Ian R

Hi all

did a search but not realy answered what I was after

Set up first

MVVS 58 proSport 3/4 run in
MVVS header and canister silencer

2 lipo igniton
prop currently 24/ 10 wood

My problem

cannot seem to get the engine to run anything near like it should

needles from closed turns 2.10 low 4 high!

revs down around 5500 pick up poor, good cooling in cowlbut shows signs of sagging in verticals ie under load, pick up from idle to power is slow

Questions
Silly one first is this a long pipe set up, I have the ignition set for long?
Is the prop too much
do you think there is problem with carb given the seetings. high run adjustment at full throttle on ground makes small difference
have I got an air leak somewhere

I have checked the pressure pipes and other connections and are correct

Any views

thanks Ian

w8ye

My Feedback: (16)

Too much prop

Walt and Sage

Try a VESS 23xA.. Should pull stumps...

apalsson

My Feedback: (1)

Hi Ian,

I tend to disagree with the two comments above. A 24x10 prop is well within the stated specs for your engine. In fact, the 24x10 is almost in the middle of the recommended props for this engine.

It sounds to me like your engine is set very rich. The MVVS manual gives some recommendations on settings, of L=1.45min and H=1.10
Try the following:
1. Set both needles to the starting point above
2. Lean out the H needle till you get maximum RPM and then richen it by around 1/8th of a turn
3. Set the engine for high-idle. Now lean out the L needle for max RPM
4. Repeat 2 and 3

I know this is not quite the procedure in the MVVS manual but it will get you to the same point

Ian R

Hi thanks for the input guys

I thought the prop was about ok, perhaps a little too much during running in, but close and I have been careful not to over load it in flight ie mostly 1/2 to 3/4  throttle

But I could not get it to richen up at the high end hence the needle so far out

i will go back and try using your settings which as you say are close to factory.

A club mate has the same motor but different pipe, his is a tuned pipe whereas I am using the MVVS cannister pipe, which I assumed to set the ignition to long pipe, i wondered if it is where the baffle is and may be I should be on short pipe ignititon setting?

If not I might go down in prop size and pitch to see if I can get it to rev into the 6500 range

any further views welcomed

Ian

apalsson

My Feedback: (1)

Ian, do you think it's possible you have a minor air leak in a fuel line, letting the engine draw air together with the petrol?

Ian R

I plumbed it with proper tygon and wire locked  the tube on. I will check and replace the pipe anyway incase it has a pinhole.

I fly turbines mostly so I  am alawys pretty careful on the fuel pipe side, but you never know I will replace it  all from the clunk to the carb

thanks Ian

pe reivers

prop and canister setup are OK.
The ignition should be plug and play, and needs no programming whatsoever, even on tuned pipes. If you programmed for the tuned pipe (long), you might loosen one sensor screw and retard or advance ignition a bit. One mm movement is about 3° ignition timing.
I think the carb settings are way off!
Do you use a dedicated line from clunk to carb? NO T-connections there please.
Is the carb filter clean? Check the internal strainer, and use a felt clunk.
Check the carb lever settings and internal parts. Use a carb fuel pressure tester. (may need professional help there)
Some Walbro carbs just do not perform as they should. If nothing seems to work, replace the carb!

Ian R

Pe

Thanks for your input

guilty as charged  I have a tee to a stopper fill valve, I  will do away with that

Felt clunk, tygon tube wire locked already

on the 58 ignition pack s std I think, I thought you could change the igntiion for normal silencer or long silencer hence why i went with the long set up

I will check the filter in carb

I have a friend who can do the pressure test

So a bit to do

24x10 wood ok for prop ie not over proped?

will let you know how I get on

thanks

Ian

pe reivers

a 24x8 is under propped.
The ignition timing should not be a big deal. Maybe 100 rpm max power or so. The weird carb tuning worries me a lot more. The engine behaviour looks like lean. It might be a leak in the T-line connection, or a clogged inner carb filter. Further investigation could include the internal carb lever height (too low), or aerodynamical forces reducing the cowl pressure in flight. These act on the regulating membrane, and can cause the carb to go lean. The prosport has a fitting on the membrane cover. Fit a line to it, and route it to a static pressure tube as used for glider variometers.

