B

Bob_pipedream

Active Member
Hi all,

Just wondering people's ideas on what could cause the following:

Background - Fixed pitch prop, new XP-O320 now completed 9.8 Tacho hours - all parts new. No flight has gone above 5000 feet due to airspace restrictions.

Engine ran fine other than occasional rough running for few seconds during initial 5 hours. However engine seemed to dislike certain rev ranges, but this appeared to cure itself as testing continued. Mixture was always full rich as the engine had to be run in.

5-8 hours she ran really well.

At 8 hours, Fuel Pressure sender stopped reading. I assumed it was a sender failure as everything was still good. I did a 1 hour flight at cruise and everything ran perfectly with no rough running at all.

Then on a short flight the following weekend, after a low pass and climb out, engine began running very rough. I changed tanks, played with the mixture and this appeared to cure things. I landed sharpish and the following weekend, I pulled the cowls off and inspected the entire fuel system. I found a big chunk of fluff covering the outlet of the gascolator which in itself could have caused engine failure! Still no Fuel Pressure reading ater cleaning so have ordered new sender. I did a flow check of boost pump and it was fine.

However on the subcesquent test flight, I found the following:
Engine starts fine, take off fine, climb is fine. However after levelling off engine ran rough. This was cured by leaning mixture - but at any rev range above 2000 RPM, using full mixture now causes rough running which is only cured by leaning (this is a new condition).

EGT on number 2? (rear lefthand cyl) is very much the highest at up to 1420. It is quite difficult to lean properly as pulling mixture causes rise in all EGTs but on number 2, reducing by 50-75 degress would put the mixture almost all the way back in.

My thinking is that one of the following may be responsible:
*Blockage/restriction still present somewhere in fuel system before gascolator (but not sure this would actually be improved by leaning mixture and would think that take off and full power would be restricted?)
*Leak on induction tube on number 2? (rear left hand cyl) causing cyl to run very lean and others to run too rich (This would give strange EGT and on take off engine revs are lower as engine under load so may only become an issue as engine picks up speed and manifold pressure increases?)
*Idle Mixture screw setting incorrect (but it does not feel as if it has moved or could move)
*Float level in carb
*Mag timing wrong - but mag drop is okay on run up (the Slick SB regarding weak cams etc. is applicable)

Sorry for long post, but just hope someone may have an idea or have had a similar experience. Fluff in gascolator really does emphasise the need to check gascolator and carb fuel strainers after first few flights in new aircraft. Also really should not fly aircraft without FP gauge working...
 
blockage?

You said that you found some "fluff" at the gascolator. What was it? Actually something foreign, or parts of the hose liner coming apart, assuming that you might be using 701 type hose. I cant speak for everyone else, but I would think that I'd be rechecking all of the fuel system from the tanks to the gascoloator.
Tom




Bob_pipedream said:
Hi all,

Just wondering people's ideas on what could cause the following:

Background - Fixed pitch prop, new XP-O320 now completed 9.8 Tacho hours - all parts new. No flight has gone above 5000 feet due to airspace restrictions.

Engine ran fine other than occasional rough running for few seconds during initial 5 hours. However engine seemed to dislike certain rev ranges, but this appeared to cure itself as testing continued. Mixture was always full rich as the engine had to be run in.

5-8 hours she ran really well.

At 8 hours, Fuel Pressure sender stopped reading. I assumed it was a sender failure as everything was still good. I did a 1 hour flight at cruise and everything ran perfectly with no rough running at all.

Then on a short flight the following weekend, after a low pass and climb out, engine began running very rough. I changed tanks, played with the mixture and this appeared to cure things. I landed sharpish and the following weekend, I pulled the cowls off and inspected the entire fuel system. I found a big chunk of fluff covering the outlet of the gascolator which in itself could have caused engine failure! Still no Fuel Pressure reading ater cleaning so have ordered new sender. I did a flow check of boost pump and it was fine.

However on the subcesquent test flight, I found the following:
Engine starts fine, take off fine, climb is fine. However after levelling off engine ran rough. This was cured by leaning mixture - but at any rev range above 2000 RPM, using full mixture now causes rough running which is only cured by leaning (this is a new condition).

