[pjp01]

Anyone have any insight into tuning a Saito FS.
Just finished a Mojo 60 and am trying to set up the Saito .91 I will be using.
I have tried the basic set up as described in the manual but it does not seem to want to idle at all. Just dies when i drop it below 1/2 throttle.
I inadvertently moved the low speed idle so not quite sure where to start with that needle. I set it at about 3 turns out to start.
It is mounted at 90 degrees and I have a 14x8 zoar using 15% coolpower.
So far have tried to peak the high end first and back off 2-300. Then lean the low end. Sadly, at about half throttle it dies.
Any info appreciated.

[kip51035]

To pre set the low speed needle:
Close the throttle on a straight pin.
Attach a piece of fuel line to the fuel inlet.
Blow in the fuel line and adjust the low needle so you can just blow through it.
This is usually a good place to start.

[Cougar429]

I would recommend removing the Low Speed needle and blow through the fuel inlet. It sounds like you may have a piece of grit in the carb. If that is not successful you may need to remove the carb and have a look.

First, let us know the history of the motor. Is it new? Is there a fuel filter installed before the carb?

I ask as there are a couple of other places to check. One is the O-rings at the carb and head on the inlet tube. If they are aged and shrunk you could have an air leak. Same with the fuel inlet/HS needle assembly. If the seal is damaged or the assembly incorrectly installed then again you could have an air leak.

Another problem could be your valve adjustments. If not correct you will find your power and run quality severely affected. Same with a motor that has been overheated and weakened the valve springs.

You may have something as simple as a pressure port or fuel line leak. Either will affect your fuel draw at lower throttle settings. Same with having a tank mounted too low to the centerline of the carb.

I have to point out one factor with a warning. With 4-strokes any adjustment you make to the mixture takes quite a bit of time to take effect. I started 4-stroking with the Saito 91 and learned a very important lesson: They DO NOT like to run lean, especially at high throttle settings. The motor can come to an immediate stop without warning and can frequently chuck the prop and nuts, even the double lock style. Make sure until you have it dialed in that absolutely no person is within the prop arc. This extends from in line with the prop to any position in front. At several thousand RPM a large prop like that can carry a lot of energy if it is ejected.

On that note I found anything larger than a 13/8 3-blade to a 14-6 2-blade a bit much for the 91.

Sorry, I wish I could give specifics, but mine is buried within a cowl and difficult to check the settings. I found once dialed in I only have to tweak the HS needle a click or two for varying environments and the LS needle never needs to be touched at all. I have a 100 and 150 stored away and a 125a now mounted to the Rare Bear, but a bit away from firing it up so I could give you more info.

[pjp01]

Thanks for the replies, I will check all of those things.
The motor is used, but from a reliable source. It has sat for about a year.
Going to give it another try tomorrow. My tach is a bit weak, so that doesnt help.

[pjp01]

By the way, in regards to tank height. My inlet(clunk) is about 2 inches lower than the carb.

[Cougar429]

You want the centerline of the tank even with the carb.

[pjp01]

Thanks, thats about where it is.

[williame3590]

High speed is easy enough but a good starting point for the low speed is to have the screw basically flush with the outside of the throttle arm. You will probably have to turn it in from there.

Bill

[pjp01]

Starting with the low speed flush with the arm seemed to help...
However, still struggling. Tried to set the high end to peak so I could back it off a couple hundred rpm. Very difficult to dicern rpm change with tach.
Seemed to peak about 8000.
Was able to get the idle down to a somewhat unreliable 2800.
At the low speed range, there seems to be a lot of fuel coming out exhaust and maybe aroung carb.
Fuel consumption is very high. Had to fill it three times during fairly brief engine runs.
It has been suggested I check the valves.

[Cougar429]

8000 RPM is too low. You may have too much prop on it. If you have a 14/6 or even a 13/8 try that.

To need that much fuel to keep it running at low speed still sounds like an air leak in the intake system or carb. In that case you lose the natural fuel draw and vaporization, requiring it swallowing nearly raw fuel to compensate.

Fuel spitting out of the carb inlet at low speeds is not that unusual and most Saitos benefit from the addition of the inlet venturi. Since you are gagging on fuel a lot more will spit out between inlet draw pulses.

Forgot to ask if you have good compression, (Saitos are higher comp than others, so it should be a bit difficult to flip over. If not then listen when slowly bringing the piston to TDC on compression. If you hear a hissing out the inlet, exhaust or even breather tube then you have a leak that will compromise performance. A tired motor behaves this way.

The early version 91 and others, (most easily denoted by the metal throttle arm, although that can be changed on its own) have several things of note. First is that the valve seats are plated and part of the base head casting. These CANNOT be lapped to help valve seating. Once the coating is gone the cylinder and head assembly are pretty much pooched, requiring replacement. The new version has valve seat inserts and also a different cam profile, called the "Quiet Cam" that softens the opening rates on the valves. I've also seen they placed the case vent below the cam, which should help lubrication, although I have never had a problem with the rear cover vent and wonder what any contamination is doing to the cam and gears before exiting.

I'm leaving in a few minutes to meet some friends for a coffee. One of them is giving me the bits he ordered for his 56 for me to put back together. That one broke off a cam gear tooth. Never saw that before and luckily the missing bits did not make it further into the engine, (it quit before that could happen). Only thing I suspect is a sudden stoppage from doing a goat into the ground, (no other evidence of that) or it suffered the lean stoppage I mentioned earlier.