alarms go off from EIS, I pull back on throttle till alarms cease, below 410 CHT 1550 EGT.I never start any leaning until above 3500’ ( then very little), at cruise I aggressively lean to 7.0-7.8 gph. My cruise is generally 4500-8500’ depending on winds/direction of flight. I have a Whirlwind ground adjustable prop, set to a little on the climb vs cruise pitch. I can turn 2760 rpms as it is today. 2.5 yrs on this prop. Prior was wood ACS WARNEKE, LANDOLL RING.

Yes nearly all flights start below 500’ . I run 2600-2700 generally in cruise always, I lean till all EGTs drop from their high of 1470-1550. #1 & #2 always ladt to drop, #2 always highest it seems. Fuel flow by my GRT setup shows 6.9-7.6 fuel flow on average. When refueling, yes, this flow is pretty close to 100% accurate….. 12gal burned shows on EFIS, 12 back to topping off.

After your HOWEVER LR, what do you mean by abnormal FF? Is it you thinking how could I make the RPMs at low FF? I have checked my Tach and it is correct. I run Slicks, 99% of my 140 hrs oer year is on 93% unleaded past 3 years. Before and after exhaust valves pics, 2 yrs between first set of 4 pics, and second.

Are you saying that at TO and WOT you are getting 1550 EGT? That must be near peak and should be well lower at full rich. That points to a big issue. In my 320 at 8000', I am turning 2740 RPM and burning 8.1 or so. That is already around 40-50*+ LOP. If you are at 7 GPH, that would be VERY deep into LOP territory and struggle to see how a carb'ed engine could go that lean. SOmething is not adding up here. I am guessing you may be further to the climb side of the pitch range than you think. Hard to say without MAP data.

BH1166 · May 15, 2023

lr172 said:
Are you saying that at TO and WOT you are getting 1550 EGT? That must be near peak and should be well lower at full rich. That points to a big issue. In my 320 at 8000', I am turning 2700 RPM and burning 8.1 or so. That is already around 40-50*+ LOP. If you are at 7 GPH, that would be VERY deep into LOP territory and struggle to see how a carb'ed engine could go that lean. SOmething is not adding up here. I am guessing you may be further to the climb side of the pitch range than you think. Hard to say without MAP data.

Id have to look at what I alarm at, but pretty accurately stating things here. Yes, WOT on TO, #1,#2 …full rich. I’m guessing I too would be 8.1gph @ 50* rich of peak seeing I’ m mid 7’s at lean of peak. I get 40-50 rpm drop at lop, no discernible roughness . Here are some ff and egt on april 2023 and April 2022. Also a shot of EFI at cruise. Thanks

DanH · May 15, 2023

BH1166 said:
Dan, I cut off date in screen prints, but believe old carb.

Ok, I asked because both show a rise in RPM with leaning, which suggests the fuel flow just prior is on the rich side of best power. However, the plots don't show pitch attitude, altitude, or airspeed, so they are inconclusive viewed alone.

lr172 · May 15, 2023

BH1166 said:
Id have to look at what I alarm at, but pretty accurately stating things here. Yes, WOT on TO, #1,#2 …full rich. I’m guessing I too would be 8.1gph @ 50* rich of peak seeing I’ m mid 7’s at lean of peak. I get 40-50 rpm drop at lop, no discernible roughness . Here are some ff and egt on april 2023 and April 2022. Also a shot of EFI at cruise. Thanks

You misunderstood or I mis-stated. I get 160 KTAS @ 8K' with 2740 RPM and 8.1 GPH and that is 40-50* LOP. 50 ROP would be around 9 GPH. RV-6A IO-320 (160) and FP prop slightly on the climb side (i.e. under pitched). I am struggling to see how you get 2700 RPM at 7 GPH unless the prop is WAY under pitched. In my case, going to 9 GPH gives me well over 2800 and have to assume it would be 2600 or less if I leaned to 7 GPH, which would be well over 100* LOP and that is generally not possible on a carb'ed engine, though I suppose there are exceptions.

lr172 · May 15, 2023

DanH said:
Ok, I asked because both show a rise in RPM with leaning, which suggests the fuel flow just prior is on the rich side of best power. .

That makes good sense, but doesn't seem to jive with the 1550 EGT on the charts just before the FF drops. I keep getting the feeling that there is just not enough data here to understand what is happening.

