Am ms440 carbs

[Terry Syd]

Now when I open the hole up more I'm guessing those two holes are still putting out fuel at full throttle as well as the main nozzle?

Definitely, those bigger holes in the air bleed/transition holes will allow more air to go through the idle circuit when idling. Therefore, you must open up the low speed needle to compensate so that you get a proper air/fuel mixture at idle.

That means that the low speed circuit is now delivering more fuel when the saw is running at WOT (and thus you need to lean out the high speed needle a bit)

It also means that the low speed circuit is running richer when the revs drop, which usually results in more low end torque.

The factories want to decrease hydrocarbon emissions at lower revs when there is more time for the mixture to escape through the exhaust port. By running the mixture on the 'lean' side of the curve, they can get away with the EPA emission requirements. If you bump up the fuel flow in the low speed circuit, you can increase the low speed torque, but you will also increase the hydrocarbon emissions. - It is a matter for you which way you want to go...

 

[MG porting]

Please don't try to half-arse this. You need to have proper tools to do these fine movements to drill the various holes. If you 'hack' it, it will be a hack job.

I understand. Lol. I will see if my buddy has one you would think he would sense he had the micro bit set. No hacking!!! Lol

 

[MG porting]

Definitely, those bigger holes in the air bleed/transition holes will allow more air to go through the idle circuit when idling. Therefore, you must open up the low speed needle to compensate so that you get a proper air/fuel mixture at idle.

That means that the low speed circuit is now delivering more fuel when the saw is running at WOT (and thus you need to lean out the high speed needle a bit)

It also means that the low speed circuit is running richer when the revs drop, which usually results in more low end torque.

The factories want to decrease hydrocarbon emissions at lower revs when there is more time for the mixture to escape through the exhaust port. By running the mixture on the 'lean' side of the curve, they can get away with the EPA emission requirements. If you bump up the fuel flow in the low speed circuit, you can increase the low speed torque, but you will also increase the hydrocarbon emissions. - It is a matter for you which way you want to go...

Ok that makes sense can't wait until I get back to it but I'm going to be payshent and make sure I have the right tools.

 

[MG porting]

Terry Syd just made you proud of me I hope called my buddy and he doesn't have the pin vice he can't find it but he said that I should just get on the web and buy a complete kit because there cheap so that's what I'm doing tomorrow more speshul tools for me so I don't have to keep bothering him for his.lol

 

[Terry Syd]

You will be surprised that over the years how many times you will use these fine drills. I figure any bloke that is working on engines could easily afford $20 for a set of micro drills and pin vise that will last him the rest of his life.

 

[MG porting]

You will be surprised that over the years how many times you will use these fine drills. I figure any bloke that is working on engines could easily afford $20 for a set of micro drills and pin vise that will last him the rest of his life.

Yea for what they cost it's well worth it I must have over five hundred different drill bits but never had a set of micro bits me and my buddy always shared are tool's but sometimes like now with this situation he didn't have the pin vice so for the money might as well get a complete set for myself just so he can borrow the pin vice when he needs it and that's ok because we both made a agreement if you brake it you replace it. Lol

 

[Bilge Rat]

Buy your buddy a pin vise too. that way you both have one.
You both will have the drills and to use them you both need a vise.

 

[MG porting]

Buy your buddy a pin vise too. that way you both have one.
You both will have the drills and to use them you both need a vise.

Yeah I should after all Christmas is just a couple weeks away.lol

 

[D B Cooper]

Found a nice Starrett pin vice on ebay for 5$

 

[Bilge Rat]

Christmas is a good excuse.

Being a tool addict
I know i have 1 pin vise
I am sure i have 3
And i think i have 4

I can find 1 every time so i have just enough.

 

[Terry Syd]

Any thought on why this is? To be honest, it has me very perplexed. (The 460 got about 10% stronger with the HD-50, all my other saws, including another ported 460, got weaker with it).

Sorry, missed your question. Nope, no idea. Perhaps if I ran the saws and then examined the carbs I might be able to come up with a plausible answer. However, being on the other side of the planet does tend to limit my trouble shooting abilities.

Isn't the 460 carb the one with the bigger venturi and the discharge nozzle off to the side? I experimented with one of those one time on a 64cc 029 and it didn't work as well as the HD-5. Bugger if I know why, it was probably the engine didn't like the difference in the fuel curves.

What we are trying to do with these carb mods is getting the two fuel curves in the carb working together. You have one fuel curve for the straight section of the carb (where the low speed circuit is located) and the high speed circuit that is controlled by the venturi. The air flow through that venturi has a significantly different fuel curve.

