Am ms440 carbs

[Terry Syd]

because with the HD 17 it idles perfect any thoughts?

Well mate, you may have to pull those damn welch plugs and do a comparison to the HD-17. It could be that the AM carb needs a bit more air bleed in the idle circuit.

Tuning a Zama twin jet is a piece of cake compared to these type of carbs. On the Zama the low speed needle ONLY adjusts the idle mixture. The two jets control the low speed circuit flow (so it is real easy to drill them to adjust) and you just have to tweak the metering spring with a shim or two to get great throttle response. - You can tune each function SEPARATELY!

With the Walbro type circuit the low speed needle changes all THREE functions at the same time. It changes the idle, the transition and the low speed circuit flow. It is a pain to try and get all three functions correct when they are all being changed - "heck, all I wanted to do was set the idle"

It may be that the HD-17 will have the answer you're looking for under that welch plug.

 

[MG porting]

Well mate, you may have to pull those damn welch plugs and do a comparison to the HD-17. It could be that the AM carb needs a bit more air bleed in the idle circuit.

Tuning a Zama twin jet is a piece of cake compared to these type of carbs. On the Zama the low speed needle ONLY adjusts the idle mixture. The two jets control the low speed circuit flow (so it is real easy to drill them to adjust) and you just have to tweak the metering spring with a shim or two to get great throttle response. - You can tune each function SEPARATELY!

With the Walbro type circuit the low speed needle changes all THREE functions at the same time. It changes the idle, the transition and the low speed circuit flow. It is a pain to try and get all three functions correct when they are all being changed - "heck, all I wanted to do was set the idle"

It may be that the HD-17 will have the answer you're looking for under that welch plug.

Yep I'm going to be doing so lol but that's how it's going to have to be if I'm going to get one of these am carb to do what it should do which probably would on a bone stalk saw but on a ported saw nope have to modify the carb without a dout.

 

[Terry Syd]

After you get the first one working and know the 'recipe' that the carb needs, then all the hard work is done, you can just duplicate it for the next one.

When I decided to try to mod the HD-5 on my 029/390 it was a nightmare. First I had to block off the EPA circuit that joined the high and low speed circuits, then drill a fuel access hole for the low speed needle.

Then I drilled the auxiliary jet, went too far, GB Welded a copper disc over it and drilled it again. Then I pulled the welch plug and drilled the front air bleed hole. Not big enough to get the idle and low speed flow I wanted, so back into the carb and drilled the back air bleed hole in front of the throttle plate. That got the carb jetting working well, but with the larger air bleed hole just as the throttle opened, it went slightly rich. So, got a metering spring with just a bit more pre-load on it and that cleaned up the transition.

Crikey, what a pain...

Good luck!

 

[Terry Syd]

If the AM carbs are relatively cheap, you might want to mod two of them at the same time. You may find when you get one working fairly well that you mod the second one the same way, BUT increase the size of say the front air bleed hole.

Then you can compare both carbs and see which works best. If the second carb works better, then go back into the first one, do the same mod to it PLUS open up the other air bleed hole to the next size. Test again and see which carb is working the best. Etc. Etc.

You don't know you've gone too far until you go too far...

 

[MG porting]

After you get the first one working and know the 'recipe' that the carb needs, then all the hard work is done, you can just duplicate it for the next one.

When I decided to try to mod the HD-5 on my 029/390 it was a nightmare. First I had to block off the EPA circuit that joined the high and low speed circuits, then drill a fuel access hole for the low speed needle.

Then I drilled the auxiliary jet, went too far, GB Welded a copper disc over it and drilled it again. Then I pulled the welch plug and drilled the front air bleed hole. Not big enough to get the idle and low speed flow I wanted, so back into the carb and drilled the back air bleed hole in front of the throttle plate. That got the carb jetting working well, but with the larger air bleed hole just as the throttle opened, it went slightly rich. So, got a metering spring with just a bit more pre-load on it and that cleaned up the transition.

Crikey, what a pain...

Good luck!

Lol. Sounds like you were getting ready to put the boxing gloves on and I'm sure I'll probably be feeling the same way but hopefully not but this is how you learn I'm just glad to have people like you who can gidde me in the right direction and I thank you very much.

 

[Terry Syd]

Yeah, how you learn. I remember when Randy wanted to mod a carb and he said he only had a few drills and was thinking of just drilling it the smallest size he had. I suggested to him to wait until he got a full micro-drill set with the pin vise - it was important to work his way into it to develop the 'feel'.

Everybody wants to just get it over and done with as fast as possible, however, what is important is getting the 'feel' for what is happening in the carb.

Randy waited (he's got a heap of various micro-drills and pin vises now) and has developed that 'feel' and can now mod all sorts of carbs.

You will learn more from your mistakes than successes...

 

[MG porting]

Lol. Yep I've kicked myself in the but many times throughout the years because I got in a big hurry and have to face the music from people who have been there and done that and told me how to do it right but nope had a idea of my own lol live and learn the hard way sometimes but I'm not rushing through this I'm going to go at it one step at a time and hopefully get something good out of it.

 

[MustangMike]

Another factor I hate to mention … but it may be a big mistake to expect the same results from AM products that are not manufactured to the same standards as OEM.

That does not mean that what you are trying to do can not be accomplished … but it may be harder or unattainable.

Sometimes OEM is worth the $$$.

