I just got this Poulan 42 cc engine that I am going to convert. It came out of a Poulan Pro 4218 chainsaw. When I took it apart I noticed a second butterfly valve above the carb. This butterfly valve only opens when the carb is at full open also After removing the carb and adapter I noticed another port above the intake port.

Question 1 Is this port for decompression to allow it to start easy or is it for something else?

Question 2 Since I'm going to make a new carb adapter anyway can I just cover and seal this port up?

Rob

My first guess is.....

This is basicly a 2 barrel carb.
The main barrel operates like a standard carb.
The secondary does not let fuel in, only air.

If this is like the Torro it should make an excellent engine.
Can you put a regular carb on it? Probally but I don't know all the ends and outs.

How much does it weigh????

At first I thought that it might be like a 2 barrel carb also but wouldn't that screw up the mixture or run more lean at the top end if it didn't allow more fuel (and lubrication) in? As for the weight of it I haven't had a chance to weigh it yet but I will post it when I find out.

Looks like a California job to me.

I think the top port is for scavenging the cylinder for clean emissions

I would be tempted to plug the top port.

Enjoy,

Jim

This is strictly for emisions it recirculates the burnt gasses(or unburnt) back through the carb. you can block it off other wise it will be really loud like a open exhaust[X(]

Darin

Good, now we don't have to build carb adaptors around that old style oval intake port anymore. I need to order some barstock... what is the overall diagonal measurement from the outside of the top to bottom holes???

If that is the 42cc it never had the oval 46cc has the oval

Oops...

Ive measured the overall dimensions and a rectangular piece 1.5 inch x 2 inch covers the flange perfectly. I'm going to make it out of 1/2 inch thk aluminum. this will also allow me to mount the carb so that there is no need for a bell-crank to actuate it.

Rob

getrdone!!!!

rweiss: It may be possible to use 2 small carbs with a adapter. I once saw a Mac Go cart engine with 3 carbs! Man did it go!!! Thanks Capt,n

I've set up 3 deuces before.
The center carb was the only carb with an idling circuit.
The others opened above 2500 rpm.
This was set solely by throttle position.
Although some were operated by vacume.

I have thought about this too.
You SHOULD be able to do this especially in the upped end of the rpm range fairly easily
with out sacrificing low or midrange.

But I have learnt that the K.I.S.S. system is usually the best system.

Aluminum may conduct heat to the carb and cause vapor lock...G10 epoxy board is best...

Time out. Stop. Reconsider. All manifolds are made from a material that does not easily transfer heat.

Bill

Do you guys no about McMaster-Carr. I buy almost all my plane stuff there

Heya,

Anyone know if this worked? Is this a common mod for this engine? Did it perform like a regular 42 after blocking the port?

Regards,

Mike

I think the aluminum is OK for the intake manifold as long as 2 gaskets are used. The only time heat will soak back from engine is right after shut down. When running the intake is very cool .....I have checked it with a heat sensing gun. Capt,n