MS460 carb on an 039

[Terry Syd]

HD 5 - same as mine, with the auxiliary main jet held in with a circlip.

You could probably pull the welch plug and drill out the air bleed/transition holes to the same specs as the 460 carb and get the same results you got with the 460 carb. The venturi is a bit smaller than the 460 carb and doesn't have the offset main discharge nozzle, but I expect that there wouldn't be that much difference in performance.

 

[Brewz]

What I am thinking about doing is cleaning up the fixed jet in the MS460 carb and filling the hole with solder after I measure it to determine the size of the hole in it.
Then drill it smaller to share the fuel load between the 2 H jets. THey must put the 2 jets in there for a reason and I assume it would be to share the load and reduce any flow velocity issues when RPM's are changing rapidly.

Terry, what is the size range of the micro drill set you use?

 

[Terry Syd]

The micro drills start at .30mm and go up, I think the top size is 1.5mm. They don't cost much and with the pen vise (it's needed, you can get them together on Ebay) it is a good addition to your tool chest. The drills can be used in other applications other than drilling jets. The micro drill sets with pen vise are around $20.

As far as you theory about the extra jet, I don't believe that is the case. What I expect happened was that when the factories started reducing the flow in the low speed circuit (notice the limiter in your HD5) they had to add the extra high speed jet to compensate for the loss in flow from the low speed circuit. The extra jet keeps the high speed needle in a reasonable range - around 1.5 turns out.

The HD5 was used on the 029-039 saws. In other words, it is an EPA approved carb that was put on a 54cc engine - and also your 64cc engine.

 

[CR888]

I think my micro drills and pen vise was under $30 delivered. Just get a set that goes up in the increments that you desire so you get more useable drills and not half of them bigger than you would ever need.

 

[Terry Syd]

Yeah, you can also get a set of micro drills in SAE sizes. They can sometimes be used to tweak a jet just a bit smaller or larger than the metric sizes.

 

[Brewz]

I have been doing a lot of reading and searching and find information supporting both sides of the camp saying fuel is and isn't delivered at high speed.
I cant find any definitive data to support either side so I am going to call it as "who knows"
We could all sit around and argue back and forth for years and never get anywhere.

At this stage, all I know for sure is that with the MS460 carb, the saw "felt" much stronger in the cut and I have about 30+ tanks of fuel through it over the last 6 months before I changed the carb.
I have also rebuilt the saw 10 tanks ago and am wondering if its just coincidence that its hit its run in peak...... once again, not sure

NOW..... The best way to solve this is to test the saw in the cut.
I dont plan to buy another MS460 carb so will use the carbs I have.
Seeing as the L circuit is controlled via a jet and the drilling of the tiny little L jet shouldn't hurt anything, I would like to end the debate on L circuit fuel or no fuel and start the testing of MS460 vs stock 039 carb.

Planning to work from home tomorrow and give the saw a run with both carbs.
It is going to piss the neighbors off but they will live. Its supposed to be 40 deg C tomorrow too

I plan to tune the 2 carbs to the same idle and WOT speed with the best throttle response I can get.
Both carbs are already set to the best I could get so will bolt them on, warm the saw up and check with my tacho.

Will be running fresh 98 octain at 40:1 with Stihl HP Ultra
20" Oregon pro lite bar, clean and dressed with Oregon 3/8 full comp, semi chisel chain that's done a tank or 2 of fuel and will be hand file sharpened before each test. Rakers still untouched. I may actually touch the rakers down to the stock .025 just to make sure the saw is loaded properly.

video will likely be done by one of my 12 year old kids so please excuse the non hollywood production

 

[Brewz]

I am really excited to see if the saw is actually stronger or if the change of carb had me convincing myself it is stronger.

The mind can be a tricky thing at times

 

[paragonbuilder]

I have been doing a lot of reading and searching and find information supporting both sides of the camp saying fuel is and isn't delivered at high speed.
I cant find any definitive data to support either side so I am going to call it as "who knows"
We could all sit around and argue back and forth for years and never get anywhere.

At this stage, all I know for sure is that with the MS460 carb, the saw "felt" much stronger in the cut and I have about 30+ tanks of fuel through it over the last 6 months before I changed the carb.
I have also rebuilt the saw 10 tanks ago and am wondering if its just coincidence that its hit its run in peak...... once again, not sure

NOW..... The best way to solve this is to test the saw in the cut.
I dont plan to buy another MS460 carb so will use the carbs I have.
Seeing as the L circuit is controlled via a jet and the drilling of the tiny little L jet shouldn't hurt anything, I would like to end the debate on L circuit fuel or no fuel and start the testing of MS460 vs stock 039 carb.

