GoNavy

My Feedback: (15)

I hope some of you with MVVS glow engine experience might be able to help me.

MVVS 77 (old style, but with carb upgrade), FAI fuel (20% castor, no nitro), 13 x 6 Zinger, broken in 1/3 gallon, K&B 1L, then 1S, plug, pitts muffler, muffler pressure; 1,470 feet ASL 65 to 80 degrees F

Starts like a charm and has great full throttle, but I am unable to achieve reliable idle, or if I do, transition is overly rich causing it to stumble and usually quit. (Slowest reliable idle is 3700 rpm)

Leaving the glow driver on the plug makes no difference. My first MVVS and I am stumped.

If this was a Super Tigre, I would know how to solve mid range; I would rotate the spray bar (CCW to lean). Will that work on this MVVS?

Factory website says to use NovaRossi C6s plug, which some sites say is a "cold plug". I think the K&Bs are medium. Is this the trouble?

Should I switch to a Perry carb?

What else can I try?

Pylonracr

Throw the Pitts muffler in the garbage and put a real muffler on it. You will be amazed at how well it runs. The 1L plug is good for that engine, but I would go to 5% nitro. A small amount of nitro will help the low speed some.

1QwkSport2.5r

Use a hot glow plug with low/no nitro fuels. Cold plugs are intended for high nitro fuels mainly in rc cars.

GoNavy

My Feedback: (15)

I copied this from the FAQs section of the MVVS website:

3. What glow plugs should be used for MVVS engines?
Glow engines 2 - 4.5 ccm: Novarossi C5S
Glow engines 6.5 - 35 ccm: Novarossi C6S

GoNavy

My Feedback: (15)

The good news is that I hold in my hand, in a box labeled "Made in the Czech Republic", a "tlumich vyfuku" aka tuned muffler #3253 and that is one of those recommended for this engine. (It must be discontinued because I can't find it as an available item on the MVVS website.) It is a machinist's work of art I must say. I will have to have to get a header to fit this engine.

Query: Will I then need to "tune" the system in the customary way (starting long, then shortening the coupler between header and pipe until max rpm is achieved), or do the factory pipes for this engine perform over a broad "tuning" range? (I have experience with only two prior tuned pipe setups.)

2nd query: Does the 3700 rpm "reliable idle" I achieved seem right? (The MVVS instructions recommend a prop in the range of 13 x 7 to 13 x 9, or 14 x 7, but add "use lighter propellers with standard silencers so that the engine will be able to reach at least...10,000 rpm".

1QwkSport2.5r

Cold plugs with low nitro fuel is bad karma in my book regardless of what the manual says. Some owners manuals say to use 5-15% nitro fuels but those European engines run on 15% never seem to run right despite the manual saying it's okay.

The problem with cold plugs is they don't retain as much heat between combustion cycles, so to keep the fire lit, the idle speed needs to be increased and the fuel mixture needs to be leaner to keep the ignition advanced enough. Perhaps your high idle may be due in part to the engine being not completely broken in yet? If it were my engine, I'd be experimenting with different glow plug heat ranges to find what allows the engine to run reliably and give the best power. It will be a balance - cold plugs give more top end power, but low speed operation suffers. Hot plugs work better with low speed operation at the expense of a little top end power. Maybe a medium temp plug will be a good balance?

fiery

My Feedback: (2)

I have owned and used MVVS 8 cc and 10 cc engines since the mid 90's when "Just Engines" in the UK sold them.

I run them on 80/20 nil nitro fuel. Lube 10% Klotz 10% Castor. Do not use low oil % fuel or fuel with 100% synth lube. They are brilliant engines but designed for 'non nitro' running as per most of the world outside the US.

1. Make sure you have the correct updated spray bar and LS needle in your carb. The first series MVVS carbs had no notch in the jet end of the spray bar and a blunt end LS needle. Result - difficult to set idle and poor (over rich) transition. You can if capable notch the spray bar and taper the LS needle end but most owners do not have the skills or patience.

2. Do not use 'hot' plugs. The MVVS engines mentioned above are both high compression engines and run poorly on hot plugs. I use the Nova Rossi C6 and it is a superb quality long reach plug and the engines love them (the factory know what they are doing). Try a range of medium to cool long reach plugs. I have have even used a Fireball yellow and O'Donnell 100 which were acceptable. I suspect an ENYA 4 plug would be fine but I have never tried one as I like long reach plugs, not medium reach.

3. Check there are no air leaks. Is the "O" ring at the base of the carb spigot sound and effecting a good seal in the boss? Is the back plate gasket sealing beyond question? Is the carb cinch bar a snug fit on the keyway? If not ... do what you need to do seal it up.

4. Use a factory muffler. Preferably the standard side muffler which sadly is no longer made. The current side muffler offered for the 10 cc is too short in the manifold and does not offer clearance in the airframe. Old stock for the 1.20 twin I suspect. A HP SS or GC .61 bolt-on muffler from MECOA could probably be adapted to suit.