Because these are fixed jet carbs without an air bleed jet on the main, they tend to keep getting richer as the air flow increases. I put an air bleed circuit on the main nozzle one time (heaps of work) and the carb worked like a bike carb on a motocrosser. Revved to the moon! I decided to block the air bleed off. It would have worked great on a kart down the back straight, but it wasn't necessary on a saw.

 

[MG porting]

Sorry, missed your question. Nope, no idea. Perhaps if I ran the saws and then examined the carbs I might be able to come up with a plausible answer. However, being on the other side of the world does tend to limit my trouble shooting abilities.

Isn't the 460 carb the one with the bigger venturi and the discharge nozzle off to the side? I experimented with one of those one time on a 64cc 029 and it didn't work as well as the HD-5. Bugger if I know why, it was probably the engine didn't like the difference in the fuel curves.

What we are trying to do with these carb mods is getting the two fuel curves in the carb working together. You have one fuel curve for the straight section of the carb (where the low speed circuit is located) and the high speed circuit that is controlled by the venturi. The air flow through that venturi has a significantly different fuel curve.

Because these are fixed jet carbs without an air bleed jet on the main, they tend to keep getting richer as the air flow increases. I put an air bleed circuit on the main nozzle one time (heaps of work) and the carb worked like a bike carb on a motocrosser. Revved to the moon! I decided to block the air bleed off. It would have worked great on a kart down the back straight, but it wasn't necessary on a saw.

That's why I'm doing what I'm doing to these two carbs to find there happy spot I think it can be done thanks to you and you great smarts guiding me.

 

[MustangMike]

Thanks for your response Terry, it has me totally baffled also. Dr Al thinks I may have rec'd a HD-50 with a richer jet? I ordered 2 HD-50s at the same time, and tested the other saws with the other HD-50.

I think it may just be an anomaly with the porting that we just don't understand, which is why testing is so interesting.

 

[MG porting]

The micro drill set is here all tho some bits were the same size but luckily the one I need is in the kit so I went ahead and drilled both holes on this carb and I'll just do one on the other carb just need to wait for the welch plugs to come in the mail. I have a question when I put the welch plug in do I punch it in flat or do I punch the outer edge flat and leaving a dome in the middle which I'm not even sure I can even do that. So as I was getting ready to drill out the holes I noticed that ones I did that the hole closest to the cylinder that one was bigger than the other two so after drilling I took that bit and it slipped right down the hole so now all three are the same maybe a good thing but maybe not we shall see.

 

[MG porting]

Terry Syd sorry the question was for you.lol

 

[Terry Syd]

Simondo gave you good advice on the welch plug installation.

tho some bits were the same size

Did you use a micrometer or calipers to confirm their sizes? You CANNOT eyeball these drills, they have to be measured.

When you start modding carbs, take one step at a time. I would have drilled one carb to test it against a stock carb. You may already be too large on the holes and you don't know it.

the hole closest to the cylinder that one was bigger than the other two

That was the idle port I mentioned. You don't need to do anything to that port.

that the hole closest to the cylinder that one was bigger than the other two so after drilling I took that bit and it slipped right down the hole so now all three are the same

So, am I to understand that you decided to drill both of the air bleed/transfer holes the same size as the idle port?

 

[MG porting]

Simondo gave you good advice on the welch plug installation.

Did you use a micrometer or calipers to confirm their sizes? You CANNOT eyeball these drills, they have to be measured.

When you start modding carbs, take one step at a time. I would have drilled one carb to test it against a stock carb. You may already be too large on the holes and you don't know it.

That was the idle port I mentioned. You don't need to do anything to that port.

So, am I to understand that you decided to drill both of the air bleed/transfer holes the same size as the idle port?

I used calipers to measure and just by luck they wound up being the same size as the idle port they must have been pretty close to it before drilling them.

 

[Terry Syd]

Did you measure the air bleed ports and write down the sizes before you started drilling?

 

[Wonkydonkey]

I’ve been meaning to pass this manual on to you,,,

 

[MG porting]

Did you measure the air bleed ports and write down the sizes before you started drilling?

Yes and wrote down bit size I used after it's one step up from where they were. The welch plugs came in today so tomorrow I'll be able to put one in and give a try and see what happens. Fingers crossed. But I've got the other AM carb and that one I'm going to just drill out one air bleed then go from there on that one the reason why I drilled both holes on the first one is because I noticed that when checking what size the holes were you could feel a lip at the bottom of the hole and I believe it was from when they put the chrome in the bore so I figured just take that lip out and go with it but like I said I've got the other carb so no biggie if it doesn't work out.