doent like starting, but ones started it goes great

[f3martin]

Hi guys

I recently purchased a new gas mvvs 26, my first gas engine. For the first few flights it went great, starting and flying. But it has now ha about 8 flights, each time its getting harder to start. The only way now is using a big starter. The problem seems to be that it doesnt suck fuel up to prime it, it also seems to have near to no compression, I can flip the prop round with my finger and not get caught without moving my fingers. But one it is starts, it runs absoloutly great, perfect, powerfull, reliable..
Can you guys please help me
many many thanks
Martin

[f3martin]

I sent an email to a writer in an rc magazine, that went as follows. I just thought I would ask your opinion before sending it back.:

I have recently purchased a new mvvs 26. It is a great engine, and my first attempt at petrol. But there is a slight problem with it, it doesn’t like starting. If I follow the instructions on how to start a petrol engine, nothing happens. It doesn’t seem to suck any fuel up while being primed.
The only way to start it seems to be with an electric starter, after just a few spins with the starter it jumps into life (we assume that it starts with a starter because it forces it to suck fuel). Once it is started, it runs great, smooth, super reliable...
The engine has now had about 3.5 to 4 litres run through it. The first few times it started fine by hand.
Do you have any idea what might be causing this problem?



The MVVS range are very good starters and I suspect it's purely down to your technique and learning the engine's needs for a quick start.
If you are able to start the engine with a starter then it would seem (as you suggest) that there isn't a problem per se with the fuel or ignition system and a logical approach should pin down where the problem lies, but here goes my attempt "at distance" (ie without being able to handle the engine directly), so bear with me as I am at a disadvantage here.
The carb on this engine is a Walbro pumper type and this works by way of a diaphragm pump that pulls fuel up from the tank (very efficiently too)! Turning the propeller a few times is usually enough to "prove" that fuel feed is working but you can choke the intake (just like your glow's) to suck fuel up.
Once you have achieved a "wet" engine - ie you have fuel in the intake, starting will be immediate but there is just a chance that your particular engine may not be generating a good spark if it will only go with an electric starter and this could be for one of several reasons.
The spark plug - two-stroke petrol’s are plug fussy and if your plug has oiled up (usually because folks put way too much oil in the fuel, thinking they are doing the engine a favour....) then a new one is the only cure - cleaning seldom works. If the plug is fine (i.e. dry and a sandy colour) then look at the ignition pick up and ensure that the gap is as specified (i.e. the little magnet in the prop driver that induces current into the pick up coil has to be really close as it passes - about a "fag paper" clearance. You can easily check if the spark is good by taking the plug out and with ignition on, checking as you rotate the engine that the plug has a good healthy blue spark that "cracks" as it fires across the electrodes. If the plug is suspect then remove it and see if you can get the spark to jump from the lead end to the engine earth - a good 2 - 5 mm gap should be easily jumped by a healthy spark.



I have tried starting it using several different methods without any luck. Even after flicking the prop several times with the choke closed and the throttle fully open it doesn’t seem to suck any fuel. It also doesn’t seem to have much to any compression. When I flick the prop, it doesn’t spin and bounce several times like I imagine it should, it goes past the compression and stops, in other words, flicking it only gives me about 1/4 of a turn rather than a full turn and then the bounces.
If I inject fuel strait into the carb, I gain compression for a few flicks, but even then it doesn’t start, and then it returns to near to no compression.
I have heard that about the spark plugs, but would the engine run flawlessly on a bad plug once started?
I have tried turning it over with the plug out. It does spark, but nothing amazing, it is a small blue spark, if it is sunny you must shade it to be able to see it. But I dont really know what is should look like, neither do I know what the distance should be from where the spark starts to where it sparks to. The plug itself looks very clean, it doesn’t look gummed up with oil but it is all a sort of brown colour. If I try to scrape the borwn off, I cant, it is obviously metal and no oil, and its jus the colour that the metal has gone. If I take the plug out strait after priming, it does not seem to be wet, this is what led me to my original conclusion of it not priming properly.
What must I do ?



No compression sounds suspicious - I think you need to have a word with Paul Landels who you will find helpful and knowledgeable on this engine as he has sold a deal of them. Compression evaluation can be misleading to the feel sometimes, but perhaps you have a ring that is either broken or stuck - unlikely but feasible!
Your plug and spark sound fine - if it's a blue (rather than weak yellow) spark then that's fine (you should be able to hear it "crack" as the sensor initiates the circuit).
I can't really offer any further suggestions without seeing the engine for myself - if the engine is in warranty, then you can do no better than return it for diagnosis and rectification, but these units are normally, very reliable.