5. Is the piston/liner fit good? If soft, and leaking compression, you will never get good idle and snappy transition. Only cure is a new P/L set.

The pipe is nice but that is a whole new issue to sort.

1QwkSport2.5r

Good information fiery. I stand corrected on those glow plugs. I've used hot plugs in high compression engines in the past with good results, but I've never run an MVVS engine. I'll definitely keep this in mind should I obtain one.

Can I ask - why does one need to use a cold plug in a high compression engine? It kinda goes against what I was taught - that you use a hotter plug when using low nitro or none at all and a colder plug in higher nitro engines. I assume the high compression advances ignition more so too hot a plug advances it too far?

fiery

My Feedback: (2)

I assume the high compression advances ignition more so too hot a plug advances it too far?

You are spot on.

With a 'hot' plug installed larger MVVS engines consume more fuel, tend to start backwards (masked if you use a starter - I always hand start) and do not achieve top RPM's. Add nitro to the equation and these woes are compounded.

GoNavy

My Feedback: (15)

I ordered two different "cold" plugs and they just arrived.

I have the "new" spray bar with tapered low speed needle; since the spray bar has the notch, it is similar to the Supertigre spray bars so by rotating the position of the spray bar I expect the problem I described can be solved.

The o-ring seal on the carb is an issue; the o-ring I have is 2mm thick, which raises the carb just enough to cause trouble for the bolt which holds the carb to the body; I will make a temporary gasket while finding a very thin o-ring, and run the engine again tomorrow, with the pitts style muffler.

Josef Vajda of MVVS in Brno, has answered 5 or 6 emails from me, and been very helpful, considering, especially, that this version of the engine has not been manufactured for some 20+ years, and told me to use a 10mm i.d. o-ring,
but I didn't ask him about the thickness dimension; If anyone knows that (it must be less than 2mm), or if you could measure the thickness of the o-ring on your MVVS engine, that would help a lot.

GoNavy

My Feedback: (15)

Fiery: On the matter of fuel consumption: This engine uses less fuel than any other two stroke I have ever had (including Fox, Supertigre, MDS,UAV Bully, Webra, K&B), including the old Webra 61 black heads. I am not running lean. I wonder what makes this thing such a fuel miser, even tho it is very powerful?

Oh, and regarding compression: Excellent. With about one hour of breakin running.

fiery

My Feedback: (2)

Josef Svajda is the designer. Despite being of very senior years he helps out around the factory and in particular assists with queries from MVVS glow users.

Many spare parts are still available for the glow engines but sadly inthe more popular displacements some parts (such as mufflers) are now unavailable. Once stock has dried up no further items are made.

Photo's below of the 'old style' carb and 'final' style. White "O" ring on the earlier one is fitted at bottom of spigot. It will need replacement and is 13 mm OD and about 2 mm in ring material diameter. Later Carb has a clear "O" ring fitted under carb body in the manner commonly seen.

Note differences in the LS needles. Earlier LS needle is nearly blunt at the tip. Spray bar has a small sawn knotch. Later LS needle has a subtle 'double taper' and the spray bar now has a tangentially angle cut 'jet'.

The later carbs work very well. An 'update kit' of a replacement new spray bar and LS needle was thoughtfully made available by the manufacturer to update earlier carbs.

Included is a shot of the 'standard' factory side muffler and rare factory diesel head for the MVVS 6,5 cc. Shims for the OS .FP .40 can be used to set clearance so the contra-piston is flush with the face of the head button once final settings are known.

https://www.youtube.com/watch?v=MfJFcPa-spQ

Also shown is my partner with my first MVVS, a 10 cc (.61 c.i.) and an MVVS 20 cc (1.20 c.i.) boxer with factory diesel heads fitted by me. It was only ever offered by the manufacturer in glow ignition. Many owners experienced difficulty with the Walbro carb on glow fuel and the engine was quietly withdrawn.

GoNavy

My Feedback: (15)

Fiery:

I have the "updated" carb with new spray bar and tapered low speed needle.
After staring at the spigot for the umteenth time, it dawned on me that there was indeed an o-ring in the provided groove (at my age things get harder to see). In my defense, I note that the ring is clear, which is harder to see than white or black. I have realigned the spray bar, and when the weather clears, am optimistic that the MVVS will display flawless performance.

Then I will have my piece of metallurgic history....Czech machining.

GoNavy

My Feedback: (15)

Fired up the 77 today, getting the needles set......and.........the fuel inlet nipple came off the carb.

Nuts, nuts and no Christmas. Looks like it was threaded in but held also with? solder?

Hobbsy

My Feedback: (102)

I moved one of Derek's pictures down here, yep it's solder, which means you can put it back.

jaka

Hi!
I hsve been running MVVS since late eighties both in pylonracing and for sport flying and it's my experience that all MVVS Engines un good with medium hot glow plugs ,like OS 8 , Enya 3 , Rossi 3 or 4, Nova Rossi 3, 4 .5 or even 6.
Nova Rossi 5 and 6 is factory installed by MVVS in all their engines.

