Robin Full Throttle Cutout

I have seen several post but no real answer. I have the Robin Suburu 33cc four stroke on a friction drive. Whenever I apply full throttle under load the engine will quit. First time it happened I was trying to pull a 10% grade and had to coast back to the bottom. I have figured out that it is "fuel starvation" because if I let up on the throttle about 1/4" before it dies then it will regain power. I have seen some post about this so I know others are having the same problem. Anyone found a fix?

I'd first check the fuel filters. The one in the tank is the easy one, the micro-screen in the carb requires pulling it apart.

Thanks for the reply. The engine was new out of the box and on the first ride when it did this Brand new gas can and fresh gas. I have a about 65 miles on it now and today when I was out I went to full throttle several times everything was fine. I was going up a hill but not a "monster" hill like when it did it before. Guess I will have to go back to one of the big hills and try it.

Could it be the pickup tube in the tank is getting air when your going up the hill and the fuel is more on one side of the tank? Usually carb problems will be consistent. Might be worth checking out.

Hmmm, new in box. Perplexing and I'm sure aggravating. I've broken in probably 10 of these engines from NIB and all of them performed flawlessly from day one. Even refurbished a couple of used EHO35s and they worked great.

I think Bandito's post might be onto something, maybe something simple like fuel level in the tank. Check to sure the fuel feeder line in the tank is straight and not kinked also. If it's a new engine the filter SHOULD be ok.

More than that, I'd assume it's a fuel issue if the engine is running well other than at max load. I guess if it were mine I'd go about a methodical check of the fuel system starting with pulling the plug to see if it looks like it's running lean and hot. Then, from the tank, filter, fuel lines and carb to see if fuel is reaching all these points as it should. Also, I'd check to make sure the carb is tightened well to the intake insulator to insure there is no air leaks. Beyond that, considering it's anew engine..........is there a chance you can get any satisfaction from where you bought it?

YES! The fix is easy. And you're right about the fuel starvation; that is EXACTLY what is
happening. Here's what's causing it.
The Subaru Robin was made to run in just about any orientation; even upside down, albeit for a short time. Think about that for a moment. It can actually be turned upside down while running and: A) keep running. and B) not spill any fuel. AH HA! There's the tip off.
These little engines suck... so hard (as in vacuum) that they will actually pull more fuel out of the tank (and faster) than the VENT can let air INTO the tank! Voila! Vacuum equilibrium; hence--Fuel starvation!
I too had the same experience going up hills WOT and losing power. I too drew the same conclusion of fuel starvation. Then one day when it occurred, I reached down and loosened the gas cap and INSTANT power restoration!--The AH HA moment.
The Fix: Remove the baffle (duckbill) in the fuel cap. That will be $45 US please. JK
Here's how:
Unscrew the cap from the tank DUH. and pry off the tether retainer.
The fuel cap is built in a couple of pieces. Pry off the inner vent retainer and remove the foam
diffuser. Yes, I'm making these names up as I go along. They aren't in any manual.
Under the foam diffuser you will see the duck bill one-way valve that lets air in but won't let the fuel out. It is made of rubber and will pry out with a tooth pick or similar. (I used an old spoke here)
Reinstall the foam, inner lid, and tether and replace the cap on the tank.
DONE and never to be bothered by this problem again!
If you are unsure about this fix, try loosening the fuel cap next time you're on that hill and if the power returns try my fix and send me your check or money order!
Look, hopefully none of you will be riding upside down so you really don't need the check valve in the lid. And you won't leak any fuel either. Just look at the many layers of baffles the fuel would have to splash through and the wee tiny holes in the tether retainer.
Good Luck!
WC

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Guess you'll have to wait on that money order. For some reason it seems to be doing fine now. But, now that you mention it, several fillups ago when I took the fuel cap off the inside of the cap came apart. I just stuck it back together and didn't think any more about it. Has done it a couple of times since then. It may be pulling enough air around it to vent properly.
Great answer and I am sure you are correct. Thanks for the reply.

Since you're on a "Roll" maybe you have an answer to another question. I have 80 miles on the bicycle and I changed the oil for the third time today. After only a couple of hours of operation the oil has a strong gas smell. I though it might just be the rings had not seated but in about 8 hours of operation I would think they would have had time. I change it at two hours, four hours, and today at about 8 hours operation. Oil was also dirty looking for only four hours. I don't think I would ever run it the recommended time in the owners manual. I think after the first change it is 50 hours.

I'm still on my first gallon of gas but it seems that power has increased over what it was on the first couple of tanks. I think I will end up getting about 120 MPG, not the 160-200 in Stanton's ad, but where I live is "Up Hill - Down Hill" then repeat.