With the choke on and using any throttle position this carb will not draw fuel. I cant get any fuel into it at all. My tank and plumbing are sound, I triple checked everything. I have been trying as per the manual and I cant even force fuel into the carb. What should I do?

The motor is new and never ran before. I just got my plane together and have been trying to start the motor, but it will not draw fuel at all, it seems like the fuel inlet is pluged. Am I missing something, the motor is the ProSport-58cc.

Barry,


Please contact the MVVS dealer, who sold the engine to you.
Walbro supplied MVVS with a batch of carburettors that were apparently assembled, with oil from a dubious source and with questionable attributes.

The internal fuel pump in the carburettor is dysfunctional as a result, despite the engine producing the proper pulses.

This can be rectified, but ask your dealer for help.

I've been told that the resolution to the carb problem is to remove the cover over the pump membrane and wash the cover, the membrane and the membrane cavity out with gasoline. This has worked for a couple of other customers that have been affected by this issue.

David

I will give a shot, is the cover the side closest to the fuel inlet? I dont want to remove the engine if I dont have to.

I too found, independent of the MVVS brand, That some Walbro's failed to work properly until cleaned and primed well. On certain occasions, the operation had to be repeated several times.
So far, I succeeded with every carb that had sound valve petals and flabby diaphragms.

Ok, boys she is running. The diaphram was bone dry, I followed Dave's instructions and it worked perfectly. I put 25 minutes on her, I had to open the low needle about half a turn to get it to run. Now I am trying to get a smooth transition to 3/4 throttle, it doesnt take much stick movement to advance the throttle. I have to make some adjustments to my radio and control linkage. She really sounds nice and man does it have stump pulling power!

Thanks again Dave.

Big Barry

No problem at all! I can't wait to hear how it works out on your Yak!

Do these motors smooth out with time? I have been opening the low-end needle to get a good transition, but now the motor runs really rough at 1/4 throttle till 1/2. The high end is fine. Does opening the needle richen? Throttle response is good going from idle to full but from full to idle if done quickly causes the motor to stop with a huge shutter. I can keep it running if I bump it to 1/4 then down to idle. I dont have much more than an a couple of hours running the motor, it idles at 1500 and will hit 6,000 with a wood Bolly 24X10. It will idle all day and pulls like a Mack truck, the transition is great, I just dont like how it runs at 1/4 throttle (lots of burbling and vibration). I blanced the prop prior to the run-in. I mixed the fuel at 30:1 using the supplied oil.

I had this problem with my mvvs58. I solved it by clearing a stuck reed . Remove the rear cover and check that thr reeds ar free.

Sounds like you are too rich on the low end Barry. You can get yourself in the right ball park by using the following method. Open the "L" needle 2 turns from fully closed and start the engine. Reduce your throttle to idle, then slowly turn the "L" needle IN to lean it out. RPMs will rise and the engine will smooth out. At some point the mixture will become too lean and the engine will slow down - back the needle out to get to the max RPM position, then turn the needle 1/4 OUT from there. That should be a good base-line setting. Now you need to tune your top end so that you are running 200-300 rpm under the maximum acheivable engine speed. Finally go back to the "L" needle and get the transition right. On a quick throttle up it is too lean if it just dies, and too rich if it sputters and dies or sputters upt to higher RPMs. Make these adjustments in very small increments, 1/16 of a turn or less!

David

I was thinking that I was too rich on the low end, I will follow your instructions and let you know how it works. This motor is very surprising, I havent been around alot of gasers, but I have held a few 50cc and 100cc planes for other flyers and this motor seems to pull as hard as some of the 100's Ive held onto. I knew it would have plenty of power for my BME YAK but after holding onto it as well as having it tied down, I can say that it should hover at about 1/3 throttle, its going to be balistic. The motor is a monster! I cant wait to fly it. It started backwards a couple of times and one time it ran backwards into my hedge and broke the tail wheel off. Good thing I have an ignition kill switch. Now I have to put on a new tail wheel. I havent even flown it yet and I'm already making repairs.

Barry,


All reed valve fed engines can run equally well backward... Like the Cox Bee and Texaco engines.
Adjust the position of the ignition pick-up to make your engine fire at TDC, during starting, then it will not happen.

For higher RPM, the VLACH ignition system will dial-in more advance.

Also, the quicker you flip-start, the less likely it is to happen.

Barry,

Driving your airplane backwards into a hedge is a good last-ditch way to get a laugh from you buddies, but I don't think it will work out well for your airplane in the long run!

As Dar says, make sure you give it a good strong flip, right through the compression stroke. Your prop should be installed so that you are hitting compression with the blade up at 1:00 or 2:00. Start your flip with the prop at 3:00 and push it right through the compression stroke. The carbon reeds dont like running backwards either, so if it happens again, make sure you kill the engine immediatley.

Of some interest, my buddy's snowmobile has an electronic reverse that fiddles with the spark advance to make the engine run backward so you can back the sled up, no transmission required!

Thanks guys for the advice, I figured out that I need to give it a good throw right through the compression stroke and it will not only start almost every time but it also will run corectly. When I ran it into the hedge the motor was just catching and I gave it a little gas as I thought it was running forwards, it poped and caught running backwards sending the plane into the hedge just as I swithched off the ignition. Its never a dull moment around here. I am going to run it some more tomorrow and lean out that low end.