The late carb with tapered idle needle is much better then the old carb with the blunt tiped idle needle, so get one of those carbs.

When it concerns fuel all larger MVVS (3,5cc and up) run much better on 5% nitro fuel.
I have been running as low oil content as 15% all syntetic oil but it's my experience most MVVS engines run better on at least 3%castor oil added to that 15% syntetic oil.

I would recommend the newest MVVS silencer for your 11cc engine. See picture below.

jaka

Hi!
I have been running MVVS since the late eighties both in pylonracing and for sport flying and it's my experience that all MVVS Engines un good with medium hot glow plugs ,like OS 8 , Enya 3 , Rossi 3 or 4, Nova Rossi 3, 4 .5 or even 6.
Nova Rossi 5 and 6 is factory installed by MVVS in all their engines.

The late carb with tapered idle needle is much better then the old carb with the blunt tiped idle needle, so get one of those carbs.

When it comes to fuel all larger MVVS (3,5cc and up) run much better on 5% nitro fuel.
I have been running as low oil content as 15% all syntetic oil but it's my experience most MVVS engines run better on at least 3% castor oil added to that 15% syntetic oil.

I would recommend the newest MVVS silencer for your 11cc engine. See picture below

GoNavy

My Feedback: (15)

I am learning a lot...thanks for all the comments.

Regarding the fuel supply nipple attachment; Upon further inspection, using a magnifying glass, it appears the part was threaded but then also cemented in place. I am installing a new part and then, really, surely, without a doubt, all will be fine.

I think.

jaka

Hi!
The fuel nipple on the carb is soldered in place. I would recommend using "Stay-Brite" silver solder and a good soldering iron. Me myself use a 40 year old 50W Weller soldering iron. Works like a charm on all kinds of things from 5mm piano landing gear wire down to finest electrical circut board soldering (with different tips of course).

GoNavy

My Feedback: (15)

Replaced the fuel nipple. Engine was running well with good transition (I rotated the needle assembly as planned), idle 3700, top end 11,400....... glow plug died. Tried two different replacements. Not a peep. Back to the shop.

GoNavy

My Feedback: (15)

Okay. Found nothing wrong in fuel system. I think it must have been flooded. Harder to recognize with an engine with so much compression even when hot. Running today, idle 3400, top end 11,400, though mid range was too rich. I see that when I reassembled the carb I did not get the inlet side in the exact same position as yesterday. I can correct that. I think that's as good as it will get.
Seems to me the carb is very fussy, even with the "update" kit. Might yet try a Perry carb.
It is a very powerful motor.

jaka

Hi!
3400 rpm at idle is way too high . You should expect around 2000rpm with a well run in engine, set up correctly. and the needle walv should not be roated!!!
As I said Before, use 5%nitro and 20% castor oil/synetic oil or a mix and use a OS,Enya 3, Nova-Rossi 4 or Rossi 3 glow plug.

GoNavy

My Feedback: (15)

I believe the engine is well run in, with 1/2 gallon used, but I have had only two other non-ringed engines in the past 30 years, so I could be wrong. Compression is excellent.
I can experiment, by going from no nitromethane to 5%, and by going from all castor oil to half castor half synthetic.
I can experiment by purchasing the variety of glow plugs mentioned. And I can realign the spray bar.

However, going to the new factory muffler, #3255N (cigar shaped, a bit like a SuperTigre), will take some time and probably require some changes to the nose and cowl of this airplane (a Dalotel), something I am not sure I want to do as it will significantly alter the appearance of the aircraft.

Question for Jan: Why do you not want me to rotate the carb inlet, dispite the fact that that rotating it solved the midrange (transition) problem?

jaka

Hi!
If you mean rotating the piece where fuel nipple is (fuel inlet orrifice) ...it's not needed! So why rotating it!?

GoNavy

My Feedback: (15)

Jan:

Yes, that is the piece that I refer to.

You say that rotating the fuel inlet orifice is "not needed".
Perhaps that has been your experience, and I suspect you have extensive experience with the MVVS 77.
I suspect you find you are able to have reliable idle, midrange and full throttle running with the orifice in the "factory"
position. (Since the part can be installed in any position, because there is no detente or stop, I suspect the "factory"
position is that which has the fuel inlet nipple parallel to the crankshaft, but that is an assumption on my part.)

However, in my case, with the orifice in that position, I could not achieve proper idle, mid range, and full throttle.
To achieve all three, something was necessary. Changing to a cold plug didn't do it. Changing the position of the orifice did.

Again, if you are saying that I should not have to alter the position from "factory", that I should be able to achieve proper performance in all three regimes, that I need to try different plugs, different nitro %, and different oil type, and a non-pitts style factory muffler, you may very well be correct.

The question I had was, if rotating the orifice solves the problem I experienced, why should I not do it?