BH1166 · May 15, 2023

lr172 said:
You misunderstood or I mis-stated. I get 160 KTAS @ 8K' with 2740 RPM and 8.1 GPH and that is 40-50* LOP. 50 ROP would be around 9 GPH. RV-6A IO-320 (160) and FP prop slightly on the climb side (i.e. under pitched). I am struggling to see how you get 2700 RPM at 7 GPH unless the prop is WAY under pitched. In my case, going to 9 GPH gives me well over 2800 and have to assume it would be 2600 or less if I leaned to 7 GPH, which would be well over 100* LOP and that is generally not possible on a carb'ed engine, though I suppose there are exceptions.

Yes misunderstood….. maybe it is way under pitched. My first settings were under pitched a lot, next settings seemed to give me what the FP Warneke prop would do in speed, but lots better climb performance, which was a reason to go to ground adjustable vs FP …. I wanted better climb due to flying a lot on top during summer in the South. I generally have to be @ or above 6500 to get to 7gph. Generally cruise is 45-750O’, 2600-2680 rpm, leaned to 7.3-7.6gph. Refueling shows these numbers accurate. I really appreciate your time and effort. Like in OP, just trying to get these temps down on TO. Now, judicious use of black knob will create a positive change cooler. I like I can fly 4 hours on 39 gallons. I like the efis /ff match within a gallon generally of the fuel pump. My RV has old style wheel pants and a couple extra gps pucks for added drag. I don’t need any faster, higher, and I like my fuel burn, just not high temps on TO WOT FULL RICH #1 #2. Again thanks and don’t give up on me. I think something is wrong, just beyond my ability to figure it out.

Bob Martin · May 15, 2023

caryr said:
One of the better things I did to my -7 years ago was to enlarge the main jet.

I consistently ran too hot for my comfort.

A bit larger on the jet fixed that.

JMHO

Same here on the larger jet......I drilled mine.
Learned a lot from John Deakin! RIP. Pelican Perch.
As far as leaning goes.....you can still control the mixture. But you change the full rich fuel flow. Example, as you climb, at some point the mixture becomes too rich and the engine will shutter which reminds you to lean.

DanH · May 15, 2023

lr172 said:
That makes good sense, but doesn't seem to jive with the 1550 EGT on the charts just before the FF drops. I keep getting the feeling that there is just not enough data here to understand what is happening.

1550 is indeed a high value, but absolute values alone don't tell much. What matters is how the EGT changes when leaning. If it rises when you pull the mixture knob, it was on the rich side of peak. If it stays the same during initial leaning and then starts down, it was already near or at peak. If it starts down early in the leaning process, it was at peak, or lean of peak.

Most would agree the preferred result is 150~200 rich pf peak at full throttle, full rich. 100~125 rich of peak is fine if cylinder head cooling is good, the payoff being a little more power.

The check, done at reduced power for safety, per Don Rivera is:

Fly the plane at 3500 Ft. Set 24 square for power. Slowly lean the mixture to find the peak EGT on one cylinder. Record the peak EGT. Put the mixture back full rich. Wait one minute, then record the full rich EGT on the same cylinder. Take the difference. There should be 185 to 230 degrees F difference in the two readings.

Stretch out your time scale on those plots so we can see what is happening. All you want is the first 15 minutes (takeoff, climb, and leaning), or the period for the test above.

Taltruda · May 15, 2023

BH1166 said:
Would increasing fuel flow by drilling/ changing jets for larger orifice have any negative impact on my ability to lean to same fuel flow before drilling/ changing.

MA4SPA 10-5217 carburetor on FP O320 D1A 6A

Seems my GRT EIS measurements at takeoff show low flow compared to others with same engine / RV . As things are, CHT and EGT #1 #2 get a bit high 400+ / 1500+. Pulling back on throttle very little has an immediate reaction … lowering both.

Seems that the 5217 carb isn’t really the right one for RVs.. I’m going through the same thing on a buddies -9a with the same carb and the same issues.. doing some digging, it seems that carb 10-3678-32 may be the better choice. Recently, a buddy has a -8A with a O-320, and when he needed a new carb, I suggested the 3678 and he called his engine shop who agreed that’s a better one than the 5217. We should have our new one installed in a week or so, I’ll report back with the results.

BH1166 · May 15, 2023

Thanks Tom, interested to know outcomes.

Dan check PM

Zero4Zulu · May 16, 2023

I have been attempting to get my CHT’s more even in climb. I have a 10-3678-32 carb. I measured my jet diameter with precision gage pins and my jet was .1065” stock. I lapped it out just smidge to .107”.

