starefly

Hello everybody,

Since yesterday I've got some issue at low speed with my 70 surpass, I've passed more than 3 hours to look for the root cause but I didn't find anything [:@]... Maybe somebody will be able to help me !
Engine is performing well at middle and high speed. Engine response is also very good. When I idle the engine, engine's RPM is decreasing slowly until it stabilize and have a smooth functioning ; After about 10-15s the engine quit abruptly as if it was no more ignition or fuel.

I'm using special four stroke fuel with 10% nitro.

I have made the following troubleshooting:
- Changed glow plug (OS-F)
- Changed all fuel lines (tank close to engine ; length are short)
- Cleaned carburetor and disassembled needle valve
- Checked fuel level (OK)
- Checked fuel tank cleanness
- Checked that there is no bubble in fuel line

To get a smooth running, needle valve is set at about 1 1/8 turn which is a little bit more rich than peak. Mixture seems to be good as transition are very good....

Does anybody have an idea ? Does the issue can come from tank pressurization ? I mean when engine is at middle and high speed, tank pressure is high ; then when throttle is reduced tank pressure is slowly decreasing until pressure is to low to "push" the fuel into the carburetor when engine stay too long at low speed and then led to the engine stop ?

Thank for your help,

Marc

starefly

I have dismantled the carburetor once again this morning, and I have found that fuel still going into the carburetor even if needle valve is fully close. I didn't remember if it was doing that before... Do you think that's normal ?

Bax

My Feedback: (11)

If the carburetor will permit fuel to flow when the high-speed needle is turned all the way in, then you have a damaged needle seat. You will need to replace the carburetor body because one cannot replace just the needle seat. You will also see a polished area on the pointed part of the needle valve that will indicate that the needle has been turned-in too far at some time in the past. If the needle does not have a rough area there, then you can still use it. Otherwise, you will need a new needle valve.

starefly

Thanks for your help. The needle has a polished area and fuel still flowing when needle is fully closed.

Do you know if there is a place to get a full new caburator even if it is discontinued (checked on OS page) ?

Bax

My Feedback: (11)

We'd not know where you'd be able to get a carburetor or carburetor body for the O.S. FS-70 Surpass. You'll need:

O.S. #44081100 Carburetor FS-70 Surpass

starefly

Hello,

I've changed all the carburetor by new parts and I still have the same issue I definitively don't know where it is coming from.
When I idle the engine, Idle is smooth during about 5sec then, Rpm begins to decrease, engine begins to smoke and finally stop. Just as there was too much fuel and not enough air.
I made a try by removing tank pressurization and the issue is still the same with a different carburetor setting. I just noticed that when I leave glow plug on engine it doesn't stop.
I have dismantled the fuel tank once again, changed fuel tubing, changed glow plug one more time but still the same issue.

Do you have any idea about what could be the root cause ?

rh1965

It sounds like the low speed fuel mixture is set too rich. Confirm this by allowing engine to idle as long as you dare and crank full throttle, lots of smoke means too rich. I did not see anything in your posts about low speed fuel mixture setting.

starefly

Unfortunately there isn't any low speed mixing on this engine. There is only a needle valve and a mixture valve for idling and transition. The point is if I set the mixture valve to get a smooth idle, engine quites when I increase throttle due to a lack of fuel. It's a nightmare ! I never had that before !

Bax

My Feedback: (11)

The FS-70 Surpass most certainly has an idle mixture adjustment. It's the small screw that's in the center of the throttle arm. You turn id clockwise to lean the idle mixture and counter-clockwise to richen the idle mixture. The instruction manual for the engine details the initial location for the idle mixture and how to get it properly-set. If you don't have the instructions, we can send an electronic copy. Just send your email request to the address below.

For proper running, you'll want the idle mixture set very rich, get the engine running at full throttle and then adjust the full-throttle mixture so that it's just rich of peak RPM. Then retard the throttle and adjust the idle mixture as necessary. Eventually, you'll get a good idle RPM and mixture. If the idle cannot be set at all, then you may have a problem with compression, and may need to look into whether the valves are leaking or you have a bad piston/ring/liner fit.

starefly

What I called the mixture valve is the "small screw that's in the center of the throttle arm". I don't use to tune the engine the way you recommended. I perform as following : First point I set high speed with the needle then I adjust the mixture to get a smooth throttle response then I check high speed once again. Otherwise compression looks to be good and I'm able to spin an APC 13x6 at more than 10K Rpm.
I'll make a try with your method and I'll open the engine to check parts ; I have dismantled the engine about 4 months ago to change the bearings and he was running pretty well after that ; maybe something has moved since....

starefly

I finally made it ! I changed the fuel and the engine is running pretty smooth right now.
The only point I've noticed is that the engine is knocking around 3500-4000 RPM... Whatever, idling is just fine.

Thanks for your help.

TheBerkshireFlyers

I have the same problem you are having, tried pretty much everything you did, still not running right, what kind of fuel do you have?

starefly

Finally used home made fuel buying methanol from a racing car supplier + RC oil + 3-4% nitro

Cheers