EGT on number 2? (rear lefthand cyl) is very much the highest at up to 1420. It is quite difficult to lean properly as pulling mixture causes rise in all EGTs but on number 2, reducing by 50-75 degress would put the mixture almost all the way back in.

My thinking is that one of the following may be responsible:
*Blockage/restriction still present somewhere in fuel system before gascolator (but not sure this would actually be improved by leaning mixture and would think that take off and full power would be restricted?)
*Leak on induction tube on number 2? (rear left hand cyl) causing cyl to run very lean and others to run too rich (This would give strange EGT and on take off engine revs are lower as engine under load so may only become an issue as engine picks up speed and manifold pressure increases?)
*Idle Mixture screw setting incorrect (but it does not feel as if it has moved or could move)
*Float level in carb
*Mag timing wrong - but mag drop is okay on run up (the Slick SB regarding weak cams etc. is applicable)

Sorry for long post, but just hope someone may have an idea or have had a similar experience. Fluff in gascolator really does emphasise the need to check gascolator and carb fuel strainers after first few flights in new aircraft. Also really should not fly aircraft without FP gauge working...
Click to expand...
 
You did not mention what fuel system supports the engine.

If is a carb, I would focus on it. The needle valve may be leaking due to contamination. Or the float is not properly set.

If it is fuel injection, the controller may be contaminated.
 
Primer

David-aviator said:
You did not mention what fuel system supports the engine.

If is a carb, I would focus on it. The needle valve may be leaking due to contamination. Or the float is not properly set.

If it is fuel injection, the controller may be contaminated.
Click to expand...

I Had a friend that had that trouble for some time? I fixed it when i found the primer unlocked, so if it it a o-320 check!.
 
Carb and hoses

Hi all thanks for the responses.

She has a carb and the fluff was lint-like and it was in the gascolator's filter. I checked the carb screen filter and that was all clear - completely clean with no trace of anything. So I doubt that any contamination will have reached the needle seats in the carb etc as the gascolator did its job. I also drained the tanks and checked them and they look clear.

My thought is that the contamination is a coincidence (which happens), as I doubt that a fuel restriction would cause her symptoms? She starts fine, the take off is fine and with the mixture leaned she runs fine bar the weird EGT thing on number 2. However I stand to be corrected!

Also the carb has the updated non-sinking foam float in it (as per the SB).

In regards to the hoses, she has all alloy tubes up to the gascolator, so it can not be hoses breaking down that caused the fluff.

It just really confuses me that she runs so well, but needs to be leaned just to run smooth. That does point to float level I guess? But could it be an induction leak?

The infuriating thing is that it will be another week of day job work before I can get to the hangar to investigate further (and my job is boring too).
 
Primer

Also she has no priming system at all (too lazy to fit it yet) so fuel system is very simple standard Vans and Facet fuel pump.
 
Bob,

I don't think it is an induction leak - that would tend to lean the mixture, but in your case manual leaning improves matters. Its worth checking all the inlet hose are tight, but it seems unlikely to be the problem.

I would take the carb off and make sure the main jet is still tight and everything looks OK, it doesn't take that long to get it all apart.

I would also check the timing. Most RVs will 'take off fine' without the engine developing full power. Check that you are getting the expected static rpm at the start of the take off run (2200 for a metal Sensenich). If its lower then there is something wrong with the engine.

Are you using a new or overhaulled engine and accessories?

1420 on an EGT seems a little hot when running at full rich - I would expect near to 1200, but absolute EGT numbers don't mean much. It could be that you are running very lean to start with - which is very common with carbed O-320s (and well documented on other threads). When the carb is off find out what size main jet you have (using number drills). It should be around 0.104" diameter, its not unusual to be around 0.097" which is the standard Cesnna & Piper jet size - but RVs flow much more air so need more fuel (Steve Sampson has this documented well on his blog).

Hope this helps

Pete
 
Spark Plugs??

Bob,
Just a thought, but because you have been running full rich on a O-320 you might pull the spark plugs and check for lead deposits. This can sometimes cause rough running and high EGT?s. I am assuming you are running 100LL.

I am no engine expert, but this solved a similar issue I had.
 
