Hey Guys,

We finally got around to starting up my Summitt III yesterday, its running an OS 61RF (with the back plate pump) on a carbon pipe. The problem we noticed is that when we run it up to full throttle it doesn't peak until we back it down and run it up again. It also surges all by itself at both high throttle and idle. Any ideas on what we should look at?

Tune pipe length for top end. Almost sounds like your getting unwanted air in the fuel system. Any bubbles in the fuel line? Also... check the pump's backing plate and make sure it is sealed to crank case.

Agreed! Fuel issues and Pipe settings would be the first place to look?

Let me just add to what Cspaced posted.

The engine maintains rpm on the high end. On the low end, the rpm's either start off high and slowly taper off, or start off low and increase. Sometimes going from idle to full, the rpm's wont reach max unless the throttle is brought back down to idle and then opened back up to full. Also the carb drips fuel....

more than likely you have a bad o-ring or two in the carb, and possibly your check valve is stuck or sticking, cleaning these areas with fresh fuel should help the o-rings in the carb need replacing. i would also bubble check all of your fuel lines and pressure lines as well

I agree, it needs carb o-rings. You can get them from Tower Hobbies...They are easy to change and I'll bet you will find the current o-rings hard and brittle once you take it apart...

It's a standard RF-P (not a Hanno) right?? The Hanno uses a different carb (6P) where as the standard RF-P uses the Type 86 carb...Does it have four nipples on the pump or just two??

edit:
attached is a PDF copy of the manual for the Type 86 carb which has the o-ring locations shown...

The o-ring part numbers are:
[link=http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=27881800&search=Go]27881800[/link]
[link=http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=27881810&search=Go]27881810[/link]
[link=http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=27881820&search=Go]27881820[/link]
[link=http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=24981837&search=Go]24981837[/link]
(If you click on each of the numbers above it will take you to the Tower's web page for that part...Order one package of each...)

Also...To avoid any confusion...The OS RF-P does not require a check valve...

Thanks for all the replies guys, much appreciated.

The pump has 4 pressure fittings on the back, I'm not sure if its the hanno mod or not - maybe Jeff can chime in on that one. I'm not running a check valve anywhere, should I be? The documentation I have with the motor lists it as the 61-RF and it uses the PA-102 pump (I guess thats the RF-P?). Thanks again for helping me figure this out!

*Edit* I just found the very instruction sheet you posted in with the paperwork, so it looks like its the type 86 carb.

No check valve...

Yes it's a standard RF-P (non Hanno)...The PA-102 pump has the four nipple arrangement and uses the Type 86 carburetor...The o-rings which I listed above will be the correct ones... (remember they are silicone o-rings so no petroleum based products around them at all!!)

Replace all those o-rings shown and you should see a vast improvement...I would not worry about changing anything on the pipe length until you have the carb o-rings swapped out...It's not running right so you can't tune the engine in it's present state...

Great, thanks for the advice - I'm ordering the o-rings now, I'll post up what happens once I've got the new ones in.