 

[Terry Syd]

'Poleman' was purchasing Chinese Zama twin jets for less than $20. Those carbs were exact duplicates of the OEM carbs. You could send him the particulars of your saw and he could mod a carb to work on your saw. Not only was it modded for performance, but it had all new parts - it was great value for money. Like, why would you re-build a stock carb when for a few more bucks you could get a brand new carb that was modded for power.

Later the Chinese started doing really cheap non-duplicates that couldn't be modded. That was the end of the cheap modded Zama twin jets.

Now a days you have to find an old original Zama twin jet in some parts bucket in a shop to mod. Not only does it have to be modded, it also has to be re-built.

Some of the Chinese carbs are worth the cost - and then there's the others...

 

[MG porting]

Ok I popped the welch plug on the am carb there's 4 holes which one do I drill out first the one on the far left? And the welch plug was a pane to get out she was well glued in there would like to know what the heck they used to glue it in there lol.

 

[Wonkydonkey]

I thought it was slightly bigger ie domed in the centre then tapped flat so it enlarges and fits tight. As well as some sort of epoxy or I’ve heard nail varnish does the job to be sure it’s sealed.

The way to get them out is puncture a small hole and leaver it out, but yo7 have to be careful where you make the puncture.. was it in the stihl carb maintance I saw this...?

 

[Wonkydonkey]

Yeh I just looky at it. Lock tight and dome flattened

If it’s any help to you I’m sure I or anyone else can send it to you

 

[MG porting]

Yeh I just looky at it. Lock tight and dome flattened

If it’s any help to you I’m sure I or anyone else can send it to you

View attachment 211937

Yep that's the ticket. Now just need to know what hole to drill.

 

[Terry Syd]

One hole will be the idle port, it sits on the engine side of the throttle plate.

One hole will provide fuel to the chamber. You can probably locate that hole by squirting the WD-40 through the feed hole for the low speed needle.

Then there are the two air bleed/transition holes that sit just in front of the throttle plate. They open progressively as the throttle plate moves across them. If you put a piece of wire through them, you should see the wire sticking up in the carb body.

Knowing the size of those holes in the HD-17 could save you a fair bit of time and effort.

I assume you have the micro-drills and pin vise to work with.

 

[MG porting]

One hole will be the idle port, it sits on the engine side of the throttle plate.

One hole will provide fuel to the chamber. You can probably locate that hole by squirting the WD-40 through the feed hole for the low speed needle.

Then there are the two air bleed/transition holes that sit just in front of the throttle plate. They open progressively as the throttle plate moves across them. If you put a piece of wire through them, you should see the wire sticking up in the carb body.

Knowing the size of those holes in the HD-17 could save you a fair bit of time and effort.

I assume you have the micro-drills and pin vise to work with.

I do not have the pin vise but I have my friends micro drill bit set. I'll take some more pics here in a bit.

 

[MG porting]

One hole will be the idle port, it sits on the engine side of the throttle plate.

One hole will provide fuel to the chamber. You can probably locate that hole by squirting the WD-40 through the feed hole for the low speed needle.

Then there are the two air bleed/transition holes that sit just in front of the throttle plate. They open progressively as the throttle plate moves across them. If you put a piece of wire through them, you should see the wire sticking up in the carb body.

Knowing the size of those holes in the HD-17 could save you a fair bit of time and effort.

I assume you have the micro-drills and pin vise to work with.

Here's a pic with the butterfly shut. here's a pic with the butterfly open. and here's the one hole that feeds fuel in. it's the one that is marked with the blue line above it.

 

[Terry Syd]

Picture #2 shows the light coming through the idle port and also the two transition holes.

By moving the throttle you will find out which of the transition holes is first to open.

I would open up the second hole the first time around as that has the least affect on fuel flow as the throttle starts to move.

Use the micro-drills to determine the size of the stock holes (it would be nice to know what sizes are in the HD-17). Use the 'back' of the drills so you don't scratch the inside of the holes. Write down those sizes, go up one size for the second transition hole.

You really need the pin vise to hold on to these very small drills/reamers.

DEFINITELY use a micrometer or calipers to confirm the size of the drills. They are very small and can get mixed up VERY easily. Never assume that you have the right size drill.

Put in another welch plug and give it a try. See where you go from there.

 

[MG porting]

Picture #2 shows the light coming through the idle port and also the two transition holes.

By moving the throttle you will find out which of the transition holes is first to open.

I would open up the second hole the first time around as that has the least affect on fuel flow as the throttle starts to move.

Use the micro-drills to determine the size of the stock holes (it would be nice to know what sizes are in the HD-17). Use the 'back' of the drills so you don't scratch the inside of the holes. Write down those sizes, go up one size for the second transition hole.

You really need the pin vise to hold on to these very small drills/reamers.

DEFINITELY use a micrometer or calipers to confirm the size of the drills. They are very small and can get mixed up VERY easily. Never assume that you have the right size drill.

Put in another welch plug and give it a try. See where you go from there.

Thank you very much for your time and help with this I might have something close to a pin vice that I can rig up maybe I'll have to dig out some stuff tomorrow and see. 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?

 

[MustangMike]

Fascinating stuff Terry, and people like you who share your expertise are what make sites like this great!

I have no plans to ever mod a carb myself, but this is great information. Luckily, I picked up some 70 jet HD-11s before they became unavailable.

I do have a question for you. Have you compared an HD-50 to an HD-17? I'm perplexed because my MOFO ported 460 responded very well to an HD-50 carb, but none of my other saws liked them. The 460 even liked it better than a HD-11.

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).

 

[Terry Syd]

I might have something close to a pin vice that I can rig up maybe I'll have to dig out some stuff tomorrow and see.

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.