carb and fuel issues

[klickitatsacket]

OK guys, take it easy on me as I am swallowing my pride here. I just put together an MS460. I took the port timing to the max. I left the exhaust alone except to widen it as far as I could, leaving 1mm on either edge of the skirt. I brought the one transfer port up to with in 1 mm and the second port up to 2 mm ( I like to stagger them). Here is the problem: I am out of adjustment on the High screw. I need more fuel. As of right now I am not too lean but do not want to leave it like this. The only idea I can come up with is to run a stricter plate on the carburetor to slow the rate of air. I could use some other ideas or suggestions

 

[Crofter]

What do you consider to be MAX? and you took the transfers up to within 1 and 2 mm of What? Providing you have'n got the transfer duration too long you may be able to get some more flow in the high speed circuit. Did you degree the transfer duration?

 

[MacDaddy]

A easy way to keep fuel and slow the flow in the motor would be use a more restrictive muffler

 

[klickitatsacket]

sorry, 1mm and 2mm from the top of the transfer port to the top of the exhaust port. I am not running any fuel through the muffler. I left the baffle in and the extra port was a minimum starter. I havn't even started to tune it yet.

 

[Lawn Masters]

So, you're saying that the limiter caps are still on the carb?

 

[klickitatsacket]

Sorry, I forgot I put an old style carb. on

 

[Lawn Masters]

Thats different then. Perhaps you should ask Stihltech about rejetting the carb.

 

[MacDaddy]

You are using the old type carb or a new one

 

[klickitatsacket]

I replaced the new carb with an old style 046 carb.

 

[klickitatsacket]

Macman do you think I should go ahead and restrict the muffler? My concern with that would be heat build up. One other thing how much compression is too much? Right now I am at 180#

 

[MacDaddy]

That should make a good running saw try covering one port on the muffler and run it and see what it acts like also try one with no baffle and see but you still might have to drill or jet the carb

 

[rupedoggy]

Just in case you overlooked the obvious, try putting the meter lever for the needle at a slightly higher level. This will give you more available fuel and when you adjust your high speed you will have more fuel going in. Also some early 046 carburetors were a problem and they cracked at the needle adjustment seat. You can never get them right again. Have you run this carburetor on another saw for a test? Mike

 

[Pioneer]

I'd try the meter needle level too, an adjustment in one of my larger saws for more fuel delivery cured a lean problem I had. If this doesn't work, you might want to try and get a carb with a slightly smaller bore size, this might bring the vacuum signal up enough to give you the adjustment range you need on the mixture screws.

 

[klickitatsacket]

This carb worked on the saw it was taken off of. I won't see the saw until Monday when I get back to the shop but will keep you informed. Thanks for the toughts.

 

[Crofter]

If you have taken the height of the transfer ports to within! 1 mm of the exhaust port, you have no time for blowdown and you will have exhaust driving back down the transfers, leaning out the mixture. Did you also raise the intake port?

 

[klickitatsacket]

Crofter just follow me through on this one step by step. 1- the saw is not running lean at this point in time. I am only looking for adjustment for the eventuality of needing it. 2- there is minimal fuel getting into the muffler. The back presure is holding it well. 3- I have the skirt on the intake side trimmed. If I was getting exhaust in back down my transfer ports then I would be getting spray back out my carburetor. I have been there before :blush: . What I have is a saw that is running great but I am to the point of using all the gas that is available with this carburetor, with out modifying it some how. Wheather that would be to restrict the flow of air and thus putting a chian on the dog or opening up the flow of fuel so that I might have adjustment. I have not even got to the tuning of the saw yet.

 

[Ranchero50]

I'd have to agree with playing with the needle adjustment or changing out the carb for a different one. Minimal time involved either way.

As to swallowing pride... All I can say is my 041AV is running great after your help recovering from the motor swallwing a carb nut.

Jamie

 

[klickitatsacket]

Thanks for the kind words ranchero. I hope the parts met your expectaitions.

 

[ehp]

it depends on what carb you have for the old 046 but the new carb will work also, that the cover off the carb that you need to use to get at the needle and seat. take the diagram off the carb , look over from your needle and seat and you will see a little brass jet that can be screwed out, it will have a very small hole in it, take care unscrewing it cause the edges of the brass will break off, then just go to a stihl dealer and tell them you want a bigger jet, they make different jets for that saw, and if not just drill that jet out but only a couple thousands at a time , if you use the new carb just take the limiters off it and put the bigger jet in it , but if you drill that jet , make sure you only drill .002 bigger because you can always drill a hole bigger but not make it smaller.
1mm on the skirt thats .0393 of an inch , that is not much for the piston to ride on but you know what you are doing

 

[timberwolf]

Glad you got it running again, interesting stuff with the port maps.

Just wondering what your thinking is on the stagered transfers, seams that idea is a bit out side the box. At least in what I have read.

And the transfer shape also, is the center slighly lowered section designed to aid in repositioning the ring back into the piston recess?