I was convinced that my fuel distribution to each cylinder was not good. I drilled side holes in the Jet/Nozzle similar to the Mooney mod jets, which is for the O360, thinking I could get better vaporization. It worked unbelievably great! Still not perfect but for carburetor it’s pretty good. I may still open up the Jet diameter a bit more.

BH1166 · May 16, 2023

DanH said:
1550 is indeed a high value, but absolute values alone don't tell much. What matters is how the EGT changes when leaning. If it rises when you pull the mixture knob, it was on the rich side of peak.

Correct, all rise slowly, then drop slowly, #2 last to peak, followed by #1. #1 and #2 will be the highest when leaned.

I’ll try the Don Rivera routine next time out this week.

DanH · May 16, 2023

BH1166 said:
#1 and #2 will be the highest when leaned.

Again, "highest" means little by itself. The highest EGT value for each cylinder is recorded only so it can be compared with the full rich EGT value for the same cylinder.

I’ll try the Don Rivera routine next time out this week.

Calm air, early in the AM is best. Set 2400 RPM at 3500, lock the throttle and, if possible, engage an altitude hold. Let everything settle, then record the full rich EGT value for all cylinders.

Now lean in small increments of fuel flow. The initial increments can be larger, maybe 0.5 GPH per pull, but later, approaching peak EGT, lean 0.1 GPH at a time. At each increment allow time for all EGTs to settle, then record all four values. Repeat until it's obvious all the values have risen to some high number, and are now decreasing with each change.

On Savvy, the increments will look like stair steps. Nice, but the list is just as good.

Return the mixture knob to full rich, allow all EGTs to settle, and record them. It's just a confirmation; the values should be close to the original full rich values.

On Savvy, EGT and fuel flow will look like stair steps. Nice, but the clipboard list is just as good.

lr172 · May 16, 2023

DanH said:
1550 is indeed a high value, but absolute values alone don't tell much. What matters is how the EGT changes when leaning. I

OP stated that EGTs peak around 1550, so relevant here to show he is well lean of the target.

DanH · May 16, 2023

lr172 said:
OP stated that EGTs peak around 1550, so relevant here to show he is well lean of the target.

Possible true...but it doesn't change what we're trying to teach, specifically, do not focus on the peak value, or any one value...only the difference between peak EGT and full rich EGT

robert@jonesrv10.net · May 16, 2023

Drilling Jets

Jets are produced with a high quality reamer. I would buy a new, bigger jet if you think that is the problem. Keep the old one in case it was not the problem.

BH1166 · Sep 2, 2023

Don Rivera routine

Dan/Larry…. I performed the check Dan shared. Rather than it being misformatted, did as a picture. I also included the savvy link to the flight. Being retired, took a while to find the time ( ha ha) to do this. AP was on, 8kts wind on nose. Sooooo, what did we learn

Top row is full rich, and at end of test, returned to sam +/-3-4f

https://apps.savvyaviation.com/flights/shared/flight/7313812/1f520dc5-6a98-4a33-97f9-8cfe48bf9191

DanH · Sep 3, 2023

BH1166 said:
Dan/Larry…. I performed the check Dan shared. Rather than it being misformatted, did as a picture. I also included the savvy link to the flight.

Spread at peak is about 0.5 GPH, which is pretty good for a carb engine; the updraft Lycoming manifold tends to distribute fuel poorly. Here most of the spread is due to #1 being leaner than the 2-3-4. The spread may tighten up with carb heat...try it. Obviously no 1550 EGT as previously reported. Got to watch that stuff. Bad data or skipped data is why a lot of us have stopped participating in long distance diagnosis.

Which brings us to the original question, is it rich enough? If the first line on your data table as full rich as reported, #1 only shows 12F between rich and peak, with the others in 50~60 ballpark. We're typically looking for 150. Are you sure it was full rich?
.

BH1166 · Sep 3, 2023

Thanks Dan. Yes positive top line is full rich via the red knob. Also after test, they returned as suspected, nearly exactly before I started the leaning routine

DanH · Sep 3, 2023

I did find one thing curious. During your takeoff roll, fuel flow is over 11 GPH at about 2350 RPM, but then drops into the 9's as airspeed rises past 100 or so.
.

MNN · Oct 26, 2023

Hey Tom just wanted to hear how the new carb worked out.

Bigger jets

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