Kema

Isn't prosport ignition 3 lipo not 2?

Airbear

Engine is way to rich turn the low side till it bottoms then backin out 1 1/2 turns do the same to the high side but back it out 2 to 2 1/2
that will get ya in the ball park.

pe reivers

It depends:
latest engines are supplied with ICU-S ignitions. The P ignitions got thumb-downs by most users who prefer the smaller battery packs.

Ian R

Hi Pe

Plumbed the fuel line direct to the carb. checked the clunk replaced all tygon and re wire locked the tubes on.

tried different fresh fuel.

no difference

So I have removed the carb and will get it checked. After that new carb!

thanks Ian

pe reivers

I suggest you try a crankcase pressure test first.
When you blow in the carb pulse line, there should be no air leaks in the front bearing area (piston halfway up), The reeds should close up fairly well. The engine pumps harder than you can blow, so with running engine they will close completely.

Ian R

hi Pe

Tried the crankcase pressure test

I have the carb off when I did it

It would appear that air is passing through the reed valve through most of the rotation of the engine
I tried it half way it passed air and so slowly turned through full rev either side of top dead centre and it seemed to leak air at the same amount

Ian

pe reivers

Like I said in the previous post, some reed leakage is normal. You can check the cage if you want, and will see that the reeds are about 0.5mm open. They will lie flat as soon as any decent pressure works against them. like in a running engine. So if you check them, look for frayed or broken reeds, or reeds that are excessively open. Also look for reeds that are tightened to the cage too much. This will cause reed deformation.
How was the rest of the engine?

Ian R

hi Pe

Reeds look ok, nothing from the front bearing as far as can tell

rest of engine appears ok good compression etc


will invstigate carb tomorrow

thanks  for help

ian

Ian R

Hi Pe

Checked carb by removing the top and botom covers. all looks like the they should do, ie no out of position or visible damage

gauze looks clear. So only thing left is pressure test.

Ian

pe reivers

While checking, also check the muffler and header for restrictions, just to be sure the engine is not choked.
When does the ignition fire? It should spark just before the piston reaches top dead center. (0.1mm before top dead center would be about OK)

Ian R

Hi Pe

Carb pressure test ok.

Your question about the exhaust made me think

I had to make a maifold for the engine to mvvs silencer for the model I am using it in , the standard MVVS would not come close for alignment

I attach the photos of mine

I did smooth the gas flow in my version so itis not the angled face theoutside would lead you toconcluded,but even so I can now see that there could be a back pressure into the cylinder. do you think this is the cause given we have tried everythink else!

Ian

pe reivers

Normally, an engine can handle some exhaust restriction because of the high exhaust gas pressures.
I am not sure what you did, but the 45° angle the header leaves in the picture reduces the exhaust area by about 30%, and that may well restrict exhaust flow in the high rpm regions. A larger prop therefore might do a lot better than your medium range 24x10 which needs to rev up.
Test the engine on a test stand with a more open header, and you will know. All else on your rig seems to be OK.

Ian R

Ok will try the test stand

 thanks for your continued help

Ian

Ian R

Hi Pe
 
Sorry for delay, well what can I say!

engine bolted to test stand  with my manifold and the MVVS canister pipe, ignition unit from model, did not put the  vent pipe on static pressure side of of carb. connected crankcase pipe to carb. same prop same fuel.

Did it run yes and pretty good.

Ok so back in model as is, surprise same problems as before would not run at high RPM.[:@]


I did notice it would pick up when cold but as soon as warmed up it would sag. I wonder if it is just the manifold or do you think the canister is getting too hot. when I bench tested it was very hot in the open I can imagine inside the model in a tunnel opended front and rear it  would still get even hotter.

I am wondering if  to get a standard can exhaust and give that a try ie no header and no canister

What do you think?

I am on the point of sending  it []back to mvvs

Ian

pe reivers

why send it back to MVVS when it runs good? It is the setup in your model that is causing the problem, not the engine itself.
Engines often do run different when in the model. You have to tune the needles again, due to vibrations and/or changes in carb membrane reference pressure.
Header the same? Same length? If it runs hotter in the model, your header needs to be longer to compensate. Add about two inches to the header length and start from there.