rcplane-RCU

My Feedback: (7)

I have a older version say 3-4 years old, it was barly used by a friend and it was treated well. I have it now after it saw no use in 2-3 years. It took a bit of adjustment but I finally got it to run/idle/and transion between all throttle levels fine and ran about 2-3 tanks of fuel during several trials etc...
I have this motor in a space walker I built and painted with automotive paint, it looks very good and it took a lot of work and that is why I took so much time with the motor so I felt I could trust it. Finally It went to the field and flew, the first few flights were fine but then it Backfired! and of course blew the spinner etc... off even with the double nut set-up. home it went, I ran it at home and all seemed fine until I took it to the field again and it backfired when running it up, blew the spinner up and destroyed a great hand carved prop! I never should have put it on until I trusted it as the props are very hard to get. I have an OS F plug 15% Byrons fuel. WHY DOES A FOUR STROKE BACKFIRE and how do you FIX IT? please give me your experience with this motor thank you Mike

wwnh.net

Its running to lean. If you adust it to max rpms then richen it for 200-300 less rpms

rcplane-RCU

My Feedback: (7)

I did not even get the motor up tp full RPMs the second time, still you think to lean?

ShempHoward

My Feedback: (3)

Maybe the low end is too lean.

BTW - That engine is more than 3-4 years old as the MKIII version came out about 4-5 years ago if I recall. The MKII was a cantankerous engine for many people and user friendly for a few others.

Mettler1

I NEVER use a wood prop on a four stroke. I use APC props and tighten them with a box end wrench. l so have a double nut. Never have had a prop thrown yet. Doesn't mean it can't happen. I just try to do whatever I can to keep it from happening. And like the previous posts said, Don't run them leaned out IF you use a box end wrench to tighten a wood prop, be careful. You might crush the prop hub. Not good!

littlepiston

My Feedback: (12)

well if its the pumped virsion (not the black pump) you have to run it to its max RPM or else the low will not lean out something else wrong timing could be off or the cowl is super charging it and forsing to much fuel in or leaning it out try it with out the cowl if it has one on it

rcplane-RCU

My Feedback: (7)

Thanks everybody, the motor has not backfired again, it did run good especally after taking the cowl off and spending some time with it. Mike

ljones5000

My Feedback: (2)

I have a 120 Surpass-pumped, 10 yrs old. As someone said, a very cantankerous engine at times. I use 15% Cool Power, a friend recommended adding 3 oz. of Klotz oil per gallon and for the past year my Surpass has run great. It is in a 1/4 scale J-3 Cub.

You might give the Klotz oil a try. Just don't ask me why it worked.

Larry

Tired Old Man

My Feedback: (1)

Just for the sake of mentioning it, you're not presurizing the tank with muffler pressure, are you?

BTW, I had one of the old Surpass II 120's. One of the worst engines I ever had. I hope yours' works out a lot better.

Silversurfer

littlepiston

My Feedback: (12)

fixed mine i have a two dollar seal go out on the pump and i tryed to get it from os ,but all they would sell was the hole pump ,well i went to my neares bearing shop and ordered two of them for five buck worked like a cham!!!! couldnt be happyer