[SleepyC]

I agree it sounds like a stuck or broken ring.

Did you follow the oil ratio reccomendations when breaking the motor in?
Also, the proper break in prop?

If you did both, sometimes a ring is just bad... not often but it does happen.

Hope that helps.

[GremlinX]

I wont say his name, but he is a member, and has the same motor. It runs ok, and seems to idle down ok, but it is a real bear to start. Often having to borrow an electric starter. I think it is a combination of radical port work and timing in order to get the HP they do from such a small motor. His always ran hot, mainly we think due to the carb blocking 1/2 the motor...

[dick hanson]

The egine is very normal in layout -mild timing the problems as described suggest that the owners are new at this game -
The engine likes 32-1 oil
the choke is NOT going to give a fast positive choke - onles you cover it with your thumb OR solder up the hole in the plate and re drill to 1/16"
Mine runs like a clock and nice snappy flipping when starting
hot starts are one flippers . I never use a starter on anything - no need to if you learn the correct choking sequence and set the carb needles correctly. The guys involved obviously need some basic training in small gassers - everybody has to start somewhere .the problem is getting informed help.

[Bat Fastard]

Dick is right. You have to cover the carb completly with your finger to get fuel to flow. When I cover it with my finger, I open the throttle to 3/4 and give about 5-6 flips till I feel fuel flowing. Then a couple more flips to work it into the engine with the choke off, turn the ignition on, put the throttle back to idle and it starts with one flip. What I would be concerned about is why you dont have any compression. Both of mine have excellent compression.
Jamie

[f3martin]

Hi guys
Thanks for the replies
I gave it one last chance before taking it out and reourning it, and it must have got scared!
i took the cowl off so as I could look at what was going on in the fuel lines. The problem was simply, it wasnt sucking fuel. I tried covering it with my thumb and still nothing. As a last shot I span the prop without letting go of it about 20 times as fast as possible with my finger on the carb, and it worked ! It sucked fuel, A little came bubbling out the choke, and 5 flicks and working
Why would the speed of priming matter? arent these meant to be super powerfull, no retourn pumps?

many thankas
Martin

[0llie]

Hi Martin

We have the MVVS 26 also and experience exactly the same symptoms, I thought as you do that the pumped carb should just pull fuel through easily but they dont after the fuel runs back to the tank.

I was advised to not drain the tank at the end of the day and plug both tank vents - This makes it harder for the fuel to drain back and it works for us.

Our starting goes as follows

First start of the day

Choke on and thumb over carb intake (Important to get a good seal) Ign off just turn the engine over slowly maybe 6 times or so until you can feel your thumb wet with fuel
Leave choke on ,switch Ign on and flick prop - It fires on 2nd flick and I get a short run
Choke off and it will start on 4th flick every time

From then on

Choke on ,switch Ign on and flick prop - It fires around 3rd flick depending on how long its been stood and I get a short run
Choke off and it will start on 4th flick every time

At first I was over priming and wetting the plug, but now it never fails with this method even though we are still running a little rich

We have it inverted in a wild hare edge and the carb is poking through the front of the cowl so getting at it is no problem at the moment but if you have it inside your cowl then you will have to blank the air bleed hole in the choke flap as mentioned in the earlier post

Cheers
Shaun and Ollie

[dick hanson]

priming speed--
first - use no filters or fill valves in th pickup line - just a TEE and a plug once filled
also make certain there is no leak not even the slightest looseness of any fuel line on a fitting --if there is, the fuel will run back
If all is sealed - starting consists of full choke ( I solder the plate bleed hole on some carbs then drill a 1/16" hole
On the 26 --the spring loaded choke can be changed in tension by unhooking the mousetrap spring and letting it uncoil one turn-
or you can swap th shaft and adda ball and spring from an indexing choke - whatever.
Full throttle full choke -flippity flippity till you feel it get wet.
open choke close throttle - engage ignition- one flip -it's running
Just like a model T Ford
"Advance the throttle -retard the spark
Add the choke and crank to start"
It is a learned procedure
My mom broke her wrist on a T because she let her thumb hang over the handle and it kicked back
All of the gassers take some basic learning
it isn't that hard .

[GremlinX]

I have been around gas stuff for a while. I definately think if you have to thumb the carb... The choke is not effective enough. Not to mention, this one is concealed in the cowl. And he seems to have to choke it hot. I suspect an airleak.