abrous

Hi,

I am wondering if anyone out there has any experience using the 45IRS with the BCM Pitts style muffler.
I have many problems with idle instabillity and I am sure that they are NOT tunning problems.
Recently, I read a Pe Reivers's responce to a guy with a similar problem. He told him that maybe caused by fuel evaporation
inside the engine due to high temperature created by the in-cowl muffler. My BCM's body is almost in contact with
engine's cylinder leaving too little space for air circulation. Using a digital thermometer I checked the head temperature
and was more or less 90-95 deg. I tried many baffling schemes with no effect. There is too little space and I can't see how
can I force the air behind the head to cool the ultra hot muffler's body. Any ideas ?

DarZeelon

Angelo,


I would not think such an installation should create a cooling problem.

I would have side-mounted the engine, so as not to make that unattractive hole on the cowl.
The standard MVVS exhaust intended for this engine, does nor lay so close to the engine...

Maybe Pé can add something.

abrous

Do you have any idea about the normal temperature range of the engine head and crankcase during operation ?
I am going to make a temperature graph on several points on the engine today.

Angelo

BaldEagel

Abros

Have a look at the QQ 85 Yak site two of the guys there are using MVVS with I belive Pitts style silencers onw guy is Angus and the other is closetguy.

Hope this helps.

Mike

pe reivers

I am a strong believer of baffling all gas engines for several reasons.
The first is, gas engines run hot because they lack the internal cooling that glow engines have. Therefore they need tto have the incoming airflow guided to provide the best cooling possible.
Secondly, the openings in the cowling front allow air to enter, but there is no well defined path for the cold air to travel, and the cold and hot air should be kept apart as well as possible. Carb air entrance should always be in the cool air section. The ignition too must be surrounded by cool air or it will suffer or fail.
The muffler inside the cowl must not be able to heat up the air inside the upper cowl, but the hot air from the muffler must be expelled out. The muffler being behind the fins will not directly cause engine problems, since the heat does not travel upstream the airflow, save for InfraRed radiation.

Head temperatures (centigrade), and engine uncowled in the open: (for 35cc and 43cc)
using an infrared gun, pointed very close range at the back base of the plug:
Too lean: 160-200
lean: 150- 160
right: 130 - 150
rich: 120-130
too rich: below 120 (plug will foul)

abrous

Its weird that tunning the engine to the rich side the problem is minimized, but then, the engine response is far away from optimum. It sounds awful too, with a lots of
"burbling" in the mid-range. Leaning the engine, cures the midrage "burbling" and response but totaly destroys the idle consistency. The engine behaves like having big mechanical
advantage on the throttle linkage (but this is not the case) or like going lean and rich in the idle range randomly. Do you think that its possible to have this problem
because of muffler? Do you think that the solution to this problem is to install a canister?
I had EXACTLY the same problem last year with a MVVS 1.60 on a different plane with totally different installation.
The only common is that I had an incowl BCM too. I am going crazy....

Angelo

pe reivers

Angelo,
What prop are you using, and how far are both needles out?
Too small a prop will cause a burbling midrange due to a low engine load. Going from high speed to idle, the engine will become more prone to burbling however. This is normal for all two stroke engines. This may also be influenced by silencer type, but is nothing to worry about as long as throttle response is good.
Instable idle mostly is caused by too lean idle mixtures, or reeds not closing well.
The high needle is not meant to cure midrange rich mixture. This needle should be set for best power (at lowest possible head temperatures) It is best to find the rpm drop-off positions both lean and rich, and then set the needle between these positions, biased towards the safer rich side . (Walbro instruction manual)
Important:
The high speed mixture is provided by both needles, the idle mixture is provided by the low needle only, so any low speed needle adjustment needs re-adjustment of the high speed.

abrous

The prop I am using is a Menz 22x8.

DarZeelon

Angelo,


This prop size is in general for 50 cc engines.
But as this MVVS 45 cc engine is very strong for a 45 cc engine, this prop size is perfect for it, or even on the small side.


...That is, if you were using the power-boosting, MVVS canister silencer intended for this engine.

Since you are using an after-market Pitts style muffler, this size is the highest load I would suggest to use on this engine.

What RPM do you see? Try getting a tachometer on it.

abrous

The RPM on my Menz 22x8 is approx 9750. I tried again this afternoon. Pe was right, the engine
behaves like lean at idle, and opening more the L needle the idle instabillity dissapeared without
noticable change in the engine response. Now I have a rock solid 1400-1500 RPM almost immediately
after throttling down.
BUT : the L needle is 2-1/4 open and the H is 2-1/2 open. It doesn't seem normal to me.....
Also the plug is no longer desert tan colored but rather coal black. Also there is a lot of
four strocking in the mid range. I tried an NX 23x8 with the same tunning. I get 5800 RPM.
I didn't noticed any change in the engine behaviour exept of the RPM drop.

DarZeelon

Angelo,


And what is the horsepower your engine is capable of making???

Do you think it can muster up over 11 HP???

The 23x8 RPM is a more acceptable figure...

pe reivers

Did you re-adjust high needle settings? The opened low needle will make the high rpm richer, so you need to adjust the high needle again. Your mixture obviously is too rich now.
Normal is what gives good results, though I think the idle needle should be not more than 2 turns open.

I think you made a type error, and mean 6750 rpm with the 22x8, for slightly over 4 hp. The BCM restricts the engine.
With the 22x8 the RPM is a little bit on the high end, but just acceptable.

abrous

9750RPM - wishful thinking - Yes, a type error. The RPM was 6750. A friend of mine will give me his old Krumsheid cannister 86-4 and I give it a try to see the difference.
The Krumsheid is smaller than MVVS 3204 - is 250mm length and 60mm diameter. Do you believe that this setup can make the difference ?
I wish to have more space to install the original canister, but unfortunately most of the 50cc planes have no room for canister at all ....
And a question : How long is the recommended header length for the 45IRS ? Is this length common regardless the canister I use ? (I guess no).
Which should be the starting header length for the Krumsheid kanister?

Best regards

Angelo

pe reivers

Angelo,
Do not worry about header length with canisters too much. Just take what is needed to fit the canister below the belly. In general, shorter headers are better for 9000 rpm Zenoah's, but low end pulling like the MVVS has will improve with long headers
You will find, there are huge differences in engine behaviour when using different silencer systems, both in power as in general carb tuning response. It is impossible to have experience with all canisters, though I know, the engine runs excellent using the original JMB that MVVS tested their 58cc engine with. Very uncritical and smooth to set up. The new 45cc canister (#3206) looses some power, but also is good and quite small.
I will soon have all needed header materials available (MTW)

sydc

Angelo,
Here's a link that might help with your problem.

http://www.justengines.unseen.org/silsjen.htm

Regards,
Sydc.

X_MAN

Hi All,

Sorry for barging in...

I am having the same setup as Abrous... MVVS 45 MG, BCM pitts style muffler, inverted engine layout.
And still at breaking-in stage.

The thing is, after going thru about 1 1/2 gallon of fuel, the crankpin and the bottom end bearing felt loose... a sort of metallic clinking noise whenever I tried to flip the prop past TDC.
On removing the end cover, I felt that there are some freeplay(sideways)on the bottom end bearing.

Just wondering whether this is normal?

Apart from this, the MVVS runs great and revs up to about 6880rpm on a Menz S 22X8 prop.