Yay

Hi guy's
I have a current model Saito 40 that will not run right.
The problem is it drops rev's without touching the throttle lever.I have it on the test stand running
just on the rich side of peak,nice smoke trail and it just starts to loose rev's, drops back around 500 rpm
then slowly runs back up to the originalsetting, it will do this a number of times,tank is full,no leaks on carby or
intake tube, will run at idle and pick up when throttle opened. Have changed plugs, tank ,prop,
fuel , checked valve clearance, oil is clear out of breather tube, does the same thing in the air.
Also changed the carby,checked fuel lines all OK
Help!
Paul
In OZ

raptor51

Hi Paul in Oz...this is Colin in S Africa,

This seems to be one of those dratted mysteries. This really sounds like a fuel feed challenge!
You have checked most things but haven't mentioned position of tank in relation to carb also length of fuel lines.

[*]Horizontal centreline of tank should ideally be in line with the carb barrel....also vertical centreline if poss.[*]Have the tank bung and outlet pipes as close to carb as poss, ie. have the intake feed line as short as poss.[*]How's the clunk in the tank set up....the pipe to that should allow the clunk to freely swing around at the rear end of the tank.[*]Also, I'm assuming that you have a pressure pipe from muffler nipple into the tank .[/list]We land in Oz on 21 September....going to visit our daughter and family near Adelaide SA.

Hope you come right soon.

cheers

Yay

Colin
All the items you listed have been done and or checked.
Yes, it is a mystery.
Paul

mike109

G'day Paul

You did not say whether this engine is new or has run before. Also, it would be instructive to know what fuel, and prop you are using.

I have two of these and they run fine but when they were new, they were a bit on the rough side and took a while to become as smooth as they are now. Perhaps the engine is simply not run in enough?

I have also found that they like a little castor oil in the mix particularly when they are new. I use 10% nitro, 5% castor, 15% synthetic and 70% methanol. I think I am using 10 x 6 props.

Cheers

Mike in Dubbo.

Yay

Mike
It was run in andran fine, now ithas started with the problem.
Prop 11x6, fuel 18% Klotz & 5 % Nitro.
In a normal situation we close the barrel in the carb and restrict the fuel & air
to lower the rev's,so I'am thinkingwhat could cause this to happen( if you take the carby out of the equation)
what inside the engine could cause this?
Paul

SrTelemaster150

Are you using the radio for throttle actuation?

If so is the servo "hunting" for position.

Could be a radio (interferance) problem.

djlyon

This is a bit of a stretch, but it could be that the idle needle is a little to far in and just barely interfering with the flow from the high speed needle.

Denis

jeffie8696

Isecond that Ihave had trouble setting them when trying to get the bottom end too lean. My FA40 is wonderful now that it is broke in .

Rudolph Hart

Hi jeffie yes i agree have had a few problems overleaning the low speed needle too.Re reading the original post makes me think sr telemaster is on the right track tho,how many of us have ever really looked at the small throttle servo??

jaka

Hi!
Are you sure you are using the OS F plug?

jeffie8696

Ihave also had a throttle servo that was jittery at idle and caused problems, it was supposedly digital but it was a cheap chinese one so who knows.

Yay

Guy's
This happened on the test stand,with no servo hooked up, moved throttlelever by wire.
Have been on shift work,will re try engine again in a few days,with a fresh OS F plug.
The second plug I tried was not an OS F,it was a Thunderbolt 4cycle plug.
Engine had been running on the Saito plug supplied.
Thanks for the input.
Paul
In OZ