Thanks all,

She is a new engine and was running okay. I guess that it could be something as stupid as sparkplugs and I will check them when I check the timing. The thing that confuses me is that she is fine at start up and fine during takeoff. If after landing, she had played up, then I would assume that it was float height, but she sits at tickover and mag check revs (2000rpm) very nicely.

The main jet and carb are all new with the engine straight from superior.

One thing, as I slow down to approach speeds I get a popping noise for a few seconds. I assumed this was cowling/fairing related, but it could be popping from the exhaust...
 
Bob,

Could I suggest that you sit down and write out all of the symptoms, and then what you know, for sure. Not what you think, or what you assume, but what you know to be true. Then write down your diagnosis for each problem, and why you have reached that conclusion. Try to be very logical, it should be straight forward to figure out where your conclusions are not support by the data you have, or what you need to verify to be true. I think you have a fuel flow or fuel distribution problem. If the fuel and the sparks are OK, are your compressions good? Can you get a similar engined RV as a chase plane to check your t/o & climb performance?

Pete
 
Hi Pete,

Have very much written everything down to look at logic. But I want a good background idea and the benefit of other people's experience. Until I find the cause, everything will be very much suspicions and guesses.

The only definite symptom I have is that to get the engine to run smooth (i.e. not coughing and spluttering) at revs above 2000RPM (possibly 1600RPM, but I did not test less than 2000) is to pull the mixture out. A sidenote is that I do not get much EGT rise on no.2 cylinder 1350 at 2400 rises to about 1420 so 50-75 ROP brings it almost down to base again.

I intend to go through every possibility on Saturday and then if time allows, test fly again. Due to the nature of the issue, I want to make sure I check every possible issue even the less logical ones before flying again as do not fancy trying to land somewhere in a field!

Just one question for everyone - does adjusting the idle mixture control screw on the carb affect the mixture setting at cruise? i.e. does the idle mixture make a contribution to the fuel intake at above idle speeds when the main jet comes into effect?

I am going to do the rundown RPM check to make sure the idle mixture is correct, but was just wondering if this could make her too rich in cruise too? My guess is that she is then running on the main jet, but surely there is some adjustment for mixture settings at cruise other than the main mixture control? Or is that all about the main jet size?

Thanks all.
 
Bob,

Idle mixture has little effect in the cruise as it is swamped by the main jet. The only way to adjust the basic mixture setting is by changing the size of the hole in the main jet. It seems very strange that the engine will not run smoothly above 2000 rpm without leaning. That suggests you are very rich - so not enough air or way too much fuel.

Do you really want to take an engine that is really not running very well into the air? It can get awfully lonely awfully quickly ...

Pete
 
Hi Pete,

Nope, would not want to take her in the air like this. Problem was there were no issues or symptoms on the ground that suggested I should not take off. So after I have been through everything that could cause this and verified that everything is good, I will do a static before takeoff and then stay in the circuit within glide approach range - but hopefully she will then be all fine again!

After I run through all the areas (plugs, timing, slick SBs etc.), I will warm her up and just make sure the idle mixture is not badly out just to elimnate that - it maybe that bad plugs, timing and idle all come together to create the issue, so best to make sure all parameters are good.

Thanks for the answers,

Bob
 
A WSITD:

What fuel pressure are you running with your Facet pump? A carb needs only a few PSI, but according to the FAcet website their pump can run upto 12...I'm wondering if you're trying to force too much fuel through the engine. It might also explain your dead pressure sender.
 
penguin said:
Bob,

Idle mixture has little effect in the cruise as it is swamped by the main jet. The only way to adjust the basic mixture setting is by changing the size of the hole in the main jet. It seems very strange that the engine will not run smoothly above 2000 rpm without leaning. That suggests you are very rich - so not enough air or way too much fuel.

Do you really want to take an engine that is really not running very well into the air? It can get awfully lonely awfully quickly ...

Pete
Click to expand...

PS the float height also affects the mixture to some extent.
 
Just a quick bit of info for anyone else with similar issues - apparently the idle mixture screw is swamped by the main jet in cruise, but I talked to an engineer today in passing and he said that he has seen that very rich settings of mixture screw can cause issues. So it is on the list.

