alfa156

Hi

We're trying out the Saito 150 Prospark conversion.
Prior to conversion, I've used this engine and ran-in very nicely.

We're 16x8 prop, running 92 octane fuel, with 1:8 Textron 2 stroke synthetic oil.
We've incorporated the Walbro carb WT-9-1 and installed a velocity stack at the air.
The ignition is installed according to the recommendation (the spark occurs just after top dead centre)

So far, I've fired up the engine, running only at part throttle.
But I'm having problems.

Symptoms
1) The engine runs rough and uneven at part throttle
2) The engine runs, but stalls after 3-4mins, showing signs of lean mixture (engine spinning up before stalling).
=> increasing 'L' fuel mixture didn't help.

Has anyone else done the same conversion or experiencing problems?

w8ye

My Feedback: (16)

How do you have the impulse signal from your engine to the pump side of the carb hooked up?

Enjoy,

Jim

tkg

My Feedback: (1)

How are you making the Walbro carb pump work??

alfa156

Hi

Attached pls find my setup.

alfa156

BTW, we installed a Perry Gas Regulatory Pump.
Also, we lean out the Low mixture.

Engine is running fine now. Will put the muffler back later.
Any good recommendations for a 4 stroke muffer?

captinjohn

Very interesting setup! After the engine has run for several min....does oil come out the breather on back of engine? You can run a line from the nipple to a small fuel tank that is vented. Then you can see how much oil is getting to bottom end. Do you have a heat sensing gun to check temps of head and crankcase? Good Luck Capt,n

alfa156

Hello

Thanks for the reply.
Yes, I do have oil coming out from the breather valve.
I also see oil building up from the exhaust. I'm running 8:1 oil ratio. So I guess it is normal.

The temperature gun shows <100C most of the times.

Engine is ok when running constantly.
It is still not very stable when revving up and down.
I suspect it is a tuning problem. Will take a look again tommorrow.

Have a nice weekend!

alfa156

Hi

Are there many steps to make the walbro carb work?
The carb I've seems very simple. Fuel line in, L and H needle .........
Also, I installed a big 3W stack ... just in case.


Very keen to run the engine in pusher form .... with the air ramming into the velocity stack.
Wonder how much more power can I liberate from the ram air charging?
[>:][>:][>:]

Or would the ram air cause problems?

tkg

My Feedback: (1)

The Walbro you are using is desiigned to work on a 2 cycle engine. They use the +- pulses from the crankcase to make a very small diaphram pump work The pump is built in to the carb. If you look at the manifold side of the carb you will see there is a small hole, this is the pump port.
There is a 4c Walbro carb WT456 it is used on a 26cc Ryobi 4c weed trimer. Thes carb is designed to get the pump pulse from the intake port.

alfa156

Ok, I see where you are coming from.
BTW where can I read more about Walbro carb?

I am not sure if my Walbro is installed properly.
I could not fire properly without the additional regulatory pumps.
[&:][&:][&:]

w8ye

My Feedback: (16)

That's what we've been worried about. Your carb has it's own pump. If it's hooked up correctly, it doesn't need a Perry pump to run it. However the pump in the usual Walbro is run from the changes in the crankcase pressure on a 2 cycle engine. There is a place on the Walbro pump where you can tap into to supply it with this pressure signal.

On your four stroke engine the crankcase needs to be vented to the atmosphere. It might possible work to have a TEE in the crankcase vent line but the best bet would be to get the carb that "TKG" suggests.

Enjoy,

Jim

alfa156

Hello

Ok, my Saito doesn't have the crankcase pressure to drive my walbro carb.
Now, where can I get the correct Walbro carb?

Thanks to all for sharing.[8D]

w8ye

My Feedback: (16)

The correct numer of the Walbro carb is WT456 as told by TKG above. Walbro carbs are sold the all over the world. You should be able to get one at a lawn mower/ weed whacker/ or chain saw repair shop. They come on the four cycle weed whackers. The US street price is in the $40 USD range for a new one.

Enjoy,

Jim

alfa156

Hello again.

Thanks for your replies.
Yes, I found the WT-456 carb already.

However, where can I find out more info on Walbro carbs?
I went to Walbro itself, it only says that WT/WA is the smallest carb that they have.
No mention that it is for 4 stroke, or how it takes in the intake pulses.

http://root.z57.com/servlets/basic.O...mr7&PNODE=2628

w8ye

My Feedback: (16)

WT/WA Walbro carbs are a series of carbs that invlove several different sizes and needs. Only the WT456 model is the one you want. The majority of the rest are for 2 cycle service.

There has been a lot of discussion on RCU concerning Walbro carbs. There are charts made of carb sizes (for Zama carbs too). There are also links to Walbro themselves. Do a search for walbro?

Enjoy,

Jim