Planning to work from home tomorrow and give the saw a run with both carbs.
It is going to piss the neighbors off but they will live. Its supposed to be 40 deg C tomorrow too

I plan to tune the 2 carbs to the same idle and WOT speed with the best throttle response I can get.
Both carbs are already set to the best I could get so will bolt them on, warm the saw up and check with my tacho.

Will be running fresh 98 octain at 40:1 with Stihl HP Ultra
20" Oregon pro lite bar, clean and dressed with Oregon 3/8 full comp, semi chisel chain that's done a tank or 2 of fuel and will be hand file sharpened before each test. Rakers still untouched. I may actually touch the rakers down to the stock .025 just to make sure the saw is loaded properly.

video will likely be done by one of my 12 year old kids so please excuse the non hollywood production

Awesome! This is how we make breakthroughs. Screw the "rules and facts", think outside the box and experiment!!


Sent from my iPhone using Tapatalk

 

[Brewz]

Ran a couple of loaded cuts with both carbs this morning

Results are interesting

Tuned them both to the same idle and to just 4 stroke at WOT which gave me 12700 to 12800 rpm with both carbs

460 carb, 10.3 and 10.7 seconds
Stock 039 carb, 8.8 and 9.4 seconds.

The 9.4 second cut had the dog spike catch at the end of the cut when the timber seperate. Slowed it down a hair.

To be honest, I couldn't really feel any difference while cutting but the numbers say 15% faster stock.

I am uploading videos to YouTube now but they are gunna take a bit

 

[Terry Syd]

LOL, well maybe I'll pull the 460 carb off mine and put the stocker back on.

So when you put a heavy load on the saw, the 039 carb pulled better than the 460 carb?

Hmm, I wondering if my ignition advance is contributing to the equation. If the 460 carb is providing too much fuel down low, then an ignition advance will compensate and allow a faster 'rise time' in the cylinder.

 

[Brewz]

I wouldnt use the term "pulled better.

I just loaded the saw up making big piles of noodles and the cut times show which one went through the timber faster.

It is possible the saw is becoming overly rich in the cut and a timing advance would help but that is just a guess.
The other possibility is that with the venturi being larger, I now have a lower air velocity and its not drawing as much fuel, leaning it out and dropping power.

I dont know........ all I know is it cut slower with the bigger carb

 

[RU NUTZ TOO]

I think you need another 460 carb to try without drilling that jet

 

[Terry Syd]

My guess is the extra timing advance I have on my saw. The extra advance works well at higher speeds, but can slow down the engine when the revs drop and there is more time for ignition. If the carb is on the rich side of the curve, it will slow down the combustion process - it tends to dampen the combustion. The result with the richer mixture is the rise time in the cylinder moves the combustion process back to where the timing is more appropriate.

I'll have to try the old carb again, this is interesting.

 

[Brewz]

Yeah, to be honest, Im just going to leave it as is and use it.
Its not a race saw but it works well.

I really want to focus my efforts on working my 026 and 066 pro saws
I would be interested to see some timed cuts on your saw Terry, with both carbs

I dug the 026 out to run it for comparison but the bloody thing made so much noodle, the sprocket cover couldn't handle the volume and would block and jam the saw.
I had it tuned on the lean side for lots of RPM's (15600 WOT) so I richened it out to run at 14700. This seemed to allow the saw to clear the noodles and it cut in about 14 seconds. The log came loose and started rocking back and forth in the cut on me and that slowed it down a bit too.

I was going to fire up the 066 as well but with the pieve of wood smaller and moving around with an 026, it was not going to be fun with the 066 so I didnt bother.

The videos are slowly uploading, going to take a couple hours by the looks.
You can hear workers across the road with a saw cutting a concrete driveway and my kids in the pool yelling and screaming

 

[RU NUTZ TOO]

dang it, came on here with the phone and realized i missed a bunch of posts again.

 

[Terry Syd]

As I recall you set both carbs for the same WOT RPM. Maybe your high speed needle is set a bit too rich. If you decide to try the 460 carb again, try leaning out the high and see if that makes a difference. I think my WOT is around 13,400. Tuning in the wood is the best option, see what cuts best.

 

[Brewz]

I tuned them to sound and they came in about the same surprisingly.

If i lived on a farm, I could stand around for hours tweaking the carbs to get that extra half second and chop down another tree for test wood, but I dont.
I grew up on the land but buying land is now prohibitively priced so I am stuck with suburbia and I hate it.

Anyway, here are the vids

039 stock carb

MS460 carb

The sheer volume of noodles gave me troubles but it has made good mulch in all the pot plants