Also my Facet fuel pump seems to be putting out 3.5psi (that is what it indicated until the fuel pressure sender went AWOL - new sender ordered for weekend).

Thanks all
 
Bob,
you have 2 problems that are not related - your fuel press indication system is inop or us as they say in the UK - check your circuit breaker or fuse first - then ck your wire connections and then try the transmitter or indicator.You just built this aircraft and did a whole lot of wire terminating and its most likely something has shaken loose .You dont have to fly the airplane to fix this problem , just turn on the fuel pump.

Next is your engine - sounds like a fouled plug. Perform a compression test and remove and clean your plugs .Should run fine.The reason for the problem is leaning technique.That one cylinder thats popping in the pipes is the likely culprit , poor ignition late burning in the exhaust stack .Now - look at the engine case and you will see numbers for ech cylinder and verify your probes are connected to the correct readings in the cockpit because your description of cylinder locations sound suspect to me - sorry mate .

Good luck
 
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Update

Hi all,

Thanks windsock and yes my numbering is suspect - number 4 is the cylinder that has a much higher EGT.

Anyway pulled everything apart today - remember engine is new superior with carb and only 12 hours. So far virtually no oil consumption (0.5 quart in all 12 hours despite doing aeros testing and a few aileron rolls which was necessary for gaining permit to fly with aeros clearance).

Mag timing almost spot on - RH 25 degrees and LH mag 25.5 degrees

No more rubbish in gascolator and replaced Fuel pressure sender which has fixed zero FP issue.

However after looking at the plugs, it became apparent where the issue may be. Last flight I had a slightly higher rpm drop on RH mag (25-50 rpm more, not much).

Number 1 exhaust downpipe is a lot less 'coloured' than the other three, so I immediatley felt that that cylinder may have an issue. To add to this I had a lot of black powered soot (not oily) in the exhaust from the front cylinders 1 and 2 (it is a four into two), whilst the other exhaust (for rear cylinders) was very very clean. Then I pulled the plugs and found the following:

1 Top - quite dirty - LH mag
1 Bottom - oily and very dirty (most dirty of all) - RH mag
2 Top - Bit dirty - RH mag
2 Bottom - quite dirty slight oil look - LH mag
3 Top - very clean - LH mag
3 Bottom - Bit dirty - RH mag
4 Top - very clean with slight oil look - RH mag
4 Bottom - very dirty and oily (almost as bad as No.1 Bott) - LH mag

Sorry for less than technical terms, but it seemed that apart from number 4 bottom plug, a pattern of issues for the front cylinders and number 1 in particular is forming. So I have cleaned all the plugs and swapped them around.

Unfortunately due to weather could not test fly.

Suspect the following - I did clean plugs when removing the inhibiting oil before first flight, but perhaps did not clean enough, but would have thought this would have burnt off quickly (some of the plugs do have smell of inhibiting oil though). Number 1 Bottom plug (which is attached to RH mag) was oily and dirty enough to suggest that it is producing a very weak spark.

So I feel that it is a dirty plug - but what is the cause? Well the front cylinders obviously run cooler than rear cylinders and number 1 is most likely due to position etc. to run too cool. So perhaps number 1 and also number 2 to a lesser extent have not had enough heat to be broken-in even though oil consumption is very low. This would cause oily plugs as oil control ring has not seated. So intend to spend next five hours at 75% plus power and 75-100 degrees ROP. Will also record more engine readings from GRT EIS. I doubt if I have a ring problem yet, but I had better do more breaking-in in order to avoid glazed bores.

Sorry for long post, but thought I would list all, just in case some poor other blighter has similar issues. I will also post final outcome!
 
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Bob,
LOW OIL USE INDICATES YOUR RINGS HAVE SEATED - GREAT - NOW START LEANING SHORTLY AFTER TAKEOFF TO GET THOSE CYLINDER TEMPS UP AND KEEP THOSE PLUGS CLEAN - YOU MAY HAVE TO LEAN ON THE GROUND AT HEATHROW AND GATWICK WHEN YOUR NUMBER 12 BEHIND THE BIG JETS FOR TAKEOFF - WIFE HAS THE KETTLE ON GOT TO GO

GOGGLES ON CHOCKS AWAY
 
Hi all,

Flew her for an hour today around the Isle Of Wight again.

She is a bit better, but Number 2 cylinder is running much lower CHT (upto 120 less) and EGT (upto 200 less) than the rear cylinders and number one is just a bit off (50-80 CHT and 80-150 EGT). The only way I can get a uniform EGT CHT spread is to lean to the point of slight roughness and this does give very uniform readings all between 50-70.

I tried adjusting the Idle mixture as she has no rise in RPM at all. I ended up with the screw out 3.5 turns and still no rise in RPM at idle cutoff. So I turned it in 4 turns (0.5 turns in from original setting) and she was very rough. Then I put it back where it was and she was fine but still no rise in RPM (not even by 10 RPM). So no idea what is going on there and I did try each setting at 750RPM, 1000RPM and 1200 RPM just to be sure. I guess dirt in the idle mixture circuit is to blame, but she has no hesitation or threat of cut-out when opening the throttle for take off.

Also Fuel Pressure did not register despite a new sender - but the oil pipe is touching the sender case, so I wonder if there is a case of differential grounds going on (oil pipe on engine and FP sender getting ground from firewall common ground terminals).

One straight-forward question I have for everyone though is would raising the CHT in number two cylinder (and a bit in number one) via a deflector also raise EGTs in that cylinder? If so, then that may be the fix.

Thanks all.
 
If leaning cures the roughness then the engine is running too rich when the problem occurs.
What can make the engine run rich?
Defective carburetor
Blocked/ restricted induction system
Leaking primmer
Excessive fuel pressure
Hot induction air
Ignition timing way out of wack
Maybe some other stuff as well, but I would be thinking what can make it run rich and check those items.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Hi Mahlon,

Have been through all that unfortunately. Timing perfect, plugs cleaned, no primer etc.

But as per my previous post - would increasing a cylinders CHT also increase EGT too?

Thanks
 
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Yeah a little bit but not degree for degree. Have you changed the carburetor... It's the most likely candidate to me.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Hi all,

Put in air dams (AKA: temp riser / blocker) and also seal the top cowl ramp ends and got the following:

Original results before air dams installed:
Revs Oil EGT1 EGT2 EGT3 EGT4 CHT1 CHT2 CHT3 CHT4
2370 159 1134 1194 1414 1405 271 327 389 374
2340 166 1157 1266 1377 1358 308 358 389 381
2420 165 1151 1256 1431 1410 303 346 375 360
2370 167 1124 1171 1386 1371 294 349 396 382
2320 165 1120 1193 1308 1269 271 318 382 367
2270 163 1356 1405 1408 1386 299 338 374 365 - aggressive leaning (engine rough)


After air dams installed
Revs Oil EGT1 EGT2 EGT3 EGT4 CHT1 CHT2 CHT3 CHT4
2370 133 1183 1188 1406 1381 261 319 328 325
2340 134 1183 1168 1406 1384 259 316 330 320
2270 134 1236 1152 1405 1385 260 316 330 320
2210 132 1160 1144 1244 1205 273 313 317 310
2320 132 1326 1371 1409 1373 276 305 319 313
2290 135 1379 1419 1424 1402 322 325 317 321
2304 133 1241 1229 1385 1358 275 317 324 320

Still big disparities in there but the max CHT has fallen from 389 to 330 and the oil temp is about 30 degrees less...
Cylinder 1 is still very cold though, but with the right amount of leaning I can get a reasonable balance.

Interestingly the EGTs have also got a bit better. So my next plan is to seal up the gaps around the engine and then increase the air dam on Cyl 1.

However could not get her to run smooth with mixture rich and going to full power and mixture rich was not nice. So I now have a useable cruise, but full power level flight or 2400rpm and it all gets uncomfortable. Take off and climb is okay though. If I pull mixture aggressively at higher than 2400rpm, I get back firing (so did not do that more than once!). Clearly there are still issues, but since she has 12 hours, I am going to just fix the the air dam, seal some gaps and then fly her for another 5-8 hours, gather more data and let the cylinders settle a bit more before tinkereing again.

Note, I have the GRT 4000 so could not log these to laptop. So I used my camera to take a picture of each screen and just cycled from EGTs through CHTs to Revs. Very easy to do one handed and as the pictures are in order and numbered it is easy to copy down the figures.
 
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Carb?

Just a quick question (have started a thread, but may as well put it here as well...)

My carb is a MA-4SPA 10-3678-32 which some people say is the wrong carb?
They suggest a 10-5009?
Can I just re-jet the 10-3678-32 - i.e. what is the difference between the 10-5009 and the 10-3678-32?
 
Thanks Brian,

Am I right in saying then that the difference between the 10-3678 carb and 10-5009 carb is just the jet size?

Thanks
 
Hi all,

Latest is now that I can get her to cruise nice with roughly inline chts and egts at 135-140kts and 2150-2250. (roughly inline is spread of 30 degrees max between hottest and coldest) .Any faster than that and the egts on 3 and 4 go high and the CHTs split badly (150-200 degrees).

That sort of suggests that it is too lean at higher revs and that the mixture goes all strange. Given that I only have 80 degrees of EGT rise till she gets rough, I am now convinced that I need to drill the jet.

She still stumbles when leveling off after climb out until mixture is leaned.

Also when carb heat is applied at 2150-2300 EGTs increase...

Front cyls 1 and 2 exhaust pipe is still getting lots of soot but rear cyls are very clean.

So time to pull carb and also need to shorten intake tubes as front cylinder tubes do not meet nicely (1/8"-3/16" too long) and rears are about 1/16-1/8" too long. This could be really screwing up the distribution, so I plan to cut them and get them rewelded (TIG stainless steel). I checked the part numbers, asked if they could be wrong, but had no joy or responses, so I just have to say that tubes should match and the rubber hose should not be making up the step.

All good fun this...
 
i havent read the rest of the post but have you thought of maybe the carb float being the problem. the symptoms are similar. good luck.
 
Final update - solution at last

Hi all,

Well I thought I had better stick this on my posts so that anyone else suffering similar issues of high rear cylinders EGTs Low front cylinder EGTs and rough running on an O-320 will have the final answer.

As mentioned earlier, I found that my new Superior O-320 has been fitted (as have all Superior O-320s) with an O-360 sump. These are interchangeable however the O-360 sump has a wider diameter sump throat diameter to match the wider diameter carb. This creates a step after the carb of about 1/8 - 3/16.

Lycoming service bulletin SB258 was printed in 1959 to address rough running in Piper Aircraft. They had found that the 10-3678-32 carb (and I think all O-320 carbs of the MA-4SPA type as they will all have this step) should not be fitted to the tapered riser sump (or O-360 sump) as there would be a step after the carb that could cause, rough operation, bad mixture distribution and lean the rear cylinders. The solution is easy and is simply an insert that converts the taper into a straight riser of same diameter as the carb.

This is exactly what I had and I had tried all the other things such as timing, plugs etc.

So I had an insert made as per the SB258. Cost to have the part made is minimal ? I got some 60mm external diameter by 5 mm wall thickness aluminium tube off of Ebay and a local engineer turned it up in about 20 minutes. I got the length of the insert which is not in the SB from the engine and it is 18.9mm ? I also had an additional small 2mm x 53mm diameter step machined into the wider end so that it would locate into the Vans throttle bracket that is clamped between carb and sump (so overall length is 20.9mm).

I fitted it yesterday and took off. The difference is amazing and far beyond what I expected. It has not only cured the rough running, narrowed the EGT spread and improved performance ? it has also made her feel almost turbine smooth. At last I have an unqualified RV grin.

I did not drill the jet or do any other mods other than cleaning the flashing out of the primary venture.

So if you have a Superior O-320 (or any O-320 for that matter, it may be a good idea to verify your sump part numbers just in case someone has put the O-360 sump on there) with a MA-4SPA carb, then you WILL be requiring this insert.

Next weekend I will record more EGT data, but even at worst condition, there was only 80 degree spread which would easily lean out (it was up to 180 before). I can also now use full mixture without chugging, coughing etc.

So perhaps the ?poor mixture distribution? reputation of the O-320 is actually more to do with some engines not having the right sump/carb combo in the beginning?
 
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